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 encoded as 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 $string is marked
internally as encoded in UTF-8. Functionally the same as
Encode::is_utf8().
- •
- "$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 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". 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