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utf8(3)


NAME

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


SYNOPSIS

      use utf8;
      no utf8;

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

      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 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-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) internal representation of string to Perl's
      internal UTF-X form.  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 expected on strings
      containing characters in the range 0x80-0xFF (oon ASCII and
      derivatives).  Note that this should not be used to convert a legacy
      byte encoding to Unicode: use Encode for that.  Affected by the
      encoding pragma.

  * $success = utf8::downgrade($string[, FAIL_OK])
      Converts (in-place) internal representation of string to be un-encoded
      bytes.  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 should not be used to convert Unicode back to a legacy byte
      encoding: use Encode for that.  Not affected by the encoding pragma.

  * utf8::encode($string)
      Converts (in-place) $string from logical characters to octet sequence
      representing it in Perl's UTF-X encoding.	 Returns nothing.  Same as
      Encode::encode_utf8(). Note that this should not be used to convert a
      legacy byte encoding to Unicode: use Encode for that.

  * utf8::decode($string)
      Attempts to convert $string in-place from Perl's UTF-X encoding into
      logical characters. Returns nothing.  Same as Encode::decode_utf8().
      Note that this should not be used to convert Unicode back to a legacy
      byte encoding: use Encode for that.

  * $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 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
  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

  perluniintro, encoding, perlrun, bytes, perlunicode

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