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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;
# 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 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 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 '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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