5 perllocale - Perl locale handling (internationalization and localization)
9 In the beginning there was ASCII, the "American Standard Code for
10 Information Interchange", which works quite well for Americans with
11 their English alphabet and dollar-denominated currency. But it doesn't
12 work so well even for other English speakers, who may use different
13 currencies, such as the pound sterling (as the symbol for that currency
14 is not in ASCII); and it's hopelessly inadequate for many of the
15 thousands of the world's other languages.
17 To address these deficiencies, the concept of locales was invented
18 (formally the ISO C, XPG4, POSIX 1.c "locale system"). And applications
19 were and are being written that use the locale mechanism. The process of
20 making such an application take account of its users' preferences in
21 these kinds of matters is called B<internationalization> (often
22 abbreviated as B<i18n>); telling such an application about a particular
23 set of preferences is known as B<localization> (B<l10n>).
25 Perl has been extended to support the locale system. This
26 is controlled per application by using one pragma, one function call,
27 and several environment variables.
29 Unfortunately, there are quite a few deficiencies with the design (and
30 often, the implementations) of locales. Unicode was invented (see
31 L<perlunitut> for an introduction to that) in part to address these
32 design deficiencies, and nowadays, there is a series of "UTF-8
33 locales", based on Unicode. These are locales whose character set is
34 Unicode, encoded in UTF-8. Starting in v5.20, Perl fully supports
35 UTF-8 locales, except for sorting and string comparisions. (Use
36 L<Unicode::Collate> for these.) Perl continues to support the old
37 non UTF-8 locales as well.
39 (Unicode is also creating C<CLDR>, the "Common Locale Data Repository",
40 L<http://cldr.unicode.org/> which includes more types of information than
41 are available in the POSIX locale system. At the time of this writing,
42 there was no CPAN module that provides access to this XML-encoded data.
43 However, many of its locales have the POSIX-only data extracted, and are
44 available as UTF-8 locales at
45 L<http://unicode.org/Public/cldr/latest/>.)
47 =head1 WHAT IS A LOCALE
49 A locale is a set of data that describes various aspects of how various
50 communities in the world categorize their world. These categories are
51 broken down into the following types (some of which include a brief
56 =item Category LC_NUMERIC: Numeric formatting
58 This indicates how numbers should be formatted for human readability,
59 for example the character used as the decimal point.
61 =item Category LC_MONETARY: Formatting of monetary amounts
64 The nbsp below makes this look better (though not great)
68 =item Category LC_TIME: Date/Time formatting
71 The nbsp below makes this look better (though not great)
75 =item Category LC_MESSAGES: Error and other messages
77 This is used by Perl itself only for accessing operating system error
78 messages via L<$!|perlvar/$ERRNO> and L<$^E|perlvar/$EXTENDED_OS_ERROR>.
80 =item Category LC_COLLATE: Collation
82 This indicates the ordering of letters for comparison and sorting.
83 In Latin alphabets, for example, "b", generally follows "a".
85 =item Category LC_CTYPE: Character Types
87 This indicates, for example if a character is an uppercase letter.
89 =item Other categories
91 Some platforms have other categories, dealing with such things as
92 measurement units and paper sizes. None of these are used directly by
93 Perl, but outside operations that Perl interacts with may use
94 these. See L</Not within the scope of any "use locale" variant> below.
98 More details on the categories used by Perl are given below in L</LOCALE
101 Together, these categories go a long way towards being able to customize
102 a single program to run in many different locations. But there are
103 deficiencies, so keep reading.
105 =head1 PREPARING TO USE LOCALES
107 Perl itself will not use locales unless specifically requested to (but
108 again note that Perl may interact with code that does use them). Even
109 if there is such a request, B<all> of the following must be true
110 for it to work properly:
116 B<Your operating system must support the locale system>. If it does,
117 you should find that the C<setlocale()> function is a documented part of
122 B<Definitions for locales that you use must be installed>. You, or
123 your system administrator, must make sure that this is the case. The
124 available locales, the location in which they are kept, and the manner
125 in which they are installed all vary from system to system. Some systems
126 provide only a few, hard-wired locales and do not allow more to be
127 added. Others allow you to add "canned" locales provided by the system
128 supplier. Still others allow you or the system administrator to define
129 and add arbitrary locales. (You may have to ask your supplier to
130 provide canned locales that are not delivered with your operating
131 system.) Read your system documentation for further illumination.
135 B<Perl must believe that the locale system is supported>. If it does,
136 C<perl -V:d_setlocale> will say that the value for C<d_setlocale> is
141 If you want a Perl application to process and present your data
142 according to a particular locale, the application code should include
143 the S<C<use locale>> pragma (see L<The use locale pragma>) where
144 appropriate, and B<at least one> of the following must be true:
150 B<The locale-determining environment variables (see L</"ENVIRONMENT">)
151 must be correctly set up> at the time the application is started, either
152 by yourself or by whomever set up your system account; or
156 B<The application must set its own locale> using the method described in
157 L<The setlocale function>.
163 =head2 The use locale pragma
165 By default, Perl itself ignores the current locale. The S<C<use locale>>
166 pragma tells Perl to use the current locale for some operations.
167 Starting in v5.16, there is an optional parameter to this pragma:
169 use locale ':not_characters';
171 This parameter allows better mixing of locales and Unicode (less useful
172 in v5.20 and later), and is
173 described fully in L</Unicode and UTF-8>, but briefly, it tells Perl to
174 not use the character portions of the locale definition, that is
175 the C<LC_CTYPE> and C<LC_COLLATE> categories. Instead it will use the
176 native character set (extended by Unicode). When using this parameter,
177 you are responsible for getting the external character set translated
178 into the native/Unicode one (which it already will be if it is one of
179 the increasingly popular UTF-8 locales). There are convenient ways of
180 doing this, as described in L</Unicode and UTF-8>.
182 The current locale is set at execution time by
183 L<setlocale()|/The setlocale function> described below. If that function
184 hasn't yet been called in the course of the program's execution, the
185 current locale is that which was determined by the L</"ENVIRONMENT"> in
186 effect at the start of the program.
187 If there is no valid environment, the current locale is whatever the
188 system default has been set to. On POSIX systems, it is likely, but
189 not necessarily, the "C" locale. On Windows, the default is set via the
190 computer's S<C<Control Panel-E<gt>Regional and Language Options>> (or its
193 The operations that are affected by locale are:
197 =item B<Not within the scope of any C<"use locale"> variant>
199 Only operations originating outside Perl should be affected, as follows:
205 The variables L<$!|perlvar/$ERRNO> (and its synonyms C<$ERRNO> and
206 C<$OS_ERROR>) and L<$^E|perlvar/$EXTENDED_OS_ERROR> (and its synonym
207 C<$EXTENDED_OS_ERROR>) when used as strings always are in terms of the
208 current locale and as if within the scope of L<"use bytes"|bytes>. This is
209 likely to change in Perl v5.22.
213 The current locale is also used when going outside of Perl with
214 operations like L<system()|perlfunc/system LIST> or
215 L<qxE<sol>E<sol>|perlop/qxE<sol>STRINGE<sol>>, if those operations are
220 Also Perl gives access to various C library functions through the
221 L<POSIX> module. Some of those functions are always affected by the
222 current locale. For example, C<POSIX::strftime()> uses C<LC_TIME>;
223 C<POSIX::strtod()> uses C<LC_NUMERIC>; C<POSIX::strcoll()> and
224 C<POSIX::strxfrm()> use C<LC_COLLATE>; and character classification
225 functions like C<POSIX::isalnum()> use C<LC_CTYPE>. All such functions
226 will behave according to the current underlying locale, even if that
227 locale isn't exposed to Perl space.
231 XS modules for all categories but C<LC_NUMERIC> get the underlying
232 locale, and hence any C library functions they call will use that
233 underlying locale. Perl always initializes C<LC_NUMERIC> to C<"C">
234 because too many modules are unable to cope with the decimal point in a
235 floating point number not being a dot (it's a comma in many locales).
236 But note that these modules are vulnerable because C<LC_NUMERIC>
237 currently can be changed at any time by a call to the C C<set_locale()>
238 by XS code or by something XS code calls, or by C<POSIX::setlocale()> by
239 Perl code. This is true also for the Perl-provided lite wrappers for XS
240 modules to use some C library C<printf> functions:
242 L<my_sprintf|perlapi/my_sprintf>,
243 L<my_snprintf|perlapi/my_snprintf>,
245 L<my_vsnprintf|perlapi/my_vsnprintf>.
250 The nbsp below makes this look better (though not great)
254 =item B<Lingering effects of C<S<use locale>>>
256 Certain Perl operations that are set-up within the scope of a
257 C<use locale> variant retain that effect even outside the scope.
264 The output format of a L<write()|perlfunc/write> is determined by an
265 earlier format declaration (L<perlfunc/format>), so whether or not the
266 output is affected by locale is determined by if the C<format()> is
267 within the scope of a C<use locale> variant, not whether the C<write()>
272 Regular expression patterns can be compiled using
273 L<qrE<sol>E<sol>|perlop/qrE<sol>STRINGE<sol>msixpodual> with actual
274 matching deferred to later. Again, it is whether or not the compilation
275 was done within the scope of C<use locale> that determines the match
276 behavior, not if the matches are done within such a scope or not.
281 The nbsp below makes this look better (though not great)
285 =item B<Under C<"use locale ':not_characters';">>
291 All the non-Perl operations.
295 B<Format declarations> (L<perlfunc/format>) and hence any subsequent
296 C<write()>s use C<LC_NUMERIC>.
300 B<stringification and output> use C<LC_NUMERIC>.
301 These include the results of
311 The nbsp below makes this look better (though not great)
315 =item B<Under just plain C<"use locale";>>
321 All the above operations
325 B<The comparison operators> (C<lt>, C<le>, C<cmp>, C<ge>, and C<gt>) use
326 C<LC_COLLATE>. C<sort()> is also affected if used without an
327 explicit comparison function, because it uses C<cmp> by default.
329 B<Note:> C<eq> and C<ne> are unaffected by locale: they always
330 perform a char-by-char comparison of their scalar operands. What's
331 more, if C<cmp> finds that its operands are equal according to the
332 collation sequence specified by the current locale, it goes on to
333 perform a char-by-char comparison, and only returns I<0> (equal) if the
334 operands are char-for-char identical. If you really want to know whether
335 two strings--which C<eq> and C<cmp> may consider different--are equal
336 as far as collation in the locale is concerned, see the discussion in
337 L<Category LC_COLLATE: Collation>.
341 B<Regular expressions and case-modification functions> (C<uc()>, C<lc()>,
342 C<ucfirst()>, and C<lcfirst()>) use C<LC_CTYPE>
348 The default behavior is restored with the S<C<no locale>> pragma, or
349 upon reaching the end of the block enclosing C<use locale>.
350 Note that C<use locale> and C<use locale ':not_characters'> may be
351 nested, and that what is in effect within an inner scope will revert to
352 the outer scope's rules at the end of the inner scope.
354 The string result of any operation that uses locale
355 information is tainted, as it is possible for a locale to be
356 untrustworthy. See L<"SECURITY">.
358 =head2 The setlocale function
360 You can switch locales as often as you wish at run time with the
361 C<POSIX::setlocale()> function:
363 # Import locale-handling tool set from POSIX module.
364 # This example uses: setlocale -- the function call
365 # LC_CTYPE -- explained below
366 # (Showing the testing for success/failure of operations is
367 # omitted in these examples to avoid distracting from the main
370 use POSIX qw(locale_h);
374 # query and save the old locale
375 $old_locale = setlocale(LC_CTYPE);
377 setlocale(LC_CTYPE, "fr_CA.ISO8859-1");
378 # LC_CTYPE now in locale "French, Canada, codeset ISO 8859-1"
380 setlocale(LC_CTYPE, "");
381 # LC_CTYPE now reset to the default defined by the
382 # LC_ALL/LC_CTYPE/LANG environment variables, or to the system
383 # default. See below for documentation.
385 # restore the old locale
386 setlocale(LC_CTYPE, $old_locale);
388 The first argument of C<setlocale()> gives the B<category>, the second the
389 B<locale>. The category tells in what aspect of data processing you
390 want to apply locale-specific rules. Category names are discussed in
391 L</LOCALE CATEGORIES> and L</"ENVIRONMENT">. The locale is the name of a
392 collection of customization information corresponding to a particular
393 combination of language, country or territory, and codeset. Read on for
394 hints on the naming of locales: not all systems name locales as in the
397 If no second argument is provided and the category is something other
398 than LC_ALL, the function returns a string naming the current locale
399 for the category. You can use this value as the second argument in a
400 subsequent call to C<setlocale()>, B<but> on some platforms the string
401 is opaque, not something that most people would be able to decipher as
402 to what locale it means.
404 If no second argument is provided and the category is LC_ALL, the
405 result is implementation-dependent. It may be a string of
406 concatenated locale names (separator also implementation-dependent)
407 or a single locale name. Please consult your L<setlocale(3)> man page for
410 If a second argument is given and it corresponds to a valid locale,
411 the locale for the category is set to that value, and the function
412 returns the now-current locale value. You can then use this in yet
413 another call to C<setlocale()>. (In some implementations, the return
414 value may sometimes differ from the value you gave as the second
415 argument--think of it as an alias for the value you gave.)
417 As the example shows, if the second argument is an empty string, the
418 category's locale is returned to the default specified by the
419 corresponding environment variables. Generally, this results in a
420 return to the default that was in force when Perl started up: changes
421 to the environment made by the application after startup may or may not
422 be noticed, depending on your system's C library.
424 Note that Perl ignores the current C<LC_CTYPE> and C<LC_COLLATE> locales
425 within the scope of a C<use locale ':not_characters'>.
427 If C<set_locale()> fails for some reason (for example, an attempt to set
428 to a locale unknown to the system), the locale for the category is not
429 changed, and the function returns C<undef>.
432 For further information about the categories, consult L<setlocale(3)>.
434 =head2 Finding locales
436 For locales available in your system, consult also L<setlocale(3)> to
437 see whether it leads to the list of available locales (search for the
438 I<SEE ALSO> section). If that fails, try the following command lines:
452 and see whether they list something resembling these
454 en_US.ISO8859-1 de_DE.ISO8859-1 ru_RU.ISO8859-5
455 en_US.iso88591 de_DE.iso88591 ru_RU.iso88595
458 english german russian
459 english.iso88591 german.iso88591 russian.iso88595
460 english.roman8 russian.koi8r
462 Sadly, even though the calling interface for C<setlocale()> has been
463 standardized, names of locales and the directories where the
464 configuration resides have not been. The basic form of the name is
465 I<language_territory>B<.>I<codeset>, but the latter parts after
466 I<language> are not always present. The I<language> and I<country>
467 are usually from the standards B<ISO 3166> and B<ISO 639>, the
468 two-letter abbreviations for the countries and the languages of the
469 world, respectively. The I<codeset> part often mentions some B<ISO
470 8859> character set, the Latin codesets. For example, C<ISO 8859-1>
471 is the so-called "Western European codeset" that can be used to encode
472 most Western European languages adequately. Again, there are several
473 ways to write even the name of that one standard. Lamentably.
475 Two special locales are worth particular mention: "C" and "POSIX".
476 Currently these are effectively the same locale: the difference is
477 mainly that the first one is defined by the C standard, the second by
478 the POSIX standard. They define the B<default locale> in which
479 every program starts in the absence of locale information in its
480 environment. (The I<default> default locale, if you will.) Its language
481 is (American) English and its character codeset ASCII or, rarely, a
482 superset thereof (such as the "DEC Multinational Character Set
483 (DEC-MCS)"). B<Warning>. The C locale delivered by some vendors
484 may not actually exactly match what the C standard calls for. So
487 B<NOTE>: Not all systems have the "POSIX" locale (not all systems are
488 POSIX-conformant), so use "C" when you need explicitly to specify this
491 =head2 LOCALE PROBLEMS
493 You may encounter the following warning message at Perl startup:
495 perl: warning: Setting locale failed.
496 perl: warning: Please check that your locale settings:
499 are supported and installed on your system.
500 perl: warning: Falling back to the standard locale ("C").
502 This means that your locale settings had LC_ALL set to "En_US" and
503 LANG exists but has no value. Perl tried to believe you but could not.
504 Instead, Perl gave up and fell back to the "C" locale, the default locale
505 that is supposed to work no matter what. (On Windows, it first tries
506 falling back to the system default locale.) This usually means your
507 locale settings were wrong, they mention locales your system has never
508 heard of, or the locale installation in your system has problems (for
509 example, some system files are broken or missing). There are quick and
510 temporary fixes to these problems, as well as more thorough and lasting
513 =head2 Testing for broken locales
515 If you are building Perl from source, the Perl test suite file
516 F<lib/locale.t> can be used to test the locales on your system.
517 Setting the environment variable C<PERL_DEBUG_FULL_TEST> to 1
518 will cause it to output detailed results. For example, on Linux, you
521 PERL_DEBUG_FULL_TEST=1 ./perl -T -Ilib lib/locale.t > locale.log 2>&1
523 Besides many other tests, it will test every locale it finds on your
524 system to see if they conform to the POSIX standard. If any have
525 errors, it will include a summary near the end of the output of which
526 locales passed all its tests, and which failed, and why.
528 =head2 Temporarily fixing locale problems
530 The two quickest fixes are either to render Perl silent about any
531 locale inconsistencies or to run Perl under the default locale "C".
533 Perl's moaning about locale problems can be silenced by setting the
534 environment variable PERL_BADLANG to a zero value, for example "0".
535 This method really just sweeps the problem under the carpet: you tell
536 Perl to shut up even when Perl sees that something is wrong. Do not
537 be surprised if later something locale-dependent misbehaves.
539 Perl can be run under the "C" locale by setting the environment
540 variable LC_ALL to "C". This method is perhaps a bit more civilized
541 than the PERL_BADLANG approach, but setting LC_ALL (or
542 other locale variables) may affect other programs as well, not just
543 Perl. In particular, external programs run from within Perl will see
544 these changes. If you make the new settings permanent (read on), all
545 programs you run see the changes. See L<"ENVIRONMENT"> for
546 the full list of relevant environment variables and L<USING LOCALES>
547 for their effects in Perl. Effects in other programs are
548 easily deducible. For example, the variable LC_COLLATE may well affect
549 your B<sort> program (or whatever the program that arranges "records"
550 alphabetically in your system is called).
552 You can test out changing these variables temporarily, and if the
553 new settings seem to help, put those settings into your shell startup
554 files. Consult your local documentation for the exact details. For in
555 Bourne-like shells (B<sh>, B<ksh>, B<bash>, B<zsh>):
557 LC_ALL=en_US.ISO8859-1
560 This assumes that we saw the locale "en_US.ISO8859-1" using the commands
561 discussed above. We decided to try that instead of the above faulty
562 locale "En_US"--and in Cshish shells (B<csh>, B<tcsh>)
564 setenv LC_ALL en_US.ISO8859-1
566 or if you have the "env" application you can do in any shell
568 env LC_ALL=en_US.ISO8859-1 perl ...
570 If you do not know what shell you have, consult your local
571 helpdesk or the equivalent.
573 =head2 Permanently fixing locale problems
575 The slower but superior fixes are when you may be able to yourself
576 fix the misconfiguration of your own environment variables. The
577 mis(sing)configuration of the whole system's locales usually requires
578 the help of your friendly system administrator.
580 First, see earlier in this document about L<Finding locales>. That tells
581 how to find which locales are really supported--and more importantly,
582 installed--on your system. In our example error message, environment
583 variables affecting the locale are listed in the order of decreasing
584 importance (and unset variables do not matter). Therefore, having
585 LC_ALL set to "En_US" must have been the bad choice, as shown by the
586 error message. First try fixing locale settings listed first.
588 Second, if using the listed commands you see something B<exactly>
589 (prefix matches do not count and case usually counts) like "En_US"
590 without the quotes, then you should be okay because you are using a
591 locale name that should be installed and available in your system.
592 In this case, see L<Permanently fixing your system's locale configuration>.
594 =head2 Permanently fixing your system's locale configuration
596 This is when you see something like:
598 perl: warning: Please check that your locale settings:
601 are supported and installed on your system.
603 but then cannot see that "En_US" listed by the above-mentioned
604 commands. You may see things like "en_US.ISO8859-1", but that isn't
605 the same. In this case, try running under a locale
606 that you can list and which somehow matches what you tried. The
607 rules for matching locale names are a bit vague because
608 standardization is weak in this area. See again the
609 L<Finding locales> about general rules.
611 =head2 Fixing system locale configuration
613 Contact a system administrator (preferably your own) and report the exact
614 error message you get, and ask them to read this same documentation you
615 are now reading. They should be able to check whether there is something
616 wrong with the locale configuration of the system. The L<Finding locales>
617 section is unfortunately a bit vague about the exact commands and places
618 because these things are not that standardized.
620 =head2 The localeconv function
622 The C<POSIX::localeconv()> function allows you to get particulars of the
623 locale-dependent numeric formatting information specified by the current
624 C<LC_NUMERIC> and C<LC_MONETARY> locales. (If you just want the name of
625 the current locale for a particular category, use C<POSIX::setlocale()>
626 with a single parameter--see L<The setlocale function>.)
628 use POSIX qw(locale_h);
630 # Get a reference to a hash of locale-dependent info
631 $locale_values = localeconv();
633 # Output sorted list of the values
634 for (sort keys %$locale_values) {
635 printf "%-20s = %s\n", $_, $locale_values->{$_}
638 C<localeconv()> takes no arguments, and returns B<a reference to> a hash.
639 The keys of this hash are variable names for formatting, such as
640 C<decimal_point> and C<thousands_sep>. The values are the
641 corresponding, er, values. See L<POSIX/localeconv> for a longer
642 example listing the categories an implementation might be expected to
643 provide; some provide more and others fewer. You don't need an
644 explicit C<use locale>, because C<localeconv()> always observes the
647 Here's a simple-minded example program that rewrites its command-line
648 parameters as integers correctly formatted in the current locale:
650 use POSIX qw(locale_h);
652 # Get some of locale's numeric formatting parameters
653 my ($thousands_sep, $grouping) =
654 @{localeconv()}{'thousands_sep', 'grouping'};
656 # Apply defaults if values are missing
657 $thousands_sep = ',' unless $thousands_sep;
659 # grouping and mon_grouping are packed lists
660 # of small integers (characters) telling the
661 # grouping (thousand_seps and mon_thousand_seps
662 # being the group dividers) of numbers and
663 # monetary quantities. The integers' meanings:
664 # 255 means no more grouping, 0 means repeat
665 # the previous grouping, 1-254 means use that
666 # as the current grouping. Grouping goes from
667 # right to left (low to high digits). In the
668 # below we cheat slightly by never using anything
669 # else than the first grouping (whatever that is).
671 @grouping = unpack("C*", $grouping);
676 # Format command line params for current locale
678 $_ = int; # Chop non-integer part
680 s/(\d)(\d{$grouping[0]}($|$thousands_sep))/$1$thousands_sep$2/;
685 =head2 I18N::Langinfo
687 Another interface for querying locale-dependent information is the
688 C<I18N::Langinfo::langinfo()> function, available at least in Unix-like
691 The following example will import the C<langinfo()> function itself and
692 three constants to be used as arguments to C<langinfo()>: a constant for
693 the abbreviated first day of the week (the numbering starts from
694 Sunday = 1) and two more constants for the affirmative and negative
695 answers for a yes/no question in the current locale.
697 use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
699 my ($abday_1, $yesstr, $nostr)
700 = map { langinfo } qw(ABDAY_1 YESSTR NOSTR);
702 print "$abday_1? [$yesstr/$nostr] ";
704 In other words, in the "C" (or English) locale the above will probably
705 print something like:
709 See L<I18N::Langinfo> for more information.
711 =head1 LOCALE CATEGORIES
713 The following subsections describe basic locale categories. Beyond these,
714 some combination categories allow manipulation of more than one
715 basic category at a time. See L<"ENVIRONMENT"> for a discussion of these.
717 =head2 Category LC_COLLATE: Collation
719 In the scope of S<C<use locale>> (but not a
720 C<use locale ':not_characters'>), Perl looks to the C<LC_COLLATE>
721 environment variable to determine the application's notions on collation
722 (ordering) of characters. For example, "b" follows "a" in Latin
723 alphabets, but where do "E<aacute>" and "E<aring>" belong? And while
724 "color" follows "chocolate" in English, what about in traditional Spanish?
726 The following collations all make sense and you may meet any of them
734 Here is a code snippet to tell what "word"
735 characters are in the current locale, in that locale's order:
738 print +(sort grep /\w/, map { chr } 0..255), "\n";
740 Compare this with the characters that you see and their order if you
741 state explicitly that the locale should be ignored:
744 print +(sort grep /\w/, map { chr } 0..255), "\n";
746 This machine-native collation (which is what you get unless S<C<use
747 locale>> has appeared earlier in the same block) must be used for
748 sorting raw binary data, whereas the locale-dependent collation of the
749 first example is useful for natural text.
751 As noted in L<USING LOCALES>, C<cmp> compares according to the current
752 collation locale when C<use locale> is in effect, but falls back to a
753 char-by-char comparison for strings that the locale says are equal. You
754 can use C<POSIX::strcoll()> if you don't want this fall-back:
756 use POSIX qw(strcoll);
758 !strcoll("space and case ignored", "SpaceAndCaseIgnored");
760 C<$equal_in_locale> will be true if the collation locale specifies a
761 dictionary-like ordering that ignores space characters completely and
764 Perl only supports single-byte locales for C<LC_COLLATE>. This means
765 that a UTF-8 locale likely will just give you machine-native ordering.
766 Use L<Unicode::Collate> for the full implementation of the Unicode
769 If you have a single string that you want to check for "equality in
770 locale" against several others, you might think you could gain a little
771 efficiency by using C<POSIX::strxfrm()> in conjunction with C<eq>:
773 use POSIX qw(strxfrm);
774 $xfrm_string = strxfrm("Mixed-case string");
775 print "locale collation ignores spaces\n"
776 if $xfrm_string eq strxfrm("Mixed-casestring");
777 print "locale collation ignores hyphens\n"
778 if $xfrm_string eq strxfrm("Mixedcase string");
779 print "locale collation ignores case\n"
780 if $xfrm_string eq strxfrm("mixed-case string");
782 C<strxfrm()> takes a string and maps it into a transformed string for use
783 in char-by-char comparisons against other transformed strings during
784 collation. "Under the hood", locale-affected Perl comparison operators
785 call C<strxfrm()> for both operands, then do a char-by-char
786 comparison of the transformed strings. By calling C<strxfrm()> explicitly
787 and using a non locale-affected comparison, the example attempts to save
788 a couple of transformations. But in fact, it doesn't save anything: Perl
789 magic (see L<perlguts/Magic Variables>) creates the transformed version of a
790 string the first time it's needed in a comparison, then keeps this version around
791 in case it's needed again. An example rewritten the easy way with
792 C<cmp> runs just about as fast. It also copes with null characters
793 embedded in strings; if you call C<strxfrm()> directly, it treats the first
794 null it finds as a terminator. don't expect the transformed strings
795 it produces to be portable across systems--or even from one revision
796 of your operating system to the next. In short, don't call C<strxfrm()>
797 directly: let Perl do it for you.
799 Note: C<use locale> isn't shown in some of these examples because it isn't
800 needed: C<strcoll()> and C<strxfrm()> are POSIX functions
801 which use the standard system-supplied C<libc> functions that
802 always obey the current C<LC_COLLATE> locale.
804 =head2 Category LC_CTYPE: Character Types
806 In the scope of S<C<use locale>> (but not a
807 C<use locale ':not_characters'>), Perl obeys the C<LC_CTYPE> locale
808 setting. This controls the application's notion of which characters are
809 alphabetic, numeric, punctuation, I<etc>. This affects Perl's C<\w>
810 regular expression metanotation,
811 which stands for alphanumeric characters--that is, alphabetic,
812 numeric, and the platform's native underscore.
813 (Consult L<perlre> for more information about
814 regular expressions.) Thanks to C<LC_CTYPE>, depending on your locale
815 setting, characters like "E<aelig>", "E<eth>", "E<szlig>", and
816 "E<oslash>" may be understood as C<\w> characters.
817 It also affects things like C<\s>, C<\D>, and the POSIX character
818 classes, like C<[[:graph:]]>. (See L<perlrecharclass> for more
819 information on all these.)
821 The C<LC_CTYPE> locale also provides the map used in transliterating
822 characters between lower and uppercase. This affects the case-mapping
823 functions--C<fc()>, C<lc()>, C<lcfirst()>, C<uc()>, and C<ucfirst()>; case-mapping
824 interpolation with C<\F>, C<\l>, C<\L>, C<\u>, or C<\U> in double-quoted
825 strings and C<s///> substitutions; and case-independent regular expression
826 pattern matching using the C<i> modifier.
828 Finally, C<LC_CTYPE> affects the (deprecated) POSIX character-class test
829 functions--C<POSIX::isalpha()>, C<POSIX::islower()>, and so on. For
830 example, if you move from the "C" locale to a 7-bit Scandinavian one,
831 you may find--possibly to your surprise--that "|" moves from the
832 C<POSIX::ispunct()> class to C<POSIX::isalpha()>.
833 Unfortunately, this creates big problems for regular expressions. "|" still
834 means alternation even though it matches C<\w>.
836 Starting in v5.20, Perl supports UTF-8 locales for C<LC_CTYPE>, but
837 otherwise Perl only supports single-byte locales, such as the ISO 8859
838 series. This means that wide character locales, for example for Asian
839 languages, are not supported. The UTF-8 locale support is actually a
840 superset of POSIX locales, because it is really full Unicode behavior
841 as if no locale were in effect at all (except for tainting; see
842 L</SECURITY>). POSIX locales, even UTF-8 ones,
843 are lacking certain concepts in Unicode, such as the idea that changing
844 the case of a character could expand to be more than one character.
845 Perl in a UTF-8 locale, will give you that expansion. Prior to v5.20,
846 Perl treated a UTF-8 locale on some platforms like an ISO 8859-1 one,
847 with some restrictions, and on other platforms more like the "C" locale.
848 For releases v5.16 and v5.18, C<S<use locale 'not_characters>> could be
849 used as a workaround for this (see L</Unicode and UTF-8>).
851 Note that there are quite a few things that are unaffected by the
852 current locale. All the escape sequences for particular characters,
853 C<\n> for example, always mean the platform's native one. This means,
854 for example, that C<\N> in regular expressions (every character
855 but new-line) works on the platform character set.
857 B<Note:> A broken or malicious C<LC_CTYPE> locale definition may result
858 in clearly ineligible characters being considered to be alphanumeric by
859 your application. For strict matching of (mundane) ASCII letters and
860 digits--for example, in command strings--locale-aware applications
861 should use C<\w> with the C</a> regular expression modifier. See L<"SECURITY">.
863 =head2 Category LC_NUMERIC: Numeric Formatting
865 After a proper C<POSIX::setlocale()> call, and within the scope of one
866 of the C<use locale> variants, Perl obeys the C<LC_NUMERIC>
867 locale information, which controls an application's idea of how numbers
868 should be formatted for human readability.
869 In most implementations the only effect is to
870 change the character used for the decimal point--perhaps from "." to ",".
871 The functions aren't aware of such niceties as thousands separation and
872 so on. (See L<The localeconv function> if you care about these things.)
874 use POSIX qw(strtod setlocale LC_NUMERIC);
877 setlocale LC_NUMERIC, "";
879 $n = 5/2; # Assign numeric 2.5 to $n
881 $a = " $n"; # Locale-dependent conversion to string
883 print "half five is $n\n"; # Locale-dependent output
885 printf "half five is %g\n", $n; # Locale-dependent output
887 print "DECIMAL POINT IS COMMA\n"
888 if $n == (strtod("2,5"))[0]; # Locale-dependent conversion
890 See also L<I18N::Langinfo> and C<RADIXCHAR>.
892 =head2 Category LC_MONETARY: Formatting of monetary amounts
894 The C standard defines the C<LC_MONETARY> category, but not a function
895 that is affected by its contents. (Those with experience of standards
896 committees will recognize that the working group decided to punt on the
897 issue.) Consequently, Perl essentially takes no notice of it. If you
898 really want to use C<LC_MONETARY>, you can query its contents--see
899 L<The localeconv function>--and use the information that it returns in your
900 application's own formatting of currency amounts. However, you may well
901 find that the information, voluminous and complex though it may be, still
902 does not quite meet your requirements: currency formatting is a hard nut
905 See also L<I18N::Langinfo> and C<CRNCYSTR>.
909 Output produced by C<POSIX::strftime()>, which builds a formatted
910 human-readable date/time string, is affected by the current C<LC_TIME>
911 locale. Thus, in a French locale, the output produced by the C<%B>
912 format element (full month name) for the first month of the year would
913 be "janvier". Here's how to get a list of long month names in the
916 use POSIX qw(strftime);
918 $long_month_name[$_] =
919 strftime("%B", 0, 0, 0, 1, $_, 96);
922 Note: C<use locale> isn't needed in this example: C<strftime()> is a POSIX
923 function which uses the standard system-supplied C<libc> function that
924 always obeys the current C<LC_TIME> locale.
926 See also L<I18N::Langinfo> and C<ABDAY_1>..C<ABDAY_7>, C<DAY_1>..C<DAY_7>,
927 C<ABMON_1>..C<ABMON_12>, and C<ABMON_1>..C<ABMON_12>.
929 =head2 Other categories
931 The remaining locale categories are not currently used by Perl itself.
932 But again note that things Perl interacts with may use these, including
933 extensions outside the standard Perl distribution, and by the
934 operating system and its utilities. Note especially that the string
935 value of C<$!> and the error messages given by external utilities may
936 be changed by C<LC_MESSAGES>. If you want to have portable error
937 codes, use C<%!>. See L<Errno>.
941 Although the main discussion of Perl security issues can be found in
942 L<perlsec>, a discussion of Perl's locale handling would be incomplete
943 if it did not draw your attention to locale-dependent security issues.
944 Locales--particularly on systems that allow unprivileged users to
945 build their own locales--are untrustworthy. A malicious (or just plain
946 broken) locale can make a locale-aware application give unexpected
947 results. Here are a few possibilities:
953 Regular expression checks for safe file names or mail addresses using
954 C<\w> may be spoofed by an C<LC_CTYPE> locale that claims that
955 characters such as "E<gt>" and "|" are alphanumeric.
959 String interpolation with case-mapping, as in, say, C<$dest =
960 "C:\U$name.$ext">, may produce dangerous results if a bogus LC_CTYPE
961 case-mapping table is in effect.
965 A sneaky C<LC_COLLATE> locale could result in the names of students with
966 "D" grades appearing ahead of those with "A"s.
970 An application that takes the trouble to use information in
971 C<LC_MONETARY> may format debits as if they were credits and vice versa
972 if that locale has been subverted. Or it might make payments in US
973 dollars instead of Hong Kong dollars.
977 The date and day names in dates formatted by C<strftime()> could be
978 manipulated to advantage by a malicious user able to subvert the
979 C<LC_DATE> locale. ("Look--it says I wasn't in the building on
984 Such dangers are not peculiar to the locale system: any aspect of an
985 application's environment which may be modified maliciously presents
986 similar challenges. Similarly, they are not specific to Perl: any
987 programming language that allows you to write programs that take
988 account of their environment exposes you to these issues.
990 Perl cannot protect you from all possibilities shown in the
991 examples--there is no substitute for your own vigilance--but, when
992 C<use locale> is in effect, Perl uses the tainting mechanism (see
993 L<perlsec>) to mark string results that become locale-dependent, and
994 which may be untrustworthy in consequence. Here is a summary of the
995 tainting behavior of operators and functions that may be affected by
1002 B<Comparison operators> (C<lt>, C<le>, C<ge>, C<gt> and C<cmp>):
1004 Scalar true/false (or less/equal/greater) result is never tainted.
1008 B<Case-mapping interpolation> (with C<\l>, C<\L>, C<\u>, C<\U>, or C<\F>)
1010 Result string containing interpolated material is tainted if
1011 C<use locale> (but not S<C<use locale ':not_characters'>>) is in effect.
1015 B<Matching operator> (C<m//>):
1017 Scalar true/false result never tainted.
1019 All subpatterns, either delivered as a list-context result or as C<$1>
1020 I<etc>., are tainted if C<use locale> (but not
1021 S<C<use locale ':not_characters'>>) is in effect, and the subpattern
1022 regular expression contains a locale-dependent construct. These
1023 constructs include C<\w> (to match an alphanumeric character), C<\W>
1024 (non-alphanumeric character), C<\b> and C<\B> (word-boundary and
1025 non-boundardy, which depend on what C<\w> and C<\W> match), C<\s>
1026 (whitespace character), C<\S> (non whitespace character), C<\d> and
1027 C<\D> (digits and non-digits), and the POSIX character classes, such as
1028 C<[:alpha:]> (see L<perlrecharclass/POSIX Character Classes>).
1030 Tainting is also likely if the pattern is to be matched
1031 case-insensitively (via C</i>). The exception is if all the code points
1032 to be matched this way are above 255 and do not have folds under Unicode
1033 rules to below 256. Tainting is not done for these because Perl
1034 only uses Unicode rules for such code points, and those rules are the
1035 same no matter what the current locale.
1037 The matched-pattern variables, C<$&>, C<$`> (pre-match), C<$'>
1038 (post-match), and C<$+> (last match) also are tainted.
1042 B<Substitution operator> (C<s///>):
1044 Has the same behavior as the match operator. Also, the left
1045 operand of C<=~> becomes tainted when C<use locale>
1046 (but not S<C<use locale ':not_characters'>>) is in effect if modified as
1047 a result of a substitution based on a regular
1048 expression match involving any of the things mentioned in the previous
1049 item, or of case-mapping, such as C<\l>, C<\L>,C<\u>, C<\U>, or C<\F>.
1053 B<Output formatting functions> (C<printf()> and C<write()>):
1055 Results are never tainted because otherwise even output from print,
1056 for example C<print(1/7)>, should be tainted if C<use locale> is in
1061 B<Case-mapping functions> (C<lc()>, C<lcfirst()>, C<uc()>, C<ucfirst()>):
1063 Results are tainted if C<use locale> (but not
1064 S<C<use locale ':not_characters'>>) is in effect.
1068 B<POSIX locale-dependent functions> (C<localeconv()>, C<strcoll()>,
1069 C<strftime()>, C<strxfrm()>):
1071 Results are never tainted.
1075 B<POSIX character class tests> (C<POSIX::isalnum()>,
1076 C<POSIX::isalpha()>, C<POSIX::isdigit()>, C<POSIX::isgraph()>,
1077 C<POSIX::islower()>, C<POSIX::isprint()>, C<POSIX::ispunct()>,
1078 C<POSIX::isspace()>, C<POSIX::isupper()>, C<POSIX::isxdigit()>):
1080 True/false results are never tainted.
1084 Three examples illustrate locale-dependent tainting.
1085 The first program, which ignores its locale, won't run: a value taken
1086 directly from the command line may not be used to name an output file
1087 when taint checks are enabled.
1089 #/usr/local/bin/perl -T
1090 # Run with taint checking
1092 # Command line sanity check omitted...
1093 $tainted_output_file = shift;
1095 open(F, ">$tainted_output_file")
1096 or warn "Open of $tainted_output_file failed: $!\n";
1098 The program can be made to run by "laundering" the tainted value through
1099 a regular expression: the second example--which still ignores locale
1100 information--runs, creating the file named on its command line
1103 #/usr/local/bin/perl -T
1105 $tainted_output_file = shift;
1106 $tainted_output_file =~ m%[\w/]+%;
1107 $untainted_output_file = $&;
1109 open(F, ">$untainted_output_file")
1110 or warn "Open of $untainted_output_file failed: $!\n";
1112 Compare this with a similar but locale-aware program:
1114 #/usr/local/bin/perl -T
1116 $tainted_output_file = shift;
1118 $tainted_output_file =~ m%[\w/]+%;
1119 $localized_output_file = $&;
1121 open(F, ">$localized_output_file")
1122 or warn "Open of $localized_output_file failed: $!\n";
1124 This third program fails to run because C<$&> is tainted: it is the result
1125 of a match involving C<\w> while C<use locale> is in effect.
1131 =item PERL_SKIP_LOCALE_INIT
1133 This environment variable, available starting in Perl v5.20, and if it
1134 evaluates to a TRUE value, tells Perl to not use the rest of the
1135 environment variables to initialize with. Instead, Perl uses whatever
1136 the current locale settings are. This is particularly useful in
1137 embedded environments, see
1138 L<perlembed/Using embedded Perl with POSIX locales>.
1142 A string that can suppress Perl's warning about failed locale settings
1143 at startup. Failure can occur if the locale support in the operating
1144 system is lacking (broken) in some way--or if you mistyped the name of
1145 a locale when you set up your environment. If this environment
1146 variable is absent, or has a value that does not evaluate to integer
1147 zero--that is, "0" or ""-- Perl will complain about locale setting
1150 B<NOTE>: PERL_BADLANG only gives you a way to hide the warning message.
1151 The message tells about some problem in your system's locale support,
1152 and you should investigate what the problem is.
1156 The following environment variables are not specific to Perl: They are
1157 part of the standardized (ISO C, XPG4, POSIX 1.c) C<setlocale()> method
1158 for controlling an application's opinion on data. Windows is non-POSIX,
1159 but Perl arranges for the following to work as described anyway.
1160 If the locale given by an environment variable is not valid, Perl tries
1161 the next lower one in priority. If none are valid, on Windows, the
1162 system default locale is then tried. If all else fails, the C<"C">
1163 locale is used. If even that doesn't work, something is badly broken,
1164 but Perl tries to forge ahead with whatever the locale settinga might
1171 C<LC_ALL> is the "override-all" locale environment variable. If
1172 set, it overrides all the rest of the locale environment variables.
1176 B<NOTE>: C<LANGUAGE> is a GNU extension, it affects you only if you
1177 are using the GNU libc. This is the case if you are using e.g. Linux.
1178 If you are using "commercial" Unixes you are most probably I<not>
1179 using GNU libc and you can ignore C<LANGUAGE>.
1181 However, in the case you are using C<LANGUAGE>: it affects the
1182 language of informational, warning, and error messages output by
1183 commands (in other words, it's like C<LC_MESSAGES>) but it has higher
1184 priority than C<LC_ALL>. Moreover, it's not a single value but
1185 instead a "path" (":"-separated list) of I<languages> (not locales).
1186 See the GNU C<gettext> library documentation for more information.
1190 In the absence of C<LC_ALL>, C<LC_CTYPE> chooses the character type
1191 locale. In the absence of both C<LC_ALL> and C<LC_CTYPE>, C<LANG>
1192 chooses the character type locale.
1196 In the absence of C<LC_ALL>, C<LC_COLLATE> chooses the collation
1197 (sorting) locale. In the absence of both C<LC_ALL> and C<LC_COLLATE>,
1198 C<LANG> chooses the collation locale.
1202 In the absence of C<LC_ALL>, C<LC_MONETARY> chooses the monetary
1203 formatting locale. In the absence of both C<LC_ALL> and C<LC_MONETARY>,
1204 C<LANG> chooses the monetary formatting locale.
1208 In the absence of C<LC_ALL>, C<LC_NUMERIC> chooses the numeric format
1209 locale. In the absence of both C<LC_ALL> and C<LC_NUMERIC>, C<LANG>
1210 chooses the numeric format.
1214 In the absence of C<LC_ALL>, C<LC_TIME> chooses the date and time
1215 formatting locale. In the absence of both C<LC_ALL> and C<LC_TIME>,
1216 C<LANG> chooses the date and time formatting locale.
1220 C<LANG> is the "catch-all" locale environment variable. If it is set, it
1221 is used as the last resort after the overall C<LC_ALL> and the
1222 category-specific C<LC_...>.
1228 The LC_NUMERIC controls the numeric output:
1231 use POSIX qw(locale_h); # Imports setlocale() and the LC_ constants.
1232 setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
1233 printf "%g\n", 1.23; # If the "fr_FR" succeeded, probably shows 1,23.
1235 and also how strings are parsed by C<POSIX::strtod()> as numbers:
1238 use POSIX qw(locale_h strtod);
1239 setlocale(LC_NUMERIC, "de_DE") or die "Entschuldigung";
1240 my $x = strtod("2,34") + 5;
1241 print $x, "\n"; # Probably shows 7,34.
1245 =head2 String C<eval> and C<LC_NUMERIC>
1247 A string L<eval|perlfunc/eval EXPR> parses its expression as standard
1248 Perl. It is therefore expecting the decimal point to be a dot. If
1249 C<LC_NUMERIC> is set to have this be a comma instead, the parsing will
1250 be confused, perhaps silently.
1253 use POSIX qw(locale_h);
1254 setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
1256 print eval "$a + 1.5";
1259 prints C<13,5>. This is because in that locale, the comma is the
1260 decimal point character. The C<eval> thus expands to:
1264 and the result is not what you likely expected. No warnings are
1265 generated. If you do string C<eval>'s within the scope of
1266 S<C<use locale>>, you should instead change the C<eval> line to do
1269 print eval "no locale; $a + 1.5";
1273 =head2 Backward compatibility
1275 Versions of Perl prior to 5.004 B<mostly> ignored locale information,
1276 generally behaving as if something similar to the C<"C"> locale were
1277 always in force, even if the program environment suggested otherwise
1278 (see L<The setlocale function>). By default, Perl still behaves this
1279 way for backward compatibility. If you want a Perl application to pay
1280 attention to locale information, you B<must> use the S<C<use locale>>
1281 pragma (see L<The use locale pragma>) or, in the unlikely event
1282 that you want to do so for just pattern matching, the
1283 C</l> regular expression modifier (see L<perlre/Character set
1284 modifiers>) to instruct it to do so.
1286 Versions of Perl from 5.002 to 5.003 did use the C<LC_CTYPE>
1287 information if available; that is, C<\w> did understand what
1288 were the letters according to the locale environment variables.
1289 The problem was that the user had no control over the feature:
1290 if the C library supported locales, Perl used them.
1292 =head2 I18N:Collate obsolete
1294 In versions of Perl prior to 5.004, per-locale collation was possible
1295 using the C<I18N::Collate> library module. This module is now mildly
1296 obsolete and should be avoided in new applications. The C<LC_COLLATE>
1297 functionality is now integrated into the Perl core language: One can
1298 use locale-specific scalar data completely normally with C<use locale>,
1299 so there is no longer any need to juggle with the scalar references of
1302 =head2 Sort speed and memory use impacts
1304 Comparing and sorting by locale is usually slower than the default
1305 sorting; slow-downs of two to four times have been observed. It will
1306 also consume more memory: once a Perl scalar variable has participated
1307 in any string comparison or sorting operation obeying the locale
1308 collation rules, it will take 3-15 times more memory than before. (The
1309 exact multiplier depends on the string's contents, the operating system
1310 and the locale.) These downsides are dictated more by the operating
1311 system's implementation of the locale system than by Perl.
1313 =head2 Freely available locale definitions
1315 The Unicode CLDR project extracts the POSIX portion of many of its
1316 locales, available at
1318 http://unicode.org/Public/cldr/latest/
1320 There is a large collection of locale definitions at:
1322 http://std.dkuug.dk/i18n/WG15-collection/locales/
1324 You should be aware that it is
1325 unsupported, and is not claimed to be fit for any purpose. If your
1326 system allows installation of arbitrary locales, you may find the
1327 definitions useful as they are, or as a basis for the development of
1330 =head2 I18n and l10n
1332 "Internationalization" is often abbreviated as B<i18n> because its first
1333 and last letters are separated by eighteen others. (You may guess why
1334 the internalin ... internaliti ... i18n tends to get abbreviated.) In
1335 the same way, "localization" is often abbreviated to B<l10n>.
1337 =head2 An imperfect standard
1339 Internationalization, as defined in the C and POSIX standards, can be
1340 criticized as incomplete, ungainly, and having too large a granularity.
1341 (Locales apply to a whole process, when it would arguably be more useful
1342 to have them apply to a single thread, window group, or whatever.) They
1343 also have a tendency, like standards groups, to divide the world into
1344 nations, when we all know that the world can equally well be divided
1345 into bankers, bikers, gamers, and so on.
1347 =head1 Unicode and UTF-8
1349 The support of Unicode is new starting from Perl version v5.6, and more fully
1350 implemented in versions v5.8 and later. See L<perluniintro>.
1352 Starting in Perl v5.20, UTF-8 locales are supported in Perl, except for
1353 C<LC_COLLATE> (use L<Unicode::Collate> instead). If you have Perl v5.16
1354 or v5.18 and can't upgrade, you can use
1356 use locale ':not_characters';
1358 When this form of the pragma is used, only the non-character portions of
1359 locales are used by Perl, for example C<LC_NUMERIC>. Perl assumes that
1360 you have translated all the characters it is to operate on into Unicode
1361 (actually the platform's native character set (ASCII or EBCDIC) plus
1362 Unicode). For data in files, this can conveniently be done by also
1367 This pragma arranges for all inputs from files to be translated into
1368 Unicode from the current locale as specified in the environment (see
1369 L</ENVIRONMENT>), and all outputs to files to be translated back
1370 into the locale. (See L<open>). On a per-filehandle basis, you can
1371 instead use the L<PerlIO::locale> module, or the L<Encode::Locale>
1372 module, both available from CPAN. The latter module also has methods to
1373 ease the handling of C<ARGV> and environment variables, and can be used
1374 on individual strings. If you know that all your locales will be
1375 UTF-8, as many are these days, you can use the L<B<-C>|perlrun/-C>
1376 command line switch.
1378 This form of the pragma allows essentially seamless handling of locales
1379 with Unicode. The collation order will be by Unicode code point order.
1381 recommended that when you need to order and sort strings that you use
1382 the standard module L<Unicode::Collate> which gives much better results
1383 in many instances than you can get with the old-style locale handling.
1385 All the modules and switches just described can be used in v5.20 with
1386 just plain C<use locale>, and, should the input locales not be UTF-8,
1387 you'll get the less than ideal behavior, described below, that you get
1388 with pre-v5.16 Perls, or when you use the locale pragma without the
1389 C<:not_characters> parameter in v5.16 and v5.18. If you are using
1390 exclusively UTF-8 locales in v5.20 and higher, the rest of this section
1391 does not apply to you.
1393 There are two cases, multi-byte and single-byte locales. First
1396 The only multi-byte (or wide character) locale that Perl is ever likely
1397 to support is UTF-8. This is due to the difficulty of implementation,
1398 the fact that high quality UTF-8 locales are now published for every
1399 area of the world (L<http://unicode.org/Public/cldr/latest/>), and that
1400 failing all that you can use the L<Encode> module to translate to/from
1401 your locale. So, you'll have to do one of those things if you're using
1402 one of these locales, such as Big5 or Shift JIS. For UTF-8 locales, in
1403 Perls (pre v5.20) that don't have full UTF-8 locale support, they may
1404 work reasonably well (depending on your C library implementation)
1406 they and Perl store characters that take up multiple bytes the same way.
1407 However, some, if not most, C library implementations may not process
1408 the characters in the upper half of the Latin-1 range (128 - 255)
1409 properly under LC_CTYPE. To see if a character is a particular type
1410 under a locale, Perl uses the functions like C<isalnum()>. Your C
1411 library may not work for UTF-8 locales with those functions, instead
1412 only working under the newer wide library functions like C<iswalnum()>.
1413 However, they are treated like single-byte locales, and will have the
1414 restrictions described below.
1416 For single-byte locales,
1417 Perl generally takes the tack to use locale rules on code points that can fit
1418 in a single byte, and Unicode rules for those that can't (though this
1419 isn't uniformly applied, see the note at the end of this section). This
1420 prevents many problems in locales that aren't UTF-8. Suppose the locale
1421 is ISO8859-7, Greek. The character at 0xD7 there is a capital Chi. But
1422 in the ISO8859-1 locale, Latin1, it is a multiplication sign. The POSIX
1423 regular expression character class C<[[:alpha:]]> will magically match
1424 0xD7 in the Greek locale but not in the Latin one.
1426 However, there are places where this breaks down. Certain Perl constructs are
1427 for Unicode only, such as C<\p{Alpha}>. They assume that 0xD7 always has its
1428 Unicode meaning (or the equivalent on EBCDIC platforms). Since Latin1 is a
1429 subset of Unicode and 0xD7 is the multiplication sign in both Latin1 and
1430 Unicode, C<\p{Alpha}> will never match it, regardless of locale. A similar
1431 issue occurs with C<\N{...}>. Prior to v5.20, It is therefore a bad
1432 idea to use C<\p{}> or
1433 C<\N{}> under plain C<use locale>--I<unless> you can guarantee that the
1434 locale will be a ISO8859-1. Use POSIX character classes instead.
1436 Another problem with this approach is that operations that cross the
1437 single byte/multiple byte boundary are not well-defined, and so are
1438 disallowed. (This boundary is between the codepoints at 255/256.)
1439 For example, lower casing LATIN CAPITAL LETTER Y WITH DIAERESIS (U+0178)
1440 should return LATIN SMALL LETTER Y WITH DIAERESIS (U+00FF). But in the
1441 Greek locale, for example, there is no character at 0xFF, and Perl
1442 has no way of knowing what the character at 0xFF is really supposed to
1443 represent. Thus it disallows the operation. In this mode, the
1444 lowercase of U+0178 is itself.
1446 The same problems ensue if you enable automatic UTF-8-ification of your
1447 standard file handles, default C<open()> layer, and C<@ARGV> on non-ISO8859-1,
1448 non-UTF-8 locales (by using either the B<-C> command line switch or the
1449 C<PERL_UNICODE> environment variable; see L<perlrun>).
1450 Things are read in as UTF-8, which would normally imply a Unicode
1451 interpretation, but the presence of a locale causes them to be interpreted
1452 in that locale instead. For example, a 0xD7 code point in the Unicode
1453 input, which should mean the multiplication sign, won't be interpreted by
1454 Perl that way under the Greek locale. This is not a problem
1455 I<provided> you make certain that all locales will always and only be either
1456 an ISO8859-1, or, if you don't have a deficient C library, a UTF-8 locale.
1458 Still another problem is that this approach can lead to two code
1459 points meaning the same character. Thus in a Greek locale, both U+03A7
1460 and U+00D7 are GREEK CAPITAL LETTER CHI.
1462 Vendor locales are notoriously buggy, and it is difficult for Perl to test
1463 its locale-handling code because this interacts with code that Perl has no
1464 control over; therefore the locale-handling code in Perl may be buggy as
1465 well. (However, the Unicode-supplied locales should be better, and
1466 there is a feed back mechanism to correct any problems. See
1467 L</Freely available locale definitions>.)
1469 If you have Perl v5.16, the problems mentioned above go away if you use
1470 the C<:not_characters> parameter to the locale pragma (except for vendor
1471 bugs in the non-character portions). If you don't have v5.16, and you
1472 I<do> have locales that work, using them may be worthwhile for certain
1473 specific purposes, as long as you keep in mind the gotchas already
1474 mentioned. For example, if the collation for your locales works, it
1475 runs faster under locales than under L<Unicode::Collate>; and you gain
1476 access to such things as the local currency symbol and the names of the
1477 months and days of the week. (But to hammer home the point, in v5.16,
1478 you get this access without the downsides of locales by using the
1479 C<:not_characters> form of the pragma.)
1481 Note: The policy of using locale rules for code points that can fit in a
1482 byte, and Unicode rules for those that can't is not uniformly applied.
1483 Pre-v5.12, it was somewhat haphazard; in v5.12 it was applied fairly
1484 consistently to regular expression matching except for bracketed
1485 character classes; in v5.14 it was extended to all regex matches; and in
1486 v5.16 to the casing operations such as C<"\L"> and C<uc()>. For
1487 collation, in all releases, the system's C<strxfrm()> function is called,
1488 and whatever it does is what you get.
1492 =head2 Broken systems
1494 In certain systems, the operating system's locale support
1495 is broken and cannot be fixed or used by Perl. Such deficiencies can
1496 and will result in mysterious hangs and/or Perl core dumps when
1497 C<use locale> is in effect. When confronted with such a system,
1498 please report in excruciating detail to <F<perlbug@perl.org>>, and
1499 also contact your vendor: bug fixes may exist for these problems
1500 in your operating system. Sometimes such bug fixes are called an
1501 operating system upgrade. If you have the source for Perl, include in
1502 the perlbug email the output of the test described above in L</Testing
1503 for broken locales>.
1507 L<I18N::Langinfo>, L<perluniintro>, L<perlunicode>, L<open>,
1508 L<POSIX/isalnum>, L<POSIX/isalpha>,
1509 L<POSIX/isdigit>, L<POSIX/isgraph>, L<POSIX/islower>,
1510 L<POSIX/isprint>, L<POSIX/ispunct>, L<POSIX/isspace>,
1511 L<POSIX/isupper>, L<POSIX/isxdigit>, L<POSIX/localeconv>,
1512 L<POSIX/setlocale>, L<POSIX/strcoll>, L<POSIX/strftime>,
1513 L<POSIX/strtod>, L<POSIX/strxfrm>.
1515 For special considerations when Perl is embedded in a C program,
1516 see L<perlembed/Using embedded Perl with POSIX locales>.
1520 Jarkko Hietaniemi's original F<perli18n.pod> heavily hacked by Dominic
1521 Dunlop, assisted by the perl5-porters. Prose worked over a bit by
1522 Tom Christiansen, and updated by Perl 5 porters.