utf8
utf8(3) Perl Programmers Reference Guide utf8(3)
NAME
utf8 - Perl pragma to enable/disable UTF-8 (or UTF-EBCDIC) in source
code
SYNOPSIS
use utf8;
no utf8;
# Convert a Perl scalar to/from UTF-8.
$num_octets = utf8::upgrade($string);
$success = utf8::downgrade($string[, FAIL_OK]);
# Change the native bytes of a Perl scalar to/from UTF-8 bytes.
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 pro-
gram 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 plat-
forms 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-8 character. This includes
most literals such as identifier names, string constants, and con-
stant 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 the octet sequence in the native encoding
(Latin-1 or EBCDIC) to the equivalent character sequence in UTF-X.
$string already encoded as characters does no harm. 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.pm is recommended for the general purposes.
Affected by the encoding pragma.
* $success = utf8::downgrade($string[, FAIL_OK])
Converts in-place the character sequence in UTF-X to the equivalent
octet sequence in the native encoding (Latin-1 or EBCDIC). $string
already encoded as octets does no harm. Returns true on success.
On failure dies or, if the value of "FAIL_OK" is true, returns
false. Can be used to make sure that the UTF-8 flag is off, e.g.
when you want to make sure that the substr() or length() function
works with the usually faster byte algorithm.
Note that this function does not handle arbitrary encodings.
Therefore Encode.pm is recommended for the general purposes.
Not affected by the encoding pragma.
NOTE: this function is experimental and may change or be removed
without notice.
* utf8::encode($string)
Converts in-place the character sequence to the corresponding octet
sequence in UTF-X. The UTF-8 flag is turned off. Returns nothing.
Note that this function does not handle arbitrary encodings.
Therefore Encode.pm is recommended for the general purposes.
* utf8::decode($string)
Attempts to convert in-place the octet sequence in UTF-X to the
corresponding character sequence. 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.
Note that this function does not handle arbitrary encodings.
Therefore Encode.pm is recommended for the general purposes.
NOTE: this function is experimental and may change or be removed
without notice.
* $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 'con-
sistent'). 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".
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 unporta-
bility: 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
perl v5.8.6 2001-09-21 utf8(3)
