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. 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. 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 to:
$octets = encode($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 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
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.
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, "\x
HH" 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 "&#x
HHHH;" 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 octets that represent 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}".
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
$str = decode 'UTF-8', $octets, sub {
my $tmp = chr shift;
from_to $tmp, 'ISO-8859-15', 'UTF-8';
return $tmp;
};
Defining Encodings¶
To define a new encoding, use:
use Encode qw(define_encoding);
define_encoding($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
$object.
See Encode::Encoding for details.
The UTF8 flag¶
Before the introduction of Unicode support in Perl, The "eq" operator
just compared the strings represented by two scalars. Beginning with Perl 5.8,
"eq" compares two strings with simultaneous consideration of
the
UTF8 flag. To explain why we made it so, I quote from page 402 of
Programming Perl, 3rd ed.
- Goal #1:
- Old byte-oriented programs should not spontaneously break on the old
byte-oriented data they used to work on.
- Goal #2:
- Old byte-oriented programs should magically start working on the new
character-oriented data when appropriate.
- Goal #3:
- Programs should run just as fast in the new character-oriented mode as in
the old byte-oriented mode.
- Goal #4:
- Perl should remain one language, rather than forking into a byte-oriented
Perl and a character-oriented Perl.
When
Programming Perl, 3rd ed. was written, not even Perl 5.6.0 had been
born yet, many features documented in the book remained unimplemented for a
long time. Perl 5.8 corrected much of this, and the introduction of the UTF8
flag is one of them. You can think of there being two fundamentally different
kinds of strings and string-operations in Perl: one a byte-oriented mode for
when the internal UTF8 flag is off, and the other a character-oriented mode
for when the internal UTF8 flag is on.
Here is how "Encode" handles the UTF8 flag.
- •
- When you encode, the resulting UTF8 flag is always off.
- •
- When you decode, the resulting UTF8 flag is
on--unless you can unambiguously represent data. Here is
what we mean by "unambiguously". After "$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 (0x
XX_FFFE and
0x
XX_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@wall.org>
Date: December 04, 2004 11:51:58 JST
To: perl-unicode@perl.org
Subject: Re: Make Encode.pm support the real UTF-8
Message-Id: <20041204025158.GA28754@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@cpan.org>. See AUTHORS for a full list of
people involved. For any questions, send mail to
<perl-unicode@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 2002-2014 Dan Kogai
<dankogai@cpan.org>.
This library is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.