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




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).

       If UTF-8 is not an option, it is recommended that one use a simple
       source filter, such as that provided by Filter::Encoding on CPAN or
       this pragma's own "Filter" option (see below).

       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):

       "use encoding ['ENCNAME'] ;"
           Please note: This mode of operation is no longer supported as of
           Perl v5.26.

           This is the normal operation.  It translates various literals
           encountered in the Perl source file from the encoding ENCNAME into
           UTF-8, and similarly converts character code points.  This is used
           when the script is a combination of ASCII (for the variable names
           and punctuation, etc), but the literal data is in the specified
           encoding.

           ENCNAME is optional.  If omitted, the encoding specified in the
           environment variable "PERL_ENCODING" is used.  If this isn't set,
           or the resolved-to encoding is not known to "Encode", the error
           "Unknown encoding 'ENCNAME'" will be thrown.

           Starting in Perl v5.8.6 ("Encode" version 2.0.1), ENCNAME may be
           the name ":locale".  This is for very specialized applications, and
           is documented in "The ":locale" sub-pragma" below.

           The literals that are converted are "q//, qq//, qr//, qw///, qx//",
           and starting in v5.8.1, "tr///".  Operations that do conversions
           include "chr", "ord", "utf8::upgrade" (but not "utf8::downgrade"),
           and "chomp".

           Also starting in v5.8.1, the "DATA" pseudo-filehandle is translated
           from the encoding into UTF-8.

           For example, 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
           that code in UTF-8:

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

           See "EXAMPLE" below for a more complete example.

           Unless "${^UNICODE}" (available starting in v5.8.2) exists and is
           non-zero, the PerlIO layers of "STDIN" and "STDOUT" are set to
           "":encoding(ENCNAME)"".  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.

           Note that "STDERR" WILL NOT be changed, regardless.

           Also note that non-STD file handles remain unaffected.  Use "use
           open" or "binmode" to change the layers of those.

       "use encoding ENCNAME Filter=>1;"
           This operates as above, but the "Filter" argument with a non-zero
           value causes the entire script, and not just literals, to be
           translated from the encoding into UTF-8.  This allows identifiers
           in the source to be in that encoding as well.  (Problems may occur
           if the encoding is not a superset of ASCII; imagine all your semi-
           colons being translated into something different.)  One can use
           this form to make

            ${"\x{4eba}"}++

           work.  (This is equivalent to "$human++", where human is a single
           Han ideograph).

           This effectively means that your source code behaves as if it were
           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.".

           This option is significantly slower than the other one.

       "no encoding;"
           Unsets the script encoding. The layers of "STDIN", "STDOUT" are
           reset to "":raw"" (the default unprocessed raw stream of bytes).


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
       o   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.

       o   Without this pragma, 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.

   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
       o   "STDIN" and "STDOUT" were not set under the filter option.  And
           "STDIN=>ENCODING" and "STDOUT=>ENCODING" didn't work like non-
           filter version.

       o   "use utf8" wasn't implicitly declared so you have to "use utf8" to
           do

            ${"\x{4eba}"}++

   Prior to Perl v5.8.1
       "NON-EUC" doublebyte encodings
           Because perl needs to parse the script before applying this pragma,
           such encodings as Shift_JIS and Big-5 that may contain '\'
           (BACKSLASH; "\x5c") in the second byte fail because the second byte
           may accidentally escape the quoting character that follows.

       "tr///"
           The encoding pragma works by decoding string literals in
           "q//,qq//,qr//,qw///, qx//" and so forth.  In perl v5.8.0, 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 v5.8.1.

           In perl v5.8.0, you can work around this 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 this is the same as the classic idiom that makes "tr///"
           'interpolate':

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


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

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

       Can't be used by more than one module in a single program.
           Only one encoding is allowed.  If you combine modules in a program
           that have different encodings, only one will be actually used.

       Other modules using "STDIN" and "STDOUT" get the encoded stream
           They may be expecting something completely different.

       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.

       "format"
           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).

       See also "CAVEATS"


HISTORY

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


SEE ALSO

       perlunicode(1), Encode(3), open(3), Filter::Util::Call(3),

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



perl v5.26.1                      2017-07-18                     encoding(3pm)

perl 5.26.1 - Generated Tue Nov 7 07:37:39 CST 2017
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