utf8(3pm) Perl Programmers Reference Guide utf8(3pm)
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:
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 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 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.
o $success = utf8::downgrade($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 $string is already stored as native 8 bit, then this
is a no-op. Can be used to make sure that the UTF-8 flag is off,
e.g. when you want to make sure that the substr() or length()
function works with the usually faster byte algorithm.
Fails if the original UTF-X sequence cannot be represented in the
native 8 bit encoding. On failure dies or, if the value of
"FAIL_OK" is true, returns false.
Returns true on success.
Note that this function does not handle arbitrary encodings.
Therefore Encode is recommended for the general purposes; see also
Encode.
o utf8::encode($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.
o $success = utf8::decode($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.
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 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
perl v5.16.3 2013-03-04 utf8(3pm)
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