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


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 standard-
       ize 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 func-
       tions 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 effectively
       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:

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



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


           On EBCDIC platforms characters in the Latin 1 charac-
           ter 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 liter-
       als), "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::" pack-
       age 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 charac-
           ter sequence in UTF-X.  $string already encoded as
           characters does no harm.  Returns the number of octets
           necessary 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
           derivatives).

           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,



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


           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 corre-
           sponding 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 con-
           tains 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 test-
           suite to check that operations have left strings in a
           consistent 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



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


       the C API functions "sv_utf8_upgrade", "sv_utf8_down-
       grade", "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 pack-
       age/class or subroutine names.  While some limited func-
       tionality 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































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