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utf8(3)                Perl Programmers Reference Guide                utf8(3)



NAME
       utf8 - Perl pragma to enable/disable UTF-8 (or UTF-EBCDIC) in source code

SYNOPSIS
           use utf8;
           no utf8;

           # Convert a Perl scalar to/from UTF-8.
           $num_octets = utf8::upgrade($string);
           $success    = utf8::downgrade($string[, FAIL_OK]);

           # Change the native bytes of a Perl scalar to/from UTF-8 bytes.
           utf8::encode($string);
           utf8::decode($string);

           $flag = utf8::is_utf8(STRING); # since Perl 5.8.1
           $flag = utf8::valid(STRING);

DESCRIPTION
       The "use utf8" pragma tells the Perl parser to allow UTF-8 in the program text in the current lexical scope
       (allow UTF-EBCDIC on EBCDIC based platforms).  The "no utf8" pragma tells Perl to switch back to treating the
       source text as literal bytes in the current lexical scope.

       This pragma is primarily a compatibility device.  Perl versions earlier than 5.6 allowed arbitrary bytes in
       source code, whereas in future we would like to standardize on the UTF-8 encoding for source text.

       Do not use this pragma for anything else than telling Perl that your script is written in UTF-8. The utility
       functions described below are useful for their own purposes, but they are not really part of the "pragmatic"
       effect.

       Until UTF-8 becomes the default format for source text, either this pragma or the encoding pragma should be
       used to recognize UTF-8 in the source.  When UTF-8 becomes the standard source format, this pragma will effec-
       tively become a no-op.  For convenience in what follows the term UTF-X is used to refer to UTF-8 on ASCII and
       ISO Latin based platforms and UTF-EBCDIC on EBCDIC based platforms.

       See also the effects of the "-C" switch and its cousin, the $ENV{PERL_UNICODE}, in perlrun.

       Enabling the "utf8" pragma has the following effect:

       ?   Bytes in the source text that have their high-bit set will be treated as being part of a literal UTF-8
           character.  This includes most literals such as identifier names, string constants, and constant regular
           expression patterns.

           On EBCDIC platforms characters in the Latin 1 character set are treated as being part of a literal UTF-
           EBCDIC character.

       Note that if you have bytes with the eighth bit on in your script (for example embedded Latin-1 in your string
       literals), "use utf8" will be unhappy since the bytes are most probably not well-formed UTF-8.  If you want to
       have such bytes and use utf8, you can disable utf8 until the end the block (or file, if at top level) by "no
       utf8;".

       If you want to automatically upgrade your 8-bit legacy bytes to UTF-8, use the encoding pragma instead of this
       pragma.  For example, if you want to implicitly upgrade your ISO 8859-1 (Latin-1) bytes to UTF-8 as used in
       e.g. "chr()" and "\x{...}", try this:

           use encoding "latin-1";
           my $c = chr(0xc4);
           my $x = "\x{c5}";

       In case you are wondering: yes, "use encoding 'utf8';" works much the same as "use utf8;".

       Utility functions

       The following functions are defined in the "utf8::" package by the Perl core.  You do not need to say "use
       utf8" to use these and in fact you should not say that  unless you really want to have UTF-8 source code.

       * $num_octets = utf8::upgrade($string)
           Converts in-place the octet sequence in the native encoding (Latin-1 or EBCDIC) to the equivalent character
           sequence in UTF-X.  $string already encoded as characters does no harm.  Returns the number of octets nec-
           essary to represent the string as UTF-X.  Can be used to make sure that the UTF-8 flag is on, so that "\w"
           or "lc()" work as Unicode on strings containing characters in the range 0x80-0xFF (on ASCII and deriva-
           tives).

           Note that this function does not handle arbitrary encodings.  Therefore Encode.pm is recommended for the
           general purposes.

           Affected by the encoding pragma.

       * $success = utf8::downgrade($string[, FAIL_OK])
           Converts in-place the character sequence in UTF-X to the equivalent octet sequence in the native encoding
           (Latin-1 or EBCDIC).  $string already encoded as octets does no harm.  Returns true on success. On failure
           dies or, if the value of "FAIL_OK" is true, returns false.  Can be used to make sure that the UTF-8 flag is
           off, e.g. when you want to make sure that the substr() or length() function works with the usually faster
           byte algorithm.

           Note that this function does not handle arbitrary encodings.  Therefore Encode.pm is recommended for the
           general purposes.

           Not affected by the encoding pragma.

           NOTE: this function is experimental and may change or be removed without notice.

       * utf8::encode($string)
           Converts in-place the character sequence to the corresponding octet sequence in UTF-X.  The UTF-8 flag is
           turned off.  Returns nothing.

           Note that this function does not handle arbitrary encodings.  Therefore Encode.pm is recommended for the
           general purposes.

       * utf8::decode($string)
           Attempts to convert in-place the octet sequence in UTF-X to the corresponding character sequence.  The
           UTF-8 flag is turned on only if the source string contains multiple-byte UTF-X characters.  If $string is
           invalid as UTF-X, returns false; otherwise returns true.

           Note that this function does not handle arbitrary encodings.  Therefore Encode.pm is recommended for the
           general purposes.

           NOTE: this function is experimental and may change or be removed without notice.

       * $flag = utf8::is_utf8(STRING)
           (Since Perl 5.8.1)  Test whether STRING is in UTF-8.  Functionally the same as Encode::is_utf8().

       * $flag = utf8::valid(STRING)
           [INTERNAL] Test whether STRING is in a consistent state regarding UTF-8.  Will return true is well-formed
           UTF-8 and has the UTF-8 flag on or if string is held as bytes (both these states are 'consistent').  Main
           reason for this routine is to allow Perl's testsuite to check that operations have left strings in a con-
           sistent state.  You most probably want to use utf8::is_utf8() instead.

       "utf8::encode" is like "utf8::upgrade", but the UTF8 flag is cleared.  See perlunicode for more on the UTF8
       flag and the C API functions "sv_utf8_upgrade", "sv_utf8_downgrade", "sv_utf8_encode", and "sv_utf8_decode",
       which are wrapped by the Perl functions "utf8::upgrade", "utf8::downgrade", "utf8::encode" and "utf8::decode".
       Note that in the Perl 5.8.0 and 5.8.1 implementation the functions utf8::is_utf8, utf8::valid, utf8::encode,
       utf8::decode, utf8::upgrade, and utf8::downgrade are always available, without a "require utf8" statement--
       this may change in future releases.

BUGS
       One can have Unicode in identifier names, but not in package/class or subroutine names.  While some limited
       functionality towards this does exist as of Perl 5.8.0, that is more accidental than designed; use of Unicode
       for the said purposes is unsupported.

       One reason of this unfinishedness is its (currently) inherent unportability: since both package names and sub-
       routine names may need to be mapped to file and directory names, the Unicode capability of the filesystem
       becomes important-- and there unfortunately aren't portable answers.

SEE ALSO
       perluniintro, encoding, perlrun, bytes, perlunicode



perl v5.8.8                       2001-09-21                           utf8(3)