A-Za-z defines all the ``letters''. 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 internationalization
(often abbreviated as i18n); telling such an application about a particular set of preferences is
known as localization (l10n).
Perl can understand language-specific data via the standardized (ISO C, XPG4, POSIX 1.c) method called ``the locale system''. The locale system is controlled per application using one pragma, one function call, and several environment variables.
NOTE: This feature is new in Perl 5.004, and does not apply unless an
application specifically requests it - see Backward compatibility. The one exception is that write now always uses the current locale - see NOTES.
setlocale function is a documented part of its
C library.
perl -V:d_setlocale will say that the value for d_setlocale is
define.
use locale pragma (see The use locale pragma) where appropriate, and at least one of the following must be true:
use locale
pragma tells Perl to use the current locale for some operations:
lt, le, cmp, ge, and gt) and the
POSIX string collation functions strcoll
and strxfrm use
LC_COLLATE. sort is also affected if it is used without an explicit
comparison function because it uses cmp by default.
Note: eq and ne are unaffected by the locale: they always perform a byte-by-byte comparison
of their scalar operands. What's more, if cmp finds that its operands are equal according to the collation sequence
specified by the current locale, it goes on to perform a byte-by-byte
comparison, and only returns (equal) if the operands are bit-for-bit identical. If you really want to
know whether two strings - which eq and cmp may consider different - are equal as far as collation in the locale is
concerned, see the discussion in
Category LC_COLLATE: Collation.
lc, ucfirst, and lcfirst) use LC_CTYPE
sprintf and write) use
LC_NUMERIC
The default behavior returns with no locale or on reaching the end of the enclosing block.
Note that the string result of any operation that uses locale information is tainted, as it is possible for a locale to be untrustworthy. See SECURITY.
# 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);
The first argument of setlocale gives the category, the second the
locale. The category tells in what aspect of data processing you want to apply
locale-specific rules. Category names are discussed in
LOCALE CATEGORIES and ENVIRONMENT. 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.
If no second argument is provided, the function returns a string naming the
current locale for the category. You can use this value as the second
argument in a subsequent call to setlocale. If a second
argument is given and it corresponds to a valid locale, the locale for the
category is set to that value, and the function returns the now-current
locale value. You can use this in a subsequent call to
setlocale. (In some implementations, the return value may
sometimes differ from the value you gave as the second argument - think of
it as an alias for the value that you gave.)
As the example shows, if the second argument is an empty string, the category's locale is returned to the default specified by the corresponding environment variables. Generally, this results in a return to the default which was in force when Perl started up: changes to the environment made by the application after start-up may or may not be noticed, depending on the implementation of your system's C library.
If the second argument does not correspond to a valid locale, the locale for the category is not changed, and the function returns undef.
For further information about the categories, consult setlocale(3). For the locales available in your system, also consult setlocale(3) and see whether it leads you to the list of the available locales (search for the SEE ALSO section). If that fails, try the following command lines:
locale -a
nlsinfo
ls /usr/lib/nls/loc
ls /usr/lib/locale
ls /usr/lib/nls
and see whether they list something resembling these
en_US.ISO8859-1 de_DE.ISO8859-1 ru_RU.ISO8859-5
en_US de_DE ru_RU
en de ru
english german russian
english.iso88591 german.iso88591 russian.iso88595
Sadly, even though the calling interface for setlocale has
been standardized, the names of the locales and the directories where the
configuration is, have not. The basic form of the name is
language_country/territory.codeset, but the latter parts are not always present.
Two special locales are worth particular mention: ``C'' and ``POSIX''. Currently these are effectively the same locale: the difference is mainly that the first one is defined by the C standard and the second by the POSIX standard. What they define is the default locale in which every program starts in the absence of locale information in its environment. (The default default locale, if you will.) Its language is (American) English and its character codeset ASCII.
NOTE: Not all systems have the ``POSIX'' locale (not all systems are POSIX-conformant), so use ``C'' when you need explicitly to specify this default locale.
use POSIX qw(locale_h);
# Get a reference to a hash of locale-dependent info
$locale_values = localeconv();
# Output sorted list of the values
for (sort keys %$locale_values) {
printf "%-20s = %s\n", $_, $locale_values->{$_}
}
localeconv takes no arguments, and returns a reference to a hash. The keys of this hash are formatting variable names such as
decimal_point and thousands_sep; the values are the corresponding values. See POSIX (3) for a longer example, which lists all the categories an implementation
might be expected to provide; some provide more and others fewer, however.
Note that you don't need use
locale: as a function with the job of querying the locale,
localeconv always observes the current locale.
Here's a simple-minded example program which rewrites its command line parameters as integers formatted correctly in the current locale:
# See comments in previous example
require 5.004;
use POSIX qw(locale_h);
# Get some of locale's numeric formatting parameters
my ($thousands_sep, $grouping) =
@{localeconv()}{'thousands_sep', 'grouping'};
# Apply defaults if values are missing
$thousands_sep = ',' unless $thousands_sep;
$grouping = 3 unless $grouping;
# Format command line params for current locale
for (@ARGV) {
$_ = int; # Chop non-integer part
1 while
s/(\d)(\d{$grouping}($|$thousands_sep))/$1$thousands_sep$2/;
print "$_";
}
print "\n";
use locale, Perl looks to the LC_COLLATE
environment variable to determine the application's notions on the
collation (ordering) of characters. ('b' follows 'a' in Latin alphabets,
but where do 'á' and 'å' belong?)
Here is a code snippet that will tell you what are the alphanumeric characters in the current locale, in the locale order:
use locale;
print +(sort grep /\w/, map { chr() } 0..255), "\n";
Compare this with the characters that you see and their order if you state explicitly that the locale should be ignored:
no locale;
print +(sort grep /\w/, map { chr() } 0..255), "\n";
This machine-native collation (which is what you get unless use
locale has appeared earlier in the same block) must be used for sorting raw binary
data, whereas the locale-dependent collation of the first example is useful
for natural text.
As noted in USING LOCALES, cmp compares according to the current collation locale when use locale is in effect, but falls back to a byte-by-byte comparison for strings which
the locale says are equal. You can use POSIX::strcoll() if you don't want
this fall-back:
use POSIX qw(strcoll);
$equal_in_locale =
!strcoll("space and case ignored", "SpaceAndCaseIgnored");
$equal_in_locale will be true if the collation locale
specifies a dictionary-like ordering which ignores space characters
completely, and which folds case.
If you have a single string which you want to check for ``equality in
locale'' against several others, you might think you could gain a little
efficiency by using POSIX::strxfrm() in conjunction with eq:
use POSIX qw(strxfrm);
$xfrm_string = strxfrm("Mixed-case string");
print "locale collation ignores spaces\n"
if $xfrm_string eq strxfrm("Mixed-casestring");
print "locale collation ignores hyphens\n"
if $xfrm_string eq strxfrm("Mixedcase string");
print "locale collation ignores case\n"
if $xfrm_string eq strxfrm("mixed-case string");
strxfrm takes a string and maps it into a transformed string
for use in byte-by-byte comparisons against other transformed strings
during collation. ``Under the hood'', locale-affected Perl comparison
operators call strxfrm for both their operands, then do a
byte-by-byte comparison of the transformed strings. By calling
strxfrm explicitly, and using a non locale-affected
comparison, the example attempts to save a couple of transformations. In
fact, it doesn't save anything: Perl magic (see Magic Variables) creates the transformed version of a string the first time it's needed in
a comparison, then keeps it around in case it's needed again. An example
rewritten the easy way with
cmp runs just about as fast. It also copes with null characters embedded in
strings; if you call strxfrm directly, it treats the first
null it finds as a terminator. And don't expect the transformed strings it
produces to be portable across systems - or even from one revision of your
operating system to the next. In short, don't call strxfrm
directly: let Perl do it for you.
Note: use locale isn't shown in some of these examples, as it isn't needed:
strcoll and strxfrm exist only to generate
locale-dependent results, and so always obey the current LC_COLLATE locale.
use locale, Perl obeys the LC_CTYPE locale setting. This controls the application's notion of which characters
are alphabetic. This affects Perl's \w regular expression metanotation, which stands for alphanumeric characters -
that is, alphabetic and numeric characters. (Consult the perlre manpage for more information about regular expressions.) Thanks to LC_CTYPE, depending on your locale setting, characters like 'æ', 'ð', 'ß', and 'ø' may be understood as \w characters.
The LC_CTYPE locale also provides the map used in translating characters between lower-
and upper-case. This affects the case-mapping functions - lc,
lcfirst, uc and ucfirst; case-mapping
interpolation with \l, \L, \u or <
\U> in double-quoted strings and in s/// substitutions; and case-independent regular expression pattern matching
using the i modifier.
Finally, LC_CTYPE affects the
POSIX character-class test functions - isalpha, islower and so on. For example, if you move from the
``C'' locale to a 7-bit Scandinavian one, you may find - possibly to your surprise - that ``|'' moves from the ispunct class to isalpha.
Note:
A broken or malicious LC_CTYPE locale definition may result in clearly ineligible characters being
considered to be alphanumeric by your application. For strict matching of
(unaccented) letters and digits - for example, in command strings -
locale-aware applications should use \w inside a no locale block. See SECURITY.
use locale, Perl obeys the LC_NUMERIC
locale information, which controls application's idea of how numbers should
be formatted for human readability by the printf,
sprintf, and write functions. String to numeric
conversion by the POSIX::strtod() function is also affected. In most
implementations the only effect is to change the character used for the
decimal point - perhaps from '.' to ',': these functions aren't aware of
such niceties as thousands separation and so on. (See The localeconv function if you care about these things.)
Note that output produced by print is never affected by the current locale: it is independent of whether use locale or no
locale is in effect, and corresponds to what you'd get from printf in the
``C'' locale. The same is true for Perl's internal conversions between numeric and string formats:
use POSIX qw(strtod);
use locale;
$n = 5/2; # Assign numeric 2.5 to $n
$a = " $n"; # Locale-independent conversion to string
print "half five is $n\n"; # Locale-independent output
printf "half five is %g\n", $n; # Locale-dependent output
print "DECIMAL POINT IS COMMA\n"
if $n == (strtod("2,5"))[0]; # Locale-dependent conversion
%B
format element (full month name) for the first month of the year would be
``janvier''. Here's how to get a list of the long month names in the
current locale:
use POSIX qw(strftime);
for (0..11) {
$long_month_name[$_] =
strftime("%B", 0, 0, 0, 1, $_, 96);
}
Note: use locale isn't needed in this example: as a function which exists only to generate
locale-dependent results, strftime always obeys the current LC_TIME locale.
LC_MESSAGES (possibly supplemented by others in particular implementations) is not
currently used by Perl - except possibly to affect the behavior of library
functions called by extensions which are not part of the standard Perl
distribution.
\w may be spoofed by an LC_CTYPE locale which claims that characters such as ``>'' and ``|'' are alphanumeric.
$dest =
"C:\U$name.$ext", may produce dangerous results if a bogus
LC_CTYPE case-mapping table is in effect.
strftime could be
manipulated to advantage by a malicious user able to subvert the
LC_DATE locale. (``Look - it says
I wasn't in the building on Sunday.'')
Perl cannot protect you from all of the possibilities shown in the examples
- there is no substitute for your own vigilance - but, when
use locale is in effect, Perl uses the tainting mechanism (see
the perlsec manpage) to mark string results which become locale-dependent, and which may be
untrustworthy in consequence. Here is a summary of the tainting behavior of
operators and functions which may be affected by the locale:
use locale is in effect.
Subpatterns, either delivered as an array-context result, or as
$1 etc. are tainted if use locale is in effect, and the subpattern regular expression contains \w (to match an alphanumeric character), \W
(non-alphanumeric character), \s (white-space character), or \S
(non white-space character). The matched pattern variable, $&, $`
(pre-match), $' (post-match), and $+ (last match) are also tainted if
use locale is in effect and the regular expression contains \w,
\W, \s, or \S.
=~ becomes tainted when use locale in effect, if it is modified as a result of a substitution based on a
regular expression match involving \w, \W, \s, or \S; or of case-mapping with \l, \L,\u or
<\U>.
use locale is in effect.
#/usr/local/bin/perl -T
# Run with taint checking
# Command-line sanity check omitted...
$tainted_output_file = shift;
open(F, ">$tainted_output_file")
or warn "Open of $untainted_output_file failed: $!\n";
The program can be made to run by ``laundering'' the tainted value through a regular expression: the second example - which still ignores locale information - runs, creating the file named on its command-line if it can.
#/usr/local/bin/perl -T
$tainted_output_file = shift;
$tainted_output_file =~ m%[\w/]+%;
$untainted_output_file = $&;
open(F, ">$untainted_output_file")
or warn "Open of $untainted_output_file failed: $!\n";
Compare this with a very similar program which is locale-aware:
#/usr/local/bin/perl -T
$tainted_output_file = shift;
use locale;
$tainted_output_file =~ m%[\w/]+%;
$localized_output_file = $&;
open(F, ">$localized_output_file")
or warn "Open of $localized_output_file failed: $!\n";
This third program fails to run because $& is tainted: it is the result
of a match involving \w when use locale is in effect.
NOTE: PERL_BADLANG only gives you a way to hide the warning message. The message tells about some problem in your system's locale support, and you should investigate what the problem is.
setlocale method for controlling an application's opinion on data.
LC_....
"C" locale (see
The setlocale function) was always in force, even if the program environment suggested otherwise.
By default, Perl still behaves this way so as to maintain backward
compatibility. If you want a Perl application to pay attention to locale
information, you must use the use locale pragma (see The use locale Pragma) to instruct it to do so.
Versions of Perl from 5.002 to 5.003 did use the LC_CTYPE
information if that was available, that is, \w did understand what are the letters according to the locale environment variables. The problem was that the user had no control over the feature: if the
C library supported locales, Perl used them.
I18N::Collate library module. This module is now mildly obsolete and should be avoided in
new applications. The LC_COLLATE
functionality is now integrated into the Perl core language: One can use
locale-specific scalar data completely normally with use locale, so there is no longer any need to juggle with the scalar references of
I18N::Collate.
use locale because the pragma is tied to the block structure of the program, and, for
historical reasons, formats exist outside that block structure.
ftp://dkuug.dk/i18n/WG15-collection. You should be aware that it is unsupported, and is not claimed to be fit
for any purpose. If your system allows the installation of arbitrary
locales, you may find the definitions useful as they are, or as a basis for
the development of your own locales.
use locale is in effect. When confronted with such a system, please report in
excruciating detail to <perlbug@perl.com>, and complain to your vendor: maybe some bug fixes exist for these
problems in your operating system. Sometimes such bug fixes are called an
operating system upgrade.
Last update: Wed Jan 22 11:04:58 EST 1997