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NAME

encoding - allows you to write your script in non-ASCII and non-UTF-8

WARNING

This module has been deprecated since perl v5.18. See "DESCRIPTION" and "BUGS".

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
no encoding;
# an alternate way, Filter
use encoding "euc-jp", Filter=>1;
# now you can use kanji identifiers -- in euc-jp!
# encode based on the current locale - specialized purposes only;
# fraught with danger!!
use encoding ':locale';

DESCRIPTION

This pragma is used to enable a Perl script to be written in encodings that aren't strictly ASCII nor UTF-8. It translates all or portions of the Perl program script from a given encoding into UTF-8, and changes the PerlIO layers of STDIN and STDOUT to the encoding specified.

This pragma dates from the days when UTF-8-enabled editors were uncommon. But that was long ago, and the need for it is greatly diminished. That, coupled with the fact that it doesn't work with threads, along with other problems, (see "BUGS") have led to its being deprecated. It is planned to remove this pragma in a future Perl version. New code should be written in UTF-8, and the use utf8 pragma used instead (see perluniintro and utf8 for details). Old code should be converted to UTF-8, via something like the recipe in the "SYNOPSIS" (though this simple approach may require manual adjustments afterwards).

The only legitimate use of this pragma is almost certainly just one per file, near the top, with file scope, as the file is likely going to only be written in one encoding. Further restrictions apply in Perls before v5.22 (see "Prior to Perl v5.22").

There are two basic modes of operation (plus turning if off):

OPTIONS

Setting STDIN and/or STDOUT individually

The encodings of STDIN and STDOUT are individually settable by parameters to the pragma:

use encoding 'euc-tw', STDIN => 'greek'  ...;

In this case, you cannot omit the first ENCNAME. STDIN => undef turns the I/O transcoding completely off for that filehandle.

When ${^UNICODE} (available starting in v5.8.2) exists and is non-zero, these options will be completely ignored. See "${^UNICODE}" in perlvar and "-C" in perlrun for details.

The :locale sub-pragma

Starting in v5.8.6, the encoding name may be :locale. This means that the encoding is taken from the current locale, and not hard-coded by the pragma. Since a script really can only be encoded in exactly one encoding, this option is dangerous. It makes sense only if the script itself is written in ASCII, and all the possible locales that will be in use when the script is executed are supersets of ASCII. That means that the script itself doesn't get changed, but the I/O handles have the specified encoding added, and the operations like chr and ord use that encoding.

The logic of finding which locale :locale uses is as follows:

  1. If the platform supports the langinfo(CODESET) interface, the codeset 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 environment variables LC_ALL 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 LC_ALL 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 (LC_ALL, LC_CTYPE, LANG) contain the strings 'UTF-8' or 'UTF8' (case-insensitive matching), the default encoding of your STDIN, STDOUT, and STDERR, and of any subsequent file open, is UTF-8.

CAVEATS

SIDE EFFECTS

DO NOT MIX MULTIPLE ENCODINGS

Notice that only literals (string or regular expression) having only legacy code points are affected: if you mix data like this

\x{100}\xDF
\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 not 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.

Prior to Perl v5.22

The pragma was a per script, not a per block lexical. Only the last use encoding or no encoding mattered, and it affected the whole script. However, the no encoding pragma was supported and use encoding could appear as many times as you want in a given script (though only the last was effective).

Since the scope wasn't lexical, other modules' use of chr, ord, etc. were affected. This leads to spooky, incorrect action at a distance that is hard to debug.

This means you would have to be very careful of the load order:

# called module
package Module_IN_BAR;
use encoding "bar";
# stuff in "bar" encoding here
1;
# caller script
use encoding "foo"
use Module_IN_BAR;
# 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 Module_IN_BAR;
use encoding "foo";

Prior to Encode version 1.87

Prior to Perl v5.8.1

EXAMPLE - Greekperl

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;

BUGS

HISTORY

This pragma first appeared in Perl v5.8.0. It has been enhanced in later releases as specified above.

SEE ALSO

perlunicode, Encode, open, Filter::Util::Call,

Ch. 15 of Programming Perl (3rd Edition) by Larry Wall, Tom Christiansen, Jon Orwant; O'Reilly & Associates; ISBN 0-596-00027-8