encoding


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';

ABSTRACT
       Let's start with a bit of history: Perl 5.6.0 introduced Unicode
       support.  You could apply "substr()" and regexes even to complex CJK
       characters -- 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 encoding
       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.

   Literal Conversions
       You can write code in EUC-JP as follows:

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

         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.

   Implicit upgrading for byte strings
       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 encoding 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.

   Side effects
       If the "encoding" pragma is in scope then the lengths returned are
       calculated from the length of $/ in Unicode characters, which is not
       always the same as the length of $/ in the native encoding.

       This pragma affects utf8::upgrade, but not utf8::downgrade.

FEATURES THAT REQUIRE 5.8.1
       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 Shift_JIS and Big-5 that may contain '\'
           (BACKSLASH; \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

           If no encoding is specified, the environment variable PERL_ENCODING
           is consulted.  If no encoding can be found, the error "Unknown
           encoding 'ENCNAME'" will be thrown.

       use encoding ENCNAME [ STDIN => ENCNAME_IN ...] ;
           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
       Shift_JIS, for example, you can still try examples in Chapter 15 of
       "Programming Perl, 3rd Ed.".  For instance, you can use UTF-8
       identifiers.

       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.

   Filter-related changes at Encode version 1.87
       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}"}++".

CAVEATS
   NOT SCOPED
       The pragma is a per script, not a per block lexical.  Only the last
       "use encoding" or "no encoding" matters, and it affects the whole
       script.  However, the <no encoding> pragma is supported and use
         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";

   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

           \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.

   tr/// with ranges
       The encoding 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/;
             \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 encoding 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.

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;

           This pragma doesn't work well with format because PerlIO does not
           get along very well with it.  When format contains non-ascii
           characters 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).

       Thread safety
           "use encoding ..." is not thread-safe (i.e., do not use in threaded
           applications).

   The Logic of :locale
       The logic of ":locale" 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.

HISTORY
       This pragma first appeared in Perl 5.8.0.  For features that require
       5.8.1 and better, see above.
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