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

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

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

NNAAMMEE #

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

SSYYNNOOPPSSIISS #

  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}"

  # Convert a code point from the platform native character set to
  # Unicode, and vice-versa.
  $unicode = utf8::native_to_unicode(ord('A')); # returns 65 on both
                                                # ASCII and EBCDIC
                                                # platforms
  $native = utf8::unicode_to_native(65);        # returns 65 on ASCII
                                                # platforms; 193 on

# EBCDIC #

  $flag = utf8::is_utf8($string); # since Perl 5.8.1
  $flag = utf8::valid($string);

DDEESSCCRRIIPPTTIIOONN #

 The "use utf8" pragma tells the Perl parser to allow UTF-8 in the program
 text in the current lexical scope.  The "no utf8" pragma tells Perl to
 switch back to treating the source text as literal bytes in the current
 lexical scope.  (On EBCDIC platforms, technically it is allowing UTF-
 EBCDIC, and not UTF-8, but this distinction is academic, so in this
 document the term UTF-8 is used to mean both).

 DDoo nnoott uussee tthhiiss pprraaggmmaa ffoorr aannyytthhiinngg eellssee tthhaann tteelllliinngg PPeerrll tthhaatt yyoouurr
 ssccrriipptt iiss wwrriitttteenn iinn UUTTFF--88.. 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.

 See also the effects of the "-C" switch and its cousin, the
 "PERL_UNICODE" environment variable, in perlrun.

 Enabling the "utf8" pragma has the following effect:

 •   Bytes in the source text that are not in the ASCII character set will
     be treated as being part of a literal UTF-8 sequence.  This includes
     most literals such as identifier names, string constants, and
     constant regular expression patterns.

 Note that if you have non-ASCII, non-UTF-8 bytes in your script (for
 example embedded Latin-1 in your string literals), "use utf8" will be
 unhappy.  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;".

UUttiilliittyy ffuunnccttiioonnss 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)"

     (Since Perl v5.8.0) Converts in-place the internal representation of
     the string from an octet sequence in the native encoding (Latin-1 or
     EBCDIC) to UTF-8. The logical character sequence itself is unchanged.
     If _$_s_t_r_i_n_g is already upgraded, then this is a no-op. Returns the
     number of octets necessary to represent the string as UTF-8.

     If your code needs to be compatible with versions of perl without
     "use feature 'unicode_strings';", you can force Unicode semantics on
     a given string:

       # force unicode semantics for $string without the
       # "unicode_strings" feature
       utf8::upgrade($string);

     For example:

       # without explicit or implicit use feature 'unicode_strings'
       my $x = "\xDF";    # LATIN SMALL LETTER SHARP S
       $x =~ /ss/i;       # won't match
       my $y = uc($x);    # won't convert
       utf8::upgrade($x);
       $x =~ /ss/i;       # matches
       my $z = uc($x);    # converts to "SS"

     NNoottee tthhaatt tthhiiss ffuunnccttiioonn ddooeess nnoott hhaannddllee aarrbbiittrraarryy eennccooddiinnggss; use
     Encode instead.

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

     (Since Perl v5.8.0) Converts in-place the internal representation of
     the string from UTF-8 to the equivalent octet sequence in the native
     encoding (Latin-1 or EBCDIC). The logical character sequence itself
     is unchanged. If _$_s_t_r_i_n_g 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 ssuubbssttrr(()) or lleennggtthh(())
     function works with the usually faster byte algorithm.

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

     Returns true on success.

     If your code expects an octet sequence this can be used to validate
     that you've received one:

       # throw an exception if not representable as octets
       utf8::downgrade($string)

       # or do your own error handling
       utf8::downgrade($string, 1) or die "string must be octets";

     NNoottee tthhaatt tthhiiss ffuunnccttiioonn ddooeess nnoott hhaannddllee aarrbbiittrraarryy eennccooddiinnggss; use
     Encode instead.

 •   "utf8::encode($string)"

     (Since Perl v5.8.0) Converts in-place the character sequence to the
     corresponding octet sequence in Perl's extended UTF-8. That is, every
     (possibly wide) character gets replaced with a sequence of one or
     more characters that represent the individual UTF-8 bytes of the
     character.  The UTF8 flag is turned off.  Returns nothing.

      my $x = "\x{100}"; # $x contains one character, with ord 0x100
      utf8::encode($x);  # $x contains two characters, with ords (on
                         # ASCII platforms) 0xc4 and 0x80.  On EBCDIC
                         # 1047, this would instead be 0x8C and 0x41.

     Similar to:

       use Encode;
       $x = Encode::encode("utf8", $x);

     NNoottee tthhaatt tthhiiss ffuunnccttiioonn ddooeess nnoott hhaannddllee aarrbbiittrraarryy eennccooddiinnggss; use
     Encode instead.

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

     (Since Perl v5.8.0) Attempts to convert in-place the octet sequence
     encoded in Perl's extended UTF-8 to the corresponding character
     sequence. That is, it replaces each sequence of characters in the
     string whose ords represent a valid (extended) UTF-8 byte sequence,
     with the corresponding single character.  The UTF-8 flag is turned on
     only if the source string contains multiple-byte UTF-8 characters.
     If _$_s_t_r_i_n_g is invalid as extended UTF-8, returns false; otherwise
     returns true.

      my $x = "\xc4\x80"; # $x contains two characters, with ords
                          # 0xc4 and 0x80
      utf8::decode($x);   # On ASCII platforms, $x contains one char,
                          # with ord 0x100.   Since these bytes aren't
                          # legal UTF-EBCDIC, on EBCDIC platforms, $x is
                          # unchanged and the function returns FALSE.
      my $y = "\xc3\x83\xc2\xab"; This has been encoded twice; this
                          # example is only for ASCII platforms
      utf8::decode($y);   # Converts $y to \xc3\xab, returns TRUE;
      utf8::decode($y);   # Further converts to \xeb, returns TRUE;
      utf8::decode($y);   # Returns FALSE, leaves $y unchanged

     NNoottee tthhaatt tthhiiss ffuunnccttiioonn ddooeess nnoott hhaannddllee aarrbbiittrraarryy eennccooddiinnggss; use
     Encode instead.

 •   "$unicode = utf8::native_to_unicode($code_point)"

     (Since Perl v5.8.0) This takes an unsigned integer (which represents
     the ordinal number of a character (or a code point) on the platform
     the program is being run on) and returns its Unicode equivalent
     value.  Since ASCII platforms natively use the Unicode code points,
     this function returns its input on them.  On EBCDIC platforms it
     converts from EBCDIC to Unicode.

     A meaningless value will currently be returned if the input is not an
     unsigned integer.

     Since Perl v5.22.0, calls to this function are optimized out on ASCII
     platforms, so there is no performance hit in using it there.

 •   "$native = utf8::unicode_to_native($code_point)"

     (Since Perl v5.8.0) This is the inverse of
     "utf8::native_to_unicode()", converting the other direction.  Again,
     on ASCII platforms, this returns its input, but on EBCDIC platforms
     it will find the native platform code point, given any Unicode one.

     A meaningless value will currently be returned if the input is not an
     unsigned integer.

     Since Perl v5.22.0, calls to this function are optimized out on ASCII
     platforms, so there is no performance hit in using it there.

 •   "$flag = utf8::is_utf8($string)"

     (Since Perl 5.8.1)  Test whether _$_s_t_r_i_n_g is marked internally as
     encoded in UTF-8.  Functionally the same as
     "Encode::is_utf8($string)".

     Typically only necessary for debugging and testing, if you need to
     dump the internals of an SV, Devel::Peek's DDuummpp(()) provides more
     detail in a compact form.

     If you still think you need this outside of debugging, testing or
     dealing with filenames, you should probably read perlunitut and "What
     is "the UTF8 flag"?" in perlunifaq.

     Don't use this flag as a marker to distinguish character and binary
     data: that should be decided for each variable when you write your
     code.

     To force unicode semantics in code portable to perl 5.8 and 5.10,
     call "utf8::upgrade($string)" unconditionally.

 •   "$flag = utf8::valid($string)"

     [INTERNAL] Test whether _$_s_t_r_i_n_g is in a consistent state regarding
     UTF-8.  Will return true if it is well-formed Perl extended UTF-8 and
     has the UTF-8 flag on oorr if _$_s_t_r_i_n_g is held as bytes (both these
     states are 'consistent').  The main reason for this routine is to
     allow Perl's test suite to check that operations have left strings in
     a consistent state.

 "utf8::encode" is like "utf8::upgrade", but the UTF8 flag is cleared.
 See perlunicode, and the C API functions "sv_utf8_upgrade",
 ""sv_utf8_downgrade" in perlapi", ""sv_utf8_encode" in perlapi", and
 ""sv_utf8_decode" in perlapi", 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.

BBUUGGSS #

 Some filesystems may not support UTF-8 file names, or they may be
 supported incompatibly with Perl.  Therefore UTF-8 names that are visible
 to the filesystem, such as module names may not work.

SSEEEE AALLSSOO #

 perlunitut, perluniintro, perlrun, bytes, perlunicode

perl v5.36.3 2023-02-15 utf8(3p)