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 pro-
       gram 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 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 plat-
       forms 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 character.  This includes
           most literals such as identifier names, string constants, and con-
           stant 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 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, 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 'con-
           sistent').  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 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 unporta-
       bility: 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.

utf8(3)

NAME

SYNOPSIS

DESCRIPTION

BUGS

SEE ALSO