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encoding(3pm) Perl Programmers Reference Guide encoding(3pm)

NAME

encoding - allows you to write your script in non-ascii or non-utf8

SYNOPSIS

use encoding "greek"; # Perl like Greek to you?

use encoding "euc-jp"; # Jperl!

# or you can even do this if your shell supports your native encoding

perl -Mencoding=latin2 -e '...' # Feeling centrally European?

perl -Mencoding=euc-kr -e '...' # Or Korean?

# more control

# A simple euc-cn => utf-8 converter

use encoding "euc-cn", STDOUT => "utf8"; while(<>){print};

# "no encoding;" supported (but not scoped!)

no encoding;

# an alternate way, Filter

use encoding "euc-jp", Filter=>1;

# now you can use kanji identifiers - in euc-jp!

# switch on locale -

# note that this probably means that unless you have a complete control

# over the environments the application is ever going to be run, you should

# NOT use the feature of encoding pragma allowing you to write your script

# in any recognized encoding because changing locale settings will wreck

# the script; you can of course still use the other features of the pragma.

use encoding ':locale';

AABBSSTTRRAACCTT

Let's start with a bit of history: Perl 5.6.0 introduced Unicode sup-

port. You could apply "substr()" and regexes even to complex CJK char-

acters - so long as the script was written in UTF-8. But back then,

text editors that supported UTF-8 were still rare and many users

instead chose to write scripts in legacy encodings, giving up a whole

new feature of Perl 5.6. Rewind to the future: starting from perl 5.8.0 with the eennccooddiinngg

pragma, you can write your script in any encoding you like (so long as

the "Encode" module supports it) and still enjoy Unicode support. This pragma achieves that by doing the following: +o Internally converts all literals ("q//,qq//,qr//,qw///, qx//") from

the encoding specified to utf8. In Perl 5.8.1 and later, literals

in "tr///" and "DATA" pseudo-filehandle are also converted.

+o Changing PerlIO layers of "STDIN" and "STDOUT" to the encoding

specified. LLiitteerraall CCoonnvveerrssiioonnss

You can write code in EUC-JP as follows:

my $Rakuda = "\xF1\xD1\xF1\xCC"; # Camel in Kanji

#<-char-><-char-> # 4 octets

s/\bCamel\b/$Rakuda/;

And with "use encoding "euc-jp"" in effect, it is the same thing as the

code in UTF-8:

my $Rakuda = "\x{99F1}\x{99DD}"; # two Unicode Characters

s/\bCamel\b/$Rakuda/;

PPeerrllIIOO llaayyeerrss ffoorr ""SSTTDD((IINN||OOUUTT))"" The eennccooddiinngg pragma also modifies the filehandle layers of STDIN and

STDOUT to the specified encoding. Therefore,

use encoding "euc-jp";

my $message = "Camel is the symbol of perl.\n";

my $Rakuda = "\xF1\xD1\xF1\xCC"; # Camel in Kanji

$message =~ s/\bCamel\b/$Rakuda/;

print $message;

Will print "\xF1\xD1\xF1\xCC is the symbol of perl.\n", not "\x{99F1}\x{99DD} is the symbol of perl.\n". You can override this by giving extra arguments; see below. IImmpplliicciitt uuppggrraaddiinngg ffoorr bbyyttee ssttrriinnggss By default, if strings operating under byte semantics and strings with Unicode character data are concatenated, the new string will be created

by decoding the byte strings as ISO 8859-1 (Latin-1).

The eennccooddiinngg pragma changes this to use the specified encoding instead.

For example:

use encoding 'utf8';

my $string = chr(20000); # a Unicode string

utf8::encode($string); # now it's a UTF-8 encoded byte string

# concatenate with another Unicode string

print length($string . chr(20000));

Will print 2, because $string is upgraded as UTF-8. Without "use

encoding 'utf8';", it will print 4 instead, since $string is three

octets when interpreted as Latin-1.

FFEEAATTUURREESS TTHHAATT RREEQQUUIIRREE 55..88..11 Some of the features offered by this pragma requires perl 5.8.1. Most of these are done by Inaba Hiroto. Any other features and changes are good for 5.8.0.

"NON-EUC" doublebyte encodings

Because perl needs to parse script before applying this pragma,

such encodings as ShiftJIS and Big-5 that may contain '\' (BACK-

SLASH; \x5c) in the second byte fails because the second byte may accidentally escape the quoting character that follows. Perl 5.8.1 or later fixes this problem. tr// "tr//" was overlooked by Perl 5 porters when they released perl 5.8.0 See the section below for details.

DATA pseudo-filehandle

Another feature that was overlooked was "DATA". UUSSAAGGEE

use encoding [ENCNAME] ;

Sets the script encoding to ENCNAME. And unless ${^UNICODE} exists

and non-zero, PerlIO layers of STDIN and STDOUT are set to ":encod-

ing(ENCNAME)".

Note that STDERR WILL NOT be changed.

Also note that non-STD file handles remain unaffected. Use "use

open" or "binmode" to change layers of those.

If no encoding is specified, the environment variable PERLENCODING

is consulted. If no encoding can be found, the error "Unknown

encoding 'ENCNAME'" will be thrown.

use encoding ENCNAME [ STDIN => ENCNAMEIN ...] ;

You can also individually set encodings of STDIN and STDOUT via the

"STDIN => ENCNAME" form. In this case, you cannot omit the first

ENCNAME. "STDIN => undef" turns the IO transcoding completely off.

When ${^UNICODE} exists and non-zero, these options will completely

ignored. ${^UNICODE} is a variable introduced in perl 5.8.1. See

perlrun see "${^UNICODE}" in perlvar and "-C" in perlrun for

details (perl 5.8.1 and later).

use encoding ENCNAME Filter=>1;

This turns the encoding pragma into a source filter. While the

default approach just decodes interpolated literals (in qq() and qr()), this will apply a source filter to the entire source code. See "The Filter Option" below for details.

no encoding;

Unsets the script encoding. The layers of STDIN, STDOUT are reset

to ":raw" (the default unprocessed raw stream of bytes). The Filter Option

The magic of "use encoding" is not applied to the names of identifiers.

In order to make "${"\x{4eba}"}++" ($human++, where human is a single

Han ideograph) work, you still need to write your script in UTF-8 - or

use a source filter. That's what 'Filter=>1' does. What does this mean? Your source code behaves as if it is written in

UTF-8 with 'use utf8' in effect. So even if your editor only supports

ShiftJIS, for example, you can still try examples in Chapter 15 of

"Programming Perl, 3rd Ed.". For instance, you can use UTF-8 identi-

fiers.

This option is significantly slower and (as of this writing) non-ASCII

identifiers are not very stable WITHOUT this option and with the source

code written in UTF-8.

FFiilltteerr-rreellaatteedd cchhaannggeess aatt EEnnccooddee vveerrssiioonn 11..8877

+o The Filter option now sets STDIN and STDOUT like non-filter

options. And "STDIN=>ENCODING" and "STDOUT=>ENCODING" work like

non-filter version.

+o "use utf8" is implicitly declared so you no longer have to "use

utf8" to "${"\x{4eba}"}++".

CCAAVVEEAATTSS NNOOTT SSCCOOPPEEDD The pragma is a per script, not a per block lexical. Only the last

"use encoding" or "no encoding" matters, and it affects tthhee wwhhoollee

ssccrriipptt. However, the pragma is supported and uussee eennccoodd-

iinngg can appear as many times as you want in a given script. The multi-

ple use of this pragma is discouraged.

By the same reason, the use this pragma inside modules is also discour-

aged (though not as strongly discouraged as the case above. See below). If you still have to write a module with this pragma, be very careful of the load order. See the codes below;

# called module

package ModuleINBAR;

use encoding "bar";

# stuff in "bar" encoding here

# caller script

use encoding "foo"

use ModuleINBAR;

# surprise! use encoding "bar" is in effect.

The best way to avoid this oddity is to use this pragma RIGHT AFTER other modules are loaded. i.e. use ModuleINBAR;

use encoding "foo";

DDOO NNOOTT MMIIXX MMUULLTTIIPPLLEE EENNCCOODDIINNGGSS Notice that only literals (string or regular expression) having only legacy code points are affected: if you mix data like this \xDF\x{100} the data is assumed to be in (Latin 1 and) Unicode, not in your native

encoding. In other words, this will match in "greek":

"\xDF" =~ /\x{3af}/ but this will not "\xDF\x{100}" =~ /\x{3af}\x{100}/

since the "\xDF" (ISO 8859-7 GREEK SMALL LETTER IOTA WITH TONOS) on the

left will nnoott be upgraded to "\x{3af}" (Unicode GREEK SMALL LETTER IOTA WITH TONOS) because of the "\x{100}" on the left. You should not be mixing your legacy data and Unicode in the same string.

This pragma also affects encoding of the 0x80..0xFF code point range:

normally characters in that range are left as eight-bit bytes (unless

they are combined with characters with code points 0x100 or larger, in

which case all characters need to become UTF-8 encoded), but if the

"encoding" pragma is present, even the 0x80..0xFF range always gets

UTF-8 encoded.

After all, the best thing about this pragma is that you don't have to

resort to \x{....} just to spell your name in a native encoding. So

feel free to put your strings in your encoding in quotes and regexes.

ttrr////// wwiitthh rraannggeess The eennccooddiinngg pragma works by decoding string literals in "q//,qq//,qr//,qw///, qx//" and so forth. In perl 5.8.0, this does not apply to "tr///". Therefore,

use encoding 'euc-jp';

#....

$kana =~ tr/\xA4\xA1-\xA4\xF3/\xA5\xA1-\xA5\xF3/;

# ---- ---- ---- ----

Does not work as

$kana =~ tr/\x{3041}-\x{3093}/\x{30a1}-\x{30f3}/;

Legend of characters above

utf8 euc-jp charnames::viacode()

---------------------

\x{3041} \xA4\xA1 HIRAGANA LETTER SMALL A \x{3093} \xA4\xF3 HIRAGANA LETTER N \x{30a1} \xA5\xA1 KATAKANA LETTER SMALL A \x{30f3} \xA5\xF3 KATAKANA LETTER N This counterintuitive behavior has been fixed in perl 5.8.1. workaround to tr///; In perl 5.8.0, you can work around as follows;

use encoding 'euc-jp';

# ....

eval qq{ \$kana =~ tr/\xA4\xA1-\xA4\xF3/\xA5\xA1-\xA5\xF3/ };

Note the "tr//" expression is surrounded by "qq{}". The idea behind is the same as classic idiom that makes "tr///" 'interpolate'.

tr/$from/$to/; # wrong!

eval qq{ tr/$from/$to/ }; # workaround.

Nevertheless, in case of eennccooddiinngg pragma even "q//" is affected so "tr///" not being decoded was obviously against the will of Perl5 Porters so it has been fixed in Perl 5.8.1 or later.

EEXXAAMMPPLLEE - GGrreeeekkppeerrll

use encoding "iso 8859-7";

# \xDF in ISO 8859-7 (Greek) is \x{3af} in Unicode.

$a = "\xDF";

$b = "\x{100}";

printf "%#x\n", ord($a); # will print 0x3af, not 0xdf

$c = $a . $b;

# $c will be "\x{3af}\x{100}", not "\x{df}\x{100}".

# chr() is affected, and ...

print "mega\n" if ord(chr(0xdf)) == 0x3af;

# ... ord() is affected by the encoding pragma ...

print "tera\n" if ord(pack("C", 0xdf)) == 0x3af;

# ... as are eq and cmp ...

print "peta\n" if "\x{3af}" eq pack("C", 0xdf); print "exa\n" if "\x{3af}" cmp pack("C", 0xdf) == 0;

# ... but pack/unpack C are not affected, in case you still

# want to go back to your native encoding

print "zetta\n" if unpack("C", (pack("C", 0xdf))) == 0xdf; KKNNOOWWNN PPRROOBBLLEEMMSS literals in regex that are longer than 127 bytes

For native multibyte encodings (either fixed or variable length),

the current implementation of the regular expressions may introduce recoding errors for regular expression literals longer than 127 bytes. EBCDIC

The encoding pragma is not supported on EBCDIC platforms. (Porters

who are willing and able to remove this limitation are welcome.) format This pragma doesn't work well with format because PerlIO does not

get along very well with it. When format contains non-ascii char-

acters it prints funny or gets "wide character warnings". To understand it, try the code below.

# Save this one in utf8

# replace *non-ascii* with a non-ascii string

my $camel;

format STDOUT =

*non-ascii*@>>>>>>>

$camel

$camel = "*non-ascii*";

binmode(STDOUT=>':encoding(utf8)'); # bang!

write; # funny

print $camel, "\n"; # fine

Without binmode this happens to work but without binmode, print() fails instead of write(). At any rate, the very use of format is questionable when it comes to unicode characters since you have to consider such things as

character width (i.e. double-width for ideographs) and directions

(i.e. BIDI for Arabic and Hebrew). The Logic of :locale The logic of ":locale" is as follows:

1. If the platform supports the langinfo(CODESET) interface, the code-

set returned is used as the default encoding for the open pragma.

2. If 1. didn't work but we are under the locale pragma, the environ-

ment variables LCALL and LANG (in that order) are matched for

encodings (the part after ".", if any), and if any found, that is

used as the default encoding for the open pragma.

3. If 1. and 2. didn't work, the environment variables LCALL and LANG

(in that order) are matched for anything looking like UTF-8, and if

any found, ":utf8" is used as the default encoding for the open

pragma. If your locale environment variables (LCALL, LCCTYPE, LANG) contain

the strings 'UTF-8' or 'UTF8' (case-insensitive matching), the default

encoding of your STDIN, STDOUT, and STDERR, and of aannyy ssuubbsseeqquueenntt ffiillee

ooppeenn, is UTF-8.

HISTORY This pragma first appeared in Perl 5.8.0. For features that require 5.8.1 and better, see above. The ":locale" subpragma was implemented in 2.01, or Perl 5.8.6.