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 variable L<$!|perlvar/$ERRNO> (and its synonyms C<$ERRNO> and
206 C<$OS_ERROR>) when used as strings always are in terms of the current
211 The current locale is also used when going outside of Perl with
212 operations like L<system()|perlfunc/system LIST> or
213 L<qxE<sol>E<sol>|perlop/qxE<sol>STRINGE<sol>>, if those operations are
218 Also Perl gives access to various C library functions through the
219 L<POSIX> module. Some of those functions are always affected by the
220 current locale. For example, C<POSIX::strftime()> uses C<LC_TIME>;
221 C<POSIX::strtod()> uses C<LC_NUMERIC>; C<POSIX::strcoll()> and
222 C<POSIX::strxfrm()> use C<LC_COLLATE>; and character classification
223 functions like C<POSIX::isalnum()> use C<LC_CTYPE>. All such functions
224 will behave according to the current underlying locale, even if that
225 locale isn't exposed to Perl space.
229 Perl also provides lite wrappers for XS modules to use some C library
230 C<printf> functions. These wrappers don't do anything with the locale,
231 and the underlying C library function is affected by the locale in
232 effect at the time of the wrapper call.
233 The affected functions are
234 L<perlapi/my_sprintf>,
235 L<perlapi/my_snprintf>,
237 L<perlapi/my_vsnprintf>.
242 The nbsp below makes this look better (though not great)
246 =item B<Lingering effects of C<S<use locale>>>
248 Certain Perl operations that are set-up within the scope of a
249 C<use locale> variant retain that effect even outside the scope.
256 The output format of a L<write()|perlfunc/write> is determined by an
257 earlier format declaration (L<perlfunc/format>), so whether or not the
258 output is affected by locale is determined by if the C<format()> is
259 within the scope of a C<use locale> variant, not whether the C<write()>
264 Regular expression patterns can be compiled using
265 L<qrE<sol>E<sol>|perlop/qrE<sol>STRINGE<sol>msixpodual> with actual
266 matching deferred to later. Again, it is whether or not the compilation
267 was done within the scope of C<use locale> that determines the match
268 behavior, not if the matches are done within such a scope or not.
273 The nbsp below makes this look better (though not great)
277 =item B<Under C<"use locale ':not_characters';">>
283 All the non-Perl operations.
287 B<Format declarations> (L<perlfunc/format>) and hence any subsequent
288 C<write()>s use C<LC_NUMERIC>.
292 B<stringification and output> use C<LC_NUMERIC>.
293 These include the results of
303 The nbsp below makes this look better (though not great)
307 =item B<Under just plain C<"use locale";>>
313 All the above operations
317 B<The comparison operators> (C<lt>, C<le>, C<cmp>, C<ge>, and C<gt>) use
318 C<LC_COLLATE>. C<sort()> is also affected if used without an
319 explicit comparison function, because it uses C<cmp> by default.
321 B<Note:> C<eq> and C<ne> are unaffected by locale: they always
322 perform a char-by-char comparison of their scalar operands. What's
323 more, if C<cmp> finds that its operands are equal according to the
324 collation sequence specified by the current locale, it goes on to
325 perform a char-by-char comparison, and only returns I<0> (equal) if the
326 operands are char-for-char identical. If you really want to know whether
327 two strings--which C<eq> and C<cmp> may consider different--are equal
328 as far as collation in the locale is concerned, see the discussion in
329 L<Category LC_COLLATE: Collation>.
333 B<Regular expressions and case-modification functions> (C<uc()>, C<lc()>,
334 C<ucfirst()>, and C<lcfirst()>) use C<LC_CTYPE>
340 The default behavior is restored with the S<C<no locale>> pragma, or
341 upon reaching the end of the block enclosing C<use locale>.
342 Note that C<use locale> and C<use locale ':not_characters'> may be
343 nested, and that what is in effect within an inner scope will revert to
344 the outer scope's rules at the end of the inner scope.
346 The string result of any operation that uses locale
347 information is tainted, as it is possible for a locale to be
348 untrustworthy. See L<"SECURITY">.
350 =head2 The setlocale function
352 You can switch locales as often as you wish at run time with the
353 C<POSIX::setlocale()> function:
355 # Import locale-handling tool set from POSIX module.
356 # This example uses: setlocale -- the function call
357 # LC_CTYPE -- explained below
358 # (Showing the testing for success/failure of operations is
359 # omitted in these examples to avoid distracting from the main
362 use POSIX qw(locale_h);
366 # query and save the old locale
367 $old_locale = setlocale(LC_CTYPE);
369 setlocale(LC_CTYPE, "fr_CA.ISO8859-1");
370 # LC_CTYPE now in locale "French, Canada, codeset ISO 8859-1"
372 setlocale(LC_CTYPE, "");
373 # LC_CTYPE now reset to the default defined by the
374 # LC_ALL/LC_CTYPE/LANG environment variables, or to the system
375 # default. See below for documentation.
377 # restore the old locale
378 setlocale(LC_CTYPE, $old_locale);
380 The first argument of C<setlocale()> gives the B<category>, the second the
381 B<locale>. The category tells in what aspect of data processing you
382 want to apply locale-specific rules. Category names are discussed in
383 L</LOCALE CATEGORIES> and L</"ENVIRONMENT">. The locale is the name of a
384 collection of customization information corresponding to a particular
385 combination of language, country or territory, and codeset. Read on for
386 hints on the naming of locales: not all systems name locales as in the
389 If no second argument is provided and the category is something other
390 than LC_ALL, the function returns a string naming the current locale
391 for the category. You can use this value as the second argument in a
392 subsequent call to C<setlocale()>, B<but> on some platforms the string
393 is opaque, not something that most people would be able to decipher as
394 to what locale it means.
396 If no second argument is provided and the category is LC_ALL, the
397 result is implementation-dependent. It may be a string of
398 concatenated locale names (separator also implementation-dependent)
399 or a single locale name. Please consult your L<setlocale(3)> man page for
402 If a second argument is given and it corresponds to a valid locale,
403 the locale for the category is set to that value, and the function
404 returns the now-current locale value. You can then use this in yet
405 another call to C<setlocale()>. (In some implementations, the return
406 value may sometimes differ from the value you gave as the second
407 argument--think of it as an alias for the value you gave.)
409 As the example shows, if the second argument is an empty string, the
410 category's locale is returned to the default specified by the
411 corresponding environment variables. Generally, this results in a
412 return to the default that was in force when Perl started up: changes
413 to the environment made by the application after startup may or may not
414 be noticed, depending on your system's C library.
416 Note that Perl ignores the current C<LC_CTYPE> and C<LC_COLLATE> locales
417 within the scope of a C<use locale ':not_characters'>.
419 If C<set_locale()> fails for some reason (for example, an attempt to set
420 to a locale unknown to the system), the locale for the category is not
421 changed, and the function returns C<undef>.
424 For further information about the categories, consult L<setlocale(3)>.
426 =head2 Finding locales
428 For locales available in your system, consult also L<setlocale(3)> to
429 see whether it leads to the list of available locales (search for the
430 I<SEE ALSO> section). If that fails, try the following command lines:
444 and see whether they list something resembling these
446 en_US.ISO8859-1 de_DE.ISO8859-1 ru_RU.ISO8859-5
447 en_US.iso88591 de_DE.iso88591 ru_RU.iso88595
450 english german russian
451 english.iso88591 german.iso88591 russian.iso88595
452 english.roman8 russian.koi8r
454 Sadly, even though the calling interface for C<setlocale()> has been
455 standardized, names of locales and the directories where the
456 configuration resides have not been. The basic form of the name is
457 I<language_territory>B<.>I<codeset>, but the latter parts after
458 I<language> are not always present. The I<language> and I<country>
459 are usually from the standards B<ISO 3166> and B<ISO 639>, the
460 two-letter abbreviations for the countries and the languages of the
461 world, respectively. The I<codeset> part often mentions some B<ISO
462 8859> character set, the Latin codesets. For example, C<ISO 8859-1>
463 is the so-called "Western European codeset" that can be used to encode
464 most Western European languages adequately. Again, there are several
465 ways to write even the name of that one standard. Lamentably.
467 Two special locales are worth particular mention: "C" and "POSIX".
468 Currently these are effectively the same locale: the difference is
469 mainly that the first one is defined by the C standard, the second by
470 the POSIX standard. They define the B<default locale> in which
471 every program starts in the absence of locale information in its
472 environment. (The I<default> default locale, if you will.) Its language
473 is (American) English and its character codeset ASCII or, rarely, a
474 superset thereof (such as the "DEC Multinational Character Set
475 (DEC-MCS)"). B<Warning>. The C locale delivered by some vendors
476 may not actually exactly match what the C standard calls for. So
479 B<NOTE>: Not all systems have the "POSIX" locale (not all systems are
480 POSIX-conformant), so use "C" when you need explicitly to specify this
483 =head2 LOCALE PROBLEMS
485 You may encounter the following warning message at Perl startup:
487 perl: warning: Setting locale failed.
488 perl: warning: Please check that your locale settings:
491 are supported and installed on your system.
492 perl: warning: Falling back to the standard locale ("C").
494 This means that your locale settings had LC_ALL set to "En_US" and
495 LANG exists but has no value. Perl tried to believe you but could not.
496 Instead, Perl gave up and fell back to the "C" locale, the default locale
497 that is supposed to work no matter what. (On Windows, it first tries
498 falling back to the system default locale.) This usually means your
499 locale settings were wrong, they mention locales your system has never
500 heard of, or the locale installation in your system has problems (for
501 example, some system files are broken or missing). There are quick and
502 temporary fixes to these problems, as well as more thorough and lasting
505 =head2 Testing for broken locales
507 If you are building Perl from source, the Perl test suite file
508 F<lib/locale.t> can be used to test the locales on your system.
509 Setting the environment variable C<PERL_DEBUG_FULL_TEST> to 1
510 will cause it to output detailed results. For example, on Linux, you
513 PERL_DEBUG_FULL_TEST=1 ./perl -T -Ilib lib/locale.t > locale.log 2>&1
515 Besides many other tests, it will test every locale it finds on your
516 system to see if they conform to the POSIX standard. If any have
517 errors, it will include a summary near the end of the output of which
518 locales passed all its tests, and which failed, and why.
520 =head2 Temporarily fixing locale problems
522 The two quickest fixes are either to render Perl silent about any
523 locale inconsistencies or to run Perl under the default locale "C".
525 Perl's moaning about locale problems can be silenced by setting the
526 environment variable PERL_BADLANG to a zero value, for example "0".
527 This method really just sweeps the problem under the carpet: you tell
528 Perl to shut up even when Perl sees that something is wrong. Do not
529 be surprised if later something locale-dependent misbehaves.
531 Perl can be run under the "C" locale by setting the environment
532 variable LC_ALL to "C". This method is perhaps a bit more civilized
533 than the PERL_BADLANG approach, but setting LC_ALL (or
534 other locale variables) may affect other programs as well, not just
535 Perl. In particular, external programs run from within Perl will see
536 these changes. If you make the new settings permanent (read on), all
537 programs you run see the changes. See L<"ENVIRONMENT"> for
538 the full list of relevant environment variables and L<USING LOCALES>
539 for their effects in Perl. Effects in other programs are
540 easily deducible. For example, the variable LC_COLLATE may well affect
541 your B<sort> program (or whatever the program that arranges "records"
542 alphabetically in your system is called).
544 You can test out changing these variables temporarily, and if the
545 new settings seem to help, put those settings into your shell startup
546 files. Consult your local documentation for the exact details. For in
547 Bourne-like shells (B<sh>, B<ksh>, B<bash>, B<zsh>):
549 LC_ALL=en_US.ISO8859-1
552 This assumes that we saw the locale "en_US.ISO8859-1" using the commands
553 discussed above. We decided to try that instead of the above faulty
554 locale "En_US"--and in Cshish shells (B<csh>, B<tcsh>)
556 setenv LC_ALL en_US.ISO8859-1
558 or if you have the "env" application you can do in any shell
560 env LC_ALL=en_US.ISO8859-1 perl ...
562 If you do not know what shell you have, consult your local
563 helpdesk or the equivalent.
565 =head2 Permanently fixing locale problems
567 The slower but superior fixes are when you may be able to yourself
568 fix the misconfiguration of your own environment variables. The
569 mis(sing)configuration of the whole system's locales usually requires
570 the help of your friendly system administrator.
572 First, see earlier in this document about L<Finding locales>. That tells
573 how to find which locales are really supported--and more importantly,
574 installed--on your system. In our example error message, environment
575 variables affecting the locale are listed in the order of decreasing
576 importance (and unset variables do not matter). Therefore, having
577 LC_ALL set to "En_US" must have been the bad choice, as shown by the
578 error message. First try fixing locale settings listed first.
580 Second, if using the listed commands you see something B<exactly>
581 (prefix matches do not count and case usually counts) like "En_US"
582 without the quotes, then you should be okay because you are using a
583 locale name that should be installed and available in your system.
584 In this case, see L<Permanently fixing your system's locale configuration>.
586 =head2 Permanently fixing your system's locale configuration
588 This is when you see something like:
590 perl: warning: Please check that your locale settings:
593 are supported and installed on your system.
595 but then cannot see that "En_US" listed by the above-mentioned
596 commands. You may see things like "en_US.ISO8859-1", but that isn't
597 the same. In this case, try running under a locale
598 that you can list and which somehow matches what you tried. The
599 rules for matching locale names are a bit vague because
600 standardization is weak in this area. See again the
601 L<Finding locales> about general rules.
603 =head2 Fixing system locale configuration
605 Contact a system administrator (preferably your own) and report the exact
606 error message you get, and ask them to read this same documentation you
607 are now reading. They should be able to check whether there is something
608 wrong with the locale configuration of the system. The L<Finding locales>
609 section is unfortunately a bit vague about the exact commands and places
610 because these things are not that standardized.
612 =head2 The localeconv function
614 The C<POSIX::localeconv()> function allows you to get particulars of the
615 locale-dependent numeric formatting information specified by the current
616 C<LC_NUMERIC> and C<LC_MONETARY> locales. (If you just want the name of
617 the current locale for a particular category, use C<POSIX::setlocale()>
618 with a single parameter--see L<The setlocale function>.)
620 use POSIX qw(locale_h);
622 # Get a reference to a hash of locale-dependent info
623 $locale_values = localeconv();
625 # Output sorted list of the values
626 for (sort keys %$locale_values) {
627 printf "%-20s = %s\n", $_, $locale_values->{$_}
630 C<localeconv()> takes no arguments, and returns B<a reference to> a hash.
631 The keys of this hash are variable names for formatting, such as
632 C<decimal_point> and C<thousands_sep>. The values are the
633 corresponding, er, values. See L<POSIX/localeconv> for a longer
634 example listing the categories an implementation might be expected to
635 provide; some provide more and others fewer. You don't need an
636 explicit C<use locale>, because C<localeconv()> always observes the
639 Here's a simple-minded example program that rewrites its command-line
640 parameters as integers correctly formatted in the current locale:
642 use POSIX qw(locale_h);
644 # Get some of locale's numeric formatting parameters
645 my ($thousands_sep, $grouping) =
646 @{localeconv()}{'thousands_sep', 'grouping'};
648 # Apply defaults if values are missing
649 $thousands_sep = ',' unless $thousands_sep;
651 # grouping and mon_grouping are packed lists
652 # of small integers (characters) telling the
653 # grouping (thousand_seps and mon_thousand_seps
654 # being the group dividers) of numbers and
655 # monetary quantities. The integers' meanings:
656 # 255 means no more grouping, 0 means repeat
657 # the previous grouping, 1-254 means use that
658 # as the current grouping. Grouping goes from
659 # right to left (low to high digits). In the
660 # below we cheat slightly by never using anything
661 # else than the first grouping (whatever that is).
663 @grouping = unpack("C*", $grouping);
668 # Format command line params for current locale
670 $_ = int; # Chop non-integer part
672 s/(\d)(\d{$grouping[0]}($|$thousands_sep))/$1$thousands_sep$2/;
677 =head2 I18N::Langinfo
679 Another interface for querying locale-dependent information is the
680 C<I18N::Langinfo::langinfo()> function, available at least in Unix-like
683 The following example will import the C<langinfo()> function itself and
684 three constants to be used as arguments to C<langinfo()>: a constant for
685 the abbreviated first day of the week (the numbering starts from
686 Sunday = 1) and two more constants for the affirmative and negative
687 answers for a yes/no question in the current locale.
689 use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
691 my ($abday_1, $yesstr, $nostr)
692 = map { langinfo } qw(ABDAY_1 YESSTR NOSTR);
694 print "$abday_1? [$yesstr/$nostr] ";
696 In other words, in the "C" (or English) locale the above will probably
697 print something like:
701 See L<I18N::Langinfo> for more information.
703 =head1 LOCALE CATEGORIES
705 The following subsections describe basic locale categories. Beyond these,
706 some combination categories allow manipulation of more than one
707 basic category at a time. See L<"ENVIRONMENT"> for a discussion of these.
709 =head2 Category LC_COLLATE: Collation
711 In the scope of S<C<use locale>> (but not a
712 C<use locale ':not_characters'>), Perl looks to the C<LC_COLLATE>
713 environment variable to determine the application's notions on collation
714 (ordering) of characters. For example, "b" follows "a" in Latin
715 alphabets, but where do "E<aacute>" and "E<aring>" belong? And while
716 "color" follows "chocolate" in English, what about in traditional Spanish?
718 The following collations all make sense and you may meet any of them
726 Here is a code snippet to tell what "word"
727 characters are in the current locale, in that locale's order:
730 print +(sort grep /\w/, map { chr } 0..255), "\n";
732 Compare this with the characters that you see and their order if you
733 state explicitly that the locale should be ignored:
736 print +(sort grep /\w/, map { chr } 0..255), "\n";
738 This machine-native collation (which is what you get unless S<C<use
739 locale>> has appeared earlier in the same block) must be used for
740 sorting raw binary data, whereas the locale-dependent collation of the
741 first example is useful for natural text.
743 As noted in L<USING LOCALES>, C<cmp> compares according to the current
744 collation locale when C<use locale> is in effect, but falls back to a
745 char-by-char comparison for strings that the locale says are equal. You
746 can use C<POSIX::strcoll()> if you don't want this fall-back:
748 use POSIX qw(strcoll);
750 !strcoll("space and case ignored", "SpaceAndCaseIgnored");
752 C<$equal_in_locale> will be true if the collation locale specifies a
753 dictionary-like ordering that ignores space characters completely and
756 Perl only supports single-byte locales for C<LC_COLLATE>. This means
757 that a UTF-8 locale likely will just give you machine-native ordering.
758 Use L<Unicode::Collate> for the full implementation of the Unicode
761 If you have a single string that you want to check for "equality in
762 locale" against several others, you might think you could gain a little
763 efficiency by using C<POSIX::strxfrm()> in conjunction with C<eq>:
765 use POSIX qw(strxfrm);
766 $xfrm_string = strxfrm("Mixed-case string");
767 print "locale collation ignores spaces\n"
768 if $xfrm_string eq strxfrm("Mixed-casestring");
769 print "locale collation ignores hyphens\n"
770 if $xfrm_string eq strxfrm("Mixedcase string");
771 print "locale collation ignores case\n"
772 if $xfrm_string eq strxfrm("mixed-case string");
774 C<strxfrm()> takes a string and maps it into a transformed string for use
775 in char-by-char comparisons against other transformed strings during
776 collation. "Under the hood", locale-affected Perl comparison operators
777 call C<strxfrm()> for both operands, then do a char-by-char
778 comparison of the transformed strings. By calling C<strxfrm()> explicitly
779 and using a non locale-affected comparison, the example attempts to save
780 a couple of transformations. But in fact, it doesn't save anything: Perl
781 magic (see L<perlguts/Magic Variables>) creates the transformed version of a
782 string the first time it's needed in a comparison, then keeps this version around
783 in case it's needed again. An example rewritten the easy way with
784 C<cmp> runs just about as fast. It also copes with null characters
785 embedded in strings; if you call C<strxfrm()> directly, it treats the first
786 null it finds as a terminator. don't expect the transformed strings
787 it produces to be portable across systems--or even from one revision
788 of your operating system to the next. In short, don't call C<strxfrm()>
789 directly: let Perl do it for you.
791 Note: C<use locale> isn't shown in some of these examples because it isn't
792 needed: C<strcoll()> and C<strxfrm()> are POSIX functions
793 which use the standard system-supplied C<libc> functions that
794 always obey the current C<LC_COLLATE> locale.
796 =head2 Category LC_CTYPE: Character Types
798 In the scope of S<C<use locale>> (but not a
799 C<use locale ':not_characters'>), Perl obeys the C<LC_CTYPE> locale
800 setting. This controls the application's notion of which characters are
801 alphabetic, numeric, punctuation, I<etc>. This affects Perl's C<\w>
802 regular expression metanotation,
803 which stands for alphanumeric characters--that is, alphabetic,
804 numeric, and the platform's native underscore.
805 (Consult L<perlre> for more information about
806 regular expressions.) Thanks to C<LC_CTYPE>, depending on your locale
807 setting, characters like "E<aelig>", "E<eth>", "E<szlig>", and
808 "E<oslash>" may be understood as C<\w> characters.
809 It also affects things like C<\s>, C<\D>, and the POSIX character
810 classes, like C<[[:graph:]]>. (See L<perlrecharclass> for more
811 information on all these.)
813 The C<LC_CTYPE> locale also provides the map used in transliterating
814 characters between lower and uppercase. This affects the case-mapping
815 functions--C<fc()>, C<lc()>, C<lcfirst()>, C<uc()>, and C<ucfirst()>; case-mapping
816 interpolation with C<\F>, C<\l>, C<\L>, C<\u>, or C<\U> in double-quoted
817 strings and C<s///> substitutions; and case-independent regular expression
818 pattern matching using the C<i> modifier.
820 Finally, C<LC_CTYPE> affects the (deprecated) POSIX character-class test
821 functions--C<POSIX::isalpha()>, C<POSIX::islower()>, and so on. For
822 example, if you move from the "C" locale to a 7-bit Scandinavian one,
823 you may find--possibly to your surprise--that "|" moves from the
824 C<POSIX::ispunct()> class to C<POSIX::isalpha()>.
825 Unfortunately, this creates big problems for regular expressions. "|" still
826 means alternation even though it matches C<\w>.
828 Starting in v5.20, Perl supports UTF-8 locales for C<LC_CTYPE>, but
829 otherwise Perl only supports single-byte locales, such as the ISO 8859
830 series. This means that wide character locales, for example for Asian
831 languages, are not supported. The UTF-8 locale support is actually a
832 superset of POSIX locales, because it is really full Unicode behavior
833 as if no locale were in effect at all (except for tainting; see
834 L</SECURITY>). POSIX locales, even UTF-8 ones,
835 are lacking certain concepts in Unicode, such as the idea that changing
836 the case of a character could expand to be more than one character.
837 Perl in a UTF-8 locale, will give you that expansion. Prior to v5.20,
838 Perl treated a UTF-8 locale on some platforms like an ISO 8859-1 one,
839 with some restrictions, and on other platforms more like the "C" locale.
840 For releases v5.16 and v5.18, C<S<use locale 'not_characters>> could be
841 used as a workaround for this (see L</Unicode and UTF-8>).
843 Note that there are quite a few things that are unaffected by the
844 current locale. All the escape sequences for particular characters,
845 C<\n> for example, always mean the platform's native one. This means,
846 for example, that C<\N> in regular expressions (every character
847 but new-line) works on the platform character set.
849 B<Note:> A broken or malicious C<LC_CTYPE> locale definition may result
850 in clearly ineligible characters being considered to be alphanumeric by
851 your application. For strict matching of (mundane) ASCII letters and
852 digits--for example, in command strings--locale-aware applications
853 should use C<\w> with the C</a> regular expression modifier. See L<"SECURITY">.
855 =head2 Category LC_NUMERIC: Numeric Formatting
857 After a proper C<POSIX::setlocale()> call, and within the scope of one
858 of the C<use locale> variants, Perl obeys the C<LC_NUMERIC>
859 locale information, which controls an application's idea of how numbers
860 should be formatted for human readability.
861 In most implementations the only effect is to
862 change the character used for the decimal point--perhaps from "." to ",".
863 The functions aren't aware of such niceties as thousands separation and
864 so on. (See L<The localeconv function> if you care about these things.)
866 use POSIX qw(strtod setlocale LC_NUMERIC);
869 setlocale LC_NUMERIC, "";
871 $n = 5/2; # Assign numeric 2.5 to $n
873 $a = " $n"; # Locale-dependent conversion to string
875 print "half five is $n\n"; # Locale-dependent output
877 printf "half five is %g\n", $n; # Locale-dependent output
879 print "DECIMAL POINT IS COMMA\n"
880 if $n == (strtod("2,5"))[0]; # Locale-dependent conversion
882 See also L<I18N::Langinfo> and C<RADIXCHAR>.
884 =head2 Category LC_MONETARY: Formatting of monetary amounts
886 The C standard defines the C<LC_MONETARY> category, but not a function
887 that is affected by its contents. (Those with experience of standards
888 committees will recognize that the working group decided to punt on the
889 issue.) Consequently, Perl essentially takes no notice of it. If you
890 really want to use C<LC_MONETARY>, you can query its contents--see
891 L<The localeconv function>--and use the information that it returns in your
892 application's own formatting of currency amounts. However, you may well
893 find that the information, voluminous and complex though it may be, still
894 does not quite meet your requirements: currency formatting is a hard nut
897 See also L<I18N::Langinfo> and C<CRNCYSTR>.
901 Output produced by C<POSIX::strftime()>, which builds a formatted
902 human-readable date/time string, is affected by the current C<LC_TIME>
903 locale. Thus, in a French locale, the output produced by the C<%B>
904 format element (full month name) for the first month of the year would
905 be "janvier". Here's how to get a list of long month names in the
908 use POSIX qw(strftime);
910 $long_month_name[$_] =
911 strftime("%B", 0, 0, 0, 1, $_, 96);
914 Note: C<use locale> isn't needed in this example: C<strftime()> is a POSIX
915 function which uses the standard system-supplied C<libc> function that
916 always obeys the current C<LC_TIME> locale.
918 See also L<I18N::Langinfo> and C<ABDAY_1>..C<ABDAY_7>, C<DAY_1>..C<DAY_7>,
919 C<ABMON_1>..C<ABMON_12>, and C<ABMON_1>..C<ABMON_12>.
921 =head2 Other categories
923 The remaining locale categories are not currently used by Perl itself.
924 But again note that things Perl interacts with may use these, including
925 extensions outside the standard Perl distribution, and by the
926 operating system and its utilities. Note especially that the string
927 value of C<$!> and the error messages given by external utilities may
928 be changed by C<LC_MESSAGES>. If you want to have portable error
929 codes, use C<%!>. See L<Errno>.
933 Although the main discussion of Perl security issues can be found in
934 L<perlsec>, a discussion of Perl's locale handling would be incomplete
935 if it did not draw your attention to locale-dependent security issues.
936 Locales--particularly on systems that allow unprivileged users to
937 build their own locales--are untrustworthy. A malicious (or just plain
938 broken) locale can make a locale-aware application give unexpected
939 results. Here are a few possibilities:
945 Regular expression checks for safe file names or mail addresses using
946 C<\w> may be spoofed by an C<LC_CTYPE> locale that claims that
947 characters such as "E<gt>" and "|" are alphanumeric.
951 String interpolation with case-mapping, as in, say, C<$dest =
952 "C:\U$name.$ext">, may produce dangerous results if a bogus LC_CTYPE
953 case-mapping table is in effect.
957 A sneaky C<LC_COLLATE> locale could result in the names of students with
958 "D" grades appearing ahead of those with "A"s.
962 An application that takes the trouble to use information in
963 C<LC_MONETARY> may format debits as if they were credits and vice versa
964 if that locale has been subverted. Or it might make payments in US
965 dollars instead of Hong Kong dollars.
969 The date and day names in dates formatted by C<strftime()> could be
970 manipulated to advantage by a malicious user able to subvert the
971 C<LC_DATE> locale. ("Look--it says I wasn't in the building on
976 Such dangers are not peculiar to the locale system: any aspect of an
977 application's environment which may be modified maliciously presents
978 similar challenges. Similarly, they are not specific to Perl: any
979 programming language that allows you to write programs that take
980 account of their environment exposes you to these issues.
982 Perl cannot protect you from all possibilities shown in the
983 examples--there is no substitute for your own vigilance--but, when
984 C<use locale> is in effect, Perl uses the tainting mechanism (see
985 L<perlsec>) to mark string results that become locale-dependent, and
986 which may be untrustworthy in consequence. Here is a summary of the
987 tainting behavior of operators and functions that may be affected by
994 B<Comparison operators> (C<lt>, C<le>, C<ge>, C<gt> and C<cmp>):
996 Scalar true/false (or less/equal/greater) result is never tainted.
1000 B<Case-mapping interpolation> (with C<\l>, C<\L>, C<\u>, C<\U>, or C<\F>)
1002 Result string containing interpolated material is tainted if
1003 C<use locale> (but not S<C<use locale ':not_characters'>>) is in effect.
1007 B<Matching operator> (C<m//>):
1009 Scalar true/false result never tainted.
1011 All subpatterns, either delivered as a list-context result or as C<$1>
1012 I<etc>., are tainted if C<use locale> (but not
1013 S<C<use locale ':not_characters'>>) is in effect, and the subpattern
1014 regular expression contains a locale-dependent construct. These
1015 constructs include C<\w> (to match an alphanumeric character), C<\W>
1016 (non-alphanumeric character), C<\b> and C<\B> (word-boundary and
1017 non-boundardy, which depend on what C<\w> and C<\W> match), C<\s>
1018 (whitespace character), C<\S> (non whitespace character), C<\d> and
1019 C<\D> (digits and non-digits), and the POSIX character classes, such as
1020 C<[:alpha:]> (see L<perlrecharclass/POSIX Character Classes>).
1022 Tainting is also likely if the pattern is to be matched
1023 case-insensitively (via C</i>). The exception is if all the code points
1024 to be matched this way are above 255 and do not have folds under Unicode
1025 rules to below 256. Tainting is not done for these because Perl
1026 only uses Unicode rules for such code points, and those rules are the
1027 same no matter what the current locale.
1029 The matched-pattern variables, C<$&>, C<$`> (pre-match), C<$'>
1030 (post-match), and C<$+> (last match) also are tainted.
1034 B<Substitution operator> (C<s///>):
1036 Has the same behavior as the match operator. Also, the left
1037 operand of C<=~> becomes tainted when C<use locale>
1038 (but not S<C<use locale ':not_characters'>>) is in effect if modified as
1039 a result of a substitution based on a regular
1040 expression match involving any of the things mentioned in the previous
1041 item, or of case-mapping, such as C<\l>, C<\L>,C<\u>, C<\U>, or C<\F>.
1045 B<Output formatting functions> (C<printf()> and C<write()>):
1047 Results are never tainted because otherwise even output from print,
1048 for example C<print(1/7)>, should be tainted if C<use locale> is in
1053 B<Case-mapping functions> (C<lc()>, C<lcfirst()>, C<uc()>, C<ucfirst()>):
1055 Results are tainted if C<use locale> (but not
1056 S<C<use locale ':not_characters'>>) is in effect.
1060 B<POSIX locale-dependent functions> (C<localeconv()>, C<strcoll()>,
1061 C<strftime()>, C<strxfrm()>):
1063 Results are never tainted.
1067 B<POSIX character class tests> (C<POSIX::isalnum()>,
1068 C<POSIX::isalpha()>, C<POSIX::isdigit()>, C<POSIX::isgraph()>,
1069 C<POSIX::islower()>, C<POSIX::isprint()>, C<POSIX::ispunct()>,
1070 C<POSIX::isspace()>, C<POSIX::isupper()>, C<POSIX::isxdigit()>):
1072 True/false results are never tainted.
1076 Three examples illustrate locale-dependent tainting.
1077 The first program, which ignores its locale, won't run: a value taken
1078 directly from the command line may not be used to name an output file
1079 when taint checks are enabled.
1081 #/usr/local/bin/perl -T
1082 # Run with taint checking
1084 # Command line sanity check omitted...
1085 $tainted_output_file = shift;
1087 open(F, ">$tainted_output_file")
1088 or warn "Open of $tainted_output_file failed: $!\n";
1090 The program can be made to run by "laundering" the tainted value through
1091 a regular expression: the second example--which still ignores locale
1092 information--runs, creating the file named on its command line
1095 #/usr/local/bin/perl -T
1097 $tainted_output_file = shift;
1098 $tainted_output_file =~ m%[\w/]+%;
1099 $untainted_output_file = $&;
1101 open(F, ">$untainted_output_file")
1102 or warn "Open of $untainted_output_file failed: $!\n";
1104 Compare this with a similar but locale-aware program:
1106 #/usr/local/bin/perl -T
1108 $tainted_output_file = shift;
1110 $tainted_output_file =~ m%[\w/]+%;
1111 $localized_output_file = $&;
1113 open(F, ">$localized_output_file")
1114 or warn "Open of $localized_output_file failed: $!\n";
1116 This third program fails to run because C<$&> is tainted: it is the result
1117 of a match involving C<\w> while C<use locale> is in effect.
1123 =item PERL_SKIP_LOCALE_INIT
1125 This environment variable, available starting in Perl v5.20, and if it
1126 evaluates to a TRUE value, tells Perl to not use the rest of the
1127 environment variables to initialize with. Instead, Perl uses whatever
1128 the current locale settings are. This is particularly useful in
1129 embedded environments, see
1130 L<perlembed/Using embedded Perl with POSIX locales>.
1134 A string that can suppress Perl's warning about failed locale settings
1135 at startup. Failure can occur if the locale support in the operating
1136 system is lacking (broken) in some way--or if you mistyped the name of
1137 a locale when you set up your environment. If this environment
1138 variable is absent, or has a value that does not evaluate to integer
1139 zero--that is, "0" or ""-- Perl will complain about locale setting
1142 B<NOTE>: PERL_BADLANG only gives you a way to hide the warning message.
1143 The message tells about some problem in your system's locale support,
1144 and you should investigate what the problem is.
1148 The following environment variables are not specific to Perl: They are
1149 part of the standardized (ISO C, XPG4, POSIX 1.c) C<setlocale()> method
1150 for controlling an application's opinion on data. Windows is non-POSIX,
1151 but Perl arranges for the following to work as described anyway.
1152 If the locale given by an environment variable is not valid, Perl tries
1153 the next lower one in priority. If none are valid, on Windows, the
1154 system default locale is then tried. If all else fails, the C<"C">
1155 locale is used. If even that doesn't work, something is badly broken,
1156 but Perl tries to forge ahead with whatever the locale settinga might
1163 C<LC_ALL> is the "override-all" locale environment variable. If
1164 set, it overrides all the rest of the locale environment variables.
1168 B<NOTE>: C<LANGUAGE> is a GNU extension, it affects you only if you
1169 are using the GNU libc. This is the case if you are using e.g. Linux.
1170 If you are using "commercial" Unixes you are most probably I<not>
1171 using GNU libc and you can ignore C<LANGUAGE>.
1173 However, in the case you are using C<LANGUAGE>: it affects the
1174 language of informational, warning, and error messages output by
1175 commands (in other words, it's like C<LC_MESSAGES>) but it has higher
1176 priority than C<LC_ALL>. Moreover, it's not a single value but
1177 instead a "path" (":"-separated list) of I<languages> (not locales).
1178 See the GNU C<gettext> library documentation for more information.
1182 In the absence of C<LC_ALL>, C<LC_CTYPE> chooses the character type
1183 locale. In the absence of both C<LC_ALL> and C<LC_CTYPE>, C<LANG>
1184 chooses the character type locale.
1188 In the absence of C<LC_ALL>, C<LC_COLLATE> chooses the collation
1189 (sorting) locale. In the absence of both C<LC_ALL> and C<LC_COLLATE>,
1190 C<LANG> chooses the collation locale.
1194 In the absence of C<LC_ALL>, C<LC_MONETARY> chooses the monetary
1195 formatting locale. In the absence of both C<LC_ALL> and C<LC_MONETARY>,
1196 C<LANG> chooses the monetary formatting locale.
1200 In the absence of C<LC_ALL>, C<LC_NUMERIC> chooses the numeric format
1201 locale. In the absence of both C<LC_ALL> and C<LC_NUMERIC>, C<LANG>
1202 chooses the numeric format.
1206 In the absence of C<LC_ALL>, C<LC_TIME> chooses the date and time
1207 formatting locale. In the absence of both C<LC_ALL> and C<LC_TIME>,
1208 C<LANG> chooses the date and time formatting locale.
1212 C<LANG> is the "catch-all" locale environment variable. If it is set, it
1213 is used as the last resort after the overall C<LC_ALL> and the
1214 category-specific C<LC_...>.
1220 The LC_NUMERIC controls the numeric output:
1223 use POSIX qw(locale_h); # Imports setlocale() and the LC_ constants.
1224 setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
1225 printf "%g\n", 1.23; # If the "fr_FR" succeeded, probably shows 1,23.
1227 and also how strings are parsed by C<POSIX::strtod()> as numbers:
1230 use POSIX qw(locale_h strtod);
1231 setlocale(LC_NUMERIC, "de_DE") or die "Entschuldigung";
1232 my $x = strtod("2,34") + 5;
1233 print $x, "\n"; # Probably shows 7,34.
1237 =head2 String C<eval> and C<LC_NUMERIC>
1239 A string L<eval|perlfunc/eval EXPR> parses its expression as standard
1240 Perl. It is therefore expecting the decimal point to be a dot. If
1241 C<LC_NUMERIC> is set to have this be a comma instead, the parsing will
1242 be confused, perhaps silently.
1245 use POSIX qw(locale_h);
1246 setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
1248 print eval "$a + 1.5";
1251 prints C<13,5>. This is because in that locale, the comma is the
1252 decimal point character. The C<eval> thus expands to:
1256 and the result is not what you likely expected. No warnings are
1257 generated. If you do string C<eval>'s within the scope of
1258 S<C<use locale>>, you should instead change the C<eval> line to do
1261 print eval "no locale; $a + 1.5";
1265 =head2 Backward compatibility
1267 Versions of Perl prior to 5.004 B<mostly> ignored locale information,
1268 generally behaving as if something similar to the C<"C"> locale were
1269 always in force, even if the program environment suggested otherwise
1270 (see L<The setlocale function>). By default, Perl still behaves this
1271 way for backward compatibility. If you want a Perl application to pay
1272 attention to locale information, you B<must> use the S<C<use locale>>
1273 pragma (see L<The use locale pragma>) or, in the unlikely event
1274 that you want to do so for just pattern matching, the
1275 C</l> regular expression modifier (see L<perlre/Character set
1276 modifiers>) to instruct it to do so.
1278 Versions of Perl from 5.002 to 5.003 did use the C<LC_CTYPE>
1279 information if available; that is, C<\w> did understand what
1280 were the letters according to the locale environment variables.
1281 The problem was that the user had no control over the feature:
1282 if the C library supported locales, Perl used them.
1284 =head2 I18N:Collate obsolete
1286 In versions of Perl prior to 5.004, per-locale collation was possible
1287 using the C<I18N::Collate> library module. This module is now mildly
1288 obsolete and should be avoided in new applications. The C<LC_COLLATE>
1289 functionality is now integrated into the Perl core language: One can
1290 use locale-specific scalar data completely normally with C<use locale>,
1291 so there is no longer any need to juggle with the scalar references of
1294 =head2 Sort speed and memory use impacts
1296 Comparing and sorting by locale is usually slower than the default
1297 sorting; slow-downs of two to four times have been observed. It will
1298 also consume more memory: once a Perl scalar variable has participated
1299 in any string comparison or sorting operation obeying the locale
1300 collation rules, it will take 3-15 times more memory than before. (The
1301 exact multiplier depends on the string's contents, the operating system
1302 and the locale.) These downsides are dictated more by the operating
1303 system's implementation of the locale system than by Perl.
1305 =head2 Freely available locale definitions
1307 The Unicode CLDR project extracts the POSIX portion of many of its
1308 locales, available at
1310 http://unicode.org/Public/cldr/latest/
1312 There is a large collection of locale definitions at:
1314 http://std.dkuug.dk/i18n/WG15-collection/locales/
1316 You should be aware that it is
1317 unsupported, and is not claimed to be fit for any purpose. If your
1318 system allows installation of arbitrary locales, you may find the
1319 definitions useful as they are, or as a basis for the development of
1322 =head2 I18n and l10n
1324 "Internationalization" is often abbreviated as B<i18n> because its first
1325 and last letters are separated by eighteen others. (You may guess why
1326 the internalin ... internaliti ... i18n tends to get abbreviated.) In
1327 the same way, "localization" is often abbreviated to B<l10n>.
1329 =head2 An imperfect standard
1331 Internationalization, as defined in the C and POSIX standards, can be
1332 criticized as incomplete, ungainly, and having too large a granularity.
1333 (Locales apply to a whole process, when it would arguably be more useful
1334 to have them apply to a single thread, window group, or whatever.) They
1335 also have a tendency, like standards groups, to divide the world into
1336 nations, when we all know that the world can equally well be divided
1337 into bankers, bikers, gamers, and so on.
1339 =head1 Unicode and UTF-8
1341 The support of Unicode is new starting from Perl version v5.6, and more fully
1342 implemented in versions v5.8 and later. See L<perluniintro>.
1344 Starting in Perl v5.20, UTF-8 locales are supported in Perl, except for
1345 C<LC_COLLATE> (use L<Unicode::Collate> instead). If you have Perl v5.16
1346 or v5.18 and can't upgrade, you can use
1348 use locale ':not_characters';
1350 When this form of the pragma is used, only the non-character portions of
1351 locales are used by Perl, for example C<LC_NUMERIC>. Perl assumes that
1352 you have translated all the characters it is to operate on into Unicode
1353 (actually the platform's native character set (ASCII or EBCDIC) plus
1354 Unicode). For data in files, this can conveniently be done by also
1359 This pragma arranges for all inputs from files to be translated into
1360 Unicode from the current locale as specified in the environment (see
1361 L</ENVIRONMENT>), and all outputs to files to be translated back
1362 into the locale. (See L<open>). On a per-filehandle basis, you can
1363 instead use the L<PerlIO::locale> module, or the L<Encode::Locale>
1364 module, both available from CPAN. The latter module also has methods to
1365 ease the handling of C<ARGV> and environment variables, and can be used
1366 on individual strings. If you know that all your locales will be
1367 UTF-8, as many are these days, you can use the L<B<-C>|perlrun/-C>
1368 command line switch.
1370 This form of the pragma allows essentially seamless handling of locales
1371 with Unicode. The collation order will be by Unicode code point order.
1373 recommended that when you need to order and sort strings that you use
1374 the standard module L<Unicode::Collate> which gives much better results
1375 in many instances than you can get with the old-style locale handling.
1377 All the modules and switches just described can be used in v5.20 with
1378 just plain C<use locale>, and, should the input locales not be UTF-8,
1379 you'll get the less than ideal behavior, described below, that you get
1380 with pre-v5.16 Perls, or when you use the locale pragma without the
1381 C<:not_characters> parameter in v5.16 and v5.18. If you are using
1382 exclusively UTF-8 locales in v5.20 and higher, the rest of this section
1383 does not apply to you.
1385 There are two cases, multi-byte and single-byte locales. First
1388 The only multi-byte (or wide character) locale that Perl is ever likely
1389 to support is UTF-8. This is due to the difficulty of implementation,
1390 the fact that high quality UTF-8 locales are now published for every
1391 area of the world (L<http://unicode.org/Public/cldr/latest/>), and that
1392 failing all that you can use the L<Encode> module to translate to/from
1393 your locale. So, you'll have to do one of those things if you're using
1394 one of these locales, such as Big5 or Shift JIS. For UTF-8 locales, in
1395 Perls (pre v5.20) that don't have full UTF-8 locale support, they may
1396 work reasonably well (depending on your C library implementation)
1398 they and Perl store characters that take up multiple bytes the same way.
1399 However, some, if not most, C library implementations may not process
1400 the characters in the upper half of the Latin-1 range (128 - 255)
1401 properly under LC_CTYPE. To see if a character is a particular type
1402 under a locale, Perl uses the functions like C<isalnum()>. Your C
1403 library may not work for UTF-8 locales with those functions, instead
1404 only working under the newer wide library functions like C<iswalnum()>.
1405 However, they are treated like single-byte locales, and will have the
1406 restrictions described below.
1408 For single-byte locales,
1409 Perl generally takes the tack to use locale rules on code points that can fit
1410 in a single byte, and Unicode rules for those that can't (though this
1411 isn't uniformly applied, see the note at the end of this section). This
1412 prevents many problems in locales that aren't UTF-8. Suppose the locale
1413 is ISO8859-7, Greek. The character at 0xD7 there is a capital Chi. But
1414 in the ISO8859-1 locale, Latin1, it is a multiplication sign. The POSIX
1415 regular expression character class C<[[:alpha:]]> will magically match
1416 0xD7 in the Greek locale but not in the Latin one.
1418 However, there are places where this breaks down. Certain Perl constructs are
1419 for Unicode only, such as C<\p{Alpha}>. They assume that 0xD7 always has its
1420 Unicode meaning (or the equivalent on EBCDIC platforms). Since Latin1 is a
1421 subset of Unicode and 0xD7 is the multiplication sign in both Latin1 and
1422 Unicode, C<\p{Alpha}> will never match it, regardless of locale. A similar
1423 issue occurs with C<\N{...}>. Prior to v5.20, It is therefore a bad
1424 idea to use C<\p{}> or
1425 C<\N{}> under plain C<use locale>--I<unless> you can guarantee that the
1426 locale will be a ISO8859-1. Use POSIX character classes instead.
1428 Another problem with this approach is that operations that cross the
1429 single byte/multiple byte boundary are not well-defined, and so are
1430 disallowed. (This boundary is between the codepoints at 255/256.).
1431 For example, lower casing LATIN CAPITAL LETTER Y WITH DIAERESIS (U+0178)
1432 should return LATIN SMALL LETTER Y WITH DIAERESIS (U+00FF). But in the
1433 Greek locale, for example, there is no character at 0xFF, and Perl
1434 has no way of knowing what the character at 0xFF is really supposed to
1435 represent. Thus it disallows the operation. In this mode, the
1436 lowercase of U+0178 is itself.
1438 The same problems ensue if you enable automatic UTF-8-ification of your
1439 standard file handles, default C<open()> layer, and C<@ARGV> on non-ISO8859-1,
1440 non-UTF-8 locales (by using either the B<-C> command line switch or the
1441 C<PERL_UNICODE> environment variable; see L<perlrun>).
1442 Things are read in as UTF-8, which would normally imply a Unicode
1443 interpretation, but the presence of a locale causes them to be interpreted
1444 in that locale instead. For example, a 0xD7 code point in the Unicode
1445 input, which should mean the multiplication sign, won't be interpreted by
1446 Perl that way under the Greek locale. This is not a problem
1447 I<provided> you make certain that all locales will always and only be either
1448 an ISO8859-1, or, if you don't have a deficient C library, a UTF-8 locale.
1450 Still another problem is that this approach can lead to two code
1451 points meaning the same character. Thus in a Greek locale, both U+03A7
1452 and U+00D7 are GREEK CAPITAL LETTER CHI.
1454 Vendor locales are notoriously buggy, and it is difficult for Perl to test
1455 its locale-handling code because this interacts with code that Perl has no
1456 control over; therefore the locale-handling code in Perl may be buggy as
1457 well. (However, the Unicode-supplied locales should be better, and
1458 there is a feed back mechanism to correct any problems. See
1459 L</Freely available locale definitions>.)
1461 If you have Perl v5.16, the problems mentioned above go away if you use
1462 the C<:not_characters> parameter to the locale pragma (except for vendor
1463 bugs in the non-character portions). If you don't have v5.16, and you
1464 I<do> have locales that work, using them may be worthwhile for certain
1465 specific purposes, as long as you keep in mind the gotchas already
1466 mentioned. For example, if the collation for your locales works, it
1467 runs faster under locales than under L<Unicode::Collate>; and you gain
1468 access to such things as the local currency symbol and the names of the
1469 months and days of the week. (But to hammer home the point, in v5.16,
1470 you get this access without the downsides of locales by using the
1471 C<:not_characters> form of the pragma.)
1473 Note: The policy of using locale rules for code points that can fit in a
1474 byte, and Unicode rules for those that can't is not uniformly applied.
1475 Pre-v5.12, it was somewhat haphazard; in v5.12 it was applied fairly
1476 consistently to regular expression matching except for bracketed
1477 character classes; in v5.14 it was extended to all regex matches; and in
1478 v5.16 to the casing operations such as C<"\L"> and C<uc()>. For
1479 collation, in all releases, the system's C<strxfrm()> function is called,
1480 and whatever it does is what you get.
1484 =head2 Broken systems
1486 In certain systems, the operating system's locale support
1487 is broken and cannot be fixed or used by Perl. Such deficiencies can
1488 and will result in mysterious hangs and/or Perl core dumps when
1489 C<use locale> is in effect. When confronted with such a system,
1490 please report in excruciating detail to <F<perlbug@perl.org>>, and
1491 also contact your vendor: bug fixes may exist for these problems
1492 in your operating system. Sometimes such bug fixes are called an
1493 operating system upgrade. If you have the source for Perl, include in
1494 the perlbug email the output of the test described above in L</Testing
1495 for broken locales>.
1499 L<I18N::Langinfo>, L<perluniintro>, L<perlunicode>, L<open>,
1500 L<POSIX/isalnum>, L<POSIX/isalpha>,
1501 L<POSIX/isdigit>, L<POSIX/isgraph>, L<POSIX/islower>,
1502 L<POSIX/isprint>, L<POSIX/ispunct>, L<POSIX/isspace>,
1503 L<POSIX/isupper>, L<POSIX/isxdigit>, L<POSIX/localeconv>,
1504 L<POSIX/setlocale>, L<POSIX/strcoll>, L<POSIX/strftime>,
1505 L<POSIX/strtod>, L<POSIX/strxfrm>.
1507 For special considerations when Perl is embedded in a C program,
1508 see L<perlembed/Using embedded Perl with POSIX locales>.
1512 Jarkko Hietaniemi's original F<perli18n.pod> heavily hacked by Dominic
1513 Dunlop, assisted by the perl5-porters. Prose worked over a bit by
1514 Tom Christiansen, and updated by Perl 5 porters.