NAME

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

SYNOPSIS

           use utf8;
           no utf8;

           # Convert the internal representation of a Perl scalar to/from UTF-8.

           $num_octets = utf8::upgrade($string);
           $success    = utf8::downgrade($string[, FAIL_OK]);

           # Change each character of a Perl scalar to/from a series of
           # characters that represent the UTF-8 bytes of each original character.

           utf8::encode($string);  # "\x{100}"  becomes "\xc4\x80"
           utf8::decode($string);  # "\xc4\x80" becomes "\x{100}"

           $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:

       •   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 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.

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

           Converts in-place the internal representation of the string from an octet sequence in
           the native encoding (Latin-1 or EBCDIC) to UTF-X. The logical character sequence
           itself is unchanged.  If $string is already stored as UTF-X, then this is a no-op.
           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.

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

           Converts in-place the internal representation of the string from UTF-X to the
           equivalent octet sequence in the native encoding (Latin-1 or EBCDIC). The logical
           character sequence itself is unchanged. If $string is already stored as native 8 bit,
           then this is a no-op.  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.

       •   utf8::encode($string)

           Converts in-place the character sequence to the corresponding octet sequence in UTF-X.
           That is, every (possibly wide) character gets replaced with a sequence of one or more
           characters that represent the individual UTF-X bytes of the character.  The UTF8 flag
           is turned off.  Returns nothing.

               my $a = "\x{100}"; # $a contains one character, with ord 0x100
               utf8::encode($a);  # $a contains two characters, with ords 0xc4 and 0x80

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

       •   $success = utf8::decode($string)

           Attempts to convert in-place the octet sequence in UTF-X to the corresponding
           character sequence. That is, it replaces each sequence of characters in the string
           whose ords represent a valid UTF-X byte sequence, with the corresponding single
           character.  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.

               my $a = "\xc4\x80"; # $a contains two characters, with ords 0xc4 and 0x80
               utf8::decode($a);   # $a contains one character, with ord 0x100

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

       •   $flag = utf8::is_utf8(STRING)

           (Since Perl 5.8.1)  Test whether STRING is encoded internally 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 if it 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 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