


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.

       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 directly usable without "use
       utf8;".

       Because it is not possible to reliably tell UTF-8 from
       native 8 bit encodings, you need either a Byte Order Mark
       at the beginning of your source code, or "use utf8;", to
       instruct perl.

       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-X
           sequence.  This includes most literals such as
           identifier names, string constants, and constant
           regular expression patterns.

           On EBCDIC platforms characters in the Latin 1



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           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-X.  If you want to have
       such bytes under "use utf8", you can disable this pragma
       until the end the block (or file, if at top level) by "no
       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.

       o   $num_octets = utf8::upgrade($string)

           Converts in-place the internal 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 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 is recommended for the
           general purposes; see also Encode.

       o   $success = utf8::downgrade($string[, FAIL_OK])

           Converts in-place the internal octet sequence in UTF-X
           to the equivalent octet sequence in the native
           encoding (Latin-1 or EBCDIC).  $string already encoded
           as native 8 bit does no harm.  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.

           Fails if the original UTF-X sequence cannot be
           represented in the native 8 bit encoding. On failure
           dies or, if the value of "FAIL_OK" is true, returns
           false.

           Returns true on success.

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




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


       o   utf8::encode($string)

           Converts in-place the character sequence to the
           corresponding octet sequence in UTF-X.  The UTF8 flag
           is turned off, so that after this operation, the
           string is a byte string.  Returns nothing.

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

       o   $success = utf8::decode($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 is recommended for the
           general purposes; see also Encode.

       o   $flag = utf8::is_utf8(STRING)

           (Since Perl 5.8.1)  Test whether STRING is in UTF-8
           internally.  Functionally the same as
           Encode::is_utf8().

       o   $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 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
       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".  Also, the functions utf8::is_utf8,
       utf8::valid, utf8::encode, utf8::decode, utf8::upgrade,
       and utf8::downgrade are actually internal, and thus always
       available, without a "require utf8" statement.

BUGS
       One can have Unicode in identifier names, but not in



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       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
       subroutine 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
       perlunitut, perluniintro, perlrun, bytes, perlunicode











































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