You are on page 1of 24


1. $ LOGNAME 2. $PWD 3. $DATE 4. $clear 5. $cal 6. $cal 2000 7. $cal 8 2006 8. $exit or logout 9. $ who 10. $finger more information 11. Who am I 12. Which or where Syn: $which pwd 13. Cat data to the exiting files Create: cat >filename ---------------------cntl+d

: It displays the current user information : present working directory : It displays the system date & time : To clear the screen : it current month and year : Displays the 2000 year calendar : displays the 8th month of 2006 : exit from current user account : displays the all user in who are currently working on server : displays the all user who are currently working on server with

: displays current user information : displays the location of the given command

: is use to create new files or to open exiting files or to append

Redirect: cat file1 file2 file3 >file4-------- redirect output Append: cat >>filename-------files ---------------------cntl+d single file $cat file1 file2 file3 >>EMP------ multi

Open file: cat <filename----- open single file multi files Cat >.filename---------for hidden files 14. Touch : It is used to create an empty file i.e. 0 byte file $cat file1, file2, file3---------- to open

SYN: $ touch filename $ touch file1 file2 file3--------15. rm EX rm filename---------------- deleting single file rm -i filename-------------- deleting files with confirmation rm file1 file2---------------- deleting multiple files rmdir dirname-------------- deleting the directory but the directory must be empty rm -r dirname------------- deleting directory recursively (i.e. with tree str) rm ri dirname------------- remove directory with confirmation rm * --------------------it delets all files create multiple files

: deleting files or directories

rm -I *-------------------- delets all files with confirmation rm t* --------------------- it delets whose file name starts with t 16. mkdir : creating directories

Syn: $mkdir dirname Sys: $Mkdir .dirname------------ hidden directory 17. Cd : change directory Sys: $cd abc $pwd------/home/madhav/abc using above cmd we can come out from abc now we at //home/madhav cd..--------------------------- to come out from current directory cd../..------------------------ parent directory cd/--------------------------- it changes to root directory cd ~------------------------- it changes to home directory

18. cp :copy source file to target file Ex Cp emp1 emp2---------------------- emp1 tp 2 coping Cp I m1 m2------------------------- overwrite confirmation? Y Cp R source directory to target directory-------cp R abc xyz 19. mv : it is used to rename or move file

Ex: mv exiting filename new filename Mv emp .emp---------------------- to hide Mv .emp emp-------------------- to unhide|more : display, list of all files & directories in a current directory : display, list of all files & directories page by page

22. ls a : display, list of all files & directories including hidden files and dirctories also in current directory 23. ls r 24. Ls R 25. Ls t current directory 26. Ls F directory 27. Ls-x current directory 28. Ls-L i.e. 9 fields : display list of all files & directories revers order in a current directory : display list of all files & directories recursively in a current directory : display list of all files & directories according to date of creation in a

: display all list of files & directories, link files, .exe files in a current

: display all list of files & directories according to width wise in a

: display all list of files & directories in a current directory in a long list

1) File types [1) -- For regular file ii) dfor dir file III) Lfor link file IV) bfor block of filesV) c for char files] [here IV, V is device files] 2) File permissions 3) no. of links 4) owner name 5) group name 6) file size in bytes 7) Date 8) time 9) filename

30. cmp

: it compares two files char by char

Sys: cmp file1 file2 Ex: a1: Hello Good Morning a2: Hello Good Evening If two lines are same then return nothing If two files are are different then it displays line number with character position 31. comm. : It display common lines b/w 2 files

Syn: Comm File1 file2 32. diff 33. pg : it display different lines b/w 2 files : it display the file contents page by page Syn: $Pg filename 34. more : it also display the file contents page by page Syn: $more filename 34. head :it display the 1st n lines from the file Sys: $ head n filename 35. tail : it display the last n lines from file Syn: tail n filename Tail +n filename---- it indicates nth line to end of the line Ex: tail +30 file (in this file total no of records is 100) it displays the records from 30th to 100 36. wc : it counts the no of lines, words, chars in a given file. Syn: $wc filename i) wc l filename------------------ it gives the no of lines in a given file ii) wc w filename--------------- it gives the no of words in a given file III) wc c filename--------------iv) wc -lw filename-------------it gives no. of char in file it gives the no of lines and character in a given file

37. WILD CARD CHARCTERS or META CHARCTERS i) *-------- it matches 0 or more chars it matches any single chars it matches any single chars in the given list it matches any single char in the given range

ii) ? ------iii) [ ] ---

iv) ------

1) ls t*--------------- it list the files starts with t

2) ls *s ------------- it list the files that ends with S

3) ls b*k-------------- it list the files starts with b and ends with k

4) ls a?-------------- it list the 2 characters filename 1st later fallowed by a and second letter is any one character

5) ls[bknt]----------- it list the files starts with b or k or n or t

6) ls [abcdefgh] or ls[a-h]*-- list the files, first char b/w a to h

7) ls [b-k][p-t][d-n]*--------- it list the files the 1st character b to k 2nd char p to t 3rd char d to n after that any no of characters 38. grep : [globally search a regular expression and print it]

Is used for to search a string or regular expression in a given file(s) I) Eg: $ grep madhav sample O/p: 2nd line



7th line ii) Eg: $grep madhav a1, a2, a3: a1:-----a2:-----a3:-----iii) $ grep techno *------ it searches for techno in current dir files (all files) iv) $grep techno soft sample----- it searches for more than one word We kept it in

v) $grep techno soft sample grep cmd options $ grep i techno sample----------------------- ignore case sensitive $ grep c techno sample----------------------- count no of lines $grep n techno sample----------------------- print along with the line numbers $grep l techno *------------------------------ list only file names $grep v techno soft sample--------------- not matches print the lines $grep ci techno sample---------------------- Ignore case sensitive found no of lines $grep techno * sample--------------------- pattern Regular expression: any string contains wildcard charctor knows as regular expression or pattern These patterns are of 3 types: Charctor pattern: the default pattern is char pattern only i) $grep techno * sample ii) $grep b [aeiou] ll sample iii) $grep b..d sample--- i.e. or matches any single charctor Word pattern :/< />

/< ------- start of the word

/>------ end of the word Grep /<techno/> sample ------------ o/p: techno Grep /<techno sample---------------- o/p: techno soft ----------------- o/p: techno 123 Grep techno/> sample ---- o/p: hellotechno, abctechno

Grep /< [0-9][0-9][0-9][0-9]/> sample-------------- it display 4 digits (i.e.1234, 4567)

Line pattern: ^----------starts of the file $----------ends of the file Ex: grep ^d sample--------------- it display the line starts withd Grep ^the sample----------------- it list the lines start with the Grep ^/<the/> simple ---------- sample the line exactly start with the Grep t$ simple------------------- list the line ends witht or last char ist Grep [0-9] $ sample-----------display the line ends with 0 to 9 digit

Grep ^ [bkt] sample------------ list the line starting with b or k ort Grep ^ [^bkt] sample---------- list the line which is not start with b or k ort Grep ^UNIX$ sample --------- display the line having only word Unix Grep ^. $---------------------- list the line which contains 4 characters (.)---------------------------------- represent single charctor Grep ^.------------------------ Sample it list all lines Grep /. Sample: -------------- it lists the line start with (.) We use \ to search *, $, ^ as a charctor------Grep ^$ sample-------------i.e.\*,|^,\$

it list empty lines

Grep c ^$ sample---------- counts no of empty lines in a file Grep v ^$ sample---------- print not matches (i.e. not empty) lines Grep v ^$sample >temp

Mv temp sample------------------- here both are delete empty files 39. fgrep expression : it is used for search multiple strings but it doesnt allow to search regular

$grep hello >techno >UNIXsample---------- it searches for hello or techno str UNIX 40. egrep : it is combination of grep and fgrep

$egrep hello >hello >UNIXsample 41. Sed $egrep ^$ sample

: to replace a string

$ sed s/existing string/new string/g filename-- sed is used to find and replace and grep is for find print i) $sed s/Unix/Linux/gi madhav: ------------ii) $sed s/^Unix/Linux/gi---------------------replaced by Linux i for case sensitive whatever lines starting with UNIX are

iii) $sed s/^$/I like Unix/g I sample-------- empty string are filled with I like UNIX iv) $Sed s/Unix//g I sample----------------- it search UNIX if found replace with nothing (empty) 42. tr : to translate a charctor i) tr a p <s-------------------it read data from sample and a is replaced by p

ii) tr aeiou AEIOU<sample---- replace char by char iii) tr , lt <emp---------------- whenever , is there replace with tab space iv) tr [a-z] [A-Z] <Siva-------43) Cut converts hole file into uppercase

: it is used for to retrieve required fields and characters from a given file Ex: madhav is good boy-- 18 chars Cut f 2-5 madhav--- o/p: adha Cut c 1-10 madhav Cut c 5-10, 15-20 madhav------- for every line 5-10, 15-20 characters

44) Paste Cat >states filename AP Tamilnadu Karnataka Kerala Maharashtra : is used for to join two or more files horizontally by using delimiter cat >cities paste d :states cities>tr

Hyderabad madras Bangalore Trivandrum Bombay

AP: Hyderabad Tamilnadu: madras Karnataka: Bangalore

45) Sort : it is used for to sort the file content. By default it sorts file contents based on ASCII values- default is ascending Sort sample i) sort r sample------ displays descending order ii) sort u sample----- it displays unique lines in the given file iii) sort n file---- N numeric comparisons iv) sort nur file v) sort sample >temp $mv temp sample Sorting the data field by field +pos-- starting field -Pos-- ending field (optional) i) Sort f +pas1 pas2 filename ii) Sort f +1 -3 filename----- starting from end before 3 iii) Sort fn +2 -3 file ------ it gives only numbers 46) Uniq sort order Ex:file1 Aaaaaa Aaaaaa Aaaaaa : it displays unique lines in the given file but the file contents should be in

i) $ uniq file

ii) $uniq u filename-- it eliminates duplicates

Aaaaaa cccccccc

ccccc ddddd

Ccccccc Ddddd Hhhhh Hhhhh Ppppp Ttttttt iii) $ Uniq d filename----displays only duplicated lines how many times lines duplicated IV) uniq c filename----- it counts dddddd hhhhhh pppppp ttttttttt Ppppp ttttttt

Aaaaaa-----2 Cccccccc----1 V) $ uniq u file >temp $ mv temp filename Delete duplicated lines from file Ddddd-----1 Hhhhhh---2 Ppppp-----1 Ttttttt-----1 47)piping(|) : it is used for to combine 2 or more cmds |take left side o/p to right side cmd as i/p i) $who |wc l--------- count total no of lines (files) in current directory ii) $ ls|wc l------------ displays total no of subdirectories in the current directory iii) ls l |grep ^d---- displays total no of subdirectories who stats with line nod iV) $head -30 sample|tail +20 sample------ display the the lines from 20 to 30 from given file v) $ grep UNIX stud | cut f 2, 3|sort filename ----- display UNIX students names & ph no in ascending order 48) $tee : it is used to for to write data to the file as well as to the screen $grep UNIX stud | cut f 2, 3 |sort |tee file1 49) Shell scripting:

It is group of UNIX commands and shell keywords The main concept of shell scripting is to handle text files I) Boune shell---- steave Bourne ----- $--------sh--- (sh as interpreter) ii) Bash shell (borne again shell) ---same as above-- advanced version of Bourne is BASH (Linux default shell) iii) Korn shell------David korn----$----------ksh (interpreter) ---- used as AIX default shell Mostly used shell is korn shell it supports re usability, all shell designed on bourn shell 50) $ksh 51) $echo $0 52) $alias : shift to korn shell : it displays current child shell name : it lists all alias names

53) Unalias alias names: to delete alias names 54) $ history 55) Echo : it displays the previously executed commands : it display the string on screen (monitor)

File permissions:(xxx/xxx/xxx) User/owner---permissions Group permissions Other permissions (first part) (second part) (third part)

+--- (add permissions to u/g/o but it does not delete exiting permission) --- (deny permissions) =---- (assign permissions (add permissions to u/g/o but it delete exiting permission)) rw-/rw-/r-- --------- Default permissions for regular files rwx/rwx/r-x--------- default permission for directories 56) chmod : it is used for to change file permissions

Syn: $chmod who/ [+/-/=]/ i) ls l filename------- rw- rwr

ii) chmod g+x filename----- rw- rwx r

iii) chmod u+x, g-w filename------ rwx r-x r iV) chmod g=w filename----- rwx w- r Octal code Read------4 Write-----2 Execute1 $chmod 756 filename------- rwx r-x rw$chmod 642 filename---- rw- r-- -w57) chown : to change owner name of the file

#chown owner name filename 58) chgrep : to change group name of the file

# chgrp group name filename 58) $write : it is user for to with the users but the user should be logged into the server ii) $mesg n-- deny the msg iii) mesg y- to allow msges

$write techno2 Hello Cmtl+d 59) awk/nawk file 60) cat

: scan for patterns in a file and process the results : concatenate (list) or file

61) chsh (paawd e/-s) userlogin_shell: change the user login shell 62) df : report the summary of disk blocks and nodes free and in use i) df k--- it displays the disk space in bytes ii) df h--- it displays disk space in kilo bytes iii) df g--- it displays the disk space in giga bytes 63)du :it displays the directory wise disk usage in form of blocks each block size is 512 bytes 64)g zip :to create a zip file

Ex $gzip filename---- o/p: filename.gz

65) gunzip : to unzip the files

Ex: gunzip filename.gz 66. compress 67) Uncompress : it also used for to zip the file--- it used to save with .z format : same as above

Gzip saves more memory than compress 68) zcat : it used to displays zip file contents in readable format $zcat sample.gz

Or $zcat sample.z 69) To kill foreground job cntl+c or cntl+z $ sleep 500 Cntl+c $ sleep 100& 70) ps or $ ps f active process) : it displays current user account running process list (show status of

71) $ps a: it displays all user accounts running process list 72) Kill Ex: kill PID 73) telnet : to connect to remote server : it kill background process

74) ftp: file transfer protocol ----- transfer files from one server to another $ ftp ipaddress Login: ------Password: -----Ftp>ls (server) Ftp>|ls(client) Ftp>get filename (to download a file)

Ftp>mget file1 file2----- (to download multi files) Ftp>put filename (to upload a file) Ftp>mput file1 file2----- (to upload multi files) 75)Ftp: to transfer files from one server user account to another server user account $su root -- to switch to admin 76) Wall : it is used for to sent broadcast message to all users who are currently working on server $wall Happy new-year Cntl+d 77)mail mail :it is used for to send the mail, if user is not logged in then also we can send

i) $ mail techno1 Cntl+d every user contains mailbox at a time we can send msg to multiple users 2) $mail techno1 techno2 techno 3 Sub: from techno Cntl+d iii) $ mail techno<stud stud send content as a mail to techno3 mail is the cmd to read mails in the mailbox $mail 1>first mail 2>second mail reading &2 it quickly opens second mail &q-- quit from mail box &w to save mail contents to a file &p print mail contents

&r-- replays &d- delete mails 78)$mail f:to read mails send to secondary mailbox 79) emacs 80) echo 81) file 82) expr 83) find :full screen editor : echo the text string to on monitor : classify the file type : evaluates the arguments, used to do arithmetic,etc in the shell : find files, matching a type or pattern : display or set the name of the current machine : link the source to target :show the status of the print jobs :print to defind printer : remove a print job from the print quee :display manual of given cmd :octal dump a binary file,in octal,ASCII,hex,decimal or char :to set or change password : filter the file and print it on the terminal : remotely copy files from this machine to another machine

84) Hostname 85)ln 86)lpq ,lpstat 87)lpr,lp 88) lprm, cancel 89) man 90)od 91)passwd 92) pr 93) rcp hostname

94) rlogine hostname: login remotely to another machine 95) rsh hostname 96) script file executed 97) source file 98) string file 99) Sty 100) uudecode file : remote shell to run on another machine : saves everything that appears on the screen to file until exit is

: read cmds from the file and execute them in the current shell : used to search binary files for ASCII strings : set or display terminal control options : decode a uuencoded file, recreating the original file

101) uuencode new name : encode the binary file to 7-bit ASCII,usefull when sending via email, to be Decode as new name at destination

102) vi 103) jobs 104) kill %1 105) top 106) osview 107) setenv : visual ,full screen editor : display background and suspended processes : remove suspended process #1 : display the current, most computer-intensive commands : display the operating system statistics : list environmental variables


What is meant by passwd file? This file maintains each and every user information with 7 fields. The 7 fields are Username: passwd: uid: gid: fullname: home: shell. What is Shell? Shell is a command line interpreter. Shell acts as an interface between user and the kernel. What is Kernel? Kernel is core part of UNIX o/s. It is a group of hundreds of system calls. What are different flavors of Unix o/s? Any operating system designed based on unix kernel called as flavour of unix. The following are some flavours of unix Linux ---- Red Hat Sun solaris --- Sun Microsystem IBM-AIX ----- IBM Hp-ux ----- HP Sco-unix ----- santa crus operations IRIX------ Silicon Graphics.

What are the different security features in Unix?

1. Password protection.

2. File permissions. 3. Encryption.

Whats the command to find out todays date? date Whats the command to find out users on the system? who How do you find out the current directory youre in? pwd What is the command to see the location of command? Where is <command name> How do you find out your own username? Whoami (or) log name

How to close the current user account? Exit How to create empty file? Touch <filename> How do you remove a file? Rm <filename> How to join multifile files vertically? Cat file1 file2 file3

The file for which we do not have write permission can be deleted using the command? rm -f <filename> How do you remove a directory and its subdirectories? rm rf <directoryname> How to rename a file? Mv <filename> How to copy multiple files and directories into some other directory? cp -r source_directory destination_directory How to see hodden files?

Ls a How to see files and subdirectories files recursively? Ls R How to see files in long list format page wise? Ls l | more How to identify whether a file is normal file or directory? $ls -l filename/directoryname if the first digit is - then it is file, if it is d then it is directory file

What is the difference between "ls -r" and "ls -R"? ls -r lists the files in reverse alphabetical order... whereas ls -R lists the files and directories recursively The difference between a soft link and a hard link? A symbolic (soft) linked file and the targeted file can be located on the same or different file system while for a hard link they must be located on the same file system.

what are the different commands used to create files? 1.touch - to create empty files (e.g) - touch <filename> <filename> 3. cat>filename List some wild card characters? ?*[] .Iit matches any single character It matches zero or more characters It matches any single character in given list It matches any single character except enter key character

what is the output of the follwing command : ls [a-mno-r]* list all the files in the current directory starting alphabet is between a to m or n or between o to r How do you count words, lines and characters in a file? Wc <filename> which command is used to identify the type of the file? file

"grep" means Globally search a regular expression and print it

How do you search for a string inside a given file? grep string filename How do you search for a string inside a current directory? grep string * How do you search for a string in a directory with the subdirectories recursed? grep -r string * Difference between grep, egrep and fgrep grep : does not accept more then one expression egrep : accepts more than one pattern for search. Also accepts patterns from a file. fgrep : accepts multiple patterns both from command line and file but does not accept regular expressions only strings. It is faster than the other two and should be used when using fixed strings. What are line patterns? ^$start of the line End of the line

How to search empty lines in a given file? Grep ^$ <filename> How to count no of blank lines in a file? Grep c ^$ <filename> How to remove Empty lines form a given file? Grep v ^$ filename > temfilename Mv tempfilename filename What is pattern to search 4 digit word in a file? Grep \<[0-9] [0-9] [0-9] [0-9]\> filename What is pattern to search the line having only three characters? Grep ^$ filename What is pattern to display lines ending with $ character in a given file? Grep \$$ filename

How to display 2 and 4 th fileds from a given file if the delimetr is :? Cut d: f 2,4 filename How to display unique lines from a given file? Sort u filename How to eliminate completely duplicate lines from a given file? Uniq u filename How to remove all duplicate lines from a file? Uniq u filename > tempfilename Mv tempfilename filename How to delete hello word from a given file? Sed s/hello// filename awk Command awk is a powful Unix command. It allows the user to manipulate files that are structured as columns of data and Once you understand the basics of awk you will find that it is surprisingly useful. You can use it to automate things in ways you have never thought about. It can be used for data processing and for automating the application of Unix commands. It also has many spreadsheet-type functionalities. There are two ways to run awk. A simple awk command can be run from the command line. More complex tasks should be written as awk programs ("scripts") to a file. Examples of each are provided below. Example: % awk 'pattern {action}' input-file > output-file meaning: take each line of the input file; if the line contains the pattern apply the action to the line and write the resulting line to the output-file. If the pattern is omitted, the action is applied to all lines: How to compare two files are same or not? Cmp How to display the first 10 lines from a file? Head -10 filename Write a one line command to convert all the capital letters of a file "test" into lower case? cat filename | tr "[A-Z]" "[a-z]"

The pipeline to list the five largest files in the current directory is ls -l | tr -s ' ' | sort -t ' ' -fnr +4 -5 | head 5 The pipeline to find out the number of times the character ? occurs in the file is tr -dc '?' < file | wc -c ( Delete all the characters except ? and then make a word count.)

How to count total no. of users working in the system? Who | wc l How to display the lines from 5 to 10 from a given file? Head -10 filename | tail +5 what will be output of following command? echo Tecnosoft | wc c 9 What is the default umask? 022 What is the default permission for File & Directory ? The Default privileges for file : 644 The default privileges for directory : 755 What UNIX command will control the default file permissions when files are created? Umask Explain the read, write, and execute permissions on a UNIX directory. Read allows you to see and list the directory contents. Write allows you to create, edit and delete files and subdirectories in the directory. Execute gives you the previous read/write permissions plus allows you to change into the directory and execute programs or shells from the directory. What is chmod, chown and chgrp? Chmod : It is used for to change permissions on files Chown : It is used for to change ownership of a file Chgrp : It is used for to change group of the file

If the owner doesnt have write permission on a file, but his/her group has, can he/she edit it? No. He/she can't,because the owner's permission overrides the group's. To see list of files and directories ,what permission required? Read permission What are PIDs? They are process IDs given to processes. A PID can vary from 0 to 65535. How do you list currently running process? ps How do you stop a background process? kill pid How do you find out about all running processes? ps -ag How do you stop all the processes, except the shell window? kill 0 How do you fire a process in the background? ./process-name & What does the command "kill -9 $! " do? kills the last background process if there is a process u want to run even after exiting the shell what is the command used? Nohup

which command will get executed even after you log out? Nohup

which signal cannot be trapped? kill 9 How to redirect standard error to a file? Answer 2> filename

What does the top command display? top command displays the current ammount of memory occupied by the currently executing processes and the details. In addition to memory usage top command displays cpu usage and process details What is the command to send message to all users who are logged in? Wall What is the command to send mail to other user? Mail username How to open secondary mail box? Mail -f What do you do if you don't want to be interrupted by other users' messages? Ans. mesg n Shell Scripting Interview questions Difference between the output of echo ** and echo * * echo ** lists all the filenames in the current directory.. echo * * lists all the filenames in the current directory twice. The other way of running shell script apart from using sh command and chmod? ans:- using ! we can run a shell script 19. How do you refer to the arguments passed to a shell script? - $1, $2 and so on. $0 is your script name. 20. Whats the conditional statement in shell scripting? - if {condition} then fi 21. How do you do number comparison in shell scripts? - -eq, -ne, -lt, -le, -gt, -ge 22. How do you test for file properties in shell scripts? - -s filename tells you if the file is not empty, -f filename tells you whether the argument is a file, and not a directory, -d filename tests if the argument is a directory, and not a file, -w filename tests for writeability, -r filename tests for readability, -x filename tests for executability 23. How do you do Boolean logic operators in shell scripting? - ! tests for logical not, -a tests for logical and, and -o tests for logical or. 24. How do you find out the number of arguments passed to the shell script? - $# 25. Whats a way to do multilevel if-elses in shell scripting? - if {condition} then {statement} elif {condition} {statement} fi 26. How do you write a for loop in shell? - for {variable name} in {list} do {statement} done

27. How do you write a while loop in shell? - while {condition} do {statement} done 28. How does a case statement look in shell scripts? - case {variable} in {possiblevalue-1}) {statement};; {possible-value-2}) {statement};; esac 29. How do you read keyboard input in shell scripts? - read {variable-name} 30. How do you define a function in a shell script? - function-name() { #some code here return } 31. How does getopts command work? - The parameters to your script can be passed as -n 15 -x 20. Inside the script, you can iterate through the getopts array as while getopts n:x option, and the variable $option contains the value of the entered option. Batch file: Batch files allow MS-DOS and Microsoft Windows users to create a lists of commands to run in sequence once the batch file has been executed. For example, a batch file could be used to run frequently run commands, deleting a series of files, moving files, etc. A simple batch file does not require any special programming skills and can be done by users who have a basic understanding of MS-DOS commands.