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Table of Contents
1 The Impatient Introduction to Perl..........................................................................................................7
1.1 The history of perl in 100 words or less..........................................................................................7
1.2 Basic Formatting for this Document...............................................................................................7
1.3 Do You Have Perl Installed.............................................................................................................8
1.4 Your First Perl Script, EVER..........................................................................................................9
1.5 Default Script Header......................................................................................................................9
1.6 Free Reference Material................................................................................................................10
1.7 Cheap Reference Material.............................................................................................................10
1.8 Acronyms and Terms....................................................................................................................10
2 Storage..................................................................................................................................................11
2.1 Scalars...........................................................................................................................................11
2.1.1 Scalar Strings.........................................................................................................................12
184.108.40.206 String Literals.................................................................................................................12
188.8.131.52 Single quotes versus Double quotes..............................................................................13
18.104.22.168 chomp.............................................................................................................................13
126.96.36.199 concatenation.................................................................................................................13
18.104.22.168 repetition........................................................................................................................13
126.96.36.199 length..............................................................................................................................13
18.104.22.168 substr..............................................................................................................................13
188.8.131.52 split.................................................................................................................................14
220.127.116.11 join.................................................................................................................................14
18.104.22.168 qw.................................................................................................................................15
188.8.131.52 Multi-Line Strings, HERE Documents........................................................................15
2.1.2 Scalar Numbers......................................................................................................................16
184.108.40.206 Numeric Literals............................................................................................................16
188.8.131.52 Numeric Functions.........................................................................................................16
188.8.131.52 abs..................................................................................................................................16
188.8.131.52 int...................................................................................................................................16
220.127.116.11 trigonometry (sin,cos)....................................................................................................17
126.96.36.199 exponentiation................................................................................................................17
188.8.131.52 sqrt..................................................................................................................................17
188.8.131.52 natural logarithms(exp,log)............................................................................................18
184.108.40.206 random numbers (rand, srand).......................................................................................18
2.1.3 Converting Between Strings and Numbers.......................................................................19
220.127.116.11 Stringify.........................................................................................................................19
126.96.36.199.1 sprintf.....................................................................................................................19
126.96.36.199 Numify...........................................................................................................................20
188.8.131.52.1 oct...........................................................................................................................21
220.127.116.11.2 hex..........................................................................................................................21
184.108.40.206.3 Base Conversion Overview....................................................................................21
2.1.4 Undefined and Uninitialized Scalars.....................................................................................22
2.1.5 Booleans................................................................................................................................23
126.96.36.199 Comparators...................................................................................................................25
126.96.36.199 Logical Operators...........................................................................................................26
184.108.40.206.1 Default Values........................................................................................................27
188.8.131.52.2 Flow Control..........................................................................................................27
18.104.22.168.3 Precedence..............................................................................................................27
126.96.36.199.4 Assignment Precedence..........................................................................................27
126.96.36.199.5 Flow Control Precedence.......................................................................................28
126.96.36.199.6 Conditional Operator..............................................................................................28
2.1.6 References..............................................................................................................................29
2.1.7 Filehandles.............................................................................................................................31
2.1.8 Scalar Review........................................................................................................................32
2.2 Arrays............................................................................................................................................32
2.2.1 scalar (@array)......................................................................................................................33
2.2.2 push(@array, LIST)...............................................................................................................34
2.2.3 pop(@array)...........................................................................................................................34
2.2.4 shift(@array)..........................................................................................................................35
2.2.5 unshift( @array, LIST)..........................................................................................................35
2.2.6 foreach (@array)....................................................................................................................36
2.2.7 sort(@array)...........................................................................................................................37
2.2.8 reverse(@array).....................................................................................................................38
2.2.9 splice(@array).......................................................................................................................39
2.2.10 Undefined and Uninitialized Arrays....................................................................................39
2.3 Hashes...........................................................................................................................................39
2.3.1 exists ( $hash{$key} )............................................................................................................41
2.3.2 delete ( $hash{key} ).............................................................................................................42
2.3.3 keys( %hash ).........................................................................................................................42
2.3.4 values( %hash )......................................................................................................................43
2.3.5 each( %hash ).........................................................................................................................43
2.4 List Context...................................................................................................................................47
2.5 References.....................................................................................................................................49
2.5.1 Named Referents...................................................................................................................50
2.5.2 References to Named Referents.............................................................................................50
2.5.3 Dereferencing........................................................................................................................50
2.5.4 Anonymous Referents...........................................................................................................51
2.5.5 Complex Data Structures.......................................................................................................53
220.127.116.11 Autovivification.............................................................................................................54
22.214.171.124 Multidimensional Arrays...............................................................................................55
18.104.22.168 Deep Cloning, Deep Copy.............................................................................................56
22.214.171.124 Data Persistence.............................................................................................................56
2.5.6 Stringification of References.................................................................................................56
2.5.7 The ref() function...................................................................................................................57
3 Control Flow.........................................................................................................................................58
3.1 Labels............................................................................................................................................60
3.2 last LABEL;..................................................................................................................................60
3.3 next LABEL;.................................................................................................................................60
.........................................................................................................................................................62 4.......................................................................................................................................................................................60 4 Packages and Namespaces and Lexical Scoping.................................................69 5.................................70 5................................................................9 Subroutine Return Value..........................................................8 Implied Arguments.........................................................4 redo LABEL............................................................2 Polymorphism.................81 9................................................63 4....................................94 13........................................................69 5.2 Garbage Collection and Subroutines.................................................................................3 INVOCANT->isa(BASEPACKAGE).......................................................................................80 9..90 13.....................................................................................................................................................1 Class.6.................................61 4.................................2 Declaring Package Variables With our................................4 INVOCANT->can(METHODNAME)................... Formally.....65 4.......................................................3 Package Variables inside a Lexical Scope...........................79 9..............................1 Inheritance..................78 8 The use Statement................................................................................................................4 Lexical Scope......5 MODULENAME -> import (LISTOFARGS).............87 11......................................................................................................7 Package Variables Revisited.....................83 11 Method Calls.....................................................................................................................6......................................................94 4 .................................................61 4...............6 The use Execution Timeline.................63 4....................................82 10 bless()...............................................................................................................................................................4 The require Statement.....................................................................80 9............................................65 4...73 5..............72 5...........................................................2 Named Subroutines.75 5.......................................67 4...........68 5 Subroutines.........................................................................................71 5..........1 Reference Count Garbage Collection..............................7 Dereferencing Code References...........................................................................................5 Passing Arguments to/from a Subroutine...........4 Data::Dumper and subroutines......................................................................................................................................................................................................................................................70 5...............................................1 Subroutine Sigil.................6 Accessing Arguments inside Subroutines via @_................88 12 Procedural Perl.......................................................................88 11......................3 Anonymous Subroutines....................6 Garbage Collection..................................................79 9.............................................................80 9..........2 The use lib Statement............................................................10 Returning False............................................................78 9 The use Statement.........................................................................................66 4.........................................................................................................................................71 5..............3.........85 11..................................................................................................................................................75 6 Compiling and Interpreting..................................................................90 13 Object Oriented Perl............................................................62 4..........13 Context Sensitive Subroutines with wantarray().....................................................................11 Using the caller() Function in Subroutines.................................................................................................................................................................................70 5................................................................................................................86 11.......2 use base....5 Lexical Variables.8 Calling local() on Package Variables....................................88 11..............................................................3 The PERL5LIB and PERLLIB Environment Variables...................................................1 Package Declaration.........................................................................................................................................................................................................74 5......................................................................................................12 The caller() function and $wantarray................................................................... Perl Modules.................................................................73 5................................................................................................................................76 7 Code Reuse.......5 Interesting Invocants...............................................................................................................................................................................................69 5..........................................................................1 The @INC Array..............................................
....................................................................................................................103 16 The Next Level........................................................................................................................................108 18 File Input and Output.........3 bless / constructors...............................99 15 CPAN...............123 20...........................................................................................................................................................................................114 19..........................................107 17..................3 SUPER.....................................................................................................................................................4 Creating Modules for CPAN with h2xs....................98 14......................................5..10 Position Assertions / Position Anchors.....................2 close..................................................................................................................................................122 20...121 20.......122 20...................................................6 Overriding Methods and SUPER..1 The \b Anchor................................................................104 17..............................................117 20....1 $1................................................................................................2 CPAN.................................................98 14.....................120 20.........................................118 20.................................................................................115 20..............................3 read.....................111 18.......116 20........................................................................................3 Operating System Commands in a GUI................................................110 18...................................................................................................................................10..........................110 18................................................................................................6 File Globbing................................4 Metacharacters..............4 write....................................99 14................6..............................5 Capturing and Clustering Parenthesis.............................................................................................13..2........................................................................................2 The \G Anchor.100 15.................................... etc Capturing parentheses........................................................................................124 20.................................................................................. The Web Site.............................................................114 19..........7 File Tree Searching..........4 Methods.............................................................................................................................120 20..................................................................................................2 Capturing parentheses not capturing.............................................................................................1 Metacharacters Within Character Classes..1 CPAN.....................................................................................................................................................112 18...................................................................................................................105 17...........7 Shortcut Character Classes...123 20.......................5 Inheritance..............................................................................................................................................................................................................................................................................................................................95 13........................1 @ARGV...................................................................................1 Variable Interpolation................2 The Backtick Operator.............110 18........................................................................................................3 Plain Old Documentation (POD) and perldoc......114 20 Regular Expressions............................................5.........................................................................................................................9 Thrifty (Minimal) Quantifiers..104 17 Command Line Arguments...............8 Greedy (Maximal) Quantifiers...................................................................................................................... $3.................2 Wildcard Example....................................................................114 19.................................................................................110 18..............1 Getopt::Declare Sophisticated Example.........................................................125 5 ..........................2 use Module.................2 Getopt::Declare...103 15......................................................121 20......................98 14............6 Character Classes............................................................... The Perl Module..............................................................................................................100 15...........124 20...................................1 open.................................................................................................................98 14............................................113 19 Operating System Commands.......................................................................................................................................................................................................................................10.........97 14 Object Oriented Review................................................. $2...................5 File Tests.....................117 20................................................................99 14.................................................3 Defining a Pattern..................................................112 18............................100 15........4 Object Destruction....................1 The system() function................................1 Modules...................................................................................................................
.................17 Regexp::Common..........................130 20................................ and then manually reformat the document to resemble its original layout..................................................... The January 2010 version attempts to remove all the hard-coded returns in the paragraph text and allow the word processor to determine where to wrap the text............130 20............127 20................................. Enjoy! Greg London 6 ..................................... It might look like there's a four-line paragraph on some page................................................................. While I was working on that rev..........3 The x Modifier....130 20......................................... but it's really four lines with hard-coded "\n" at the end of each line...... I fixed a couple of typos and tweaked a sentence or two....132 22 Perl..........................................2 The m And s Modifiers........................................129 20................................................127 20.......................................12 Modifiers For m{} Operator.......................................................... and Tk................................................................. I had to take the PDF...........131 21 Parsing with Parse::RecDescent..135 23 GNU Free Documentation License.....11............................... copy and paste the text............ but the revision on 17 February 2009 is that reconstructed version.................... GUI.................130 20..............................127 20..................................................... One of the problems with that version is that the text had hard-returns coded into it from the cut/paste..........................13 Modifiers for s{}{} Operator.......................................................................................................................................14 Modifiers for tr{}{} Operator............. It was painfully tedious........................1 Global Modifiers..............................................................136 A quick explanation of the revision history.......130 20...............................................................11..................20.............................................................16 Common Patterns................................................................... To recover.............................................................. I lost the original Open Office files for "Impatient Perl".............................11............................11 Modifiers..15 The qr{} function...............................
They also use a monospaced font. Text sections will extend to the far left margin and will use a non-monospaced font. A few changes have occurred between then and now. Text sections contain descriptive text.pm This code will be placed in a file called MyFile.1 The history of perl in 100 words or less In the mid 1980s. Code sections are indented. so he invented Perl. Larry Wall was working as a sys-admin and found that he needed to do a number of common. and shell sections.pl The first line of myscript.pm #!/usr/local/env perl ###filename:myscript. ###filename:MyFile.pl This code will be placed in a file called myscript. and probably will not be available for some time. It is not available yet. each file will be labeled. Generally. 1. If the code section covers multiple files. yet oddball functions over and over again. not a WORD PROCESSOR to create these files. This sentence is part of a text section. And he did not like any of the scripting languages that were around at the time. Version 1 was released circa 1987. This document should also find use as a handy desk reference for some of the more common perl related questions. which represents code to type into a script. and is executed via a shell command. the code is contained in one file. code sections. The current version of Perl has exceeded 5.8.2 Basic Formatting for this Document This document is formatted into text sections. Perl 6 is on the drawing board as a fundamental rewrite of the language.3 and is a highly recommended upgrade.1 The Impatient Introduction to Perl This document is for people who either want to learn perl or are already programming in perl and just do not have the patience to scrounge for information to learn and use perl. You will need to use a TEXT EDITOR. This is a code section. 1.pl will be the line with #!/usr/local/env perl 7 .
In this example. Much of this will translate to Mac Perl and Windows Perl. the code for a simple "Hello World" script is shown here. In simple examples.org CPAN is an acronym for Comprehensive Perl Archive Network. > Hello World THIS DOCUMENT REFERS TO (LI/U)NIX PERL ONLY.3. print "Hello World\n". immediately followed by the output from running the script. get your sys-admin to install perl for you. The CPAN site contains the latest perl for download and installation. If you are a beginner. It can be typed into a file of any name.> > > > > > > > > > > > > shell sections are indented like code sections shell sections also use monospaced fonts. if any exists. The command to execute the script is not important either. The command to run the script is dropped to save space. the code is important.8.cpan. shell sections also show the output of a script. Even if you are not a beginner. so they are they only things shown. shell sections show commands to type on the command line. shell sections differ from code sections in that shell sections start with a '>' character which represents a shell prompt. you can download it for free from http://www. 1. as well as a TON of perl modules for your use.3 Do You Have Perl Installed To find out if you have perl installed and its version: > perl -v You should have at least version 5. The name of the file is not important. the code is shown in a code section. As an example. but the exact translation will be left as an exercise to the reader. 8 . get your sys-admin to install perl for you. If you have an older version or if you have no perl installed at all. and the output is important.
unless otherwise stated. You can save yourself a little typing if you make the file executable: > chmod +x hello.4 Your First Perl Script. It uses your PATH environment variable to determine which perl executable to run.pl Hello World This calls perl and passes it the name of the script to execute. use strict.) Run the script: > perl hello. # comment print "Hello World \n". you can control which version of perl they will run by changing your PATH variable without having to change your script.pl Hello World If ". Anything from a # character to the end of the line is a comment. > hello. 1. you will have to run the script by typing: > .5 Default Script Header All the code examples in this document are assumed to have the following script header. #!/usr/bin/env perl use warnings.1./hello. EVER Create a file called hello. use Data::Dumper. (The #! on the first line is sometimes pronounced "shebang") (The .pl using your favorite text editor." is not in your PATH variable.pl extension is simply a standard accepted extension for perl scripts.pl And then run the script directly. If you need to have different versions of perl installed on your system. 9 . use strict.pl HOORAY! Now go update your resume. Type in the following: #!/usr/bin/env perl use warnings.
"Pearl" shortened to "Perl" to gain status as a 4-letter word.com Still more free documentation on the web: http://learn. "vivify" meaning "alive". and Jon Orwant.cpan. The name was invented first.org More free documentation on the web: http://www. Note that this is "Perl" with a capital "P".html Mailing Lists on CPAN: http://list. Generally applies to perl variables that can grant themselves into being without an explicit declaration from the 10 . The publisher.org/cpan-faq. alright. Sethi. and each one has a different animal on its cover.perldoc.e. O'Reilly. Highly recommended book to have handy at all times. It is sometimes referred to as the "Camel Book" by way of the camel drawing on its cover. the standard mantra for computer inflexibility was this: "I really hate this darn machine. The "perl" with a lower case "p" refers to the executable found somewhere near /usr/local/bin/perl CPAN: Comprehensive Perl Archive Network. Well.Note that Data::Dumper takes some time to load and you wouldn't want to use Data::Dumper on some timing-critical project. But for learning perl with simple scripts. Well. so they could not be TOO lazy.perl. (They had to write perl in C. it is probably an O'Reilly book.) AUTOVIVIFY: "auto" meaning "self". 1.8 Acronyms and Terms Perl: Originally. DWIM: Do What I Mean.6 Free Reference Material You can get quick help from the standard perl installation. I wish that they would sell it. Tom Christiansen. If you're writing a "real" script (i. Therefore if you hear reference to some animal book. Once upon a time. and Ullman. then don't use Data::Dumper by default. camel. because that refers to a book called "Compilers" by Aho. unless its the "Dragon Book".cpan. but only what I tell it. The acronyms followed. Now considered an acronym for Practical Extraction and Report Language. See http://www. To bring oneself to life. one where time-torun and memory-usage are issues to be considered). has printed enough computer books to choke a. It never does what I want.org 1. DWIM is just a way of saying the language was designed by some really lazy programmers so that you could be even lazier than they were. as well as Petty Eclectic Rubbish Lister. well.7 Cheap Reference Material "Programming Perl" by Larry Wall.cpan. > > > > perl -h perldoc perldoc -h perldoc perldoc FAQs on CPAN: http://www.org for more. 1. the execution speed isn't that high of a priority. only use it if you really need it." DWIM-iness is an attempt to embed perl with telepathic powers such that it can understand what you wanted to write in your code even though you forgot to actually type it.
Later became known as a UFO. 2. Sometimes. except that "foo" is a common variable name used in perl. An acknowledgment that any programming problem has more than one solution. A "$" is a stylized "S". Foo Fighters: A phrase used around the time of WWII by radar operators to describe a signal that could not be explained. Arrays. An acronym for Fouled Up Beyond All Recognition and similar interpretations. Sometimes. 2 Storage Perl has three basic storage types: Scalars. Specifically.1 Scalars Scalars are preceded with a dollar sign sigil. it will be explained later. The noun form is "autovivification". $ref_to_name = \$name # # # # # The "my" keyword declares a lexical variable. and Filehandles. when "do what I mean" meets autovivification in perl. And now. and for some reason. and perl is often awash in variables named "foo" and "bar". $pi = 3.1415. autovivification wins. Fubar: Another WWII phrase used to indicate that a mission had gone seriously awry or that a piece of equipment was inoperative. sigil : A symbol. Arrays and Hashes use Scalars to build more complex data types. it gives a perl newbie just enough rope to hang himself. $name = 'John Doe'. The most basic storage type is a Scalar.programmer. in section 4 11 . Part of perl's DWIM-ness. Rather than have perl decide which solution is best. it gives you all the tools and lets you choose. autovivification is not what you meant your code to do. you deserve to maintain it. Perl is smart enough to know which type you are putting into a scalar and handle it. Scalars can store Strings. my my my my my $diameter = 42. References. In Perl a sigil refers to the symbol in front of a variable. If you don't know what that means. and Hashes. This allows a programmer to select the tool that will let him get his job done. This has nothing to do with perl either. especially if the programmer wishes to hide the fact that he did not understand his code well enough to come up with better names. don't worry about it. "Autovivify" is a verb. This has nothing to do with perl. $initial = 'g'. except that fubar somehow got mangled into foobar. Numbers (integers and floats). a Haiku: Do What I Mean and Autovivification sometimes unwanted TMTOWTDI: There is More Than One Way To Do It. If you use a $foo variable in your code.
1 Scalar Strings Scalars can store strings. Without use warnings.) Autovivify : to bring oneself to life. There is no reason that warnings and strictness should not be turned on in your scripts. my ($first. perl will autovivify a new variable called "pie". 2. perl just handles it for you automatically. autovivification can be an unholy monster. This is called autovivication. using a variable causes perl to create one and initialize it to undef. > first is 'John' > last is 'Doe' 12 . depending how the undefined variable is used. print hello. therefore $circumference is zero.Without "use strict. > hello. You do not have to declare the length of the string. Autovivified to undef. and assume that is what you meant to do. my $greeting = "hello. # numified to 0. In some situations. initialize it to zero.1. Error: Unquoted string "hello" may clash with reserved word You can use single quotes or double quotes to set off a string literal: my $name = 'mud'. # oops.1. my $circumference = $pie * $diameter. This undef value will stringify to "" or numify to 0." and without declaring a variable with a "my". print $greeting. (Stringification and Numification are covered later. use strict. $pie doesn't exist. $name\n". autovivication is handy.1.1 String Literals String literals must be in single or double quotes or you will get an error. print "last is '$last'\n". in certain situations.$last)=qw( John Doe ). print "first is '$first'\n". 2. However. mud You can also create a list of string literals using the qw() function.
6 length Find out how many characters are in a string with length().1. chomp($string). my $line = '-' x 80.1. print 'hello $name'. The return value of chomp is what was chomped (seldom used). 13 .1.1. My $string = "hello world\n". LENGTH).. # $line is eighty hypens 2. my $name = 'mud'. chomp leaves the string alone. print "hello $name \n". > hello $name Double quotes means that you get SOME variable interpolation during string evaluation. will not be interpolated properly in double quotes. OFFSET.2. 2.4 concatenation String concatenation uses the period character ".1.3 chomp You may get rid of a newline character at the end of a string by chomp-ing the string. 2. Complex variables. my $name = 'mud'.1. such as a hash lookup.5 repetition Repeat a string with the "x" operator." my $fullname = 'mud' .1.7 substr substr ( STRING_EXPRESSION. my $len = length($line).2 Single quotes versus Double quotes Single quoted strings are a "what you see is what you get" kind of thing. warn "string is '$string' \n" > string is 'hello world' .. If there are no newlines.1.1.1. 2. > hello mud Note: a double-quoted "\n" is a new-line character. The chomp function removes one new line from the end of the string even if there are multiple newlines at the end. # $len is 80 2.1.1. "bath".
Use the split function to break a string expression into components when the components are separated by a common substring pattern. fold. You can break a string into individual characters by calling split with an empty string pattern "". replacing the chunk as well. 2).$gender. The substr function gives you fast access to get and modify chunks of a string. STRING_EXPRESSION.1. my ($first. The substr function then returns the chunk.1.. You need a string contained in a variable that can be modified.1. substr($string. The /PATTERN/ in split() is a Regular Expression. > string is 'apples and bananas and peaches'..Spin.$last.\s* comma-separated data 2. The substr function can also be assigned to. You can quickly get a chunk of LENGTH characters starting at OFFSET from the beginning or end of the string (negative offsets go from the end).). > chunk is 'in' . warn "string is '$string'". .. which is complicated enough to get its own chapter. STRING2. and mutilate strings using substr(). my $tab_sep_data = "John\tDoe\tmale\t42". 'apples'. For example. my $string = 'the rain in spain'.LIMIT). some common regular expression PATTERNS for split are: \t tab-separated data \s+ whitespace-separated data \s*. > string is 'the rain beyond spain' . 9. 2..$age) = split(/\t/. 2) = 'beyond'.9 join join('SEPARATOR STRING'. warn "string is '$string'".. my $string = join(" and ". $tab_sep_data).1. STRING1. tab separated data in a single string can be split into separate strings. However. my $chunk = substr('the rain in spain'.. 'bananas'.. 14 . rather than using a constant literal in the example above. Use join to stitch a list of strings into a single string. warn "chunk is '$chunk'". 9.8 split split(/PATTERN/.. 'peaches').
Perl then reads the lines after the '<<' as string literal content until it sees the end of string label positioned at the beginning of a line.1.. HERE Documents Perl allows you to place a multi-line string in your code by using what it calls a "here document".1.. Enclosing the label in single quotes means that no string interpolation occurs.11 Multi-Line Strings. > string is 'apples and bananas and peaches'.1. warn "string is '$string'". Do What I Mean and Autovivification sometimes unwanted ENDOFDOCUMENT warn "string is '$string'". 15 . followed by the name of the label indicating the end of the here document..10 qw The qw() function takes a list of barewords and quotes them for you. qw(apples bananas peaches)). my $string = join(" and ".1. The '<<' indicates a HERE document. My $string = <<"ENDOFDOCUMENT". > string is 'Do What I Mean and > Autovivification > sometimes unwanted' at . Enclosing the label in double quotes means that perl variables in the document will get interpolated as strings.2. 2..
floating point. # hexadecimal $low_address = 0b100101.1.4 my $var2 = abs(5.2.2 Numeric Functions 2.9.2 Scalar Numbers Perl generally uses floats internally to store numbers. Binary numbers begin with "0b" hexadecimal numbers begin with "0x" Octal number begin with a "0" All other numeric literals are assumed to be decimal.3 abs Use abs to get the absolute value of a number. # octal $high_address = 0xfa94. # y_int is -5 (-5 is "bigger" than -5. octal. my my my my my $solar_temp_c = 1. # var1 is 3. my $price = 9.4).2. my $days_in_week = 7.9 2.1 Numeric Literals Perl allows several different formats for numeric literals. # scalar => float 2. my $dollars = int ($price). # centigrade $solar_temp_f = 27_000_000. not 10! false advertising! my $y_pos = -5. my $y_int = int($y_pos).9) 16 . # dollars is 9.9).1. Truncating means that positive numbers always get smaller and negative numbers always get bigger. which means you do NOT get rounding.6.2. my $var1 = abs(-3. Note that this truncates everything after the decimal point.2.5e7.4 int Use "int" to convert a floating point number to an integer. and scientific notation. If you specify something that is obviously an integer.95. as well as decimal. Either way.0. and hexadecimal. # var2 is 5. you simply use it as a scalar. # scalar => integer my $temperature = 98. # Fahrenheit $base_address = 01234567.1.2. including integer.1. # binary 2. it will use an integer.1.
Use the Math::Complex module on CPAN.1. # dollars is 10 2.5 trigonometry (sin. my $seven_squared = 7 ** 2. #125 my $three_to_the_fourth = 3 ** 4. # 3 Standard perl cannot handle imaginary numbers.851 OOPS! If you need inverse sine. my $square_root_of_123 = sqrt(123).95.6 exponentiation Use the "**" operator to raise a number to some power.2.2. # 81 Use fractional powers to take a root of a number: my $square_root_of_49 = 49 ** (1/2). my my my my $angle = 45. # 49 my $five_cubed = 5 ** 3. # 11. $price).If you want to round a float to the nearest integer. # 0.785 rad $sine_rad = sin($radians). 2. # 45 deg $radians = $angle * ( 3. 2. # 5 my $fourth_root_of_81 = 81 ** (1/4).cos) The sin() and cos() functions return the sine and cosine of a value given in RADIANS. my $dollars = sprintf("%. # . # 7 my $cube_root_of_125 = 125 ** (1/3).7 sqrt Use sqrt to take the square root of a positive number.0905 17 . you will need to write a bit of code. # 0.1. inverse cosine.707 Correct! $sine_deg = sin($angle). If you have a value in DEGREES.1. One way to accomplish it is to use sprintf: my $price = 9.2. multiply it by (pi/180) first.0f". or tangent then use the Math::Trig module on CPAN.14 / 180 ).
srand will seed the PRNG with something from the system that will give it decent randomness. to what power do we need to raise the # number 10 to get the value of 12345? my $answer = log_x_base_b(12345. If no value is passed in. you should not need to call it at all. The exp function is straightforward exponentiation: # big_num = 2. You should only need to seed the PRNG once. then use this subroutine: sub log_x_base_b {return log($_[0])/log($_[1]). Natural logarithms simply use the inverse of the value (i.9 random numbers (rand.7e18) = 42 my $inv_exp = $value_of_e ** (1/$big_num).e. # 2.} # want the log base 10 of 12345 # i.7e18 The log function returns the inverse exp() function. my $value_of_e = exp(1).log) The exp function returns e to the power of the value given.1. # 2. you just need to know the value of the magic number e (~ 2.7183 ** (1/1. rand returns a number in the range ( 0 <= return < 1 ) The srand function will seed the PRNG with the value passed in. 2.2.7183 ** 42 = 1.10). because perl will call srand at startup.2. srand) The rand function is a pseudorandom number generator (PRNG).718281828).1.8 natural logarithms(exp.7e18 my $big_num = $value_of_e ** 42. 18 . # inv_exp = 42 If you want another base. # inv_exp = 2. rand returns a number that satisfies ( 0 <= return <= input ) If no value is passed in. You can pass in a fixed value to guarantee the values returned by rand will always follow the same sequence (and therefore are predictable). which is to say.e.7183 my $big_num= exp(42). 1/value) with exponentiation. my $inv_exp = log($big_num).1 Note that inverse natural logs can be done with exponentiation. If you have a version of perl greater than or equal to 5.2.004. call exp(1).7183 ** 42 = 1. To get e. # answer = 4. If a value is passed in. log returns the number to which you would have to raise e to get the value passed in.
. > mass is '7..3. > volume is '4' . my $mass = 7.2f".1.3' 2.1. my $mass = 7.3 Converting Between Strings and Numbers Many languages require the programmer to explicitly convert numbers to strings before printing them out and to convert strings to numbers before performing arithmetic on them. my $str = sprintf("%06. If you want to force stringification.1 sprintf Use sprintf to control exactly how perl will convert a number into string format. If you do not want the default format.14' .$pi).= ''. warn "volume is '$volume'\n". sprintf ( FORMAT_STRING. simply concatenate a null string onto the end of the value. > str is '003..3 my $string_mass = $mass .2.3' . 19 . my $volume = 4.1415.3...1. For example: my $pi = 3.3.3. Perl will attempt to convert the numbers into the appropriate string representation. Even though $mass is stored internally as a floating point number and $volume is stored internally as an integer. use sprintf. # '7. the code did not have to explicitly convert these numbers to string format before printing them out. Perl will automatically convert a number (integer or floating point) to a string format before printing it out. warn "str is '$str'". # 7. Perl will attempt to apply Do What I Mean to your code and just Do The Right Thing.1. There are two basic conversions that can occur: stringification and numification. Perl is not one of these languages. 2. LIST_OF_VALUES ). warn "mass is '$mass'\n".1 Stringify Stringify: Converting something other than a string to a string form..
use the following FORMAT_STRINGS: hexadecimal "%lx" The letter 'l' (L) octal "%lo" indicates the input is binary "%lb" an integer. possibly decimal integer "%ld" a Long integer.Decoding the above format string: % => format 0 => fill leading spaces with zero 6 => total length. octal. my $user_input = '19.1. For example. decimal float "%f" scientific "%e" 2. a user might enter the string "19. # 19.95" which must be converted to a float before perl can perform any arithmetic on it. You can force numification of a value by adding integer zero to it.2 Numify Numify: Converting something other than a number to a numeric form. or decimal formated string.95 If the string is NOT in base ten format. binary. # '19. then use oct() or hex() 20 .2 => put two places after the decimal point f => floating point notation To convert a number to a hexadecimal.95' my $price = $user_input+0. including decimal point .3. Sometimes you have string information that actually represents a number.95'.
3. hexadecimal.3. 21 .3.2. use this: # 08 assumes width is 8 characters my $p_hex = sprintf("%08lx". call oct on it. or binary format and convert it to an integer. you could assume that octal strings must start with "0".1. 2. The hex() function is like oct() except that hex() only handles hex base strings.1. and it does not require a "0x" prefix. OR decimal strings. my $p_bin = sprintf("%08lb". $decimal). Convert from decimal to another base using sprintf: my $hex = sprintf("%lx". else assume it's decimal. $decimal). my $oct = sprintf("%lo". This means calling oct() on a decimal number could be a bad thing. This example uses regular expressions and the conditional operator. hexadecimal. my $bin = sprintf("%lb". $decimal).1 oct The oct function can take a string that fits the octal.1. If you want to pad the most significant bits with zeroes and you know the width. Then. binary formatted strings must start with "0b" hexadecimal formatted strings must start with "0x" All other numbers are assumed to be octal strings.3 Base Conversion Overview Given a decimal number: my $decimal=12. my $num = ($str=~m{^0}) ? oct($str) : $str + 0. To handle a string that could contain octal. $decimal).2. binary. 2. my $p_oct = sprintf("%08lo".2.2 hex The hex() function takes a string in hex format and converts it to integer. Note: even though the string might not start with a zero (as required by octal literals). $decimal). if the string starts with zero. oct will assume the string is octal. $decimal).2.
this conversion is silent. If you use a scalar that is undefined. the function returns a boolean "true" (1) If the scalar is NOT defined. # 8 2. If the scalar is defined. Since perl automatically performs this conversion no matter what.4 Undefined and Uninitialized Scalars All the examples above initialized the scalars to some known value before using them. 255)). use the conditional operator and oct(). warn length(sprintf("%lb". # dec convert_to_decimal('032'). } warn warn warn warn convert_to_decimal('42'). perl will stringify or numify it based on how you are using the variable. You can declare a variable but not initialize it. 22 . convert it to binary using sprintf (don't pad with zeros) and then call length() on it. # oct convert_to_decimal('0xff'). there is no string or numeric operation that will tell you if the scalar is undefined or not.If you have a string and you want to convert it to decimal. With warnings/strict on. the function returns a boolean "false" (""). but a warning is emitted. the conversion still takes place. Use the defined() function to test whether a scalar is defined or not.1. in which case. # hex convert_to_decimal('0b1001011'). # bin If you want to know how many bits it would take to store a number. sub convert_to_decimal { ($_[0]=~m{^0}) ? Oct($_[0]) : $_[0] + 0. An undefined scalar stringifies to an empty string: "" An undefined scalar numifies to zero: 0 Without warnings or strict turned on. the variable is undefined.
} else {print "undefined\n". and you want to return it to its uninitialized state.If you have a scalar with a defined value in it. perl interprets scalar strings and numbers as "true" or "false" based on some rules: 1)Strings "" and "0" are FALSE. any other number is TRUE 3) all references are TRUE 4) undef is FALSE Note that these are SCALARS. and then treated as a string or number by the above rules. Any variable that is not a SCALAR is first evaluated in scalar context.} > test 1 :undefined > test 2 :defined > test 3 :undefined 2. This will be exactly as if you declared the variable with no initial value. use this: return wantarray() ? () : 0. An array with one undef value has a scalar() value of 1 and is therefore evaluated as TRUE.5 Booleans Perl does not have a boolean "type" per se. any other string or stringification is TRUE 2) Number 0 is FALSE. The scalar context of an ARRAY is its size. # undef print "test 1 :". if(defined($var)) {print "defined\n". my $var. Instead. if(defined($var)) {print "defined\n". assign undef to it. if(defined($var)) {print "defined\n".1. # undef as if never initialized print "test 3 :".} else {print "undefined\n". A subroutine returns a scalar or a list depending on the context in which it is called. #FALSE 23 . To explicitly return FALSE in a subroutine. # FALSE This is sufficiently troublesome to type for such a common thing that an empty return statement within a subroutine will do the same thing: return.} else {print "undefined\n".} $var = undef.} $var = 42. # defined print "test 2 :".
1415 # true integer 11 # true string 'yowser' # true If you are doing a lot of work with numbers on a variable.2 TRUE ALL other values are interpreted as TRUE.5. which is FALSE.0" instead of a float 0. string '0. Note that the string '0. even though you might not have expected them to be false. just in case you end up with a string "0.1. If you are processing a number as a string and want to evaluate it as a BOOLEAN. make sure you explicitly NUMIFY it before testing its BOOLEANNESS.1. Built in Perl functions that return a boolean will return an integer one (1) for TRUE and an empty string ("") for FALSE.0 # false string '0' # false string '' # false undef # false 2. you may wish to force numification on that variable ($var+0) before it gets boolean tested.0'+0) will get numified to 0. which means the following scalars are considered TRUE.5.0' is TRUE.2.1 FALSE The following scalars are interpreted as FALSE: integer 0 # false float 0.0' # true string '00' # true string 'false' # true float 3.0 and get some seriously hard to find bugs. but ('0. 24 .
If you use a numeric operator to compare two strings. or +1. then you will get the wrong result when you compare the strings ("9" lt "100").3 Comparators Comparison operators return booleans. perl will attempt to numify the strings and then compare them numerically. Function String Numeric Function String Numeric equal to eq == not equal to ne != less than lt < greater than gt > less than or equal to le <= greater than or equal to ge >= comparison (lt=-1. indicating the compared values are less than. if warnings/strict is not on. Number 9 is less than (<=) number 100. The "Comparison" operator ("<=>" and "cmp") return a -1. equal to. or greater than. assigning the numification of "John" to integer zero.5. String "9" is greater than (gt) string "100". gt=+1) cmp <=> equal to Note that if you use a string operator to compare two numbers. it will fail miserably and SILENTLY. you will get their alphabetical string comparison. Comparing "John" <= "Jacob" will cause perl to convert "John" into a number and fail miserably. This will occur silently. 0. Perl will stringify the numbers and then perform the compare. perl will emit no warning.1. 25 . Distinct comparison operators exist for comparing strings and for comparing numbers. And if you wanted the numbers compared numerically but used string comparison. The numeric comparison operator '<=>' is sometimes called the "spaceship operator". eq=0. specifically an integer 1 for true and a null string "" for false. However.2.
and '!' operators. so it is useful to learn how precedence affects their behavior. 'not'.2. The difference between the two is that one set has a higher precedence than the other set. function operator usage return value AND && $one && $two if ($one is false) $one else $two OR || $one || $two if ($one is true) $one else $two NOT ! ! $one if ($one is false) true else false The lower precedence logical operators are the 'and'. 26 . function operator usage return value AND and $one and $two if ($one is false) $one else $two OR or $one or $two if ($one is true) $one else $two NOT not not $one if ($one is false) true else false XOR xor $one xor $two if ( ($one true and $two false) or ($one false and $two true) ) then return true else false Both sets of operators are very common in perl code. The higher precedence logical operators are the '&&'.4 Logical Operators Perl has two sets of operators to perform logical AND. 'or'. some examples of how to use them. OR. NOT functions. But first.5. and 'xor' operators.1. '||'.
5.0.2 Flow Control The open() function here will attempt to open $filename for reading and attach $filehandle to it. 2. is exactly the same as this: $left = $left || 220.127.116.11. and FALSE OR'ed with die () means that perl will evaluate the die() function to finish the logical evaluation.0.4 Assignment Precedence When working with an assignment.220.127.116.11 Precedence The reason we used '||' in the first example and 'or' in the second example is because the operators have different precedence. 2. The 'or' and 'and' operators have a precedence that is LOWER than an assignment.0). If open() fails in any way. sub mysub { my( $left. $right ||= 2. followed by any remaining 'and' and 'or' operators. Right: my $default = 0 || 1. This: $left ||= 1. $left ||= 1. # default is 1 27 . $filename) or die "cant open".1. but the end result is code that is actually quite readable.5. and we used the one with the precedence we needed.4. $right )=@_.4. If the user calls the subroutine with missing arguments.0. meaning the assignment would occur first.2. the undefined parameters will instead receive their default values. # deal with $left and $right here. open (my $filehandle.0 and 2.1 Default Values This subroutine has two input parameters ($left and $right) with default values (1.1. It won't complete because execution will die. use '||' and '&&'. } The '||=' operator is a fancy shorthand. 2. it returns FALSE.0. because they have a higher precedence than (and are evaluated before) the assignment '='.
and close $fh. but it is probably better to get in the habit of using the right operator for the right job. its not a problem. and is also called a trinary operator.1.5 Flow Control Precedence When using logical operators to perform flow control. 28 . which will ALWAYS assign $default to the first value and discard the second value. 2. use 'or' and 'and' operators. The '||' and '&&' have higher precedence than functions and may execute before the first function call. The conditional operator has this form: my $RESULT = $BOOLEAN1 ? $VALUE1 : $VALUE2. 2. which will ALWAYS evaluate $fh as true.Wrong: my $default = 0 or 1. so people sometimes call it the trinary or ternary operator when they mean conditional operator. Right: close $fh or die "Error:could not close".5. As long as perl doesn't add another trinary operator. and the program continues on its merry way. the conditional operator is perl's ONLY trinary operator.1. because they have lower precedence than functions and other statements that form the boolean inputs to the 'or' or 'and' operator. As it happens. # default is 0 The second (wrong) example is equivalent to this: (my $default = 0) or 1.4. It is even more rarely called the ?: operator. It is always possible to override precedence with parentheses. Wrong: close $fh || die "Error: could not close". NEVER die.6 Conditional Operator The conditional operator mimics the conditional testing of an if-else block.5.4. The second (wrong) example is equivalent to this: close ($fh || die "Error"). The conditional operator uses three operands. If close() fails. the return value is discarded.
if($BOOLEAN1) { $RESULT = $VALUE1 } else { $RESULT = $VALUE2 } The conditional operator allows you to declare the variable and perform the assignment all in one short line of code. Unlike C. effectively allowing you to create a chain of if-elsifelsif-else statements. One interesting expression that you could replace $VALUE2 with is another conditional operator.6 References A reference points to the variable to which it refers. Note that $BOOLEAN1. you cannot manually alter the address of a perl reference. $VALUE1 $VALUE2 $VALUE3 $VALUE4 The above example is equivalent to this mouthful: my $RESULT. $age = 42.This can be rewritten as an if-else block like this: my $RESULT. It is kind of like a pointer in C. which says "the data I want is at this address".1. $age_ref = \$age. You can only create a reference to a variable that is visible from your current scope. rather than being limited to a simple scalar value. For example: my $RESULT = $BOOLEAN1 ? : $BOOLEAN2 ? : $BOOLEAN3 ? : $BOOLEAN4 ? : $VALUE5. 29 . $name_ref = \$name. if($BOOLEAN1) elsif($BOOLEAN2) elsif($BOOLEAN3) elsif($BOOLEAN4) eles { $RESULT = { $RESULT { $RESULT { $RESULT { $RESULT $VALUE5 } = = = = $VALUE1 $VALUE2 $VALUE3 $VALUE4 } } } } 2. $VALUE1 and $VALUE2 can be replaced by any normal perl expression. Create a reference by placing a "\" in front of the variable: my my my my $name = 'John'.
. warn "age_ref is '$age_ref'". such as "SCALAR (0x83938949)" and have perl give you a reference to whatever is at that address. Perl is pretty loosy goosey about what it will let you do. This tells you that $age_ref is a reference to a SCALAR (which we know is called $age). > age_ref is 'SCALAR(0x812e6ec)' . you cannot give perl a string..E. but not even perl is so crazy as to give people complete access to the system memory. 30 . It also tells you the address of the variable to which we are referring is 0x812e6ec.Perl will stringify a reference so that you can print it and see what it is. You cannot referencify a string. I.
You can dereference a reference by putting an extra sigil (of the appropriate type) in front of the reference variable. my $deref_name = $$ref_to_name. 2.txt". warn $deref_name. my $ref_to_name = \$name. print $fh "hello world\n". References are interesting enough that they get their own section. But this will be absolutely essential when working with Arrays and Hashes.. This does not seem very impressive with a reference to a scalar: my $name = 'John'. But I introduce them here so that I can introduce a really cool module that uses references: Data::Dumper.. my $name = 'John'. print $fh "this is simple file writing\n".7 Filehandles Scalars can store a filehandle. close($fh). > John . '>out.txt'). but I introduce it here to give a complete picture of what scalars can hold. and store the handle to that file in the scalar. warn Dumper \$ref_to_name. my $ref_to_name = \$name. There is some magic going on there that I have not explained. File IO gets its own section. 31 . Data::Dumper will take a reference to ANYTHING and print out the thing to which it refers in a human readable form. > $VAR1 = \'John'. The scalar $fh in the example above holds the filehandle to "out. but that is a quick intro to scalar filehandles.1. open(my $fh. calling open() on that scalar and a string filename will tell perl to open the file specified by the string. Printing to the filehandle actually outputs the string to the file. Given a scalar that is undefined (uninitialized).
use the "@" sigil.) The first element of an array always starts at ZERO (0). When you index into the array.. 32 . my @numbers = qw ( zero one two three ). The "@" is a stylized "a".0. Stringify: to convert something to a string format Numify: to convert something to a numeric format The following scalars are interpreted as boolean FALSE: integer 0.. string "". Perl arrays are ONE-DIMENSIONAL ONLY. and FILEHANDLES. 2.1. NUMBERS (floats and ints). > two .2. When you refer to an entire array. undef All other scalar values are interpreted as boolean TRUE. (Do Not Panic.8 Scalar Review Scalars can store STRINGS.2 Arrays Arrays are preceded with an "at" sigil. my @numbers = qw ( zero one two three ). string "0". warn $string. my $string = $numbers[2]. An array stores a bunch of scalars that are accessed via an integer index. REFERENCES. float 0. the "@" character changes to a "$" and the numeric index is placed in square brackets.
# this is same as undef > ${\$VAR1->[0]}. 2. 9*11. > $VAR1 = [ > undef. # undef > ${\$VAR1->[0]}. my @colors = qw ( red green blue ). 3. my $last=$colors[-1]. 'yaba'. '//'. which is initialized to 1 Arrays can store ANYTHING that can be stored in a scalar my @junk_drawer = ( 'pliers'.1. warn $quantity. try running this piece of code: my @mem_hog. $months[5]='May'.. $mem_hog[10000000000000000000000]=1. # $months[1] > ${\$VAR1->[0]}. Perl autovivifies whatever space it needs. # $months[0] and $months[2.4] are autovivified # and initialized to undef print Dumper \@months. # index 0 is undefined > 'January'.1 scalar (@array) To get how many elements are in the array. my @months.1. > last is 'blue' .14. $months[1]='January'.. Negative indexes start from the end of the array and work backwards. If you want to see if you can blow your memory. # undef > 'May' # $months[5] > ]. use "scalar" my @phonetic = qw ( alpha bravo charlie delta ). # the array is filled with undefs # except the last entry. 'daba' ). '*'.The length of an array is not pre-declared. warn "last is '$last'".. my $quantity = scalar(@phonetic).2. 33 .. > 4 .. 1.
you will get the same thing.3 pop(@array) Use pop() to get the last element off of the end of the array (the highest index). > > > > > > > $VAR1 = [ 'milk'. my @groceries = qw ( milk bread ). This will shorten the array by one. my @names = qw ( alice bob charlie ).2. push(@groceries. my $last_name = pop(@names).. 34 . warn $quant. my $quant = @phonetic. print Dumper \@names. warn "popped = $last_name".2. The return value of pop() is the value popped off of the array. 2. print Dumper \@groceries. my @phonetic = qw ( alpha bravo charlie ). qw ( eggs bacon cheese )). 'bacon'.. but calling scalar() is much more clear. This will increase the length of the array by the number of items added.. > > > > > popped = charlie . > 3 . LIST) Use push() to add elements onto the end of the array (the highest index). 2.When you assign an entire array into a scalar variable. 'bob' ]. 'cheese' ]. This is explained later in the "list context" section.. $VAR1 = [ 'alice'. 'bread'. 'eggs'.2 push(@array.
5 unshift( @array. my $start = shift(@curses). at index ZERO). 35 .2. # 2 'oak' # 3 ].e. at index zero).2. This will length the array by the number of elements in LIST. 2. > > > > > > $VAR1 = [ 'birch'. my @curses = qw ( fee fie foe fum ).4 shift(@array) Use shift() to remove one element from the beginning/bottom of an array (i. LIST) use unshift() to add elements to the BEGINNING/BOTTOM of an array (i.2. warn Dumper \@curses. 'foe'. my @trees = qw ( pine maple oak ). unshift(@trees. 'fum' ]. The return value is the value removed from the array. The array will be shorted by one. # index 0 'pine'.e. > > > > > > fee $VAR1 = [ 'fie'. warn $start. 'birch'). now 1 'maple'. # old index 0. All elements will be shifted DOWN one index. warn Dumper \@trees. All the other elements in the array will be shifted up to make room.
my @numbers = qw (zero one two three). Its formal definition is: LABEL foreach VAR (LIST) BLOCK This is a control flow structure that is covered in more detail in the "control flow" section. } > > > > fruit fruit fruit fruit is is is is 'apples' 'oranges' 'lemons' 'pears' DO NOT ADD OR DELETE ELEMENTS TO AN ARRAY BEING PROCESSED IN A FOREACH LOOP.6 foreach (@array) Use foreach to iterate through all the elements of a list. Use a simple foreach loop to do something to each element in an array: my @fruits = qw ( apples oranges lemons pears ). foreach my $fruit (@fruits) { print "fruit is '$fruit'\n".2.2. which is still part of array. BAD!! 36 . and redo statements. The foreach structure supports last. print "num is '$num'\n". foreach my $num (@numbers) { shift(@numbers) if($num eq 'one'). but I failed to print out 'two'. next. } > > > # # # num is 'zero' num is 'one' num is 'three' note: I deleted 'zero'.
The return value is the sorted version of the array. Changes to VAR propagate to changing the array. 242. > 'oranges'. 83948 ). my @integers = ( 23. 13. } print Dumper \@integers. my @sorted_array = sort(@scores). # 1's 13. 27. print Dumper \@sorted_array .2. 2. > > > > > > $VAR1 = [ 123. # 1's 150. foreach my $num (@integers) { $num+=100. 9384. The array passed in is left untouched. 27. my @sorted_array = sort(@fruit). # 1's 200. 150 ). Sorting a list of numbers will sort them alphabetically as well. 76 ]. 142. 200. > > > > > > > > $VAR1 = [ 1000. 84048 ].7 sort(@array) Use sort() to sort an array alphabetically.VAR acts as an alias to the element of the array itself. print Dumper \@sorted_array . 76. > 'bananas'. >$VAR1 = [ > 'apples'. 9484. which probably is not what you want. 37 . > 'pears' > ]. my @scores = ( 1000. my @fruit = qw ( pears apples bananas oranges ).
27. my @sorted_array = sort {$a<=>$b} (@scores). 27. The first element becomes the last element. 76.The sort() function can also take a code block ( any piece of code between curly braces ) which defines how to perform the sort if given any two elements from the array. > 1000 > ]. 150. 150 ). The last element becomes the first element. > 184.108.40.206 reverse(@array) The reverse() function takes a list and returns an array in reverse order.13.27. > 27. This is how you would sort an array numerically. 200.76. and defines how to compare the two entries. > 76. > 13.150). The code block uses two global variables. 2. my @scores = ( 1000. 76. print Dumper \@numbers . 13. print Dumper \@sorted_array . my @numbers = reverse (1000. 200. 38 . $a and $b. > $VAR1 = [ > 150. > > > > > > > > $VAR1 = [ 13. 1000 ].
1. Therefore you can test to see if an array is initialized by calling scalar() on it. This would fill the array with one element at index zero with a value of undefined. The first item will be treated as the key. warn join(" ". assign an empty list to it. This will clear out any entries. and leave you with a completely empty array. 2.3 Hashes Hashes are preceded with a percent sign sigil. my @array = (). Perl will extract them in pairs.9 splice(@array) Use splice() to add or remove elements into or out of any index range of an array. 0. LENGTH .e.) You can assign any even number of scalars to a hash.) There is no order to the elements in a hash. my @words = qw ( hello there ). OFFSET . and the second item will be treated as the value. # RIGHT 2. (Do Not Panic.. This is equivalent to calling defined() on a scalar variable.2. there is. 39 . 'out'). > hello out there . LIST ). splice ( ARRAY .10 Undefined and Uninitialized Arrays An array is initialized as having no entries.2. but you should not use a hash with an assumption about what order the data will come out. # WRONG To clear an array to its original uninitialized state.. then the array is uninitialized. integer 0). Any elements from LIST will be inserted at OFFSET into ARRAY. The elements in ARRAY starting at OFFSET and going for LENGTH indexes will be removed from ARRAY. If scalar() returns false (i. splice(@words. (Well. If you want to uninitialize an array that contains data. The "%" is a stylized "key/value" pair. @words). A hash stores a bunch of scalars that are accessed via a string index called a "key" Perl hashes are ONE-DIMENSIONAL ONLY. my @array = undef. then you do NOT want to assign it undef like you would a scalar.2.
the "%" character changes to a "$" and the key is placed in curly braces. The keys of a hash are not pre-declared. the key is NOT created.When you refer to an entire hash. my %inventory. print Dumper \%inventory./test. warn "peaches is '$peaches'". my %info = qw ( name John age 42 ). and undef is returned. >$VAR1 = { > 'bananas' => 5.. > John . my $peaches = $inventory{peaches}. warn $data. $inventory{apples}=42.. If the key does not exist during a FETCH. $inventory{apples}=42. my $data = $info{name}. use the "%" sigil. $inventory{pears}=17. $inventory{bananas}=5. If the key does not exist during an ASSIGNMENT. > > > > > Use of uninitialized value in concatenation peaches is '' at . 40 . print Dumper \%inventory. > 'apples' => 42. my %inventory. $VAR1 = { 'apples' => 42 }. my %info = qw ( name John age 42 ).pl line 13. the key is created and given the assigned value. > 'pears' => 17 > }. When you look up a key in the hash.
1 exists ( $hash{$key} ) Use exists() to see if a key exists in a hash. $stateinfo{Florida}->{Abbreviation}='FL'. unless(exists($pets{fish})) { print "No fish here\n". > $VAR1 = { > 'Florida' => > > > }.2. and only the last key has exists() tested on it. if (exists($stateinfo{Maine})) { if (exists($stateinfo{Maine}->{StateBird})) { warn "it exists". } Warning: during multi-key lookup. but we only test for the existence of {Maine}>{StateBird}. $stateinfo{Florida}->{Abbreviation}='FL'. all the lower level keys are autovivified. since a key might exist but store a value of FALSE my %pets = ( cats=>2. This only happens if you have a hash of hash references.3. and build your way up to the final key lookup if you do not want to autovivify the lower level keys. which has the side effect of creating the key {Maine} in the hash. my %stateinfo. References are covered later. > $VAR1 = { > > > > > }. } print Dumper \%stateinfo. You cannot simply test the value of a key. } } print Dumper \%stateinfo. 'Florida' => { 'Abbreviation' => 'FL' }. my %stateinfo. but this is a "feature" specific to exists() that can lead to very subtle bugs. if (exists($stateinfo{Maine}->{StateBird})) { warn "it exists". 'Maine' => {} You must test each level of key individually. dogs=>1 ). we explicitly create the key "Florida". { 'Abbreviation' => 'FL' } 41 . Note in the following example.
42 . The only way to remove a key/value pair from a hash is with delete(). ). ). Note in the example below that the order of assignment is different from the order printed out. The order of the keys will be based on the internal hashing algorithm used. print Dumper \%pets. 'cats' => undef. > $VAR1 = { > > > }.3.3. Once a key is created in a hash. 'dogs' => 1 2.3 keys( %hash ) Use keys() to return a list of all the keys in a hash. then you may wish to use the each() function described below. and should not be something your program depends upon. delete($pets{fish}). my %pets = ( fish=>3. dogs=>1. foreach my $pet (keys(%pets)) { print "pet is '$pet'\n".2.2 delete ( $hash{key} ) Use delete to delete a key/value pair from a hash. } > pet is 'cats' > pet is 'dogs' > pet is 'fish' If the hash is very large. dogs=>1. cats=>2. cats=>2. my %pets = ( fish=>3. $pets{cats}=undef. assigning undef to it will keep the key in the hash and will only assign the value to undef.
} > pet='cats'. 2. qty='3' 43 . 1. > $VAR1 = [ > > > > ]. print Dumper \@pet_keys.3. qty='1' > pet='fish'. ).4 values( %hash ) Use values() to return a list of all the values in a hash. cats=>2. > $VAR1 = [ > > > > ]. 'cats'. qty='$qty'\n". 'dogs'. one at a time.$qty)=each(%pets)) { print "pet='$pet'. then you may wish to use the each() function described below.5 each( %hash ) Use each() to iterate through each key/value pair in a hash. dogs=>1. 'fish' 2. my %pets = ( fish=>3. The order of the values will match the order of the keys return in keys(). dogs=>1. my %pets = ( fish=>3. my @pet_vals = values(%pets). print Dumper \@pet_vals. qty='2' > pet='dogs'. 3 If the hash is very large. my @pet_keys = keys(%pets).3. while(my($pet. cats=>2. ).2.
$qty)=each(%pets). ). # dogs one_time. } } one_time. You can delete keys while iterating a hash with each(). The subroutine is called multiple times without using a while() loop. # cats one_time. # then each() must have hit end of hash if(defined($pet)) { print "pet='$pet'. qty='$qty'\n". my %pets = ( fish=>3. dogs=>1. Calling keys() on the hash will reset the iterator. which is boolean false.Every call to each() returns the next key/value pair in the hash. # end of hash one_time. keys(%hash). This is how the while loop is able to loop through each key/value and then exit when done. This iterator is used by perl to remember where it is in the hash for the next call to each(). This example uses a subroutine to call each() once and print out the result. sub one_time { my($pet. Do not add keys while iterating a hash with each(). # dogs keys(%pets). cats=>2. the next call to each() will return an empty list. Every hash has one "each iterator" attached to it. # cats one_time. The each() function does not have to be used inside a while loop. The list returned by keys() can be discarded. # dogs 44 . } else { print "end of hash\n". # fish one_time. # reset the hash iterator one_time. # if key is not defined. # cats one_time. After the last key/value pair is returned.
pet='fish'.> > > > > > > > pet='cats'. namely at the end of the list. cats=>2.. and the process repeats itself indefinitely. pet='cats'. pet='dogs'. } else { print "there are less $orig_pet " . calls each() again. pet='dogs'. which means calling each() on a hash in a loop that then calls each() on the same hash another loop will cause problems."than $cmp_pet\n". The outside loop calls each() which continues where the inside loop left off. dogs=>1.$orig_qty)=each(%pets)) { while(my($cmp_pet. The example below goes through the %pets hash and attempts to compare the quantity of different pets and print out their comparison. end of hash pet='cats'. 45 . The code then enters the inside loop. while(my($orig_pet. pet='dogs'. The inside loop calls each() and gets "dogs". The inside loop calls each() one more time and gets an empty list. } } } > > > > > > > > > there there there there there there there there . The inside loop continues. qty='2' qty='1' qty='2' qty='1' qty='3' qty='2' qty='1' There is only one iterator variable connected with each hash. and gets "fish". are are are are are are are are more less more less more less more less cats cats cats cats cats cats cats cats than than than than than than than than dogs fish dogs fish dogs fish dogs fish The outside loop calls each() and gets "cats".$cmp_qty)=each(%pets)) { if($orig_qty>$cmp_qty) { print "there are more $orig_pet " . and returns "cats".. The inside loop exits. )."than $cmp_pet\n". my %pets = ( fish=>3.
} } } > > > > > > there there there there there there are are are are are are more less less less more more cats cats dogs dogs fish fish than than than than than than dogs fish fish cats cats dogs If you do not know the outer loop key. dogs=>1. The inner loop continues to call each() until it gets the key that matches the outer loop key. cats=>2. )."than $cmp_pet\n". This also fixes a problem in the above example in that we probably do not want to compare a key to itself. my %pets = ( fish=>3. and loop through the array of keys using foreach. while(my($orig_pet. then the only other solution is to call keys on the hash for all inner loops. either because its in someone else's code and they do not pass it to you.$cmp_qty)=each(%pets). The inner loop will then not rely on the internal hash iterator value."than $cmp_pet\n". last if($cmp_pet eq $orig_pet). next unless(defined($cmp_pet)). if($orig_qty>$cmp_qty) { print "there are more $orig_pet " . The inner loop must skip the end of the hash (an undefined key) and continue the inner loop. store the keys in an array.$orig_qty)=each(%pets)) { while(1) { my($cmp_pet.One solution for this each() limitation is shown below. } else { print "there are less $orig_pet " . or some similar problem. 46 .
dogs=>1 ). In the above example the order of scalars is retained: milk. print Dumper \@checkout_counter. > 'eggs'. my @cart2=qw( eggs bacon juice ). cats=>2. @cart1 and @cart2. 'cats'. Everything in list context gets reduced to an ordered series of scalars. using the first scalar as a key and the following scalar as its value. but there is no way to know. You cannot declare a "list context" in perl the way you might declare an @array or %hash. > 'bacon'. @cart2 ). In fact. The initial values for the hash get converted into an ordered list of scalars ( 'fish'. List context affects how perl executes your source code.4 List Context List context is a concept built into the grammar of perl. @cart1 might have been empty. Basically. there is no way to know where the contents of @cart1 end and the contents of @cart2 begin. my @cart1 = qw( milk bread eggs). 3. We have used list context repeatedly to initialize arrays and hashes and it worked as we would intuitively expect: my %pets = ( fish=>3. 1 ) These scalars are then used in list context to initialize the hash. pulled up to the @checkout_counter and unloaded their carts without putting one of those separator bars in between them. 47 . and so on throughout the list. my @cart1=qw( milk bread butter). > 'juice' > ]. > 'butter'. butter is the order of scalars in @cart1 and the order of the scalars at the beginning of @checkout_counter. two people with grocery carts. The person behind the @checkout_counter has no idea whose groceries are whose. 'dogs'. bread. > $VAR1 = [ > 'milk'. Sometimes. > 'bread'. 2. The original container that held the scalars is forgotten. and all the contents of @checkout_counter could belong to @cart2. looking at just @checkout_counter.2. Here is an example. However. my @checkout_counter = ( @cart1. list context can be extremely handy.
List context applies anytime data is passed around in perl. Scalars, arrays, and hashes are all affected by
list context. In the example below, @house is intended to contain a list of all the items in the house.
However, because the %pets hash was reduced to scalars in list context, the values 3,2,1 are
disassociated from their keys. The @house variable is not very useful.
my %pets = ( fish=>3, cats=>2, dogs=>1 );
my @refrigerator=qw(milk bread eggs);
my @house=('couch',%pets,@refrigerator,'chair');
print Dumper \@house;
> ];
There are times when list context on a hash does make sense.
my %encrypt=(tank=>'turtle',bomber=>'eagle');
my %decrypt=reverse(%encrypt) ;
print Dumper \%decrypt;
'eagle' => 'bomber',
'turtle' => 'tank'
> };
The %encrypt hash contains a hash look up to encrypt plaintext into cyphertext. Anytime you want to
use the word "bomber", you actually send the word "eagle". The decryption is the opposite. Anytime
you receive the word "eagle" you need to translate that to the word "bomber".
Using the %encrypt hash to perform decryption would require a loop that called each() on the %encrypt
hash, looping until it found the value that matched the word received over the radio. This could take too
Instead, because there is no overlap between keys and values, (two different words don't encrypt to the
same word), we can simply treat the %encrypt hash as a list, call the array reverse() function on it,
which flips the list around from end to end, and then store that reversed list into a %decrypt hash.
2.5 References
References are a thing that refer (point) to something else.
The "something else" is called the "referent", the thing being pointed to.
Taking a reference and using it to access the referent is called "dereferencing".
A good real-world example is a driver's license. Your license "points" to where you live because it lists
your home address. Your license is a "reference". The "referent" is your home. And if you have
forgotten where you live, you can take your license and "dereferencing" it to get yourself home.
It is possible that you have roommates, which would mean multiple references exist to point to the
same home. But there can only be one home per address.
In perl, references are stored in scalars. You can create a reference by creating some data (scalar, array,
hash) and putting a "\" in front of it.
my %home= (
my $license_for_alice = \%home;
my $license_for_bob = \%home;
Alice and Bob are roommates and their licenses are references to the same %home. This means that
Alice could bring in a bunch of new pets and Bob could eat the bread out of the refrigerator even
though Alice might have been the one to put it there. To do this, Alice and Bob need to dereference
their licenses and get into the original %home hash.
$ {$license_for_alice} {dogs} += 5;
delete($ {$license_for_bob} {milk});
print Dumper \%home;
'eggs' => 12,
'cats' => 2,
'bread' => 2,
'dogs' => 6,
'fish' => 3
> };
2.5.1 Named Referents
A referent is any original data structure: a scalar, array, or hash. Below, we declare some named
referents: age, colors, and pets.
my $age = 42;
my @colors = qw( red green blue );
my %pets=(fish=>3,cats=>2,dogs=>1);
2.5.2 References to Named Referents
A reference points to the referent. To take a reference to a named referent, put a "\" in front of the
named referent.
my $ref_to_age = \$age;
my $r_2_colors = \@colors;
my $r_pets = \%pets;
2.5.3 Dereferencing
To dereference, place the reference in curly braces and prefix it with the sigil of the appropriate type.
This will give access to the entire original referent.
${$ref_to_age}++; # happy birthday
my %copy_of_pets = %{$r_pets};
print "age is '$age'\n";
> age is '43'
If there is no ambiguity in dereferencing, the curly braces are not needed.
$$ref_to_age ++; # another birthday
print "age is '$age'\n";
> age is '44'
# 5 new dogs 'fish' => 3 }. $r_pets = \%pets.cats=>2. Take the reference. $VAR1 = { 'cats' => 2. my %pets=(fish=>3. 2. # green turned to yellow 'blue' ]. and pets. ${$r_colors}[1] = 'yellow'.dogs=>1). ${$r_colors}[1] = 'yellow'. 'yellow'. put the contents of the array in square brackets.dogs=>1). follow it by "->". $r_colors->[1] = 'yellow'. $r_colors = \@colors.cats=>2.4 Anonymous Referents Here are some referents named age. @colors = qw( red green blue ). This: ${$r_pets} {dogs} += 5. 51 . $r_age = \$age. my $r_pets = \%pets. my $r_colors = \@colors. %pets=(fish=>3. > $VAR1 = [ 'red'. Because array and hash referents are so common. and then follow that by either "[index]" or "{key}". ${$r_pets} {dogs} += 5. my my my my my my $age = 42. my @colors = qw( red green blue ). print Dumper \%pets. colors. Each named referent has a reference to it as well. is exactly the same as this: $r_pets->{dogs} += 5.5. An anonymous referent has no name for the underlying data structure and can only be accessed through the reference.It is also possible to dereference into an array or hash with a specific index or key. It is also possible in perl to create an ANONYMOUS REFERENT. 'dogs' => 6. perl has a shorthand notation for indexing into an array or looking up a key in a hash using a reference. print Dumper \@colors. To create an anonymous array referent.
Likewise.dogs=>1 }.cats=>2. > 'dogs' => 1. my $colors_ref = [ 'red'. To create an anonymous hash referent. The curly braces will create the underlying hash with no name. 'blue' ]. > $VAR1 = [ > 'red'. but that array has no name to directly access its data. > 'green'. and return a reference to that unnamed array. Note that $colors_ref is a reference to an array.The square brackets will create the underlying array with no name. > $VAR1 = { > 'cats' => 2. 52 . You must use $pets_ref to access the data in the hash. but that hash has no name to directly access its data. and return a reference to that unnamed hash. print Dumper $colors_ref. You must use $colors_ref to access the data in the array. > 'blue' > ]. > 'fish' => 3 > }. 'green'. put the contents of the hash in curly braces. print Dumper $pets_ref. my $pets_ref = { fish=>3. $pets_ref is a reference to a hash.
5. cats=>2. # Alice added more canines $house->{pets}->{dogs}+=5. > 'bread'. my @refrigerator=qw(milk bread eggs). my $house={ pets=>\%pets. 53 . one a hash reference and the other an array reference. refrigerator=>\@refrigerator }. > 'dogs' => 1. > $VAR1 = { > 'pets' => { > 'cats' => 2. print Dumper $house. dogs=>1 ). complex data structures are now possible. "pets" and "refrigerator". # Bob drank all the milk shift(@{$house->{refrigerator}}). my %pets = ( fish=>3. > 'eggs' > ] > }. > 'fish' => 3 > }. These keys are associated with values that are references as well. which contains two keys. Using references is one way to avoid the problems associated with list context.5 Complex Data Structures Arrays and hashes can only store scalar values. Here is another look at the house example.2. But because scalars can hold references. > 'refrigerator' => [ > 'milk'. but now using references. The $house variable is a reference to an anonymous hash. Dereferencing a complex data structure can be done with the arrow notation or by enclosing the reference in curly braces and prefixing it with the appropriate sigil.
Perl autovivifies everything under the assumption that that is what you wanted to do. The autovivified referents are anonymous.5. Perl will assume you know what you are doing with your structures. > $VAR1 = [ > undef. If this is NOT what you want to do.2. In the example below. We then fetch from this undefined scalar. as if it were a reference to an array of a hash of an array of a hash of an array. my $val = $scal->[2]->{somekey}->[1]->{otherkey}->[1]. > ${\$VAR1->[0]}. check for the existence of each hash key and check that the array contains at least enough array entries to handle the given index. we start out with an undefined scalar called $scal.1 Autovivification Perl autovivifies any structure needed when assigning or fetching from a reference. my $scal. print Dumper $scal. 54 . > { > 'otherkey' => [] > } > ] > } > ].5. > { > 'somekey' => [ > ${\$VAR1->[0]}.
depth=$k". } } } print Dumper $mda. col=$j. depth=1' > ].$j<2.$i<2.2. col=1. depth=1' > ] > ]. col=0. my $mda. > [ > 'row=1. col=1. depth=1' > ] > ] > ]. depth=0'.$i++){ for(my $j=0. > 'row=0. col=0. depth=0'. > 'row=0. > $VAR1 = [ > [ > [ > 'row=0. depth=1' > ]. 55 .$k++){ $mda->[$i]->[$j]->[$k] = "row=$i.5. col=0. col=0. col=1. > [ > 'row=0. depth=0'. > 'row=1.5. depth=0'.2 Multidimensional Arrays Perl implements multidimensional arrays using one-dimensional arrays and references. > 'row=1.$k<2.$j++) { for(my $k=0. for(my $i=0. col=1. > [ > [ > 'row=1.
pm perl module. indicating you want to import the 'nstore'.8 installed. nstore ($scal. 'filename'). and install. The 'dclone' subroutine takes a reference to any kind of data structure and returns a reference to a deep cloned version of that data structure. $scal->[2]->{somekey}->[1]->{otherkey}->[1].2. consider an upgrade. such as print it. reboot computer.3 Deep Cloning. warn "reference is '$reference'". 2. read the section about CPAN later in this document.5. Then use Storable in your perl code. my $scal.. it isn't that important. for now. $scal->[2]->{somekey}->[1]->{otherkey}->[1]. Otherwise. my $referent = 42. > Can't use string ("SCALAR(0x812e6ec)") as > a SCALAR ref while "strict refs" in use 56 .5. > reference is 'SCALAR(0x812e6ec)' . my $reference = 'SCALAR(0x812e6ec)'. download Storable from CPAN. 2. If you don't have 5. my $reference = \$referent. my $scal.pm module also contains two subroutines for storing the contents of any perl data structure to a file and retrieving it later. and 'retrieve' subroutines. use Storable qw(nstore dclone retrieve). 'dclone'. Storable comes standard with perl 5.6 Stringification of References Perl will stringify a reference if you try to do anything string-like with it. use Storable qw(nstore dclone retrieve). my $value = $$reference. But perl will not allow you to create a string and attempt to turn it into a reference. The 'use' statement is explained later in this document as well.. # exit.5.5. Deep Copy If you need to create an entirely separate but identical clone of a complex data structure.4 Data Persistence The Storable.5. use the Storable. # $twin is an identical clone of $scal my $twin = dclone $scal. and restart script my $revived = retrieve('filename').8.
what_is_it( 42 ). my $string = ref($scalar). 57 . even if the value to which it points is false. 2. my $value = $$reference.2. But if you call ref() on a nonreference. my $temp = \42.5. Instead of SCALAR(0x812e6ec). > string is 'SCALAR' > string is 'ARRAY' > string is 'HASH' > string is '' Note that this is like stringification of a reference except without the address being part of the string.3] ). Also note that if you stringify a non-reference. what_is_it( [1. print "string is '$string'\n". warn "string is '$string'". } what_is_it( \'hello' ). my $reference = 'SCALAR(0x812e6ec)'. > string is 'SCALAR' Here we call ref() on several types of variable: sub what_is_it { my ($scalar)=@_. it will evaluate true when treated as a boolean. which is always false.7 The ref() function The ref() function takes a scalar and returns a string indicating what kind of referent the scalar is referencing. my $string = ref($temp). warn "value not defined" unless(defined($value)). If the scalar is not a reference. warn "value is '$value'\n". you get the scalar value. > value not defined > Use of uninitialized value in concatenation Because a reference is always a string that looks something like "SCALAR(0x812e6ec)".Turning strict off only gives you undef. what_is_it( {cats=>2} ). its just SCALAR. you get an empty string. ref() returns false (an empty string). no strict.
3 Control Flow Standard statements get executed in sequential order in perl. my $greeting = "Hello. my $name = 'John Smith'. if( $price == 0 ) { print "Free Beer!\n". $name\n". print $greeting. } 58 . Control flow statements allow you to alter the order of execution while the program is running.
# example==> MY_NAME: ## SINGLE_STATEMENT ==> a single perl statement # NOT including the semicolon. TEST.. TEST. } LABEL BLOCK LABEL BLOCK continue BLOCK # BOOL ==> boolean (see boolean section above) SINGLE_STATEMENT if (BOOL). unless (BOOL) BLOCK elsif (BOOL) BLOCK . see arrays and # list context sections later in text LABEL foreach (LIST) BLOCK LABEL foreach VAR (LIST) BLOCK LABEL foreach VAR (LIST) BLOCK continue BLOCK 59 .. CONT ) BLOCK # LIST is a list of scalars. # print "hello\n" ## BLOCK ==> zero or more statements contained # in curly braces { print "hi". CONT are all expressions # INIT is an initialization expression # INIT is evaluated once prior to loop entry # TEST is BOOLEAN expression that controls loop exit # TEST is evaluated each time after # BLOCK is executed # CONT is a continuation expression # CONT is evaluated each time TEST is evaluated TRUE LABEL for ( INIT. if (BOOL) BLOCK elsif (BOOL) BLOCK ..Perl supports the following control flow structures: ## LABEL is an optional name that identifies the # control flow structure.. # It is a bareword identifier followed by a colon... if (BOOL) BLOCK if (BOOL) BLOCK else BLOCK if (BOOL) BLOCK elsif (BOOL) BLOCK elsif ().. else BLOCK LABEL while (BOOL) BLOCK LABEL while (BOOL) BLOCK continue BLOCK LABEL until (BOOL) BLOCK LABEL until (BOOL) BLOCK continue BLOCK # INIT. else BLOCK unless (BOOL) BLOCK unless (BOOL) BLOCK else BLOCK unless (BOOL) BLOCK elsif (BOOL) BLOCK elsif ()..
or if no continue block exists. execution starts the next iteration of the control construct if it is a loop construct. The next command skips the remaining BLOCK. It does not execute any continue block (even if it exists). Inside a BLOCK of a control flow structure. or redo. A label is used to give its associated control flow structure a name.4 redo LABEL.3. last. last. 60 . if there is a continue block. It does not execute any continue block if one exists. then the command will operate on the control structure given. Execution then resumes at the start of the control structure without evaluating the conditional again. redo LABEL. 3. If the structure has a LABEL.2 last LABEL. After the continue block finishes.3 next LABEL. 3. you can call next. execution resumes there.1 Labels Labels are always optional. then the command will operate on the inner-most control structure. The last command goes to the end of the entire control structure. The redo command skips the remaining BLOCK. If no label is given to next. redo. A label is an identifier followed by a colon. last LABEL. If a label is given. 3. you can call next LABEL.
@other_package::refrigerator. there are two ways to create and use package variables: 1) Use the fully package qualified name everywhere in your code: # can use variable without declaring it with 'my' $some_package::answer=42. followed by a double colon. you will want to "use" these again. warn "The value is '$some_package::answer'\n". eval. or file belongs to the namespace given by NAMESPACE. The standard warnings. followed by the package name. subroutine. use Data::Dumper. $package_this::age. 61 ." etc. and Data::Dumper are attached to the namespace in which they were turned on with "use warnings. use warnings. followed by the variable name. perl assumes it is in the the most recently declared package namespace that was declared.1 Package Declaration Perl has a package declaration statement that looks like this: package NAMESPACE. use strict.4 Packages and Namespaces and Lexical Scoping 4. strictness. Anytime you declare a new package namespace. If you use an UNQUALIFIED variable in your code. All perl scripts start with an implied declaration of: package main. This is called a package QUALIFIED variable meaning the package name is explicitly stated. This package declaration indicates that the rest of the enclosing block. You can access package variables with the appropriate sigil. %package_that::pets. When you have strict-ness turned on. package SomeOtherPackage.
> speak is 'oink' . that package namespace declaration remains in effect until the end of the block.2 Declaring Package Variables With our 2) Use "our" to declare the variable. as example (2) above refers to the $name package variable. You can even declare variables in someone else's package namespace.. } # END OF CODE BLOCK warn "speak is '$speak'".0 or later for "our" declarations. 62 . The difference between the two methods is that always using package qualified variable names means you do NOT have to declare the package you are in. and you can refer to the variable just on its variable name. package this_package. There is no restrictions in perl that prevent you from doing this. warn "Hogs::speak is '$Hogs::speak'". To encourage programmers to play nice with each other's namespaces. 4. Using "our" is the preferred method. The "our" declaration is a shorthand for declaring a package variable. > Hogs::speak is 'oink' .6. at which time. without ever having to declare the namespace explicitly. our $speak = 'oink'. { # START OF CODE BLOCK package Heifers.. However.. Declaring a variable with "our" will create the variable in the current namespace. package Hogs.4. You can create variables in ANY namespace you want. the package namespace reverts to the previous namespace. If the namespace is other than "main". the fully package qualified name is NOT required. we can access it any way we wish. once a package variable is declared with "our". our $name='John'. our $speak = 'moo'. warn "name is '$name'". our $speak = 'oink'. You must have perl 5.. package Hogs. the "our" function was created. then you will need to declare the package namespace explicitly.3 Package Variables inside a Lexical Scope When you declare a package inside a code block. Once the package variable exists. We do not HAVE to use the "our" shortcut even if we used it to declare it.
Lexical variables declared inside a lexical scope do not survive outside the lexical scope. Within a lexical scope.4 Lexical Scope Lexical refers to words or text. { package Heifers." only exists inside the curly braces of the source code. and to show how lexical variables differ from "our" variables. Its just that outside the code block. We had to turn warnings and strict off just to get it to compile because with warnings and strict on. the "our Heifers. > speak is '' The lexical variable "$speak" goes out of scope at the end of the code block (at the "}" character). Outside those curly braces. So "lexical scope" refers to anything that is visible or has an effect only withing a certain boundary of the source text or source code. the package declaration has gone out of scope. no strict. > Heifers::speak is 'moo' 4. { my $speak = 'moo'. and we now have to use a fully package qualified name to get to the variables in Heifers package. no warnings. Scope refers to vision. In the above examples. which is a technical way of saying its "worn off". } warn "speak is '$speak'\n". as in telescope.The Heifers namespace still exists. The package variables declared inside the code block "survive" after the code block ends." declaration has worn off. as does all the variables that were declared in that namespace. things that have lexical limitations (such as a package declaration) are only "visible" inside that lexical space. 4. 63 . perl will know $speak does not exist when you attempt to print it. A lexical scope exists while execution takes place inside of a particular chunk of source code. so it does not exist when we try to print it out after the block. so it will throw an exception and quit. our $speak = 'moo'. the "package Heifers. } print "Heifers::speak is '$Heifers::speak'\n".5 Lexical Variables Lexical variables are declared with the "my" keyword. This "wearing off" is a function of the code block being a "lexical scope" and a package declaration only lasts to the end of the current lexical scope. The easiest way to demonstrate lexical scoping is lexical variables.
print "$lex_ref\n". They generally keep you from stepping on someone else's toes. eval.. and $lex_var is at a different address each time. never go out of scope. package main. The example below shows that "my $cnt" is not the same as the "main::cnt": no warnings. we create a new $lex_var each time through the loop. or file. } > SCALAR(0x812e770) > SCALAR(0x812e6c8) > SCALAR(0x812e6e0) > SCALAR(0x81624c8) > SCALAR(0x814cf64) Lexical variables are just plain good. my @cupboard. } warn "some_lex is '$some_lex'".Lexically scoped variables have three main features: 1) Lexical variables do not belong to any package namespace. 5) { my $lex_var ='canned goods'. my $cnt='I am just a lexical'. so you cannot prefix them with a package name. it is created dynamically. warn "main::cnt is '$main::cnt'". Note in the example below. > main::cnt is '' 2) Lexical variables are only directly accessible from the point where they are declared to the end of the nearest enclosing block. Package variables are permanent. Every time a variable is declared with "my". perl will remove it from its memory. during execution. $lex_ref). The location of the variable will change each time. never get garbage collected. subroutine. 64 . > some_lex is '' 3) Lexical variables are subject to "garbage collection" at the end of scope. no strict. and are accessible from anyone's script. { my $some_lex = 'I am lex'. my $lex_ref = \$lex_var. They also keep your data more private than a package variable. for (1 . push(@cupboard. If nothing is using a lexical variable at the end of scope.
} warn "some_lex is '$some_lex'". warn "referring var refers to '$$referring_var'". and it retained its value of "I am lex".4. But perl can use garbage collected space for other lexical variables. The example below shows two variables that refer to each other but nothing refers to the two variables. no strict.6. Note that the named variable $some_lex went out of scope at the end of the code block and could not be accessed by name. rather the freed up memory is used for possible declarations of new lexically scoped variables that could be declared later in the program. 4. > some_lex is '' > referring var refers to 'I am lex' When the lexical $some_lex went out of scope. Perl will not garbage collect these variables even though they are completely inaccessible by the end of the code block. { my ($first. we could no longer access it directly. Once the memory is allocated for perl. If a lexical variable is a referent of another variable. But since $referring_var is a reference to $some_lex. it remains under perl's jurisdiction.$last)=(\$last. perl will check to see if anyone is using that variable.\$first).$last). { my $some_lex = 'I am lex'. so circular references will not get collected even if nothing points to the circle. It is rudimentary reference counting.1 Reference Count Garbage Collection Perl uses reference count based garbage collection. and if no one is using it. This means that your program will never get smaller because of lexical variables going of of scope.6 Garbage Collection When a lexical variable goes out of scope. my $referring_var. The data in $some_lex was still accessible through referring_var. then $some_lex was never garbage collected. } 65 . ($first. then the lexical will not be garbage collected when it goes out of scope. The freed up memory is not returned to the system. $referring_var=\$some_lex. perl will delete that variable and free up memory.
is declared inside a code block and would normally get garbage collected at the end of the block. dec. print "cnt is '$cnt'\n". { my $cnt=0. the only things that can access it after the code block are the subroutines.4. > cnt > cnt > cnt > cnt > cnt > cnt is is is is is is '1' '2' '3' '2' '1' '2' Subroutine names are like names of package variables. In the example below. $cnt. print "cnt is '$cnt'\n". inc. However. Therefore. If a subroutine uses a lexical variable. they never go out of scope or get garbage collected.} } inc. Since $cnt goes out of scope. once declared. The inc and dec subroutines are subroutine closures.} sub dec{$cnt--. sub inc{$cnt++. however perl knows that $cnt is needed by the subroutines and therefore keeps it around.6. then that variable will not be garbage collected as long as the subroutine exists. two subroutines are declared in that same code block that use $cnt. Subroutines that use a lexical variable declared outside of the subroutine declaration are called "CLOSURES".2 Garbage Collection and Subroutines Garbage collection does not rely strictly on references to a variable to determine if it should be garbage collected. 66 . Note that a reference to $cnt is never taken. The subroutine gets placed in the current declared package namespace. named subroutines are like package variables in that. inc. dec. inc. so $cnt is not garbage collected. the lexical variable.
which means they can be a convenient way for several different blocks of perl code to talk amongst themselves using an agreed upon global variable as their channel. Run. and they could all access the $Development::Verbose variable and act accordingly.4. Imagine several subroutines across several files that all want to check a global variable: $Development::Verbose. } } sub Run { if ($Development::Verbose){ print "running\n". They are global. our $Verbose=1. package Development. } } Compile. Link. and they inherit all the possible problems associated with using global variables in your code. If this variable is true. in different package namespaces. sub Compile { if ($Development::Verbose) { print "compiling\n". 67 . } } sub Link { if ($Development::Verbose){ print "linking\n". these subroutines print little or no information. If it is false. > compiling > linking > running The three subroutines could be in different files. they do have some advantages. they are just global variables. In the event you DO end up using a package variable in your code. these subroutines print detailed information.7 Package Variables Revisited Package variables are not evil.
package Development. Run. Link. and then set the global back to what it was. That new value is seen by anyone accessing the variable. The local function takes a package variable. } } sub Link { if ($Development::Verbose){ print "linking\n". calls the original Run routine. } } sub Run { if ($Development::Verbose){ print "running\n". And at the end of the lexical scope in which local() was called. set it to a new and temporary value. the original value for the variable is returned. say we wish to create a RunSilent subroutine that stores $Development::Verbose in a temp variable. execute some foreign code that will access this global.8 Calling local() on Package Variables When working with global variables.4. 68 . saves off the original value. and then sets $Development::Verbose back to its original value. The RunSilent subroutine could be written like this: sub RunSilent { local($Development::Verbose)=0. > compiling > linking This can also be accomplished with the "local()" function. our $Verbose=1. sub Compile { if ($Development::Verbose) { print "compiling\n". $Development::Verbose=0. there are times when you want to save the current value of the global variable. $Development::Verbose=$temp. } Compile. } } sub RunSilent { my $temp = $Development::Verbose. Continuing the previous example. allows you to assign a temp value to it. RunSilent. Run.
&Ping. sub Ping {print "ping\n". similar to the way you can declare named variables and anonymous variables. the sigil for subroutines is optional. The "my" lexical variables were not introduced until perl version 4. > ping > ping > ping > ping 69 . perl was given the local() function.2 Named Subroutines Below is the named subroutine declaration syntax: sub NAME BLOCK NAME can be any valid perl identifier.} Ping. Local is also a good way to create a temporary variable and make sure you don't step on someone else's variable of the same name. BLOCK is a code block enclosed in parenthesis.1 Subroutine Sigil Subroutines use the ampersand ( & ) as their sigil. 5 Subroutines Perl allows you to declare named subroutines and anonymous subroutines. package MyArea. 5. arrays. you may access it with just NAME if you are in the correct package. But while the sigils for scalars. and hashes are mandatory. 5.} Perl originally started with nothing but package variables. So once a named subroutine is declared. So to deal with all the package variables. or with a fully package qualified name if you are outside the package. MyArea::Ping. &MyArea::Ping. The NAME of the subroutine is placed in the current package namespace. And you can use the optional ampersand sigil in either case. in the same way "our" variables go into the current package namespace.
looking in current package YourArea > ping > ping > Undefined subroutine &YourArea::Ping 5. my $temp = sub {print "Hello\n".}. all arguments go through the list context crushing machine and get reduced to a list of scalars. The subroutine will not know if the list of scalars it receives came from scalars. 5. a subroutine can be declared with a prototype. things like Data::Dumper cannot look inside the code block and show you the actual code. For normal subroutines. } my $temp = sub {print "Hello\n". or hashes.5 Passing Arguments to/from a Subroutine Any values you want to pass to a subroutine get put in the parenthesis at the subroutine call. > ref returned 'CODE' 5.Once the current package declaration changes. my $string = ref($scalar). To avoid some of the list context crushing. MyArea::Ping. The original containers are not known inside the subroutine. package MyArea. and similar to how {} returns a hash reference. similar to how [] returns an array reference. &Ping. &MyArea::Ping. > $VAR1 = sub { "DUMMY" }. print "ref returned '$string'\n". what_is_it($temp). arrays.}. Instead Data::Dumper does not even try and just gives you a place holder that returns a dummy string.4 Data::Dumper and subroutines The contents of the code block are invisible to anything outside the code block. # error. sub what_is_it { my ($scalar)=@_. print Dumper $temp. you MUST use a fully package qualified subroutine name to call the subroutine.} package YourArea. For this reason. 70 . which are discussed later.3 Anonymous Subroutines Below is the anonymous subroutine declaration syntax: sub BLOCK This will return a code reference. sub Ping {print "ping\n".
my $temp = sub {print "Hello\n". sub swap { (@_) = reverse(@_). #WRONG } 5. # preferred > Hello > Hello > Hello 71 . the arguments are accessed via a special array called @_.$right)=@_. return $left<=>$right. If swap were defined like this. since all the arguments passed in were reduced to list context. &{$temp}. sub swap { my ($left. $temp->(). @_ = ($right. Therefore.6 Accessing Arguments inside Subroutines via @_ Inside the subroutine.5. warn "two is '$two'".7 Dereferencing Code References Dereferencing a code reference causes the subroutine to be called. the preferred way to extract them is to assign @_ to a list of scalars with meaningful names. swap($one. A code reference can be dereferenced by preceding it with an ampersand sigil or by using the arrow operator and parenthesis ">()". > one is 'I am two' > two is 'I am one' Assigning to the entire @_ array does not work. &$temp. my $two = "I am two".$right)=@_. } The @_ array is "magical" in that it is really a list of aliases for the original arguments passed in. the variables $one and $two would remain unchanged. If the arguments are fixed and known.}. The @_ array can be processed just like any other regular array.$two). you have to assign to the individual elements. The preferred way is to use the arrow operator with parens. warn "one is '$one'". sub compare { my ($left. } my $one = "I am one".$left). these arguments fit nicely into an array. Subroutine parameters are effectively IN/OUT. assigning a value to an element in @_ will change the value in the original variable that was passed into the subroutine call.
when using code references. However. $code_ref->(). # doesn't look like I'm passing any params # but perl will pass @_ implicitly.2.3). # explicitly pass @_ $code_ref->( 'one'. dereferencing using the "&" may cause implied arguments to be passed to the new subroutine. This can cause subtly odd behavior if you are not expecting it. > $VAR1 = [ > 1.5. } sub first_level { # using '&' sigil and no parens. &second_level. no implicit @_ $code_ref->(@_). sub second_level { print Dumper \@_.8 Implied Arguments When calling a subroutine with the "&" sigil prefix and no parenthesis. # pass new parameters 72 . > 2. the arrow operator is the preferred way to dereference a code reference. > 3 > ]. 'two' ). This generally is not a problem with named subroutines because you probably will not use the "&" sigil. For this reason. } first_level(1. the current @_ array gets implicitly passed to the subroutine being called. # pass nothing.
# undef or empty list } my $scal_var = this_is_false. print Dumper \@arr_var. A return statement by itself will return undef in scalar context and an empty list in list context. } my $scal_var = ret_scal. my @arr_var = this_is_false. sub this_is_false { return. # return a single scalar sub ret_scal { return "boo". > $VAR1 = \'boo'.5.3). # return a list of values sub ret_arr { return (1.0 or "") will work in scalar context. it will create an array with the first element set to undef. > 3 > ]. } my @arr_var =ret_arr. 73 . Returning a simple "undef" value (or 0 or 0. This is the preferred way to return false in a subroutine. print Dumper \$scal_var. but in array context. An explicit return statement is the preferred approach if any return value is desired. The return value can be explicit. In boolean context.9 Subroutine Return Value Subroutines can return a single value or a list of values.10 Returning False The return value of a subroutine is often used within a boolean test. The problem is that the subroutine needs to know if it is called in scalar context or array context. 5. or it can be implied to be the last statement of the subroutine. > 2. an array with one or more elements is considered true.2. > $VAR1 = [ > 1.
print Dumper \@info. The package qualified name of the subroutine that was called was main::HowWasICalled. > undef. The caller() function returns a list of information in the following order 0 1 2 3 4 5 6 7 8 9 $package package namespace at time of call $filename filename where called occurred $line line number in file where call occurred $subroutine name of subroutine called $hasargs true if explicit arguments passed in $wantarray list=1. > 1. 74 . use caller(0). the code is in a file called test. > undef.pl'.11 Using the caller() Function in Subroutines The caller() function can be used in a subroutine to find out information about where the subroutine was called from and how it was called. > 'UUUUUUUUUUUU' > ]. The package qualified name must be given since you don't know what package is current where the subroutine was called from. The call occurred in package main. Caller takes one argument that indicates how far back in the call stack to get its information from. scalar=0.pl. > '. } HowWasICalled. that information is hidden in lexical scope. disregard $bitmask internal use only. >$VAR1 = [ > 'main'.5. void=undef $evaltext evaluated text if an eval block $is_require true if created by "require" or "use" $hints internal use only. > 13. disregard Note in the example above./test. > 2. and it occurred at line 13 of the file. sub HowWasICalled { my @info = caller(0). For information about the current subroutine. the default package namespace. > 'main::HowWasICalled'. > undef.
5.12 The caller() function and $wantarray
The argument of interest is the $wantarray argument. This indicates what return value is expected of
the subroutine from where it was called. The subroutine could have been called in void context
meaning the return value is thrown away. Or it could have been called and the return value assigned to
a scalar. Or it could have been called and the return value assigned to a list of scalars.
sub CheckMyWantArray {
my @info = caller(0);
my $wantarray = $info[5];
$wantarray='undef' unless(defined($wantarray));
print "wantarray is '$wantarray'\n";
CheckMyWantArray; #undef
my $scal = CheckMyWantArray; # 0
my @arr = CheckMyWantArray; # 1
> wantarray is 'undef'
> wantarray is '0'
> wantarray is '1'
5.13 Context Sensitive Subroutines with wantarray()
You can use the wantarray variable from caller() to create a subroutine that is sensitive to the context in
which it was called.
sub ArrayProcessor {
my @info = caller(0);
my $wantarray = $info[5];
return unless(defined($wantarray));
if($wantarray) {
return @_;
} else {
return scalar(@_);
my @arr=qw(alpha bravo charlie);
my $scal = ArrayProcessor(@arr); # 3
my @ret_arr = ArrayProcessor(@arr); # alpha ...
print "scal is '$scal'\n";
print Dumper \@ret_arr;
> scal is '3'
> 'alpha',
> 'bravo',
> 'charlie'
> ];
6 Compiling and Interpreting
When perl works on your source code, it will always be in one of two modes: compiling or interpreting.
Perl has some hooks to allow access into these different cycles. They are code blocks that are prefixed
with BEGIN, CHECK, INIT, and END.
Compiling: translating the source text into machine usable internal format.
Interpreting: executing the machine usable, internal format.
The BEGIN block is immediate.
BEGIN -> execute block as soon as it is compiled, even before compiling anything else.
The other blocks, including normal code, do not execute until after the entire program has been
compiled. When anything other than a BEGIN block is encountered, they are compiled and scheduled
for execution, but perl continues compiling the rest of the program. The execution order is CHECK,
INIT, normal code, and END blocks.
CHECK -> Schedule these blocks for execution after all source code has been compiled.
INIT-> Schedule these blocks for execution after the CHECK blocks have executed.
normal code -> Schedule normal code to execute after all INIT blocks.
END -> Schedule for execution after normal code has completed.
Multiple BEGIN blocks are executed immediately in NORMAL declaration order.
Multiple CHECK blocks are scheduled to execute in REVERSE declaration order.
Multiple INIT blocks are scheduled to execute in NORMAL declaration order.
Multiple END blocks are scheduled to execute in REVERSE declaration order.
An example containing several CHECK, INIT, normal code, and END blocks. The output shows the
execution order:
END { print "END 1\n" }
CHECK { print "CHECK 1\n"
BEGIN { print "BEGIN 1\n"
INIT { print "INIT 1\n" }
print "normal\n";
INIT { print "INIT 2\n" }
BEGIN { print "BEGIN 2\n"
CHECK { print "CHECK 2\n"
END { print "END 2\n" }
> normal
These declared subroutines can be called and public variables can be accessed by any perl script that uses the module. 78 . Perl Modules Lets say you come up with some really great chunks of perl code that you want to use in several different programs. The content of a perl module is any valid perl code. perl modules contain declarations. It is standard convention that all perl modules start out with a "package" declaration that declares the package namespace to be the same as the module name.pm" extension. # MUST BE LAST STATEMENT IN FILE All perl modules must end with "1. you might put it in a module called Dog. Dog::Speak. 8 The use Statement The "use" statement allows a perl script to bring in a perl module and use whatever declarations have been made available by the module. The Dog module declares its package namespace to be Dog. and then "use" that module... After any new package declaration you will need to turn on warnings. The best place to put code to be used in many different programs is in a "Perl Module". Perhaps you have some subroutines that are especially handy. ends up in the current package namespace. such as subroutine declarations and possibly declarations of private or public variables.pm and script.pm package Dog." otherwise you will get a compile error: Dog. a file called script. Continuing our example. use Data::Dumper.pm did not return a true value . would have to be in the same directory. use strict. Generally. etc. > Woof! Both files. A perl module is really just a file with an invented name and a ". If you had some handy code for modeling a dog. Once the Dog module has been used. The module then declares a subroutine called "Speak".pl. like any normal subroutine. and perhaps they have some private data associated with them. ###filename: Dog.pm. which. sub Speak { print "Woof!\n". use warnings. } 1. The "pm" is short for "perl module". Dog. Here is an example of our Dog module. anyone can call the subroutine by calling Dog::Speak. and then you would use the "use" statement to read in the module.7 Code Reuse.pl could bring in the Dog module like this: use Dog. Dog.
So perl would look for Pets::Dog::GermanShepard in Pets/Dog/ for a file called GermanShepard. These are all valid MODULENAMES: use use use use Dog. The "use" statement is exactly equivalent to this: BEGIN { require MODULENAME. Pets::Cat::Persian. use Dogs. User created module names should be mixed case. Perl will initialize this array to some default directories to look for any modules. it would be a "/". MODULENAME->import( LISTOFARGS ). If you want to create a subdirectory just for your modules.'/home/username/perlmodules'). For Linux style systems. The "require" statement is what actually reads in the module file. you can add this subdirectory to @INC and perl will find any modules located there. "require" will translate the double colons into whatever directory separator is used on your system. Formally The "use" statement can be formally defined as this: use MODULENAME ( LISTOFARGS ). Pets::Dog::GermanShepard. though. Because the "require" statement is in a BEGIN block. 79 .9 The use Statement." Module names with all upper case letters are just ugly and could get confused with built in words. Module names with all lower case are reserved for built in pragmas. So this will not work: push(@INC.pm 9. meaning it would be either a single identifier or multiple identifiers separated by double-colons. } The MODULENAME follows the package namespace convention. When performing the search for the module file. it will execute immediately after being compiled.1 The @INC Array The "require" statement will look for the module path/file in all the directories listed in a global array called @INC. such as "use warnings. Pets::Dog.
use Dogs. The "use" statement will get compiled and executed immediately. The "glob" function uses the shell translations on a path. for you Linux heads.'/home/username/perlmodules'). Consult your shell documentation to determine how to set this environment variable. before the "push" is executed. The PERL5LIB variable is a colon separated list of directory paths. the module gets executed immediately as well.2 The use lib Statement The "use lib" statement is my preferred way of adding directory paths to the @INC array. So if you want to include a directory under your home directory. note that the home directory symbol "~" is only meaningful in a linux shell. 80 . Any code that is not a declaration will execute at this point. Also. so @INC will not be changed when "use" is called. because it does not need a BEGIN block. If you don't have PERL5LIB set. 9.This is because the "push" statement will get compiled and then be scheduled for execution after the entire program has been compiled. } use Dogs. Perl does not understand it. This means any executable code gets executed. you will need to call "glob" to translate "~" to something perl will understand. 9.4 The require Statement Once the require statement has found the module. perl will search for MODULENAME in any directory listed in the PERLLIB environment variable. use lib glob('~/perlmodules'). The MODULENAME->import statement is then executed. You could say something like this: BEGIN { push(@INC. perl compiles it. Just say something like this: use lib '/home/username/perlmodules'.3 The PERL5LIB and PERLLIB Environment Variables The "require" statement also searches for MODULENAME in any directories listed in the environment variable called PERL5LIB. 9. Because the require statement is in a BEGIN block.
Which is why you can say use Data::Dumper. print Data::Dumper::Dumper \@var. which has not been introduced yet. More advancedly. if your perl module declares a subroutine called "import" then it will get executed at this time. The import method is a way for a module to import subroutines or variables to the caller's package.9. print Dumper \@var. one of the bells and whistles of a method call is a thing called "inheritance". Basically. which has not been introduced yet. 81 . This happens when you use Data::Dumper in your script. A method call is a fancy way of doing a subroutine call with a couple of extra bells and whistles bolted on. instead of having to say: use Data::Dumper. A subroutine called "Dumper" from the package Data::Dumper gets imported into your package namespace.5 MODULENAME -> import (LISTOFARGS) The MODULENAME->import(LISTOFARGS) statement is a "method call". if your perl module OR ITS BASE CLASS(ES) declares a subroutine called "import" then it will get executed at this time. So. to be more accurate.
print "with the following args\n".pl line 4./script. warn "just after use Dog". use strict.pm line 4. use Dog ('GermanShepard'). > calling import at Dog. } sub import { warn "calling import". #!/usr/local/env perl ###filename:script.pm package Dog. use Data::Dumper. > just before use Dog at .pl line 6. } 1. sub Speak { print "Woof!\n".pm line 7. print Dumper \@_. warn "executing normal code". Dog::Speak. > with the following args > $VAR1 = [ > 'Dog'. > Woof! 82 . > 'GermanShepard' > ]. ###filename:Dog.pl use warnings. use Data::Dumper. #MUST BE LAST STATEMENT IN FILE > executing normal code at Dog. warn "just before use Dog". use strict.6 The use Execution Timeline The following example shows the complete execution timeline during a use statement. > just after use Dog at ./script.9. use warnings.
83 . STRING. but bless() by itself is overwhelmingly simple.pl line 8./script. my @arr=(1. The bless() function is the basis for Object Oriented Perl. > CODE at . # referent my $rarr = \@arr./script. The bless function takes a reference and a string as input. # call ref() warn "str is '$str'".2. then calling ref($rarr) will return the string "ARRAY". > SCALAR at . > '' at . warn ref({}). and a reference. $rarr=\@arr."'".3). # reference to referent my $str = ref($rarr). bless REFERENCE. or empty-string depending on what type of referent it is referred to. > HASH at . @arr. CODE. warn "'"./script.pl line 4./script./script.10 bless() The bless() function is so simple that people usually have a hard time understanding it because they make it far more complicated than it really is.ref(4). warn ref(\4). The bless function modifies the referent pointed to by the reference and attaches the given string such that ref() will return that string. warn ref(sub{}). Quick reference refresher: Given an array referent. ref() will return SCALAR. > ARRAY at . All bless does is change the string that would be returned when ref() is called. ARRAY. > str is 'ARRAY' Normally.pl line 5. The bless function will then return the original reference.pl line 7. warn ref([]). HASH.pl line 6.
> Action at ."Box")). warn ref(bless({}. however it was given a new name.pl line 6. That is it./script. my $str = ref($rarr). then people would refer to it as "holy water". Note this is exactly the same as the code in the first example. It does not affect the contents of the referent. and because of that name it might be used differently. > Curlies at .pl line 5. We will see this difference with method calls.pl line 7. bless() changes the name of a referent."Action"))."Four")). but with one line added to do the bless: my @arr=(1./script. In perl. 84 . warn ref(bless(sub{}.2. # referent my $rarr = \@arr. > Box at . "Counter").pl line 8. only the name returned by ref()./script.Here is an example of bless() in action./script. we can call ref() on the return value and accomplish it in one line: my $sca=4. All bless() does is affect the value returned by ref(). the referent might be used differently or behave differently."Curlies")). > Four at . But because of this new name. warn ref(bless([]. > str is 'Counter' Since bless() returns the reference. You might be wondering why the word "bless" was chosen. # call ref() warn "str is '$str'". # reference to referent bless($rarr. warn ref(bless(\$sca. The constitution and makeup of the water did not change.3). If a religious figure took water and blessed it.
This may not seem very useful. } Speak. package Dog. it goes into the current package namespace. Dog -> Speak. but the simplest thing it can be is just a bareword package name to go look for the subroutine called METHOD. The MODULENAME->import(LISTOFARGS) was a method call. but we had to do some handwaving to get beyond it. calling it a fancy subroutine call. } Dog -> Speak (3). and be guaranteed it will work every time. use Data::Dumper. sub Speak { print Dumper \@_. 85 . use strict. The second difference between a subroutine call and a method call is inheritance. but an INVOCANT can be many different things. > Woof > Woof A method call is similar. The INVOCANT is the thing that "invoked" the METHOD. You can call the subroutine using its short name if you are still in the package. package Dog. So what is different? First. the INVOCANT always gets unshifted into the @_ array in the subroutine call. sub Speak { print "Woof\n". use warnings. An invocant can be several different things. Dog::Speak. Here is the generic definition: INVOCANT -> METHOD ( LISTOFARGS ). Or you can use the fully qualified package name. some more useful than others. # INVOCANT > 3 # first user argument > ]. Quick review of package qualified subroutine names: When you declare a subroutine.11 Method Calls We have seen method calls before. > Woof So it is almost the same as using a package qualified subroutine name Dog::Speak. > $VAR1 = [ > 'Dog'.
pm line 6. But German Shepards still bark like all dogs. The unexplained bit of magic is that inheritance uses the "use base" statement to determine what packages to inherit from. It then looked for a subroutine called Dog::Speak. for(1 . not Dog. > Woof at Dog. ###filename:Shepard. warn "invocant is '$invocant'".pm package Dog. When script. #!/usr/local/env perl ###filename:script. Shepard INHERITED the Speak subroutine from the Dog package. $count) = @_. use warnings. } } 1. Shepard->Speak(2). So then it looked and found a BASE of Shepard called Dog.11. sub Track { warn "sniff. use base Dog. > sniff. use strict. perl still passes Dog::Speak the original invocant.pm package Shepard. sub Speak { my ($invocant.pm line 8.. Also notice that the subroutine Dog::Speak received an invocant of "Shepard".pm line 4.pm line 8. It did not find one. use Data::Dumper. $count) { warn "Woof". Even though perl ended up calling Dog::Speak. Say we model a German Shepard that has the ability to track a scent better than other breeds. Shepard->Track. > Woof at Dog. 86 . which was "Shepard" in this case.pl used Shepard.pl always used Shepard as the invocant for its method calls. sniff". > invocant is 'Shepard' at Dog. perl first looked in the Shepard namespace for a subroutine called Shepard::Speak. The specific breeds of dogs will likely be able to inherit some behaviors (subroutine/methods) from a base class that describes all dogs. sniff at Shepard. and called that subroutine. found one. } 1.pl use Shepard.1 Inheritance Say you want to model several specific breeds of dogs. And script.pl called Shepard->Speak. ###filename:Dog. Notice that script.
left-to-right. 87 . it will then go through the contents of the @ISA array. When a method call looks in a package namespace for a subroutine and does not find one.MODULENAME) is new.2 use base This statement: use base MODULENAME.11. This is not necessarily the "best" way to search. If this approach does not work for your application. is functionally identical to this: BEGIN { require MODULENAME. MODULENAME). but it is how perl searches. The @ISA array contains any packages that are BASE packages of the current package. push(@ISA. The @ISA array is named that way because "Shepard" IS A "Dog". } The require statement goes and looks for MODULENAME. therefore ISA.pm using the search pattern that we described in the "use" section earlier. you can change it with a module from CPAN. The push(@ISA. The search order is depth-first. so you will want to learn it.
Remember bless() changes the string returned by ref().pm => MothersMother. FathersFather FathersMother ). when using a reference as an invocant. = ().3 INVOCANT->isa(BASEPACKAGE) The "isa" method will tell you if BASEPACKAGE exists anywhere in the @ISA inheritance tree. # FALSE (can't track a scent) 11.pm => qw ( qw ( qw ( @ISA @ISA @ISA @ISA Father Mother ). Shepard->can("Speak").Imagine a Child module has the following family inheritance tree: Child. # TRUE Child->isa("Shepard"). = (). perl will call ref() on the reference and use the string returned as starting package namespace to begin searching for the method/subroutine.pm => @ISA = Father. # FALSE 11. 88 .pm => @ISA = Mother. # TRUE (Woof) Child->can("Track"). Perl allows a more interesting invocant to be used with method calls: a blessed referent. = ().pm => FathersMother. Well. Perl will search for Child->Method through the inheritance tree in the following order: Child Father FathersFather FathersMother Mother MothersFather MothersMother 11. Shepard->Track. Child->isa("MothersMother").pm => MothersFather.4 INVOCANT->can(METHODNAME) The "can" method will tell you if the INVOCANT can call METHODNAME successfully.pm => @ISA = FathersFather. = ().5 Interesting Invocants So far we have only used bareword invocants that correspond to package names. MothersFather MothersMother ).
Here is our simple Dog example but with a blessed invocant.
package Dog;
use warnings; use strict; use Data::Dumper;
sub Speak {
my ($invocant, $count) = @_;
warn "invocant is '$invocant'";
for(1 .. $count) { warn "Woof"; }
} 1;
#!/usr/local/env perl
use Dog;
my $invocant=bless {},'Dog'; ### BLESSED INVOCANT
> invocant is 'Dog=HASH(0x8124394)' at Dog.pm line 6
> Woof at Dog.pm line 8.
> Woof at Dog.pm line 8.
The my $invocant=bless {},"Dog"; is the new line. The bless part creates an anonymous
hash, {}, and blesses it with the name "Dog". If you called ref($invocant), it would return the string
So perl uses "Dog" as its "child" class to begin its method search through the hierarchy tree. When it
finds the method, it passes the original invocant, the anonmous hash, to the method as the first
Well, since we have an anonymous hash passed around anyway, maybe we could use it to store some
information about the different dogs that we are dealing with. In fact, we already know all the grammar
we need to know about Object Oriented Perl Programming, we just need to speak different sentences
12 Procedural Perl
So far, all the perl coding we have done has been "procedural" perl. When you hear "procedural" think
of "Picard", as in Captain Picard of the starship Enterprise. Picard always gave the ship's computer
commands in the form of procedural statements.
Computer, set warp drive to 5.
Computer, set shields to "off".
Computer, fire weapons: phasers and photon
The subject of the sentences was always "Computer". In procedural programming, the subject
"computer" is implied, the way the subject "you" is implied in the sentence: "Stop!"
The verb and direct object of Picard's sentences become the subroutine name in proceedural
programming. Whatever is left become arguments passed in to the subroutine call.
fire_weapons qw(phasers photon_torpedoes);
13 Object Oriented Perl
Object oriented perl does not use an implied "Computer" as the subject for its sentences. Instead, it uses
what was the direct object in the procedural sentences and makes it the subject in object oriented
Warp Drive, set yourself to 5.
Shields, set yourself to "off".
Phasors, fire yourself.
Torpedoes, fire yourself.
But how would we code these sentences?
Here is a minimal example of object oriented perl. There is a class called "Animal". It has a constructor
called MakeNew and a method called Speak. The script uses the Animal module, creates instances of
Animal objects, and calls the Speak method on each one.
package Animal;
sub MakeNew {
my ($invocant,$name)=@_;
my $object = {};
bless($object, $invocant);
return $object;
sub Speak {
my ($obj)=@_;
my $name = $obj->{Name};
print "$name growls\n";
our constructor
class and name are passed in
hash to store data
put name into hash
bless hash into class
return hash/instance/object
some method
hash/instance/object passed in
get name of this instance
say who is speaking
#!/usr/local/env perl
use Animal;
# note that 'Animal' is passed in to MakeNew
# as first parameter. 'Samson' is second parameter.
# 'Animal' becomes $invocant. 'Samson' becomes $name.
my $lion = Animal->MakeNew('Samson'); # create an instance
# note that the blessed hash reference, $lion, is passed
# into Speak method as first parameter. It becomes $obj.
$lion->Speak(); # call method on this instance
my $tiger = Animal->MakeNew('Fuzzball');
my $bear = Animal->MakeNew('Smokey');
> Samson growls
> Fuzzball growls
> Smokey growls
puts the Name into a hash. Then we create a Dog module that uses Animal as its base to get the contructor. Assume we want to keep track of several dogs at once. Lets return to a familiar example. blesses the hash. This module contains one subroutine that takes the invocant and a Name. rather than as individually named variables. the advantages of object oriented become more obvious. so we create an Animal. we want a common way to handle all pets. The method prints the name of the dog when they bark so we know who said what. Perhaps we are coding up an inventory system for a pet store. This return value becomes a "Animal" object.So what? Basic Object Oriented does nothing that cannot be just as easily done in procedural perl. and returns a reference to the hash. our Dog module. This subroutine is an object contructor. But once you start adding things like inheritance and polymorphism. 92 . The first thing we want to do is process objects as an array. We then add a method to let dogs bark. First.pm perl module.
my $name=$obj->{Name}. Dog->New($name)). my @pets. rather than the implied "Computer" of procedural programming. } > Butch says Woof at Dog. use base Animal. adverbs. ###filename:Animal. This is object oriented programming. foreach my $pet (@pets) { $pet->Speak. it would be "Pet.pm package Dog.pl creates three dogs and stores them in an array. The subject of the sentence is "Pet".$name)=@_.pm line 7.$invocant). warn "$name says Woof".pm line 7.pm package Animal.pl says $pet->Speak.The script. Notice the last foreach loop in script.pl use Dog. etc ). The script then goes through the array and calls the Speak method on each object. 93 . } # have every pet speak for themselves. } 1. return bless({Name=>$name}. sub Speak { my ($obj)=@_. Object Oriented Programming statements are of the form: $subject -> verb ( adjectives. } 1. speak for yourself". because if you translated that statement to English. # create 3 Dog objects and put them in @pets array foreach my $name qw(Butch Spike Fluffy) { push(@pets. > Fluffy says Woof at Dog. sub New { my ($invocant. > Spike says Woof at Dog. ###filename:Dog.pm line 7. #!/usr/local/env perl ###filename:script.
Furball says Meow at Cat.pm package Cat. Fang says Meow at Cat. we might want to add a Cat class to handle cats at the pet store. #!/usr/local/env perl ###filename:script. Spike says Woof at Dog. } # have all the pets say something. If it's an OO package.pl to put some cats in the @pets array.pm line 7.1 Class The term "class" refers to a perl package/module that is used in an object oriented way. Then we modify script. Dog->New($name)). A perl package that is designed for procedural use is simply called a package. sub Speak { my $obj=shift. } 1. use Cat. Expanding our previous example. # polymorphism at work } > > > > > > Butch says Woof at Dog.pm line 7. Cat->New($name)). ###filename:Cat. warn "$name says Meow". my @pets.2 Polymorphism Polymorphism is a real fancy way of saying having different types of objects that have the same methods. 94 . use base Animal. 13. #create some dog objects foreach my $name qw(Butch Spike Fluffy) { push(@pets.pm line 7. foreach my $pet (@pets) { $pet->Speak. } # create some cat objects foreach my $name qw(Fang Furball Fluffy) { push(@pets.pm line 7. Fluffy says Woof at Dog.pm line 7.13. my $name=$obj->{Name}. Fluffy says Meow at Cat.pm line 7.pl use Dog. you can call it a "class".
Whether its a dog or cat. use Shepard. ###filename:Shepard. > Spike says Woof at Dog. $dog->Speak. warn "$name says Woof". This is polymorphism.pm line 8. } sub Speak { my $name=$_[0]->{Name}.pm package Dog.pm line 6. } 1.pm. To shorten the example. ### SUPER } 1. But this scatters hardcoded names of the base class throughout Shepard. the animal will say whatever is appropriate for its type.Notice how the last loop goes through all the pets and has each one speak for themselves.$_[0]). the constructor New was moved to Dog. the only way that Shepard can call Dog's version of speak is to use a fully package qualified name Dog::Speak(). #!/usr/local/env perl ###filename:script. 13. which would make changing the base class a lot of work. Back to the dogs. $_[0]->SUPER::Speak. ###filename:Dog. > Spike says Grrr at Shepard. my $dog=Shepard->New("Spike").pm package Shepard.pl use warnings. warn "$name says Grrr". and then calls its ancestor's Dog version of speak. sub New { return bless({Name=>$_[1]}. use Data::Dumper. sub Speak { my $name=$_[0]->{Name}. Without the magic of SUPER. use strict. The code processes a bunch of objects and calls the same method on each object. The Shepard module uses Dog as its base. and has a Speak method that growls.3 SUPER SUPER:: is an interesting bit of magic that allows a child object with a method call that same method name in its parent's class. 95 . use base Dog. And each object just knows how to do what it should do.
For example. I will refer you to the "NEXT. you might want a method that calls its parent method but then multiplies the result by minus one or something. MothersMother was a complete stranger he would not meet for years to come. then SUPER will not work. there is no easy. and FathersFather. every class could do its part. However. SUPER does have its uses. The FatherOfTheBride would pay for the wedding. Unfortunately." There are some limitations with SUPER. though. Many times a class might exist that does ALMOST what you want it to do. it would get into an infinite loop calling itself recursively. 96 . Father and Mother as parents. SUPER is a way of saying. So designing Father to rely on his future. etc as grandparents). SUPER will do the trick. Imagine an object of type "Child". This means if the method FathersFather needed to call was in MothersMother. When Father was coded. and so on and so forth.pm" module available on CPAN. Instead of a class called "Child" imagine a class called "CoupleAboutToGetMarried". and every base class has a method called "ContributeToWedding". This could be considered a good thing. it is legitimate to have what you might consider to be "universal" methods that exist for every class. the only modules that will get looked at is "FathersFather" and "FathersMother". In that case. and then call SUPER::ContributeToWedding. If "Father" has a method called Speak and that method calls SUPER::Speak. have-not-evenmet-her-yet mother-in-law. built-in way to do this in perl. Consider the big family tree inheritance diagram in the "use base" section of this document (the one with Child as the root.If Shepard's version of Speak simply said $_[0]->Speak. Rather than modify the original code to do what you want it to. since you would assume that Father was designed only knowing about FathersFather and FathersMother. SUPER looks up the hierarchy starting at the class from where it was called. you could instead create a derived class that inherits the base class and rewrite the method to do what you want it to do. In cases like this. FathersMother. "look at my ancestors and call their version of this method. the FatherOfTheGroom would pay for the rehersal dinner. could be considered a bad thing.
If no such method exists. $dog=undef. Just prior to deleting the object and any of its internal data. use strict. and the object is scheduled for garbage collection. perl will call the DESTROY method on the object.4 Object Destruction Object destruction occurs when all the references to a specific object have gone out of lexical scope. The DESTROY method has similar limitations as SUPER.pm line 7. If Mother and Father both have a DESTROY method. use Dog.pm module on CPAN also solves this limitation. > Spike has been sold at Dog. } 1. ###filename:Dog. The NEXT. #!/usr/local/env perl ###filename:script.pl use warnings." has been sold"). With an object that has a complex hierarchical family tree. perl silently moves on and cleans up the object data. then Mother's not going to handle her demise properly and you will likely have ghosts when you run your program.pm package Dog. } sub DESTROY { warn (($_[0]->{Name}). perl will only call the FIRST method of DESTROY that it finds in the ancestry.13.$_[0]). my $dog=Dog->New("Spike"). 97 . use Data::Dumper. sub New { return bless({Name=>$_[1]}.
2 use Module The code in a perl module can be made available to your script by saying "use MODULE. it will provide subroutine declarations that can be called like normal subroutines. and then return the reference. then the module is sometimes referred to as a "class". In the Animal.14 Object Oriented Review 14. this would look like: my $pet = Animal->New('Spike') The name of the constructor can be any valid subroutine name. The object is usually a hash. and the Values correspond to the attribute values specific to that particular instance. The best way to add directories to the @INC variable is to say use lib "/path/to/dir".1 Modules The basis for code reuse in perl is a module. The module can be designed for procedural programming or object oriented programming (OO). If the module is designed for object oriented use. Once its referent is blessed. The best way of calling a constructor is to use the arrow operator: my $object = Classname->Constructor(arguments).pm module example. and different instances had Name values of "Fluffy".pm class. Keys to the hash correspond to object attribute names. and so on. it can be used as an object. A perl module is a file that ends in ". "Spike". If the module is OO. 98 . 14.3 bless / constructors If the module is designed for procedural programming. In the Animal.pm" and declares a package namespace that (hopefully) matches the name of the file. it will declare subroutines that will be used as constructors or methods. but is usually "new" or "New". use the reference to bless the variable into the class. and the reference is a handy way of passing the object around. 14. Constructors are subroutines that create a reference to some variable." The "use" statement will look for the module in the directories listed in the PERL5LIB environment variable and then the directories listed in the @INC variable. Any double-colons (::) in the module name being used get converted to a directory separator symbol of the operating system. one key was "Name".
use the "use base" statement. etc. change values. "Speak" was a method that used the Name of the instance to print out "$name says woof". then a derived class can override the base class method by declaring its own subroutine called MethodName. A method is simply a subroutine that receives a reference to the instance variable as its first argument. The preferred way of calling a method is using the arrow method.6 Overriding Methods and SUPER Classes can override the methods of their base classes. $ObjectInstance -> Method ( list of arguments ). 99 . this would look like: $pet->Speak. use base BaseClassName. If a base class contains a method called "MethodName". The GermanShepard method named Speak called the Dog version of Speak by calling: $obj->SUPER::Speak. The classes Cat and Dog inherit from the base class Animal. Both Dog and Cat classes inherit the constructor "New" method from the Animal base class. In the Animal. methods can be called on the instance to get information. In one example above. 14. 14. it may want to call its base class method.14. The only way to accomplish this is with the SUPER:: pseudopackage name.4 Methods Once an instance of an object has been constructed. Cat and Dog are "derived" from Animal. the GermanShepard derived class overrode the Dog base class Speak method with its own method. If a derived class overrides a method of its base class. the Cat and Dog classes both inherit from a common Animal class. This allows many similar classes to put all their common methods in a single base class. In the examples above. To have a class inherit from a base class.pm example. perform operations. or "verbs" in a sentences with instances being the "subject". Methods should be thought of as "actions" to be performed on the instance.5 Inheritance Classes can inherit methods from base classes. In the above examples.
tar. and most importantly. which provides a shell interface for automating the downloading of perl modules from the CPAN website.1 CPAN.tar. If the README looks promising. A "perldoc" utility comes with perl that allows viewing of POD. The Web Site CPAN is a website that contains all things perl: help. There is also a CPAN perl module. and installs it for you.2 CPAN. There is a CPAN website. it installs both modules for you with one command. and then set your PERL5LIB environment variable to point to that directory. a plethora of perl module so that you can re-use someone else's code.gz (you should use the latest version. If you do not have root privileges and the module is pure perl (just a .org CPAN contains a number of search engines. which is "Plain Old Documentation" embedded within the perl modules downloaded from CPAN.60 From here. which is contained in NEXT-0.pm module is a module that automates the installation process. then download the tarball. 15.pm file to your home directory (or anywhere you have read/write privileges). This example is for the NEXT.cpan. The Perl Module The CPAN.pm module. The "exit" step is shown just so you remember to log out from root. most modules install with the exact same commands: > > > > > > perl Makefile.gz extension. Here is the standard installation steps for a module. if available. source code to install perl.60. FAQs.pm file). 15. http://www.) > gunzip NEXT-0. which will be a file with a tar.15 CPAN CPAN is an acronym for "Comprehensive Perl Archive Network".60. And finally. there is a "h2xs" utility. you give it the name of a module.PL make make test su root make install exit The "make install" step requires root privileges. you can view the README file that is usually available online before actually downloading the module.tar > cd NEXT-0. and it downloads it from the web. it will install any dependencies for you as well. More interestingly. which contains a plethora of perl module for anyone to download. then you can copy the . If you install a module that requires a separate module. 100 .60. untars it. Once you find a module that might do what you need.gz > tar -xf NEXT-0. which automates the creation of a module to be uploaded to CPAN.
Install these on your system before running the CPAN module. Change to root.pm will also want ncftpget. which is an Internet file transfer program for scripts. Most can be answered with the default value (press <return>).CPAN.pm will want you to have lynx installed on your machine. 101 .pm module shell. > su root > perl -MCPAN -e shell The first time it is run. The CPAN. and then run the CPAN. Lynx is a text-based webbrowser.pm module is run from a shell mode as root (you need root privileges to do the install). it will ask you a bunch of configuration questions. CPAN.
ask or ignore)? [ask] Where is your gzip program? [/usr/bin/gzip] Where is your tar program? [/bin/tar] Where is your unzip program? [/usr/bin/unzip] Where is your make program? [/usr/bin/make] Where is your lynx program? [] > /usr/bin/lynx Where is your wget program? [/usr/bin/wget] Where is your ncftpget program? [] > /usr/bin/ncftpget Where is your ftp program? [/usr/bin/ftp] What is your favorite pager program? [/usr/bin/less] What is your favorite shell? [/bin/bash] Parameters for the 'perl Makefile. separated by blanks [] > 3 5 7 11 13 Enter another URL or RETURN to quit: [] Your favorite WAIT server? [wait://ls6-www.uni-dortmund. put them on one line.informatik.PL' command? Your choice: [] Parameters for the 'make' command? Your choice: [] Parameters for the 'make install' command? Your choice: [] Timeout for inactivity during Makefile. The next time you run cpan. 102 .de:1404] cpan> That last line is actually the cpan shell prompt. it will go directly to the cpan shell prompt.Here is a log from the CPAN being run for the first time on my machine: Are you ready for manual configuration? [yes] CPAN build and cache directory? [/home/greg/.PL? [0] Your ftp_proxy? Your http_proxy? Your no_proxy? Select your continent (or several nearby continents) [] > 5 Select your country (or several nearby countries) [] > 3 Select as many URLs as you like.cpan] Cache size for build directory (in MB)? [10] Perform cache scanning (atstart or never)? [atstart] Cache metadata (yes/no)? [yes] Your terminal expects ISO-8859-1 (yes/no)? [yes] Policy on building prerequisites (follow.
You do not need to know POD to write perl code.t # edit test cd . cpan> force install Tk Or you can get the tarball from www.pm module with all the trimmings. it will not install the module. This first command will create a directory called "Animal" and populate it with all the files you need. among other things.cpan. > perldoc perldoc > perldoc NEXT > perldoc Data::Dumper 15. type the following command: cpan> install Bundle::CPAN cpan> reload cpan You should then be able to install any perl module with a single command. # go to make directory perl Makefile.pm # edit module cd .4 Creating Modules for CPAN with h2xs If you wish to create a module that you intend to upload to CPAN.3 Plain Old Documentation (POD) and perldoc Modules on CPAN are generally documented with POD. perl comes with a utility "h2xs" which.gz file 103 .tar. > > > > > > > > > > h2xs -X -n Animal # create the structure cd Animal/lib # go into module dir edit Animal. If cpan encounters any problems. At the cpan shell prompt. Perl comes with a builtin utility called "perldoc" which allows you to look up perl documentation in POD format./t # go into test dir edit Animal. then use the "force" command.gz tarball that can be uploaded to CPAN and downloaded by others using the cpan.. 15. But you will want to know how to read POD from all the modules you download from CPAN. will create a minimal set of all the files needed.tar.org and install it manually. The remainder of the commands show you what steps you need to take to create a . If you wish to force the install.The first thing you will probably want to do is make sure you have the latest and greatest cpan. POD embeds documentation directly into the perl code.PL # create make file make # run make make test # run the test in t/ make dist # create a ..pm module.
+define+FAST More advanced arguments: Single character switches can be lumped together. The "--" argument could be used to indicate that arguments before it are to be used as perl arguments and that arguments after it are to be passed directly to a compiler program that the script will call. -f=options. Options operate independent of spacing. and using "-f optionfile.txt An argument could indicate to stop processing the remaining arguments and to process them at a later point in the script. Instead of "-x -y -z". 17 Command Line Arguments Scripts are often controlled by the arguments passed into it via the command line when the script is executed. such as "-h" to get help.txt -f = options. Some of perl's builtin features are somewhat limited and a CPAN module greatly enhances and/or simplifies its usage.pl -in test42. > mytest. any new topics may include a discussion of a perl builtin feature or something available from CPAN.16 The Next Level You now know the fundamentals of procedural perl and object oriented perl.txt" would be easier than putting those options on the command line each and every time that function is needed.pl -f optionfile. > myscript.pl -v Switches might by followed by an argument associated with the switch.txt -v Options can have full and abbreviated versions to activate the same option.txt -.txt 104 . Arguments might be a switch. A "-in" switch might be followed by a filename to be used as input. you could say "-xyz".pl -in data. Options can be stored in a separate file. A file might contain a number of options always needed to do a standard function. > anotherscript. > thatscript.pl -h A "-v" switch might turn verboseness on. > thisscript. The option "-verbose" can also work as "-v". From this point forward. This would allow a user to use the option file and then add other options on the command line.
'test. > > > > > > > > > .pl "*. > script. use Data::Dumper.pl *. #!/usr/bin/env perl ###filename:script.pl use warnings.txt'. #!/usr/bin/env perl ###filename:script.pl" $VAR1 = [ '*.pl'. If you need to pass in a wild-card such as *. .pl -v -f options.pl use warnings. except for quoted strings. print Dumper \@ARGV. > 'hello world' > ].1 @ARGV Perl provides access to all the command line arguments via a global array @ARGV. use strict.17. > '-f'./test.pl' ]. use strict. The text on the command line is broken up anywhere whitespace occurs.txt then you will need to put it in quotes or your operating system will replace it with a list of files that match the wildcard pattern./test.pl' ]. > 'options. use Data::Dumper. print Dumper \@ARGV.pl $VAR1 = [ 'script. 105 .txt "hello world" > $VAR1 = [ > '-v'.
Package "main" is the default package and a good place to put command line argument related variables.Simple processing of @ARGV would shift off the bottom argument. # create subroutines for options that do things sub print_help { print "-d for debug\n-f for filename\n". process it. } } Package (our) variables are used instead of lexical (my) variables because command line arguments should be considered global and package variables are accessible everywhere.} else { die "unknown argument '$arg'".pl script. } # get the first/next argument and process it. If you need to handle a few simple command line arguments in your script. # create a package variable for each option our $fn. and move on to the next argument. you would want this to turn on debugging in any separate modules that you write. 106 . code would check for $main::debug being true or false. not just your script. If you need to support more advanced command line arguments. Outside of package main. If you wrote a script that used "-d" to turn on debug information. you should look at Getopt::Declare. then the above example of processing @ARGV one at a time is probably sufficient. while(scalar(@ARGV)) { my $arg=shift(@ARGV). if($arg eq '-h') {print_help.} elsif($arg eq '-f') {$fn = shift(@ARGV). or a lot of simple ones. The following example will handle simple command line arguments described above. our $debug=0.} elsif($arg eq '-d') {$debug=1.
the global variables $fn and $debug are used with their full package name. The text passed into Getopt::Declare is a multi-line quoted q() string. > script. my $args = Getopt::Declare->new( q ( -in <filename> Define input file {$main::fn=$filename. The text within the curly braces {$main::fn=$filename. Notice that -h is not defined in the string. Also. print "fn is '$fn'\n". The <unknown> marker is used to define what action to take with unknown arguments. Note that within the curly braces. If [undocumented] is contained anywhere in the command line argument description.} is treated as executable code and evaled if the declared argument is encountered on the command line. If -v is on the command line.17. then that argument will not be listed in the help text. our $debug=0.} <unknown> { die "unknown arg '$unknown'\n". The above example with -h. but will still be recognized if placed on the command line 107 . This string defines the arguments that are acceptable. This is because Getopt::Declare recognizes -h to print out help based on the declaration.2 Getopt::Declare The Getopt::Declare module allows for an easy way to define more complicated command line arguments. Getopt::Declare recognizes -v as a version command line argument.} -d Turn debugging On {$main::debug=1. our $fn=''. and -d options could be written using Getopt::Declare like this: use Getopt::Declare. not that the starting curly brace must begin on its own line separate from the argument declaration and description. print "Debug is '$debug'\n". it will print out the version of the file based on $main::VERSION (if it exists) and the date the file was saved. } )).pl -h >Options: > -in <filename> Define input file > -d Turn debugging On The argument declaration and the argument description is separated by one or more tabs in the string passed into Getopt::Declare.-f. arguments that are not defined in the declaration.
1. 17. 4. 108 . 5. allowing nested argument files. It can be turned off with -quiet. place [repeatable] in the description. a declared argument will only be allowed to occur on the command line once. Filenames to be handled by the script can be listed on the command line without any argument prefix 2. Any options after a double dash (--) are left in @ARGV for later processing. 6. and any action associated with it. An undocumented -Dump option turns on dumping. calling finish() with a true value will cause the command line arguments to stop being processed at that point.(secret arguments) A [ditto] flag in the description will use the same text description as the argument just before it. Inside the curly braces.1 Getopt::Declare Sophisticated Example The example on the next page shows Getopt::Declare being used more to its potential.2. If the argument can occur more than once. Verbosity can be turned on with -verbose. 3. Additional arguments can be placed in an external file and loaded with -args filename. The Error() subroutine will report the name of the file containing any error while processing the arguments. Normally. A short and long version of the same argument can be listed by placing the optional second half in square brackets: -verb[ose] This will recognize -verb and -verbose as the same argument. Argument files can refer to other argument files. Any arguments that are not defined will generate an error.
our $VERSION=1.} else {main::Error("unknown arg '$unknown'"). { local($main::arg_file).$unknown).} -verb[ose] Turn verbose On {$main::verbose=1. our $arg_file='Command Line'. $main::arg_file = $input. $myparser->parse().} -h Print Help {$main::myparser->usage.} --Dump [undocumented] Dump on {$main::dump=1.01.($_[0]). 109 . sub Verbose {if($verbose){print $_[0].} my $grammar = q( -args <input> Arg file [repeatable] { unless(-e $input) {main::Error("no file '$input'").} <unknown> Filename [repeatable] { if($unknown!~m{^[-+]}) {push(@main::files.Argument separator {finish(1). our $debug=0. } main::Verbose ("finished parsing '$input'\n").} -quiet Turn verbose Off {$main::verbose=0.} -. our $dump=0. } -d Turn debugging On {$main::debug=1. # -v will use this our @files.} } ). $main::myparser->parse([$input]).}} sub Error {die"Error: ". main::Verbose ("returning to '$main::arg_file'\n").['-BUILD'])." from '$arg_file'\n". our $verbose=0. our $myparser = new Getopt::Declare ($grammar.# advanced command line argument processing use Getopt::Declare.} main::Verbose("Parsing '$input'\n").
perl will create a filehandle and assign it to that scalar. close($filehandle) or die "Could not close". 18. '>>' Append. and the scalar goes out of scope or is assigned undef. '>' Write. Create if non-existing.txt') or die "Could not open file". The valid flags are defined as follows: '<' Read. or append. is the first character of the string. If the filehandle is stored in a scalar. All file IO revolves around file handles. 18. Do not clobber existing file.3 read Once open. Clobber if already exists. Each pass through the conditional test reads the next line from the file and places it in the $_ variable. i. 'filename.2 close Once open. The most common is to read the filehandle a line at a time using the "angle" operator.6 and later and is the preferred method for dealing with filehandles. If the first argument to open() is an undefined scalar. 18.18 File Input and Output Perl has a number of functions used for reading from and writing to files. Create if non-existing. The angle operator is the filehandle surrounded by angle brackets. DEFAULT. write. you can read from a filehandle a number of ways. use the open() function. This is available in perl version 5. <$filehandle> When used as the boolean conditional controlling a while() loop. Do not create. Do not clobber existing file. If no flag is specified. 110 . you can close a filehandle by calling the close function and passing it the filehandle. the loop reads the filehandle a line at a time until the end of file is reached. and the flag. then perl will automatically close the filehandle for you. if present.e. The second argument to open() is the name of the file and an optional flag that indicates to open the file as read. The filename is a simple string. open(my $filehandle.1 open To generate a filehandle and attach it to a specific file. the file defaults to being opened for read.
and you are just going through each line and parsing it. my $addr=nlin.This script shows a cat -n style function. my $age =nlin.4 write If the file is opened for write or append.txt') or die "could not open". use Carp. and you need to read it in a certain order. print "$num: $line\n". my $line = $_. close $fh. But it requires that you test the return value to make sure it is defined. This is useful if you are reading a file where every line has a different meaning. chomp($line). print $fh "once\n".txt'). my $num=0. } my $name=nlin. while(<$fh>) { $num++. You can then call the subroutine each time you want a line. print $fh "a time\n". age: $age\n". 'input. print "Name: $name. print $fh "upon\n". '>output. 18. open (my $fh. open (my $fh. Another way to read from a filehandle is to assign the angle operator of the filehandle to a scalar. } The above example is useful if every line of the file contains the same kind of information. This will read the next line from the filehandle. address: $addr. sub nlin { defined(my $line =<$fh>) or croak "premature eof". return $line. 'input. you can wrap it up in a subroutine to hide the error checking.txt'). chomp($line). otherwise you hit the end of file. 111 . you can write to the filehandle using the print function. defined(my $line = <$fh>) or die "premature eof". To make a little more useful. open (my $fh.
5 File Tests Perl can perform tests on a file to glean information about the file. The "~" in Linux is a shell feature that is translated to the user's real directory path under the hood. Some common tests include: -e -f -d -l -r -w -z -p -S -T file file file file file file file file file file exists is a plain file is a directory is a symbolic link is readable is writable size is zero is a named pipe is a socket is a text file (perl's definition) 18.cshrc'). if you wish to get a list of all the files that end with a . All the tests have the following syntax: -x FILE The "x" is a single character indicating the test to perform. 112 .6 File Globbing The glob() function takes a string expression and returns a list of files that match that expression using shell style filename expansion and translation. my $startup_file = glob('~/. To translate to a real directory path.txt" because "~" only means something to the shell. Perl's open() function cannot open "~/list. use glob(). my @files = glob ( STRING_EXPRESSION ). FILE is a filename (string) or filehandle. For example. This is also useful to translate Linux style "~" home directories to a usable file path.txt").18. All tests return a true (1) or false ("") value about the file.txt expression: my @textfiles = glob ("*.
find(\&process.} } For more information: perldoc File::Find 113 . return. This process() subroutine prints out all .7 File Tree Searching For sophisticated searching. use the File::Find module. use File::Find. If your process() subroutine sets the package variable $File::Find::prune to 1. It is included in perl 5.. } The process() subroutine is a subroutine that you define.} if((-d $fullname) and ($fullname=~m{CVS})) {$File::Find::prune=1. if ($fullname =~ m{\.$pwd). sub process { .txt$}) {print "found text file $fullname\n".6. The process() subroutine will be called on every file and directory in $pwd and recursively into every subdirectory and file below. including searches down an entire directory structure.1.. chomp($pwd). the path to the file is available in $File::Find::dir and the name of the file is in $_.18. sub process { my $fullname = $File::Find::name. The package variable $File::Find::name contains the name of the current file or directory. then find() will not recurse any further into the current directory. my $pwd=`pwd`. If you process() was called on a file and not just a directory. Your process() subroutine can read this variable and perform whatever testing it wants on the fullname.txt files encountered and it avoids entering any CVS directories.
If you want to capture what goes to STDOUT and manipulate it within your script. When you execute a command via the system() function.txt". a return value of ZERO is usually good. A simple example is the "finger" command on Linux. which means the user will see the output scroll by on the screen. but if you are doing system commands in perl and you are using Tk. This is a very cool module that allows you to run system commands in the background as a separate process from you main perl script. 114 .system("command string"). all this text will go to STDOUT and will be seen by the user when they execute your script. there is a third way to run system commands within your perl script. The system() function executes the command string in a shell and returns you the return code of the command. In Linux. You can then process this in your perl script like any other string.3 Operating System Commands in a GUI If your perl script is generating a GUI using the Tk package. using the Tk::ExecuteCommand module. So to use the system() function and check the return value. the output of the command goes to STDOUT. and then it is lost forever. If you call system() on the finger command. then you will likely want to use the system() function. If you type: linux> finger username Linux will dump a bunch of text to STDOUT.1 The system() function If you want to execute some command and you do not care what the output looks like. a non-zero indicates some sort of error. system($cmd)==0 or die "Error: could not '$cmd'". my $string_results = `finger username`. you just want to know if it worked.2 The Backtick Operator If you want to capture the STDOUT of a operating system command. The module provides the user with a "Go/Cancel" button and allows the user to cancel the command in the middle of execution if it is taking too long. you should look into Tk::ExecuteCommand. 2.`command string`. use the backtick operator.19 Operating System Commands Two ways to issue operating system commands within your perl script are the system function and the backtick operator. 19. 19. 1. 19. The $string_results variable will contain all the text that would have gone to STDOUT. then you will want to use the backtick operator. you might do something like this: my $cmd = "rm -f junk. We have not covered the GUI toolkit for perl (Tk).
adverbs. This is functionally equivalent to this: $_ =~ m/patt/. and 'tr' for translate. The most common delimiter used is probably the m// and s/// delimiters. such as {} or () or // or ## or just about any character you wish to use. You may see perl code that simply looks like this: /patt/. find out what matched the patterns. There are three different regular expression operators in perl: 1.20 Regular Expressions Regular expressions are the text processing workhorse of perl.match m{PATTERN} 2. but I prefer to use m{} and s{}{} because they are clearer for me. 115 .=~ pattern does match string expression 2. Binding in Regular Expressions can be looked at in a similar fashion: $string =~ verb ( pattern ). Generic OOP structure can be represented as $subject -> verb ( adjectives.transliterate tr{OLD_CHAR_SET}{NEW_CHAR_SET} Perl allows any delimiter in these operators. where "verb" is limited to 'm' for match. etc ).substitute s{OLDPATTERN}{NEWPATTERN} 3. you can search strings for patterns. 's' for substitution. With regular expressions. There are two ways to "bind" these operators to a string expression: 1. and substitute the matched patterns with new strings.!~ pattern does NOT match string expression Binding can be thought of as "Object Oriented Programming" for regular expressions.
my $actual = "Toyota". $car =~ s{$actual}{$wanted}. decrypted: How I love thee. print "decrypted: $love_letter\n". print "$car\n".\n". print "encrypted: $love_letter". $love_letter =~ tr{A-Za-z}{N-ZA-Mn-za-m}. # upgrade my car my $car = "my car is a toyota\n". > > > > *deleted spam* my car is a jaguar encrypted: Ubj V ybir gurr. subjecting the pattern to one pass of variable interpolation as if the pattern were contained in double-quotes. print $car. } print "$email\n". my $wanted = "Jaguar". $car =~ s{toyota}{jaguar}. # simple encryption. Regular expressions also allow you to look for patterns with different types of "wildcards".Here are some examples: # spam filter my $email = "This is a great Free Offer\n". if($email =~ m{Free Offer}) {$email="*deleted spam*\n".1 Variable Interpolation The braces that surround the pattern act as double-quote marks. This allows the pattern to be contained within variables and interpolated during the regular expression. The above examples all look for fixed patterns within the string. my $car = "My car is a Toyota\n". $love_letter =~ tr{A-Za-z}{N-ZA-Mn-za-m}. > My car is a Jaguar 116 . 20. Caesar cypher my $love_letter = "How I love thee.
dat. the parenthesis were in the pattern but did not occur in the string. my $size = $1. } } > output. foreach my $line (@lines) { #################################### # \S is a wildcard meaning # "anything that is not white-space".dat size: 512 filename: address.txt size: 1024 filename: input. my @lines = split "\n". 0-9". Each line also contains the pattern {size: } followed by one or more digits that indicate the actual size of that file.3 Defining a Pattern A pattern can be a literal pattern such as {Free Offer}. Notice in the above example.$size\n".1024 > input. yet the pattern matched. ########################### # \d is a wildcard meaning # "any digit. print "$name.512 > address. ########################### $line =~ m{size: (\d+)}. we process an array of lines.1048576 20. <<"MARKER" filename: output.20. # the "+" means "one or more" #################################### if($line =~ m{filename: (\S+)}) { my $name = $1.txt.db size: 1048576 MARKER . It can also contain metacharacters such as the parenthesis. 117 . It can contain wildcards such as {\d}. each containing the pattern {filename: } followed by one or more non-whitespace characters forming the actual filename.db.2 Wildcard Example In the example below.
4 Metacharacters Metacharacters do not get interpreted as literal characters. Instead they tell perl to interpret the metacharacter (and sometimes the characters around metacharacter) in a different way. then simply treat next character as a non-metacharacter. match any single character in class * (quantifier): match previous item zero or more times + (quantifier): match previous item one or more times ? (quantifier): match previous item zero or one time { } (quantifier): match previous item a number of times in given range ^ (position marker): beginning of string (or possibly after "\n") $ (position marker): end of string (or possibly before "\n") 118 . then match that character class. | alternation: (patt1 | patt2) means (patt1 OR patt2) ( ) (?: ) . The following are metacharacters in perl regular expression patterns: \ | ( ) [ ] { } ^ $ * + ? . If not a shortcut. \ (backslash) if next character combined with this backslash forms a character class shortcut. [ ] grouping (clustering) and capturing grouping (clustering) only. no capturing.20. (somewhat faster) match any single character (usually not "\n") define a character class.
" Sincerely. and 'fffffast' if($str =~ m{f{3. plus sign at .} > > > > > > > alt at . asterisk at ... if($str =~ m{c." . class at .t}){warn "period"......} # ? quantifier. Change the value assigned to $str and re-run the script. captured '$1'". period at .} # ^ position marker.Examples below. group matched.." zzzz.} # [] define a character class: 'a' or 'o' or 'u' # match 'cat' 'cot' 'cut' if($str =~ m{c[aou]t}){warn "class"..} # .} # () grouping and capturing # match 'goodday' or 'goodbye' if($str =~ m{(good(day|bye))}) {warn "group matched." $str = "Dear sir.. match previous item one or more # match 'snake' 'ssnake' 'sssssssnake' if($str =~ m{s+nake}){warn "plus sign".} # * quantifier. matches beginning of string # match 'Dear' only if it occurs at start of string if($str =~ m{^Dear}){warn "caret". Hummingbirds are ffffast. matches end of string # match 'John' only if it occurs at end of string if($str =~ m{John$}){warn "dollar". match previous. captured 'goodday' at .. # | alternation # match "hello" or "goodbye" if($str =~ m{hello|goodbye}){warn "alt".} # $ position marker. previous item is optional # match only 'dog' and 'dogs' if($str =~ m{dogs?}){warn "question"..5}ast}){warn "curly brace".} # {} quantifier.. 119 . question at . Experiment with what matches and what does not match the different regular expression patterns. 'ffffast'.... my . hello and goodday! " dogs and cats and sssnakes put me to sleep. John".} # + quantifier. any single character # match 'cat' 'cbt' 'cct' 'c%t' 'c+t' 'c?t' . match previous item zero or more # match '' or 'z' or 'zz' or 'zzz' or 'zzzzzzzz' if($str =~ m{z*}){warn "asterisk". 3 <= qty <= 5 # match only 'fffast'." .
$3. … variables. The left parenthesis are counted from left to right as they occur within the pattern. > caret at . multiplication has a higher precedence than addition.> curly brace at . my $last = $2. $3. $2. we want to cluster "day|bye" so that the alternation symbol "|" will go with "day" or "bye". my $first = $1. rather than "goodday" or "goodbye".. therefore we use cluster-only parentheses. $first $last\n". etc Capturing parentheses Clustering parentheses will also Capture the part of the string that matched the pattern within parentheses. matching either "cat" or "cats". The captured values are accessible through some "magical" variables called $1. The expression "2 + 3 * 4" does the multiplication first and then the addition. Normally. $2. the pattern would match "goodday" or "bye".} 120 . .. print "Hello. matching "cats" or null string. John Smith Because capturing takes a little extra time to store the captured result into the $1. Clustering parentheses work in the same fashion. my $test="Firstname: John Lastname: Smith".5 Capturing and Clustering Parenthesis Normal parentheses will both cluster and capture the pattern they contain. The pattern {cats?} will apply the "?" quantifier to the letter "s".. In the below example.. sometimes you just want to cluster without the overhead of capturing. Each left parenthesis increments the number used to access the captured string. yielding the result of "20"... The pattern {(cats)?} will apply the "?" quantifier to the entire pattern within the parentheses. 20. Clustering affects the order of evaluation similar to the way parentheses affect the order of evaluation within a mathematical expression. yielding the result of "14". $2.. 20. ############################################ # $1 $2 $test=~m{Firstname: (\w+) Lastname: (\w+)}. The expression "(2 + 3) * 4" forces the addition to occur first. > dollar at . captured '$1'". starting at 1. > Hello. so we do not need to capture the "day|bye" part of the pattern. Without the clustering parenthesis..5. The pattern contains capturing parens around the entire pattern. if($str =~ m{(good(?:day|bye))}) {warn "group matched.1 $1.
Cluster-only parenthesis don't capture the enclosed pattern, and they don't count when determining
which magic variable, $1, $2, $3 ..., will contain the values from the
capturing parentheses.
my $test = 'goodday John';
if($test =~ m{(good(?:day|bye)) (\w+)})
{ print "You said $1 to $2\n"; }
> You said goodday to John
20.5.2 Capturing parentheses not capturing
If a regular expression containing capturing parentheses does not match the string, the magic variables
$1, $2, $3, etc will retain whatever PREVIOUS value they had from any PREVIOUS regular
expression. This means that you MUST check to make sure the regular expression matches BEFORE
you use the $1, $2, $3, etc variables.
In the example below, the second regular expression does not match, therefore $1 retains its old value
of 'be'. Instead of printing out something like "Name is Horatio" or "Name is" and failing on an
undefined value, perl instead keeps the old value for $1 and prints "Name is 'be'", instead.
my $string1 = 'To be, or not to be';
$string1 =~ m{not to (\w+)}; # matches, $1='be'
warn "The question is to $1";
my $string2 = 'that is the question';
$string2 =~ m{I knew him once, (\w+)}; # no match
warn "Name is '$1'";
# no match, so $1 retains its old value 'be'
> The question is to be at ./script.pl line 7.
> Name is 'be' at ./script.pl line 11.
20.6 Character Classes
The "." metacharacter will match any single character. This is equivalent to a character class that
includes every possible character. You can easily define smaller character classes of your own using
the square brackets []. Whatever characters are listed within the square brackets are part of that
character class. Perl will then match any one character within that class.
[aeiouAEIOU] any vowel
[0123456789] any digit
20.6.1 Metacharacters Within Character Classes
Within the square brackets used to define a character class, all previously defined metacharacters cease
to act as metacharacters and are interpreted as simple literal characters. Characters classes have their
own special metacharacters.
(backslash) demeta the next character
(hyphen) Indicates a consecutive character range, inclusively.
[a-f] indicates the letters a,b,c,d,e,f.
Character ranges are based off of ASCII numeric values.
If it is the first character of the class, then this indicates the class
is any character EXCEPT the ones in the square brackets.
Warning: [^aeiou] means anything but a lower case vowel. This
is not the same as "any consonant". The class [^aeiou] will
match punctuation, numbers, and unicode characters.
20.7 Shortcut Character Classes
Perl has shortcut character classes for some more common classes.
any digit
any NON-digit
[ \t\n\r\f]
any whitespace
[^ \t\n\r\f]
any NON-whitespace
any word character (valid perl identifier)
any NON-word character
20.8 Greedy (Maximal) Quantifiers
Quantifiers are used within regular expressions to indicate how many times the previous item occurs
within the pattern. By default, quantifiers are "greedy" or "maximal", meaning that they will match as
many characters as possible and still be true.
match zero or more times (match as much as possible)
match one or more times (match as much as possible)
match zero or one times (match as much as possible)
match exactly "count" times
{min, }
match at least "min" times (match as much as possible)
{min,max} match at least "min" and at most "max" times
(match as much as possible)
20.9 Thrifty (Minimal) Quantifiers
Placing a "?" after a quantifier disables greediness, making them "non-greedy", "thrifty", or "minimal"
quantifiers. Minimal quantifiers match as few characters as possible and still be true.
match zero or more times
(match as little as possible and still be true)
match one or more times
(match as little as possible and still be true)
match at least min times
(match as little as possible and still be true)
{min, max}?
match at least "min" and at most "max" times
(match as little as possible and still be true)
This example shows the difference between minimal and maximal quantifiers.
my $string = "12340000";
if($string =~ m{^(\d+)0+$})
{ print "greedy '$1'\n"; }
if($string =~ m{^(\d+?)0+$})
{ print "thrifty '$1'\n"; }
> greedy '1234000'
> thrifty '1234'
20.10 Position Assertions / Position Anchors Inside a regular expression pattern. matches "\n" also.20. if($test1=~m{\bjump\b}) { print "test1 matches\n". If the /m (multiline) modifier is present. Instead. \Z Matches the end of the string only.'. but will chomp() a "\n" if that was the last character in string. Not affected by /m modifier. Not affected by /m modifier. the pattern before and after that anchor must occur within a certain position within the string. If a position anchor occurs within a pattern. If this is the first regular expression begin performed on the string then \G will match the beginning of the string. $ Matches the end of the string. Indicates the position after the character of the last pattern match performed on the string. This example matches "jump" but not "jumprope": my $test1='He can jump very high. they translate into a "position" within the string. some symbols do not translate into a character or character class. } > test1 matches > test2 does not match 124 . \z Match the end of string only. ^ Matches the beginning of the string. matches "\n" also. } my $test2='Pick up that jumprope.1 The \b Anchor Use the \b anchor when you want to match a whole word pattern but not part of a word.'. \b word "b"oundary A word boundary occurs in four places. unless($test2=~m{\bjump\b}) { print "test2 does not match\n". If the /m (multiline) modifier is present. 1) at a transition from a \w character to a \W character 2) at a transition from a \W character to a \w character 3) at the beginning of the string 4) at the end of the string \B NOT \b \G usually used with /g modifier (probably want /c modifier too). Use the pos() function to get and set the current \G position within the string. \A Match the beginning of string only.10.
2 The \G Anchor The \G anchor is a sophisticated anchor used to perform a progression of many regular expression pattern matches on the same string. 125 . using the \G anchor to indicate the location where the previous regular expression finished. The \G anchor represents the position within the string where the previous regular expression finished. The first time a regular expression is performed on a string. The \G anchor is usually used with the "cg" modifiers. the \G anchor represents the beginning of the string. The pos() function will return the character index in the string (index zero is to the left of the first character in the string) representing the location of the \G anchor. The location of the \G anchor within a string can be determined by calling the pos() function on the string.10. Assigning to pos($str) will change the position of the \G anchor for that string. the first regular expression that fails to match will reset the \G anchor back to zero.20. The "cg" modifiers tell perl to NOT reset the \G anchor to zero if the regular expression fails to match. This will allow a series of regular expressions to operate on a string. Without the "cg" modifiers.
} $str=~m{\GBookcollection: }cg. } > > > > > > > > pos is 16 pos is 32 book is 'Programming Perl' pos is 65 book is 'Perl Cookbook' pos is 80 book is 'Impatient Perl' pos is 95 Another way to code the above script is to use substitution regular expressions and substitute each matched part with empty strings.The example below uses the \G anchor to extract bits of information from a single string. my $str = "Firstname: John Lastname: Smith Bookcollection: Programming Perl. print "pos is ".pos($str). After every regular expression. Notice how the pos() value keeps increasing. if($str=~m{\GFirstname: (\w+) }cg) { my $first = $1.]+)."\n".pos($str). } if($str=~m{\GLastname: (\w+) }cg) { my $last = $1. while($str=~m{\G\s*([^. Impatient Perl". print "pos is ". The problem is that a substitution creates a new string and copies the remaining characters to that string. In the above example. the difference can be quite significant.?}cg) { print "book is '$1'\n". Perl Cookbook. resulting in a much slower script."\n". the script prints the pos() value of the string.pos($str). but if you have a script that is parsing through a lot of text."\n". 126 . print "pos is ". the speed difference would not be noticeable to the user.
20." will NOT match "\n" ^ and $ position anchors will match literal beginning and end of string and also "\n" characters within the string. CaT. m{cat}i matches cat. (DEFAULT) ". m treat string as Multiple lines.1 Global Modifiers The following modifiers can be used with m{}. s treat string as a Single line." will match "\n" within the string. ".11. This allows the pattern to be spread out over multiple lines and for regular perl comments to be inserted within the pattern but be ignored by the regular expression engine. ^ and $ indicate start/end of "line" instead of start/end of string. 127 . CAT.20. ^ and $ position anchors will only match literal beginning and end of string.11 Modifiers Regular expressions can take optional modifiers that tell perl additional information about how to interpret the regular expression. $str =~ tr{oldset}{newset}modifiers.2 The m And s Modifiers The default behavior of perl regular expressions is "m". treating strings as a multiple lines. $str =~ m{pattern}modifiers. i case Insensitive. etc x ignore spaces and tabs and carriage returns in pattern. If neither a "m" or "s" modifier is used on a regular expression. $str =~ s{oldpatt}{newpatt}modifiers. Cat. Modifiers are placed after the regular expression. ^ matches after "\n" $ matches before "\n" o compile the pattern Once.11. outside any curly braces. s{}{}. perl will default to "m" behavior. possible speed improvement. CAt. or tr{}{}. 20.
"Perl Cookbook\n" .*)}) { print "default is '$1'\n"."Impatient Perl". using "^" and "$" to indicate start and end of lines. and the ". and the ". The only difference is the modifier used on the regular expression. The single line version prints out the captured pattern across three different lines.*)}m) { print "multiline is '$1'\n". then the "^" anchor will only match the literal beginning of the string. even if the string is multiple lines with embedded "\n" characters. } > > > > > default is 'Programming Perl ' multiline is 'Programming Perl ' singleline is 'Programming Perl Perl Cookbook Impatient Perl' 128 . the captured string includes the newline "\n" characters which shows up in the printed output.If the "m" modifier is used. If a string contains multiple lines separated by "\n".*)}s) { print "singleline is '$1'\n". my $string = "Library: Programming Perl \n" ." character set will match any character EXCEPT "\n". } if($string =~ m{Library: (. then the default behavior (the "m" behavior) is to treat the string as multiple lines. Notice in the "s" version. This example shows the exact same pattern bound to the exact same string. then the "^" anchor will match the beginning of the string or "\n" characters. the "$" anchor will match the end of the string or any "\n" characters." class will match any character including "\n". With the "s" modifier. If the "s" modifier is used. the "s" modifier forces perl to treat it as a single line. the "$" anchor will only match the literal end of string. if($string =~ m{Library: (. } if($string =~ m{Library: (.
If the pattern expects whitespace in the string. "fraction is '$fraction'\n". and carriage returns in the pattern.20. tabs. for easier reading. if( $string =~ m { ^ \s* ([-+]?) # positive or negative or optional \s* ( \d+ ) # integer portion ( \. my $exponent = $4 || ''.11.23423' exponent is ' e -12' A couple of notes for the above example: The x modifier strips out all spaces. it's always a good idea to anchor your regular expression somewhere in your string. with comments. "integer is '$integer'\n".3 The x Modifier The x modifier allows a complex regular expression pattern to be spread out over multiple lines. The pattern is spread out over multiple lines with comments to support maintainability. The following pattern is looking for a number that follows scientific notation. Most whitespace within a pattern with the x modifier is ignored. The double-pipe expressions guarantee that the variables are assigned to whatever the pattern matched or empty string if no match occurred. Also. my $fraction = $3 || ''. it must be explicitly stated using \s or \t or \n or some similar character class.134. with "^" or "$" or "\G". Without them.23423 e -12'. 129 . } > > > > sign is '-' integer is '134' fraction is '. "exponent is '$exponent'\n". print print print print "sign is '$sign'\n". an unmatched pattern match will yield an "undef" in the $1 (or $2 or $3) variable associated with the match. \d+ )? # fractional is optional ( \s* e \s* [+-]? \d+)? # exponent is optional }x ) { my $sign = $1 || ''. my $integer = $2 || ''. my $string = '.
20.13 Modifiers for s{}{} Operator The following modifiers apply to the s{oldpatt}{newpatt} operator only. the \G marker is reset to zero if the pattern does not match. my $number = qr{[+-]?\s*\d+(?:\. # remove perl comments next if($str =~ m{^\s*$}).12 Modifiers For m{} Operator The following modifiers apply to the m{pattern} operator only: g Globally find all matchs.\d+)?\s*(?:e\s*[+-]?\s*\d+)?}. g Globally replace all occurrences of oldpatt with newpatt e interpret newpatt as a perl-based string Expression. This maintains the \G marker at its last matched position.14 Modifiers for tr{}{} Operator The following modifiers apply to the tr{oldset}{newset} operator only. # remove all whitespace $str =~ s{#. 130 .16 Common Patterns Some simple and common regular expression patterns are shown here: $str =~ s{\s}{}g. c Complement the searchlist d Delete found but unreplaced characters s Squash duplicate replaced characters 20. Without this modifier. m{} will find the first occurrence of the pattern. check out the Regexp::Common module on CPAN.15 The qr{} function The qr{} function takes a string and interprets it as a regular expression. the result of the expression becomes the replacement string. 20.# next if only whitespace For common but more complicated regular expressions. returning a value that can be stored in a scalar for pattern matching at a later time. Without this modifier.20.*}{}. 20. cg Continue search after Global search fails.
Here is how to find out what the floating point number pattern looks like in Regexp::Common: use Regexp::Common. If you are doing some complicated pattern matching. > match is '-12.423E-42 the number".])(?: [0123456789]*)(?:(?:[. print "$patt\n".}))?)(?: (?:[E])(?:(?:[+-]?)(?:[0123456789]+))|)) As complicated as this is. the data in the hash are the patterns to use within regular expressions. The hash lookup can be used directly within your regular expression: use Regexp::Common. and others). it might be worth a moment to check out Regexp::Common and see if someone already did the work to match the pattern you need. lopsided. it is a lot easier to reuse someone else's code than to try and reinvent your own. delimited text with escapes. wheel. but fairly complicated. print "match is '$1'\n". perl scripts that use it will have a "magic" hash called %RE imported into their namespace. > (?:(?i)(?:[+-]?)(?:(?=[0123456789]|[. faulty. email addresses. integers and floating point numbers of different bases. The keys to this hash are human understandable names.])(?:[0123456789]{0. regular expression patterns (balanced parentheses and brackets. $str =~ m{($RE{num}{real})}.423E-42' 131 . cpan> install Regexp::Common Once Regexp::Common is installed.17 Regexp::Common The Regexp::Common module contains many common.20. my $str = "this is -12. my $patt = $RE{num}{real}.
city. The data is always in a fixed location. phonenumber. dateof-birth. and these rules can be combined fairly easily to create complex rules. In simpler terms. If the data being parsed is not quite so rigid in its definition. regular expressions may become a cumbersome means to extract the desired data. cpan> install Parse::RecDescent Parse::RecDescent describes itself as a module that incrementally generates top-down recursivedescent text parsers from simple yacc-like grammar specifications. ZIP. Instead. and the module parses the data according to those rules. address. 132 . Parse::RecDescent uses regular expression styled patterns to define grammar rules.21 Parsing with Parse::RecDescent Perl's regular expression patterns are sufficient for many situations. and a regular expression can be used to perform searches within that data. state. firstname. such as extracting information out of a tab separated database that is organized by lastname. the Parse::RecDescent module may prove useful in that it allows whole gramatical rules to be defined.
Jim. print "> ".Here is a quick example from perldoc Parse::RecDescent use Parse::RecDescent. } "dead. print "He's dead.\n". Bones. or pronoun 133 . print "try typing these lines:\n". Bones. Jim!\n". not a magician! press <CTL><D> when finished > Dammit. Jim. } > > > > > > > > > > > > try typing these lines: He's dead. not a magician!\n". Jim. Bones. not a" job "!" "Just do what you can." name "!" "Shut up. I'm a doctor. while(<>) { $parse->McCoy($_). my $parse = new Parse::RecDescent($grammar). print "press <CTL><D> when finished\n". > He's dead.\n". print "> ". Jim! Shut up. I'm a doctor. > You green blooded Vulcan! ERROR (line 1): Invalid McCoy: Was expecting curse. Jim! Dammit. not a magician! Just do what you can. I'm a doctor. print "Dammit.} curse: 'Dammit' | 'Goddammit' name: 'Jim' | 'Spock' | 'Scotty' job: 'magician' | 'miracle worker' | 'perl hacker' pronoun: "He's" | "She's" | "It's" | "They're" }." { print | pronoun { print | <error> = q{ name ". my $grammar McCoy: curse ". Bones. I'm a doctor.
134 . Parse::RecDescent uses perl"s regular expression patterns in its pattern matching. the longer it takes to run. the more rules. Since it recursively descends through its set of rules.Parse::RecDescent is not the solution for every pattern matching problem. so you need to learn basic regular expression patterns before you use Parse::RecDescent. and normal regular expressions are becoming difficult to manage. which can be a problem if you are parsing a gigabyte-sized file. Parse::RecDescent currently must read in the entire text being parsed. And Parse::RecDescent has an additional learning curve above and beyond perl's regular expressions. If the data you are mining is fairly complex. Parse::RecDescent is slower than simple regular expressions. then Parse::RecDescent would be the next logical module to look at.
I recommend the "Mastering Perl/Tk" book.} )->grid(-row=>1. Perl has a Graphical User Interface (GUI) toolkit module available on CPAN called Tk. drawing the GUI. $top->Button ( -text=>"Hello". The MainLoop is a subroutine call that invokes the event loop. my $top=new MainWindow. all the examples have had a command line interface. and Tk So far. the word "Hi" is printed to the command line (the -command option). 135 . > widget Here is a simple "hello world" style program using Tk: use Tk. Several large books have been written about the Tk GUI toolkit for perl. the Tk module has a widget demonstration program that can be run from the command line to see what widgets are available and what they look like. a small GUI will popup on the screen (the MainWindow item) with a button (the $top->Button call) labeled "Hello" (the -text option). the widget will not show up in the GUI). cpan> install Tk The Tk module is a GUI toolkit that contains a plethora of buttons and labels and entry items and other widgets needed to create a graphical user interface to your scripts. responding to button clicks. And it would be impossible to give any decent introduction to this module in a page or two. MainLoop. When the above example is executed. If you plan on creating GUI's in your scripts. etc. The ->grid method invokes the geometry manager on the widget and places it somewhere in the GUI (without geometry management. Once installed. -command=>sub{print "Hi\n".-column=>1). When the mouse left-clicks on the button. type "widget" to run the demonstration program. User input and output occurred through the same command line used to execute the perl script itself. At the command line. GUI.22 Perl.
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..................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................104 comparison .......................................................................................................................................................................................................53 concatenation..........................114 base conversion.........89 boolean..............................................................................................................25 compiling...........16 AND.......110 closures......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................25 code reference..............23 caller...............................94 clone...............................................................................................................83 blessed invocant.......................................................................................................105 Command Line Arguments.......................120 Character Classes...............76 bless.............................................................................................................................................................................................................................................83p.........................................59 control flow......................................98 bless REFERENCE...................................................................................................................................................................................26 anonymous.....................................71 code reuse....................................................................................................................................................................................................................................................................................................................................13 conditional operator............107 @ARGV...............................70 array........................................................................................................ Getopt::Declare....................................76 chomp..................................................76 complex data structures....................121 CHECK.......................................................................................................................... STRING.............................................................88 Capturing and Clustering Parenthesis..........................................................................................................................32 Autovivification..........................................................................................................................................................................................................................................................................Alphabetical Index abs...........................51 anonymous subroutine.................................................................................78 command line...................................................................................................................70 anonymous subroutines..............................................................................59 144 ......................................................................................................................................................................................................................................................................................................................................................................................................................................................................... bless / constructors..74 can..............................................................25 comparison operator...........................................................................28 continue..........................................................................................................................................................................66 cmp.......................................................................................................................................................................................................................................................69 argument passing............................................................................................................................................................................................................................................................13 class.......................56 close..........54 backtick............................................................................................................................................................................................................................................................................................................................................................................................21 BEGIN........................................................................................32 $..............................................................................................................................................................................................................................................................................32 @..........................................................
................59 foreach..................................................................................... 59 145 ................................42 dereference.cos.......................................110 open.........................................71 double quote....................................................................................................................................................................................................................................................................................111 File Test......112 File Tests..................59 elsif.........112 -S...............23p.....................................................................................................................................................................................................................25 execution timeline....................................... close........................... -d.......59 END......................... file glob..................................................................................................76 eq.........................................................................................................................................................................12 e...........112 -r................................................................................................................................................................................................100 CPAN...................................................................................................................................................................................100 Creating Modules.....................................................................................110 File IO....................18 exponentiation...................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................112 -f...........................................................................100 CPAN.......................................................................................................................................................................................................................................................................................................................................................................... The Web Site......................................................................41 exp............................................................................22 delete..............................43 else................................................................................................................................................................................................................................................................112 -e............................................................................................................................112 -l.......112 -T.............................................110 write.................................................................................................................................................................25 equal to..............112 -z.................................................................................. The Perl Module.......................................................................................................113 for..............................................................................................................................................................................................................................56 defined..............................................................................................36...112 File::Find...........................................17 false...........................................................................................................................................................................................................................................................................................................................................................................................112 -p................................................................................................................................................................................................................................................................................................................................................................................................112 -w....................................................................................................................................................82 exists.............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................56 dclone...............................56 deep clone..................................................................................................................................................................................................................17 CPAN.............................................................................................................................................................................................18 each........................................................................112 File Input and Output...............................................................................................................................................................110 read..........................................................................................................................................103 Data Persistence....................................................................................................................................................................................................................................................................................................................................................................................................................50 dereferencing code references...........................................................................................................................................................................................................................................................................
....................................................................................86............................................................................47 literal...............................................................12 local.........................................................................................................................................................................................garbage collection........................................127 greater than...............................................................................................39 $...................................................................................................16 interpreting.................................................................................................................................60 last.........................................................16 string..........76 int...................16 hexadecimal....................................................................................................................................................................................................................................................................................................................................................................................................................... Inheritance..................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................88 INVOCANT->isa(BASEPACKAGE).........................................................................25 lexical scope...........................................................................................................................14 keys..............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................15 hex............................................................................................................................................16 if...................................................................................................................................25 Greedy (Maximal) Quantifiers................................................... 99 INIT......................................................................................................................................................................................................103 hash....................................................................................................................................................................................................................................... binary..............112 Global Modifiers...................................................................................18 log_x_base_b...............25 length........13 less than..............................................................................................................................................................................................60 le............................................................................................................135 h2xs...........................................................123 gt..................................................................................................................63 list..........................................................................................................................................18 146 ........................................................79pp..........................................................................................................................................25 GUI and Perl::Tk................................................107 glob.........................16 octal...........................................................................................................................................88 join....................................................................................17 import.............................................................................................................................................................................................................................................................................76 INVOCANT -> METHOD............................................................63 lexical variable.......................................................................................68 log..........40 here document...........................................................................................................................................................25 greater than or equal to......................................................................................................................................................................................................................................................................................................................................................21 hexadecimal..........................................................................................................................88 isa........................................................................59 imaginary numbers...............................................................................................................................................................................................................................................................25 less than or equal to .....................................................................................42 label................................85 INVOCANT->can(METHODNAME)..................................................................................................................127 Global Modifiers (regular expressions)........................................................... ge.........64p..................................................................25 Getopt::Declare...................
..............................................................................................................................................................................................................................................................................................................................................................................................................................................................................114 backtick.....................................................................................................................................................................................................................................................................................83 Object Oriented Perl.............................................................................................................................26 our..................................................................................................98 multidimensional array...............................................................55 multiline string....................................................................................................................................................122 method calls...........................................................................................................................................................................................................................................................................................................16 numeric............................................................................132 perl modules............................................25 next..........................................................................16 rounding.......................................................................................61 natural logarithms...........................61 Parse::RecDescent.................69 named subroutines..................................................................................................................................................................98 oct.... literal......................................115 Math::Complex.............................25 m/patt/..........................................56 numbers..............................................97 object oriented perl........................................................................................................................................................................................61 package main..............17 Math::Trig.................................................................................................................................................logical operators.........................................................................................................................................................................................................60 NOT..........................................................................................................17 numify.................................................................................................................................................................................................................69 namespace........................................................................................................................................................................................................................50 named subroutine..................................20 Object Destruction.....................................................25 nstore.......................................................................................................................................................................................................................................................................................................................................................................................................................26 not equal to...............................................................61 package qualified variable ................................................................................................................................26 lt.................................................................................................................................................................................................................................................114 system.....................................................................110 Operating System Commands........................................................................................................................................................................99 Modules........................................................................................................................................16 open...................................................................................................................................................................................................................................99 package..21 octal..............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................114 Tk::ExecuteCommand...................................................62 Overriding Methods .................................................................................................................................................................................................................................................................................................................................................................................................18 ne....................................................................................................114 `............................................................................................................................78 PERL5LIB.................................................................................15 named referent.85 Methods..................................................................................................................................114 OR.................................90 Object Oriented Review.....................17 Metacharacters Within Character Classes...................................................................................................................................................................................................80 147 ..............................................................
.......................................................................................................................124 quantifier............................110 redo.....49 referent...............................................................115 a character class...............................................................................................................123 grouping...............................................................................................................................................................................................94 pop......................................................................................103 Polymorphism........................118 alternation................................................................................................................................................................................................................49............................................................................................................................................................................................................118 Capturing and Clustering Parenthesis............................................................38 148 ...............78 reverse............................................................118 Shortcut Character Classes....................................................................................................................................................................................................................................................................................................79p............................................................................................................................................................................................................................................................117 !~...................................................................13 require................................................................................................................................................................................................................121 clustering..............................................................................................................................................................................................perldoc...................................................................................................................................................123 Variable Interpolation............................................................................................... 84 Regexp::Common...................................................................................56 return..................120 Character Classes................................................................................................ 15 rand........................12 single..................................................................................................................................... $2.............................118 capturing...............................................103 POD........................................................12 qw......57........................................................................................................................131 Regular Expressions...... doube.............127 Greedy (Maximal) Quantifiers...............................................................................................................................................................................................................................18 read..........115 Metacharacters................................................................................................................................................................................................................................................115 $1.115 =~............................................................................................................................................................................................................................................................................................103 Plain Old Documentation....................................................................................................................118 Position Assertions / Position Anchors.......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................117 Global Modifiers......................................................................................................................................................................................................................................................124 push........................................12...................................................................................................................118 m/patt/......................................................................................................................................................................................................................................................................................................... 84 reference................................18 random numbers............................................................................ retrieve...........................................................................................................................................................................................................................................................34 quote..................................................................................................................................................................120 repetition....118 Defining a Pattern............... $3..............................................................................................................................................122 Thrifty (Minimal) Quantifiers..............................60 ref.................................................................................................................................................................................73 reuse....................................116 Wildcard Example....................................................34 Position Assertions / Position Anchors..................................................................................................................................................
...........................23p...................................................................................................................................................................................................................................................................................................................................................................................................................................................122 sin..............................................87 use lib..........................................................................18 Storable..................................................................................................................................17 scalar..................................................................................................................................28 Thrifty (Minimal) Quantifiers..................................................80 use Module........16 string............................................................................19 subroutine...............28 true........................................................................................................... argument passing......................................................................................................................................................................................13 SUPER.......................56 string...........................................................................17 srand...................................................................................................................................................................................................................................................................................12 numbers.......................................................................11............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................12 single quote.............................78 use base MODULENAME.......................................................................35 Shortcut Character Classes.............................................pm.......................... double quote......................................................................................................................................................................................................................................................99 SUPER::...............................................................rounding.......................................................................................................................................................................................................................................................................................................................................................................................................................................................................14 sprintf.....................................................................................................................................................................................................................................................................12 sort...................................................................................................12 $................. 33 Autovivify...35 use................................................................................................................66 named........................................95 system................................73 subroutines..................................................................................................................................................................................98 149 .............................................69 substr.......................................................................................................22 unless.....................................................................................................................................................................................69 anonymous................19 sqrt..................114 trigonometry..............................................................................11 shift.17 trinary operator..................................................................................................................37 spaceship operator.....................66 subroutine return value..............123 Tk::ExecuteCommand..............................................................................................................................................................................12 stringify..............................39 split...........69 closures............................................................................................................................................................................................................................................................................................................................................................70 subroutine closures................................................................................................................................................59 unshift.....................................................................................................................................................................................................................................................................................................................17 single quote................................................................... undefined...........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................25 splice............................................................................................................................................................................................................................114 ternary operator........................................................
..................................................26 $......................................................................................................................................................................................................................................................................................................................25 =~........................................................................................................................................................................................75 while......................................................................................................................................................................................................................................................................................................112 :.............................................................................................................................26 <.........................................................112 -z...........................................................................................................................................................................................................................................................................................................112 -p.....................................................................................................................................................................................................................................................................................................................................................................................................................11 150 ............................................................................................................................................................................................................................................................................................................25 <$fh>...................43 wantarray...........................................................................................................................................................................................115 >................28 !.....................................................................................................................................................................................................................................................................26 -d...........................................125 &&.......................................112 -T.......17 \b...........................................................................................................................................................................................................112 -r.................................................................................................................28 '...12 []...................................................................79 values................................................................................................................................................................................................................................................................................71 @ARGV..................................................................................................................................................................................................................................................................59 write..........................................................................................................................................................111 ==.........................................................................................................................................................................111 xor................................32 @_.............................................................................................................................................................................................................................................................................................................................................112 -w.................................................................112 -x.......................105 @INC.....................................................................................................................................................................................................................................................12 "...........25 <<.......121 @.........................................87 **.............................................................................................................................................................................................................................112 -l...............................................................................................................................................................................................................................................................................124 \G........................................................................................................................................................................................................................................................................................................................................................................................11 scalar...................25 <=>...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................25 ||.................................................................112 -S..................26 !=..................................25 >=...................................................................................................................................................................................................................................................................112 -f...............................25 !~.................................................................................................................................15 <=...................................................................................................................................115 ?...................................................................................................................................................................26 XOR.......................................................................................................................................................................................................................................................112 -e.......................................use MODULENAME..........................................................................................................................................................79 @ISA................................
............120 The End............................. 151 ......................$1............... $2.................... $3..................................................