perllocale.1

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.\" ========================================================================
.\"
.IX Title "PERLLOCALE 1"
.TH PERLLOCALE 1 "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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.nh
.SH "NAME"
perllocale \- Perl locale handling (internationalization and localization)
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Perl supports language-specific notions of data such as \*(L"is this
a letter\*(R", \*(L"what is the uppercase equivalent of this letter\*(R", and
\&\*(L"which of these letters comes first\*(R".  These are important issues,
especially for languages other than English\*(--but also for English: it
would be nai\*:ve to imagine that \f(CW\*(C`A\-Za\-z\*(C'\fR defines all the \*(L"letters\*(R"
needed to write in English. Perl is also aware that some character other
than '.' may be preferred as a decimal point, and that output date
representations may be language-specific.  The process of making an
application take account of its users' preferences in such matters is
called \fBinternationalization\fR (often abbreviated as \fBi18n\fR); telling
such an application about a particular set of preferences is known as
\&\fBlocalization\fR (\fBl10n\fR).
.PP
Perl can understand language-specific data via the standardized (\s-1ISO\s0 C,
\&\s-1XPG4\s0, \s-1POSIX\s0 1.c) method called \*(L"the locale system\*(R". The locale system is
controlled per application using one pragma, one function call, and
several environment variables.
.PP
\&\fB\s-1NOTE\s0\fR: This feature is new in Perl 5.004, and does not apply unless an
application specifically requests it\*(--see \*(L"Backward compatibility\*(R".
The one exception is that \fIwrite()\fR now \fBalways\fR uses the current locale
\&\- see \*(L"\s-1NOTES\s0\*(R".
.SH "PREPARING TO USE LOCALES"
.IX Header "PREPARING TO USE LOCALES"
If Perl applications are to understand and present your data
correctly according a locale of your choice, \fBall\fR of the following
must be true:
.IP "\(bu" 4
\&\fBYour operating system must support the locale system\fR.  If it does,
you should find that the \fIsetlocale()\fR function is a documented part of
its C library.
.IP "\(bu" 4
\&\fBDefinitions for locales that you use must be installed\fR.  You, or
your system administrator, must make sure that this is the case. The
available locales, the location in which they are kept, and the manner
in which they are installed all vary from system to system.  Some systems
provide only a few, hard-wired locales and do not allow more to be
added.  Others allow you to add \*(L"canned\*(R" locales provided by the system
supplier.  Still others allow you or the system administrator to define
and add arbitrary locales.  (You may have to ask your supplier to
provide canned locales that are not delivered with your operating
system.)  Read your system documentation for further illumination.
.IP "\(bu" 4
\&\fBPerl must believe that the locale system is supported\fR.  If it does,
\&\f(CW\*(C`perl \-V:d_setlocale\*(C'\fR will say that the value for \f(CW\*(C`d_setlocale\*(C'\fR is
\&\f(CW\*(C`define\*(C'\fR.
.PP
If you want a Perl application to process and present your data
according to a particular locale, the application code should include
the \f(CW\*(C`use\ locale\*(C'\fR pragma (see \*(L"The use locale pragma\*(R") where
appropriate, and \fBat least one\fR of the following must be true:
.IP "\(bu" 4
\&\fBThe locale-determining environment variables (see \*(L"\s-1ENVIRONMENT\s0\*(R")
must be correctly set up\fR at the time the application is started, either
by yourself or by whoever set up your system account.
.IP "\(bu" 4
\&\fBThe application must set its own locale\fR using the method described in
\&\*(L"The setlocale function\*(R".
.SH "USING LOCALES"
.IX Header "USING LOCALES"
.Sh "The use locale pragma"
.IX Subsection "The use locale pragma"
By default, Perl ignores the current locale.  The \f(CW\*(C`use\ locale\*(C'\fR
pragma tells Perl to use the current locale for some operations:
.IP "\(bu" 4
\&\fBThe comparison operators\fR (\f(CW\*(C`lt\*(C'\fR, \f(CW\*(C`le\*(C'\fR, \f(CW\*(C`cmp\*(C'\fR, \f(CW\*(C`ge\*(C'\fR, and \f(CW\*(C`gt\*(C'\fR) and
the \s-1POSIX\s0 string collation functions \fIstrcoll()\fR and \fIstrxfrm()\fR use
\&\f(CW\*(C`LC_COLLATE\*(C'\fR.  \fIsort()\fR is also affected if used without an
explicit comparison function, because it uses \f(CW\*(C`cmp\*(C'\fR by default.
.Sp
\&\fBNote:\fR \f(CW\*(C`eq\*(C'\fR and \f(CW\*(C`ne\*(C'\fR are unaffected by locale: they always
perform a char-by-char comparison of their scalar operands.  What's
more, if \f(CW\*(C`cmp\*(C'\fR finds that its operands are equal according to the
collation sequence specified by the current locale, it goes on to
perform a char-by-char comparison, and only returns \fI0\fR (equal) if the
operands are char-for-char identical.  If you really want to know whether
two strings\*(--which \f(CW\*(C`eq\*(C'\fR and \f(CW\*(C`cmp\*(C'\fR may consider different\*(--are equal
as far as collation in the locale is concerned, see the discussion in
\&\*(L"Category \s-1LC_COLLATE:\s0 Collation\*(R".
.IP "\(bu" 4
\&\fBRegular expressions and case-modification functions\fR (\fIuc()\fR, \fIlc()\fR,
\&\fIucfirst()\fR, and \fIlcfirst()\fR) use \f(CW\*(C`LC_CTYPE\*(C'\fR
.IP "\(bu" 4
\&\fBThe formatting functions\fR (\fIprintf()\fR, \fIsprintf()\fR and \fIwrite()\fR) use
\&\f(CW\*(C`LC_NUMERIC\*(C'\fR
.IP "\(bu" 4
\&\fBThe \s-1POSIX\s0 date formatting function\fR (\fIstrftime()\fR) uses \f(CW\*(C`LC_TIME\*(C'\fR.
.PP
\&\f(CW\*(C`LC_COLLATE\*(C'\fR, \f(CW\*(C`LC_CTYPE\*(C'\fR, and so on, are discussed further in 
\&\*(L"\s-1LOCALE\s0 \s-1CATEGORIES\s0\*(R".
.PP
The default behavior is restored with the \f(CW\*(C`no\ locale\*(C'\fR pragma, or
upon reaching the end of block enclosing \f(CW\*(C`use locale\*(C'\fR.
.PP
The string result of any operation that uses locale
information is tainted, as it is possible for a locale to be
untrustworthy.  See \*(L"\s-1SECURITY\s0\*(R".
.Sh "The setlocale function"
.IX Subsection "The setlocale function"
You can switch locales as often as you wish at run time with the
\&\fIPOSIX::setlocale()\fR function:
.PP
.Vb 2
\&        # This functionality not usable prior to Perl 5.004
\&        require 5.004;
\&
\&        # Import locale\-handling tool set from POSIX module.
\&        # This example uses: setlocale \-\- the function call
\&        #                    LC_CTYPE \-\- explained below
\&        use POSIX qw(locale_h);
\&
\&        # query and save the old locale
\&        $old_locale = setlocale(LC_CTYPE);
\&
\&        setlocale(LC_CTYPE, "fr_CA.ISO8859\-1");
\&        # LC_CTYPE now in locale "French, Canada, codeset ISO 8859\-1"
\&
\&        setlocale(LC_CTYPE, "");
\&        # LC_CTYPE now reset to default defined by LC_ALL/LC_CTYPE/LANG
\&        # environment variables.  See below for documentation.
\&
\&        # restore the old locale
\&        setlocale(LC_CTYPE, $old_locale);
.Ve
.PP
The first argument of \fIsetlocale()\fR gives the \fBcategory\fR, the second the
\&\fBlocale\fR.  The category tells in what aspect of data processing you
want to apply locale-specific rules.  Category names are discussed in
\&\*(L"\s-1LOCALE\s0 \s-1CATEGORIES\s0\*(R" and \*(L"\s-1ENVIRONMENT\s0\*(R".  The locale is the name of a
collection of customization information corresponding to a particular
combination of language, country or territory, and codeset.  Read on for
hints on the naming of locales: not all systems name locales as in the
example.
.PP
If no second argument is provided and the category is something else
than \s-1LC_ALL\s0, the function returns a string naming the current locale