Encode(3) User Contributed Perl Documentation Encode(3)
NAME
Encode - character encodings in Perl
SYNOPSIS
use Encode qw(decode encode);
$characters = decode('UTF-8', $octets, Encode::FB_CROAK);
$octets = encode('UTF-8', $characters, Encode::FB_CROAK);
Table of Contents
Encode consists of a collection of modules whose details are too
extensive to fit in one document. This one itself explains the top-
level APIs and general topics at a glance. For other topics and more
details, see the documentation for these modules:
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
DESCRIPTION
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.
When Perl is processing "binary data", the programmer wants Perl to
process "sequences of bytes". This is not a problem for Perl: because a
byte has 256 possible values, it easily fits in Perl's much larger
"logical character".
This document mostly explains the how. perlunitut and perlunifaq
explain the why.
TERMINOLOGY
character
A character in the range 0 .. 2**32-1 (or more); what Perl's strings
are made of.
byte
A character in the range 0..255; a special case of a Perl character.
octet
8 bits of data, with ordinal values 0..255; term for bytes passed to or
from a non-Perl context, such as a disk file, standard I/O stream,
database, command-line argument, environment variable, socket etc.
THE PERL ENCODING API
Basic methods
encode
$octets = encode(ENCODING, STRING[, CHECK])
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".
For example, to convert a string from Perl's internal format into
ISO-8859-1, also known as Latin1:
$octets = encode("iso-8859-1", $string);
CAVEAT: When you run "$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.
decode
$string = decode(ENCODING, OCTETS[, CHECK])
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. The returns the resulting string. 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".
For example, to convert ISO-8859-1 data into a string in Perl's
internal format:
$string = decode("iso-8859-1", $octets);
CAVEAT: When you run "$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 unless $octets consists entirely of ASCII
data on ASCII machines or EBCDIC on EBCDIC machines. See "The UTF8
flag" below.
If the $string is "undef", then "undef" is returned.
find_encoding
[$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);
croak qq(encoding "$name" not found) unless ref $obj;
$obj->decode($bytes);
};
with more error checking.
You can therefore save time by reusing this object as follows;
my $enc = find_encoding("iso-8859-1");
while(<>) {
my $utf8 = $enc->decode($_);
... # now do something with $utf8;
}
Besides "decode" and "encode", other methods are available as well.
For instance, "name()" returns the canonical name of the encoding
object.
find_encoding("latin1")->name; # iso-8859-1
See Encode::Encoding for details.
from_to
[$length =] from_to($octets, FROM_ENC, TO_ENC [, CHECK])
Converts in-place data between two encodings. The data in $octets must
be encoded as octets and not as characters in Perl's internal format.
For example, to convert ISO-8859-1 data into Microsoft's CP1250
encoding:
from_to($octets, "iso-8859-1", "cp1250");
and to convert it back:
from_to($octets, "cp1250", "iso-8859-1");
Because the conversion happens in place, the data to be converted
cannot be a string constant: it must be a scalar variable.
"from_to()" returns the length of the converted string in octets on
success, and "undef" on error.
CAVEAT: The following operations may look the same, but are not:
from_to($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 the UTF8 flag on. #1 is equivalent to:
$data = encode("utf8", decode("iso-8859-1", $data));
See "The UTF8 flag" below.
Also note that:
from_to($octets, $from, $to, $check);
is equivalent t:o
$octets = encode($to, decode($from, $octets), $check);
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:
$octets = encode($to, decode($from, $octets, $check_from), $check_to);
encode_utf8
$octets = encode_utf8($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.
decode_utf8
$string = decode_utf8($octets [, CHECK]);
Equivalent to "$string = decode("utf8", $octets [, CHECK])". The
sequence of octets represented by $octets is decoded from UTF-8 into a
sequence of logical characters. Because not all sequences of octets
are valid UTF-8, it is quite possible for this function to fail. For
CHECK, see "Handling Malformed Data".
Listing available encodings
use Encode;
@list = Encode->encodings();
Returns a list of canonical names of available encodings that have
already been loaded. To get a list of all available encodings
including those that have not yet been loaded, say:
@all_encodings = Encode->encodings(":all");
Or you can give the name of a specific module:
@with_jp = Encode->encodings("Encode::JP");
When ""::"" is not in the name, ""Encode::"" is assumed.
@ebcdic = Encode->encodings("EBCDIC");
To find out in detail which encodings are supported by this package,
see Encode::Supported.
Defining Aliases
To add a new alias to a given encoding, use:
use Encode;
use Encode::Alias;
define_alias(NEWNAME => ENCODING);
After that, NEWNAME can be used as an alias for ENCODING. ENCODING may
be either the name of an encoding or an encoding object.
Before you do that, first make sure the alias is nonexistent using
"resolve_alias()", which returns the canonical name thereof. For
example:
Encode::resolve_alias("latin1") eq "iso-8859-1" # true
Encode::resolve_alias("iso-8859-12") # false; nonexistent
Encode::resolve_alias($name) eq $name # true if $name is canonical
"resolve_alias()" does not need "use Encode::Alias"; it can be 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;
my $enc = find_encoding("UTF-8");
warn $enc->name; # utf-8-strict
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
open(INPUT, "< :encoding(shiftjis)", $infile)
|| die "Can't open < $infile for reading: $!";
open(OUTPUT, "> :encoding(euc-jp)", $outfile)
|| die "Can't open > $output for writing: $!";
while (<INPUT>) { # auto decodes $_
print OUTPUT; # auto encodes $_
}
close(INPUT) || die "can't close $infile: $!";
close(OUTPUT) || die "can't close $outfile: $!";
### Version 2 via from_to()
open(INPUT, "< :raw", $infile)
|| die "Can't open < $infile for reading: $!";
open(OUTPUT, "> :raw", $outfile)
|| die "Can't open > $output for writing: $!";
while (<INPUT>) {
from_to($_, "shiftjis", "euc-jp", 1); # switch encoding
print OUTPUT; # emit raw (but properly encoded) data
}
close(INPUT) || die "can't close $infile: $!";
close(OUTPUT) || die "can't close $outfile: $!";
In the first version above, you let the appropriate encoding layer
handle the conversion. In the second, you explicitly translate from
one encoding to the other.
Unfortunately, it may be that encodings are "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
find_encoding("euc-cn")->perlio_ok; # true wherever PerlIO is available
use Encode qw(perlio_ok); # imported upon request
perlio_ok("euc-jp")
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.
NOTE: Not all encodings support this feature. Some encodings ignore
the CHECK argument. For example, Encode::Unicode ignores CHECK and it
always croaks on error.
List of CHECK values
FB_DEFAULT
I<CHECK> = Encode::FB_DEFAULT ( == 0)
If CHECK is 0, encoding and decoding replace any malformed character
with a substitution character. When you encode, SUBCHAR is used. When
you decode, the Unicode REPLACEMENT CHARACTER, code point U+FFFD, is
used. If the data is supposed to be UTF-8, an optional lexical warning
of warning category "utf8" is given.
FB_CROAK
I<CHECK> = Encode::FB_CROAK ( == 1)
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".
FB_QUIET
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:
my($buffer, $string) = ("", "");
while (read($fh, $buffer, 256, length($buffer))) {
$string .= decode($encoding, $buffer, Encode::FB_QUIET);
# $buffer now contains the unprocessed partial character
}
FB_WARN
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.
FB_PERLQQ FB_HTMLCREF FB_XMLCREF
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)".
FB_DEFAULT FB_CROAK FB_QUIET FB_WARN FB_PERLQQ
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
LEAVE_SRC
Encode::LEAVE_SRC
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
a string that represents the fallback character. For instance:
$ascii = encode("ascii", $utf8, sub{ sprintf "<U+%04X>", shift });
Acts like "FB_PERLQQ" but U+XXXX is used instead of "\x{XXXX}".
Defining Encodings
To define a new encoding, use:
use Encode qw(define_encoding);
define_encoding($object, CANONICAL_NAME [, alias...]);
CANONICAL_NAME will be associated with $object. The object should
provide the interface described in Encode::Encoding. If more than two
arguments are provided, additional arguments are considered aliases for
$object.
See Encode::Encoding for details.
The UTF8 flag
Before the introduction of Unicode support in Perl, The "eq" operator
just compared the strings represented by two scalars. Beginning with
Perl 5.8, "eq" compares two strings with simultaneous consideration of
the UTF8 flag. To explain why we made it so, I quote from page 402 of
Programming Perl, 3rd ed.
Goal #1:
Old byte-oriented programs should not spontaneously break on the old
byte-oriented data they used to work on.
Goal #2:
Old byte-oriented programs should magically start working on the new
character-oriented data when appropriate.
Goal #3:
Programs should run just as fast in the new character-oriented mode
as in the old byte-oriented mode.
Goal #4:
Perl should remain one language, rather than forking into a byte-
oriented Perl and a character-oriented Perl.
When Programming Perl, 3rd ed. was written, not even Perl 5.6.0 had
been born yet, many features documented in the book remained
unimplemented for a long time. Perl 5.8 corrected much of this, and
the introduction of the UTF8 flag is one of them. You can think of
there being two fundamentally different kinds of strings and string-
operations in Perl: one a byte-oriented mode for when the internal
UTF8 flag is off, and the other a character-oriented mode for when the
internal UTF8 flag is on.
Here is how "Encode" handles the UTF8 flag.
o When you encode, the resulting UTF8 flag is always off.
o When you decode, the resulting UTF8 flag is on--unless you can
unambiguously represent data. Here is what we mean by
"unambiguously". After "$utf8 = decode("foo", $octet)",
When $octet is... The UTF8 flag in $utf8 is
---------------------------------------------
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.
This UTF8 flag is not visible in Perl scripts, exactly for the same
reason you cannot (or rather, you don't have to) see whether a scalar
contains a string, an integer, or a floating-point number. But you
can still peek and poke these if you will. See the next section.
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 in a future
release.
is_utf8
is_utf8(STRING [, CHECK])
[INTERNAL] Tests whether the UTF8 flag is turned on in the STRING. If
CHECK is true, also checks whether STRING contains well-formed UTF-8.
Returns true if successful, false otherwise.
As of Perl 5.8.1, utf8 also has the "utf8::is_utf8" function.
_utf8_on
_utf8_on(STRING)
[INTERNAL] Turns the STRING's internal UTF8 flag on. The STRING is not
checked for containing only well-formed UTF-8. Do not use this unless
you know with absolute certainty that the STRING holds only well-formed
UTF-8. Returns the previous state of the UTF8 flag (so please don't
treat the return value as indicating success or failure), or "undef" if
STRING is not a string.
NOTE: For security reasons, this function does not work on tainted
values.
_utf8_off
_utf8_off(STRING)
[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.
NOTE: For security reasons, this function does not work on tainted
values.
UTF-8 vs. utf8 vs. UTF8
....We now view strings not as sequences of bytes, but as sequences
of numbers in the range 0 .. 2**32-1 (or in the case of 64-bit
computers, 0 .. 2**64-1) -- Programming Perl, 3rd ed.
That has historically been Perl's notion of UTF-8, as that is how UTF-8
was first conceived by Ken Thompson when he invented it. However,
thanks to later revisions to the applicable standards, official UTF-8
is now rather stricter than that. For example, its range is much
narrower (0 .. 0x10_FFFF to cover only 21 bits instead of 32 or 64
bits) and some sequences are not allowed, like those used in surrogate
pairs, the 31 non-character code points 0xFDD0 .. 0xFDEF, the last two
code points in any plane (0xXX_FFFE and 0xXX_FFFF), all non-shortest
encodings, etc.
The former default in which Perl would always use a loose
interpretation of UTF-8 has now been overruled:
From: Larry Wall <larry AT wall.org>
Date: December 04, 2004 11:51:58 JST
To: perl-unicode AT perl.org
Subject: Re: Make Encode.pm support the real UTF-8
Message-Id: <20041204025158.GA28754 AT wall.org>
On Fri, Dec 03, 2004 at 10:12:12PM +0000, Tim Bunce wrote:
: I've no problem with 'utf8' being perl's unrestricted uft8 encoding,
: but "UTF-8" is the name of the standard and should give the
: corresponding behaviour.
For what it's worth, that's how I've always kept them straight in my
head.
Also for what it's worth, Perl 6 will mostly default to strict but
make it easy to switch back to lax.
Larry
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".
encode("utf8", "\x{FFFF_FFFF}", 1); # okay
encode("UTF-8", "\x{FFFF_FFFF}", 1); # croaks
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:
find_encoding("UTF-8")->name # is 'utf-8-strict'
find_encoding("utf-8")->name # ditto. names are case insensitive
find_encoding("utf_8")->name # ditto. "_" are treated as "-"
find_encoding("UTF8")->name # is 'utf8'.
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.
SEE ALSO
Encode::Encoding, Encode::Supported, Encode::PerlIO, encoding,
perlebcdic, "open" in perlfunc, perlunicode, perluniintro, perlunifaq,
perlunitut utf8, the Perl Unicode Mailing List
<http://lists.perl.org/list/perl-unicode.html>;
MAINTAINER
This project was originated by the late Nick Ing-Simmons and later
maintained by Dan Kogai <dankogai AT cpan.org>. See AUTHORS for a full
list of people involved. For any questions, send mail to
<perl-unicode AT perl.org> so that we can all share.
While Dan Kogai retains the copyright as a maintainer, credit should go
to all those involved. See AUTHORS for a list of those who submitted
code to the project.
COPYRIGHT
Copyright 2002-2013 Dan Kogai <dankogai AT cpan.org>.
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
perl v5.16.3 2014-06-10 Encode(3)
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