| Encode - character encodings in Perl |
Encode - character encodings in Perl
use Encode qw(decode encode);
$characters = decode('UTF-8', $octets, Encode::FB_CROAK);
$octets = encode('UTF-8', $characters, Encode::FB_CROAK);
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:
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 the perlebcdic manpage.
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. the perlunitut manpage and the perlunifaq manpage explain the why.
A character in the range 0 .. 2**32-1 (or more); what Perl's strings are made of.
A character in the range 0..255; a special case of a Perl character.
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.
$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.
CAVEAT: the input scalar STRING might be modified in-place depending on what is set in CHECK. See LEAVE_SRC if you want your inputs to be left unchanged.
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("UTF-8", $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 UTF-8 string. See The UTF8 flag below.
If the $string is undef, then undef is returned.
str2bytes may be used as an alias for encode.
$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.
CAVEAT: the input scalar OCTETS might be modified in-place depending on what is set in CHECK. See LEAVE_SRC if you want your inputs to be left unchanged.
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("UTF-8", $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 $string is undef, then undef is returned.
bytes2str may be used as an alias for decode.
[$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.
$string = decode($name, $bytes);
is in fact
$string = 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 $string = $enc->decode($_);
... # now do something with $string;
}
Besides decode and encode, other methods are
available as well. For instance, name() returns the canonical
name of the encoding object.
find_encoding("latin1")->name; # iso-8859-1
See the Encode::Encoding manpage for details.
[$obj =] find_mime_encoding(MIME_ENCODING)
Returns the encoding object corresponding to MIME_ENCODING. Acts
same as find_encoding() but mime_name() of returned object must
match to MIME_ENCODING. So as opposite of find_encoding()
canonical names and aliases are not used when searching for object.
find_mime_encoding("utf8"); # returns undef because "utf8" is not valid I<MIME_ENCODING>
find_mime_encoding("utf-8"); # returns encode object "utf-8-strict"
find_mime_encoding("UTF-8"); # same as "utf-8" because I<MIME_ENCODING> is case insensitive
find_mime_encoding("utf-8-strict"); returns undef because "utf-8-strict" is not valid I<MIME_ENCODING>
[$length =] from_to($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", "UTF-8"); #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("UTF-8", 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);
$octets = encode_utf8($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) utf8 representation, this function cannot fail.
WARNING: do not use this function for data exchange as it can produce
not strict utf8 $octets! For strictly valid UTF-8 output use
$octets = encode("UTF-8", $string).
$string = decode_utf8($octets [, CHECK]);
Equivalent to $string = decode("utf8", $octets [, CHECK]).
The sequence of octets represented by $octets is decoded
from (loose, not strict) utf8 into a sequence of logical characters.
Because not all sequences of octets are valid not strict utf8,
it is quite possible for this function to fail.
For CHECK, see Handling Malformed Data.
WARNING: do not use this function for data exchange as it can produce
$string with not strict utf8 representation! For strictly valid UTF-8
$string representation use $string = decode("UTF-8", $octets [, CHECK]).
CAVEAT: the input $octets might be modified in-place depending on what is set in CHECK. See LEAVE_SRC if you want your inputs to be left unchanged.
use Encode; @list = Encode->encodings();
Returns a list of canonical names of available encodings that have already been loaded. To get a list of all available encodings including those that have not yet been loaded, say:
@all_encodings = Encode->encodings(":all");
Or you can give the name of a specific module:
@with_jp = Encode->encodings("Encode::JP");
When ``::'' is not in the name, ``Encode::'' is assumed.
@ebcdic = Encode->encodings("EBCDIC");
To find out in detail which encodings are supported by this package, see the Encode::Supported manpage.
To add a new alias to a given encoding, use:
use Encode; use Encode::Alias; define_alias(NEWNAME => ENCODING);
After that, NEWNAME can be used as an alias for ENCODING. ENCODING may be either the name of an encoding or an encoding object.
Before you do that, first make sure the alias is nonexistent using
resolve_alias(), which returns the canonical name thereof.
For example:
Encode::resolve_alias("latin1") eq "iso-8859-1" # true
Encode::resolve_alias("iso-8859-12") # false; nonexistent
Encode::resolve_alias($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 the Encode::Alias manpage for details.
The canonical name of a given encoding does not necessarily agree with
IANA Character Set Registry, commonly seen as Content-Type:
text/plain; charset=I<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: the Encode::Encoding manpage
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
the Encode::Encoding manpage and the Encode::PerlIO manpage.
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, the Encode::Unicode manpage ignores CHECK and it always croaks on error.
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.
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.
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
}
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.
CAVEAT: All warnings from Encode module are reported, independently of
pragma warnings settings. If you want to follow settings of
lexical warnings configured by pragma warnings then append
also check value ENCODE::ONLY_PRAGMA_WARNINGS. This value is available
since Encode version 2.99.
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.
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
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.
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}.
Fallback for decode must return decoded string (sequence of characters)
and takes a list of ordinal values as its arguments. 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 = join '', map chr, @_;
return decode 'ISO-8859-15', $tmp;
};
To define a new encoding, use:
use Encode qw(define_encoding);
define_encoding($object, CANONICAL_NAME [, alias...]);
CANONICAL_NAME will be associated with $object. The object should provide the interface described in the Encode::Encoding manpage. If more than two arguments are provided, additional arguments are considered aliases for $object.
See the Encode::Encoding manpage for details.
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.
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.
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.
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(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.
Typically only necessary for debugging and testing. Don't use this flag as a marker to distinguish character and binary data, that should be decided for each variable when you write your code.
CAVEAT: If STRING has UTF8 flag set, it does NOT mean that STRING is UTF-8 encoded and vice-versa.
As of Perl 5.8.1, the utf8 manpage also has the utf8::is_utf8 function.
_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(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.
....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@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.
the Encode::Encoding manpage, the Encode::Supported manpage, the Encode::PerlIO manpage, the encoding manpage, the perlebcdic manpage, open in the perlfunc manpage, the perlunicode manpage, the perluniintro manpage, the perlunifaq manpage, the perlunitut manpage the utf8 manpage, the Perl Unicode Mailing List http://lists.perl.org/list/perl-unicode.html
This project was originated by the late Nick Ing-Simmons and later
maintained by Dan Kogai
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 2002-2014 Dan Kogai
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
| Encode - character encodings in Perl |