utf8.3

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.\" ========================================================================
.\"
.IX Title "utf8 3"
.TH utf8 3 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.SH "NAME"
utf8 \- Perl pragma to enable/disable UTF\-8 (or UTF\-EBCDIC) in source code
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&    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
\&    $flag = utf8::valid(STRING);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \f(CW\*(C`use utf8\*(C'\fR pragma tells the Perl parser to allow \s-1UTF\-8\s0 in the
program text in the current lexical scope (allow UTF-EBCDIC on \s-1EBCDIC\s0 based
platforms).  The \f(CW\*(C`no utf8\*(C'\fR pragma tells Perl to switch back to treating
the source text as literal bytes in the current lexical scope.
.PP
\&\fBDo not use this pragma for anything else than telling Perl that your
script is written in \s-1UTF\-8\s0.\fR The utility functions described below are
directly usable without \f(CW\*(C`use utf8;\*(C'\fR.
.PP
Because it is not possible to reliably tell \s-1UTF\-8\s0 from native 8 bit
encodings, you need either a Byte Order Mark at the beginning of your
source code, or \f(CW\*(C`use utf8;\*(C'\fR, to instruct perl.
.PP
When \s-1UTF\-8\s0 becomes the standard source format, this pragma will
effectively become a no-op.  For convenience in what follows the term
\&\fIUTF-X\fR is used to refer to \s-1UTF\-8\s0 on \s-1ASCII\s0 and \s-1ISO\s0 Latin based
platforms and UTF-EBCDIC on \s-1EBCDIC\s0 based platforms.
.PP
See also the effects of the \f(CW\*(C`\-C\*(C'\fR switch and its cousin, the
\&\f(CW$ENV{PERL_UNICODE}\fR, in perlrun.
.PP
Enabling the \f(CW\*(C`utf8\*(C'\fR pragma has the following effect:
.IP "\(bu" 4
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.
.Sp
On \s-1EBCDIC\s0 platforms characters in the Latin 1 character set are
treated as being part of a literal UTF-EBCDIC character.
.PP
Note that if you have bytes with the eighth bit on in your script
(for example embedded Latin\-1 in your string literals), \f(CW\*(C`use utf8\*(C'\fR
will be unhappy since the bytes are most probably not well-formed
UTF-X.  If you want to have such bytes under \f(CW\*(C`use utf8\*(C'\fR, you can disable
this pragma until the end the block (or file, if at top level) by
\&\f(CW\*(C`no utf8;\*(C'\fR.
.Sh "Utility functions"
.IX Subsection "Utility functions"
The following functions are defined in the \f(CW\*(C`utf8::\*(C'\fR package by the
Perl core.  You do not need to say \f(CW\*(C`use utf8\*(C'\fR to use these and in fact
you should not say that  unless you really want to have \s-1UTF\-8\s0 source code.
.IP "\(bu" 4
\&\f(CW$num_octets\fR = utf8::upgrade($string)
.Sp
Converts in-place the internal octet sequence in the native encoding
(Latin\-1 or \s-1EBCDIC\s0) to the equivalent character sequence in \fIUTF-X\fR.
\&\fI\f(CI$string\fI\fR already encoded as characters does no harm.  Returns the
number of octets necessary to represent the string as \fIUTF-X\fR.  Can be
used to make sure that the \s-1UTF\-8\s0 flag is on, so that \f(CW\*(C`\ew\*(C'\fR or \f(CW\*(C`lc()\*(C'\fR
work as Unicode on strings containing characters in the range 0x80\-0xFF
(on \s-1ASCII\s0 and derivatives).
.Sp
\&\fBNote that this function does not handle arbitrary encodings.\fR
Therefore Encode is recommended for the general purposes; see also
Encode.
.IP "\(bu" 4
\&\f(CW$success\fR = utf8::downgrade($string[, \s-1FAIL_OK\s0])
.Sp
Converts in-place the internal octet sequence in \fIUTF-X\fR to the
equivalent octet sequence in the native encoding (Latin\-1 or \s-1EBCDIC\s0).
\&\fI\f(CI$string\fI\fR already encoded as native 8 bit does no harm.  Can be used to
make sure that the \s-1UTF\-8\s0 flag is off, e.g. when you want to make sure
that the \fIsubstr()\fR or \fIlength()\fR function works with the usually faster
byte algorithm.
.Sp
Fails if the original \fIUTF-X\fR sequence cannot be represented in the
native 8 bit encoding. On failure dies or, if the value of \f(CW\*(C`FAIL_OK\*(C'\fR is
true, returns false.
.Sp
Returns true on success.
.Sp
\&\fBNote that this function does not handle arbitrary encodings.\fR
Therefore Encode is recommended for the general purposes; see also
Encode.
.IP "\(bu" 4
utf8::encode($string)
.Sp
Converts in-place the character sequence to the corresponding octet
sequence in \fIUTF-X\fR.  The \s-1UTF8\s0 flag is turned off, so that after this
operation, the string is a byte string.  Returns nothing.
.Sp
\&\fBNote that this function does not handle arbitrary encodings.\fR
Therefore Encode is recommended for the general purposes; see also
Encode.
.IP "\(bu" 4
\&\f(CW$success\fR = utf8::decode($string)
.Sp
Attempts to convert in-place the octet sequence in \fIUTF-X\fR to the
corresponding character sequence.  The \s-1UTF\-8\s0 flag is turned on only if
the source string contains multiple-byte \fIUTF-X\fR characters.  If
\&\fI\f(CI$string\fI\fR is invalid as \fIUTF-X\fR, returns false; otherwise returns
true.
.Sp
\&\fBNote that this function does not handle arbitrary encodings.\fR
Therefore Encode is recommended for the general purposes; see also
Encode.
.IP "\(bu" 4
\&\f(CW$flag\fR = utf8::is_utf8(\s-1STRING\s0)
.Sp
(Since Perl 5.8.1)  Test whether \s-1STRING\s0 is in \s-1UTF\-8\s0 internally.
Functionally the same as \fIEncode::is_utf8()\fR.
.IP "\(bu" 4
\&\f(CW$flag\fR = utf8::valid(\s-1STRING\s0)
.Sp
[\s-1INTERNAL\s0] Test whether \s-1STRING\s0 is in a consistent state regarding
\&\s-1UTF\-8\s0.  Will return true is well-formed \s-1UTF\-8\s0 and has the \s-1UTF\-8\s0 flag
on \fBor\fR 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 \fIutf8::is_utf8()\fR instead.
.PP
\&\f(CW\*(C`utf8::encode\*(C'\fR is like \f(CW\*(C`utf8::upgrade\*(C'\fR, but the \s-1UTF8\s0 flag is
cleared.  See perlunicode for more on the \s-1UTF8\s0 flag and the C \s-1API\s0
functions \f(CW\*(C`sv_utf8_upgrade\*(C'\fR, \f(CW\*(C`sv_utf8_downgrade\*(C'\fR, \f(CW\*(C`sv_utf8_encode\*(C'\fR,
and \f(CW\*(C`sv_utf8_decode\*(C'\fR, which are wrapped by the Perl functions
\&\f(CW\*(C`utf8::upgrade\*(C'\fR, \f(CW\*(C`utf8::downgrade\*(C'\fR, \f(CW\*(C`utf8::encode\*(C'\fR and
\&\f(CW\*(C`utf8::decode\*(C'\fR.  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 \f(CW\*(C`require utf8\*(C'\fR
statement.
.SH "BUGS"
.IX Header "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.
.PP
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.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
perlunitut, perluniintro, perlrun, bytes, perlunicode