MirOS Manual: encoding(3p)


ext::Encode::encoPerl(Programmers Refereext::Encode::encoding(3p)

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';

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 sup-
     ported 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:

     +   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.

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

     Literal Conversions

     You can write code in EUC-JP as follows:

       my $Rakuda = "\xF1\xD1\xF1\xCC"; # Camel in Kanji
                    #<-char-><-char->   # 4 octets
       s/\bCamel\b/$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/;

     PerlIO layers for "STD(IN|OUT)"

     The encoding 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.

     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 encod-
     ing 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

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     $string is three octets when interpreted as Latin-1.

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
         Another feature that was overlooked was "DATA".

USAGE

     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 ":encoding(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
         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.  ${^UNICODE} is a variable intro-
         duced in perl 5.8.1.  See perlrun see "${^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.

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         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

     +   The Filter option now sets STDIN and STDOUT like non-
         filter options. And "STDIN=>ENCODING" and
         "STDOUT=>ENCODING" work like non-filter version.

     +   "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 encoding can appear as many times as
     you want in a given script. The multiple use of this pragma
     is discouraged.

     By the same reason, the use this pragma inside modules is
     also discouraged (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;

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       # 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";

     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 charac-
     ters 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

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ext::Encode::encoPerl(Programmers Refereext::Encode::encoding(3p)

     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/;
       #           -------- -------- -------- --------

     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 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.

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         $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;

KNOWN PROBLEMS

     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 plat-
         forms. (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 con-
         tains non-ascii characters it prints funny or gets "wide
         character warnings". To understand it, try the code
         below.

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           # 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 bin-
         mode, 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 con-
         sider 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) inter-
         face, the codeset returned is used as the default encod-
         ing 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.

     The ":locale" subpragma was implemented in 2.01, or Perl
     5.8.6.

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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

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