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Encode - character encodings


use Encode;

Table of Contents

Encode consists of a collection of modules whose details are too big to fit in one document. This POD itself explains the top-level APIs and general topics at a glance. For other topics and more details, see the PODs below:

Name			        Description
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 interfaces between Perl's strings and the rest of the system. Perl strings are sequences of characters.

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

Traditionally, computer data has been moved around in 8-bit chunks often called "bytes". These chunks are also known as "octets" in networking standards. 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.

When Perl is processing "binary data", the programmer wants Perl to process "sequences of bytes". This is not a problem for Perl - as a byte has 256 possible values, it easily fits in Perl's much larger "logical character".



$octets = encode(ENCODING, $string [, CHECK])

Encodes a 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".

For example, to convert a string from Perl's internal format to iso-8859-1 (also known as Latin1),

$octets = encode("iso-8859-1", $string);

CAVEAT: When you run $octets = encode("utf8", $string), then $octets may not be equal to $string. Though they both contain the same data, the utf8 flag for $octets is always off. When you encode anything, utf8 flag of the result is always off, even when it contains completely valid utf8 string. See "The UTF-8 flag" below.

encode($valid_encoding, undef) is harmless but warns you for Use of uninitialized value in subroutine entry. encode($valid_encoding, '') is harmless and warnless.

$string = decode(ENCODING, $octets [, CHECK])

Decodes a sequence of octets assumed to be in ENCODING into Perl's internal form and returns the resulting string. As in 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".

For example, to convert ISO-8859-1 data to a string in Perl's internal format:

$string = decode("iso-8859-1", $octets);

CAVEAT: When you run $string = decode("utf8", $octets), then $string may not be equal to $octets. Though they both contain the same data, the utf8 flag for $string is on unless $octets entirely consists of ASCII data (or EBCDIC on EBCDIC machines). See "The UTF-8 flag" below.

decode($valid_encoding, undef) is harmless but warns you for Use of uninitialized value in subroutine entry. decode($valid_encoding, '') is harmless and warnless.

[$length =] from_to($octets, FROM_ENC, TO_ENC [, CHECK])

Converts in-place data between two encodings. The data in $octets must be encoded as octets and not as characters in Perl's internal format. For example, to convert ISO-8859-1 data to Microsoft's CP1250 encoding:

from_to($octets, "iso-8859-1", "cp1250");

and to convert it back:

from_to($octets, "cp1250", "iso-8859-1");

Note that because the conversion happens in place, the data to be converted cannot be a string constant; it must be a scalar variable.

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

CAVEAT: The following operations look the same but are not quite so;

from_to($data, "iso-8859-1", "utf8"); #1
$data = decode("iso-8859-1", $data);  #2

Both #1 and #2 make $data consist of a completely valid UTF-8 string but only #2 turns utf8 flag on. #1 is equivalent to

$data = encode("utf8", decode("iso-8859-1", $data));

See "The UTF-8 flag" below.

$octets = encode_utf8($string);

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

$string = decode_utf8($octets [, CHECK]);

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. Not all sequences of octets form valid UTF-8 encodings, so it is possible for this call to fail. For CHECK, see "Handling Malformed Data".

Listing available encodings

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

Returns a list of the canonical names of the available encodings that are loaded. To get a list of all available encodings including the ones that are not loaded yet, say

@all_encodings = Encode->encodings(":all");

Or you can give the name of a specific module.

@with_jp = Encode->encodings("Encode::JP");

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

@ebcdic = Encode->encodings("EBCDIC");

To find out in detail which encodings are supported by this package, see Encode::Supported.

Defining Aliases

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

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

After that, newName can be used as an alias for ENCODING. ENCODING may be either the name of an encoding or an encoding object

But before you do so, make sure the alias is nonexistent with resolve_alias(), which returns the canonical name thereof. i.e.

Encode::resolve_alias("latin1") eq "iso-8859-1" # true
Encode::resolve_alias("iso-8859-12")   # false; nonexistent
Encode::resolve_alias($name) eq $name  # true if $name is canonical

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

See Encode::Alias for details.

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 totally identical in their functionality.

# via PerlIO
open my $in,  "<:encoding(shiftjis)", $infile  or die;
open my $out, ">:encoding(euc-jp)",   $outfile or die;
while(<$in>){ print $out $_; }

# via from_to
open my $in,  "<", $infile  or die;
open my $out, ">", $outfile or die;
  from_to($_, "shiftjis", "euc-jp", 1);
  print $out $_;

Unfortunately, it may be that encodings are PerlIO-savvy. You can check if your encoding is supported by PerlIO by calling the perlio_ok method.

Encode::perlio_ok("hz");             # False
find_encoding("euc-cn")->perlio_ok;  # True where PerlIO is available

use Encode qw(perlio_ok);            # exported upon request

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

Handling Malformed Data

Unimplemented fallback schemes

In the future, you will be able to use a code reference to a callback function for the value of CHECK but its API is still undecided.

The fallback scheme does not work on EBCDIC platforms.

Defining Encodings

To define a new encoding, use:

use Encode qw(define_encoding);
define_encoding($object, 'canonicalName' [, alias...]);

canonicalName will be associated with $object. The object should provide the interface described in Encode::Encoding. If more than two arguments are provided then additional arguments are taken as aliases for $object.

See Encode::Encoding for more details.

The UTF-8 flag

Before the introduction of utf8 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 will quote page 402 of Programming Perl, 3rd ed.

Goal #1:

Old byte-oriented programs should not spontaneously break on the old byte-oriented data they used to work on.

Goal #2:

Old byte-oriented programs should magically start working on the new character-oriented data when appropriate.

Goal #3:

Programs should run just as fast in the new character-oriented mode as in the old byte-oriented mode.

Goal #4:

Perl should remain one language, rather than forking into a byte-oriented Perl and a character-oriented Perl.

Back when Programming Perl, 3rd ed. was written, not even Perl 5.6.0 was born and many features documented in the book remained unimplemented for a long time. Perl 5.8 corrected this and the introduction of the UTF-8 flag is one of them. You can think of this perl notion as of a byte-oriented mode (utf8 flag off) and a character-oriented mode (utf8 flag on).

Here is how Encode takes care of the utf8 flag.

Messing with Perl's Internals

The following API uses parts of Perl's internals in the current implementation. As such, they are efficient but may change.

is_utf8(STRING [, CHECK])

[INTERNAL] Tests whether the UTF-8 flag is turned on in the STRING. If CHECK is true, also checks the data in STRING for being well-formed UTF-8. Returns true if successful, false otherwise.


[INTERNAL] Turns on the UTF-8 flag in STRING. The data in STRING is not checked for being well-formed UTF-8. Do not use unless you know that the STRING is well-formed UTF-8. Returns the previous state of the UTF-8 flag (so please don't treat the return value as indicating success or failure), or undef if STRING is not a string.


[INTERNAL] Turns off the UTF-8 flag in STRING. Do not use frivolously. Returns the previous state of the UTF-8 flag (so please don't treat the return value as indicating success or failure), or undef if STRING is not a string.


Encode::Encoding, Encode::Supported, Encode::PerlIO, encoding, perlebcdic, "open" in perlfunc, perlunicode, utf8, the Perl Unicode Mailing List <>


This project was originated by Nick Ing-Simmons and later maintained by Dan Kogai <>. See AUTHORS for a full list of people involved. For any questions, use <> so we can all share.

2 POD Errors

The following errors were encountered while parsing the POD:

Around line 520:

You can't have =items (as at line 526) unless the first thing after the =over is an =item

Around line 599:

You forgot a '=back' before '=head2'