Encode(3) character encodings in Perl


use Encode qw(decode encode);

Table of Contents

Encode::Alias - Alias definitions to encodings
Encode::Encoding - Encode Implementation Base Class
Encode::Supported - List of Supported Encodings
Encode::CN - Simplified Chinese Encodings
Encode::JP - Japanese Encodings
Encode::KR - Korean Encodings
Encode::TW - Traditional Chinese Encodings


The "Encode" module provides the interface between Perl strings and the rest of the system. Perl strings are sequences of characters.

The repertoire of characters that Perl can represent is a superset of those defined by the Unicode Consortium. On most platforms the ordinal values of a character as returned by "ord(S)" is the Unicode codepoint for that character. The exceptions are platforms where the legacy encoding is some variant of EBCDIC rather than a superset of ASCII; see perlebcdic.

During recent history, data is moved around a computer in 8-bit chunks, often called ``bytes'' but also known as ``octets'' in standards documents. Perl is widely used to manipulate data of many types: not only strings of characters representing human or computer languages, but also ``binary'' data, being the machine's representation of numbers, pixels in an image, or just about anything.











Basic methods



Encodes the scalar value STRING from Perl's internal form into ENCODING and returns a sequence of octets. ENCODING can be either a canonical name or an alias. For encoding names and aliases, see ``Defining Aliases''. For CHECK, see ``Handling Malformed Data''.



CAVEAT: When you run "$octets = encode("utf8", $string)", then $octets might not be equal to $string. Though both contain the same data, the UTF8 flag for $octets is always off. When you encode anything, the UTF8 flag on the result is always off, even when it contains a completely valid utf8 string. See ``The UTF8 flag'' below.

If the $string is "undef", then "undef" is returned.



This function returns the string that results from decoding the scalar value OCTETS, assumed to be a sequence of octets in ENCODING, into Perl's internal form. As with encode(), ENCODING can be either a canonical name or an alias. For encoding names and aliases, see ``Defining Aliases''; for CHECK, see ``Handling Malformed Data''.



CAVEAT: When you run "$string = decode("utf8", $octets)", then $string might not be equal to $octets. Though both contain the same data, the UTF8 flag for $string is on. See ``The UTF8 flag'' below.



  [$obj =] find_encoding(ENCODING)

Returns the encoding object corresponding to ENCODING. Returns "undef" if no matching ENCODING is find. The returned object is what does the actual encoding or decoding.

  $utf8 = decode($name, $bytes);

is in fact

    $utf8 = do {
        $obj = find_encoding($name);

with more error checking.

You can therefore save time by reusing this object as follows;

    while(<>) {
        ... # now do something with $utf8;

Besides ``decode'' and ``encode'', other methods are available as well. For instance, "name()" returns the canonical name of the encoding object.


See Encode::Encoding for details.





and to convert it back:



"from_to()" returns the length of the converted string in octets on success, and "undef" on error.





See ``The UTF8 flag'' below.

Also note that:


is equivalent to:


Yes, it does not respect the $check during decoding. It is deliberately done that way. If you need minute control, use "decode" followed by "encode" as follows:



  $octets = encode_utf8($string);

Equivalent to "$octets = encode("utf8", $string)". The characters in $string are encoded in Perl's internal format, and the result is returned as a sequence of octets. Because all possible characters in Perl have a (loose, not strict) UTF-8 representation, this function cannot fail.



Equivalent to "$string = decode("utf8", $octets [, CHECK])". The sequence of octets represented by $octets is decoded from UTF-8 into a sequence of logical characters. Because not all sequences of octets are valid UTF-8, it is quite possible for this function to fail. For CHECK, see ``Handling Malformed Data''.

Listing available encodings

  use Encode;
  @list = Encode->encodings();



Or you can give the name of a specific module:


When ""::"`` is not in the name, ''"Encode::"" is assumed.



Defining Aliases

To add a new alias to a given encoding, use:

  use Encode;
  use Encode::Alias;
  define_alias(NEWNAME => ENCODING);


Before you do that, first make sure the alias is nonexistent using "resolve_alias()", which returns the canonical name thereof. For example:


"resolve_alias()" does not need "use Encode::Alias"; it can be imported via "use Encode qw(resolve_alias)".

See Encode::Alias for details.

Finding IANA Character Set Registry names

The canonical name of a given encoding does not necessarily agree with IANA Character Set Registry, commonly seen as "Content-Type: text/plain; charset=WHATEVER". For most cases, the canonical name works, but sometimes it does not, most notably with ``utf-8-strict''.

As of "Encode" version 2.21, a new method "mime_name()" is therefore added.

  use Encode;
  warn $enc->mime_name; # UTF-8

See also: Encode::Encoding

Encoding via PerlIO

If your perl supports "PerlIO" (which is the default), you can use a "PerlIO" layer to decode and encode directly via a filehandle. The following two examples are fully identical in functionality:

  ### Version 1 via PerlIO
    while (<INPUT>) {   # auto decodes $_
        print OUTPUT;   # auto encodes $_
  ### Version 2 via from_to()
    while (<INPUT>) {
        print OUTPUT;   # emit raw (but properly encoded) data


Unfortunately, it may be that encodings are not "PerlIO"-savvy. You can check to see whether your encoding is supported by "PerlIO" by invoking the "perlio_ok" method on it:

  Encode::perlio_ok("hz");             # false
  use Encode qw(perlio_ok);            # imported upon request

Fortunately, all encodings that come with "Encode" core are "PerlIO"-savvy except for "hz" and "ISO-2022-kr". For the gory details, see Encode::Encoding and Encode::PerlIO.

Handling Malformed Data

The optional CHECK argument tells "Encode" what to do when encountering malformed data. Without CHECK, "Encode::FB_DEFAULT" (== 0) is assumed.

As of version 2.12, "Encode" supports coderef values for "CHECK"; see below.


List of CHECK values






If CHECK is 1, methods immediately die with an error message. Therefore, when CHECK is 1, you should trap exceptions with "eval{}", unless you really want to let it "die".


  I<CHECK> = Encode::FB_QUIET

If CHECK is set to "Encode::FB_QUIET", encoding and decoding immediately return the portion of the data that has been processed so far when an error occurs. The data argument is overwritten with everything after that point; that is, the unprocessed portion of the data. This is handy when you have to call "decode" repeatedly in the case where your source data may contain partial multi-byte character sequences, (that is, you are reading with a fixed-width buffer). Here's some sample code to do exactly that:

        # $buffer now contains the unprocessed partial character


  I<CHECK> = Encode::FB_WARN

This is the same as "FB_QUIET" above, except that instead of being silent on errors, it issues a warning. This is handy for when you are debugging.


perlqq mode (CHECK = Encode::FB_PERLQQ)
HTML charref mode (CHECK = Encode::FB_HTMLCREF)
XML charref mode (CHECK = Encode::FB_XMLCREF)

For encodings that are implemented by the "Encode::XS" module, "CHECK" "==" "Encode::FB_PERLQQ" puts "encode" and "decode" into "perlqq" fallback mode.

When you decode, "\xHH" is inserted for a malformed character, where HH is the hex representation of the octet that could not be decoded to utf8. When you encode, "\x{HHHH}" will be inserted, where HHHH is the Unicode code point (in any number of hex digits) of the character that cannot be found in the character repertoire of the encoding.

The HTML/XML character reference modes are about the same. In place of "\x{HHHH}", HTML uses "&#NNN;" where NNN is a decimal number, and XML uses "&#xHHHH;" where HHHH is the hexadecimal number.

In "Encode" 2.10 or later, "LEAVE_SRC" is also implied.

The bitmask

These modes are all actually set via a bitmask. Here is how the "FB_XXX" constants are laid out. You can import the "FB_XXX" constants via "use Encode qw(:fallbacks)", and you can import the generic bitmask constants via "use Encode qw(:fallback_all)".

 DIE_ON_ERR    0x0001             X
 WARN_ON_ERR   0x0002                               X
 RETURN_ON_ERR 0x0004                      X        X
 LEAVE_SRC     0x0008                                        X
 PERLQQ        0x0100                                        X
 HTMLCREF      0x0200
 XMLCREF       0x0400



If the "Encode::LEAVE_SRC" bit is not set but CHECK is set, then the source string to encode() or decode() will be overwritten in place. If you're not interested in this, then bitwise-OR it with the bitmask.

coderef for CHECK

As of "Encode" 2.12, "CHECK" can also be a code reference which takes the ordinal value of the unmapped character as an argument and returns octets that represent the fallback character. For instance:


Acts like "FB_PERLQQ" but U+XXXX is used instead of "\x{XXXX}".

Even the fallback for "decode" must return octets, which are then decoded with the character encoding that "decode" accepts. So for example if you wish to decode octets as UTF-8, and use ISO-8859-15 as a fallback for bytes that are not valid UTF-8, you could write

        my $tmp = chr shift;
        return $tmp;

Defining Encodings

To define a new encoding, use:

    use Encode qw(define_encoding);


See Encode::Encoding for details.

The UTF8 flag

Before the introduction of Unicode support in Perl, The "eq" operator just compared the strings represented by two scalars. Beginning with Perl 5.8, "eq" compares two strings with simultaneous consideration of the UTF8 flag. To explain why we made it so, I quote from page 402 of Programming Perl, 3rd ed.
Goal #1:
Goal #2:
Goal #3:
Goal #4:


Here is how "Encode" handles the UTF8 flag.

  • When you decode, the resulting UTF8 flag is on--unless you can unambiguously represent data. Here is what we mean by ``unambiguously''. After "$utf8 = decode("foo", $octet)",

      In ASCII only (or EBCDIC only)            OFF
      In ISO-8859-1                              ON
      In any other Encoding                      ON

    As you see, there is one exception: in ASCII. That way you can assume Goal #1. And with "Encode", Goal #2 is assumed but you still have to be careful in the cases mentioned in the CAVEAT paragraphs above.


Messing with Perl's Internals



  is_utf8(STRING [, CHECK])


As of Perl 5.8.1, utf8 also has the "utf8::is_utf8" function.







[INTERNAL] Turns the STRING's internal UTF8 flag off. Do not use frivolously. Returns the previous state of the UTF8 flag, or "undef" if STRING is not a string. Do not treat the return value as indicative of success or failure, because that isn't what it means: it is only the previous setting.


UTF-8 vs. utf8 vs. UTF8




  From: Larry Wall <[email protected]>
  Date: December 04, 2004 11:51:58 JST
  To: [email protected]
  Subject: Re: Make Encode.pm support the real UTF-8
  Message-Id: <[email protected]>
  : corresponding behaviour.
  make it easy to switch back to lax.

Got that? As of Perl 5.8.7, ``UTF-8'' means UTF-8 in its current sense, which is conservative and strict and security-conscious, whereas ``utf8'' means UTF-8 in its former sense, which was liberal and loose and lax. "Encode" version 2.10 or later thus groks this subtle but critically important distinction between "UTF-8" and "utf8".


In the "Encode" module, "UTF-8" is actually a canonical name for "utf-8-strict". That hyphen between the "UTF" and the "8" is critical; without it, "Encode" goes ``liberal'' and (perhaps overly-)permissive:


Perl's internal UTF8 flag is called ``UTF8'', without a hyphen. It indicates whether a string is internally encoded as ``utf8'', also without a hyphen.


This project was originated by the late Nick Ing-Simmons and later maintained by Dan Kogai <[email protected]>. See AUTHORS for a full list of people involved. For any questions, send mail to <[email protected]> so that we can all share.



Copyright 2002-2014 Dan Kogai <[email protected]>.
