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 was 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, and their use for character sets
31 has mostly been supplanted by Unicode (see L<perlunitut> for an
32 introduction to that, and keep on reading here for how Unicode interacts
33 with locales in Perl).
35 Perl continues to support the old locale system, and starting in v5.16,
36 provides a hybrid way to use the Unicode character set, along with the
37 other portions of locales that may not be so problematic.
38 (Unicode is also creating C<CLDR>, the "Common Locale Data Repository",
39 L<http://cldr.unicode.org/> which includes more types of information than
40 are available in the POSIX locale system. At the time of this writing,
41 there was no CPAN module that provides access to this XML-encoded data.
42 However, many of its locales have the POSIX-only data extracted, and are
43 available at L<http://unicode.org/Public/cldr/latest/>.)
45 =head1 WHAT IS A LOCALE
47 A locale is a set of data that describes various aspects of how various
48 communities in the world categorize their world. These categories are
49 broken down into the following types (some of which include a brief
54 =item Category LC_NUMERIC: Numeric formatting
56 This indicates how numbers should be formatted for human readability,
57 for example the character used as the decimal point.
59 =item Category LC_MONETARY: Formatting of monetary amounts
62 The nbsp below makes this look better
66 =item Category LC_TIME: Date/Time formatting
69 The nbsp below makes this look better
73 =item Category LC_MESSAGES: Error and other messages
75 This for the most part is beyond the scope of Perl
77 =item Category LC_COLLATE: Collation
79 This indicates the ordering of letters for comparision and sorting.
80 In Latin alphabets, for example, "b", generally follows "a".
82 =item Category LC_CTYPE: Character Types
84 This indicates, for example if a character is an uppercase letter.
88 More details on the categories are given below in L</LOCALE CATEGORIES>.
90 Together, these categories go a long way towards being able to customize
91 a single program to run in many different locations. But there are
92 deficiencies, so keep reading.
94 =head1 PREPARING TO USE LOCALES
96 Perl will not use locales unless specifically requested to (see L</NOTES> below
97 for the partial exception of C<write()>). But even if there is such a
98 request, B<all> of the following must be true for it to work properly:
104 B<Your operating system must support the locale system>. If it does,
105 you should find that the setlocale() function is a documented part of
110 B<Definitions for locales that you use must be installed>. You, or
111 your system administrator, must make sure that this is the case. The
112 available locales, the location in which they are kept, and the manner
113 in which they are installed all vary from system to system. Some systems
114 provide only a few, hard-wired locales and do not allow more to be
115 added. Others allow you to add "canned" locales provided by the system
116 supplier. Still others allow you or the system administrator to define
117 and add arbitrary locales. (You may have to ask your supplier to
118 provide canned locales that are not delivered with your operating
119 system.) Read your system documentation for further illumination.
123 B<Perl must believe that the locale system is supported>. If it does,
124 C<perl -V:d_setlocale> will say that the value for C<d_setlocale> is
129 If you want a Perl application to process and present your data
130 according to a particular locale, the application code should include
131 the S<C<use locale>> pragma (see L<The use locale pragma>) where
132 appropriate, and B<at least one> of the following must be true:
138 B<The locale-determining environment variables (see L</"ENVIRONMENT">)
139 must be correctly set up> at the time the application is started, either
140 by yourself or by whomever set up your system account; or
144 B<The application must set its own locale> using the method described in
145 L<The setlocale function>.
151 =head2 The use locale pragma
153 By default, Perl ignores the current locale. The S<C<use locale>>
154 pragma tells Perl to use the current locale for some operations.
155 Starting in v5.16, there is an optional parameter to this pragma:
157 use locale ':not_characters';
159 This parameter allows better mixing of locales and Unicode, and is
160 described fully in L</Unicode and UTF-8>, but briefly, it tells Perl to
161 not use the character portions of the locale definition, that is
162 the C<LC_CTYPE> and C<LC_COLLATE> categories. Instead it will use the
163 native (extended by Unicode) character set. When using this parameter,
164 you are responsible for getting the external character set translated
165 into the native/Unicode one (which it already will be if it is one of
166 the increasingly popular UTF-8 locales). There are convenient ways of
167 doing this, as described in L</Unicode and UTF-8>.
169 The current locale is set at execution time by
170 L<setlocale()|/The setlocale function> described below. If that function
171 hasn't yet been called in the course of the program's execution, the
172 current locale is that which was determined by the L</"ENVIRONMENT"> in
173 effect at the start of the program, except that
174 C<L<LC_NUMERIC|/Category LC_NUMERIC: Numeric Formatting>> is always
175 initialized to the C locale (mentioned under L<Finding locales>).
176 If there is no valid environment, the current locale is undefined. It
177 is likely, but not necessarily, the "C" locale.
179 The operations that are affected by locale are:
183 =item B<Under C<use locale ':not_characters';>>
189 B<Format declarations> (format()) use C<LC_NUMERIC>
193 B<The POSIX date formatting function> (strftime()) uses C<LC_TIME>.
198 The nbsp below makes this look better
202 =item B<Under just plain C<use locale;>>
204 The above operations are affected, as well as the following:
210 B<The comparison operators> (C<lt>, C<le>, C<cmp>, C<ge>, and C<gt>) and
211 the POSIX string collation functions strcoll() and strxfrm() use
212 C<LC_COLLATE>. sort() is also affected if used without an
213 explicit comparison function, because it uses C<cmp> by default.
215 B<Note:> C<eq> and C<ne> are unaffected by locale: they always
216 perform a char-by-char comparison of their scalar operands. What's
217 more, if C<cmp> finds that its operands are equal according to the
218 collation sequence specified by the current locale, it goes on to
219 perform a char-by-char comparison, and only returns I<0> (equal) if the
220 operands are char-for-char identical. If you really want to know whether
221 two strings--which C<eq> and C<cmp> may consider different--are equal
222 as far as collation in the locale is concerned, see the discussion in
223 L<Category LC_COLLATE: Collation>.
227 B<Regular expressions and case-modification functions> (uc(), lc(),
228 ucfirst(), and lcfirst()) use C<LC_CTYPE>
234 The default behavior is restored with the S<C<no locale>> pragma, or
235 upon reaching the end of the block enclosing C<use locale>.
236 Note that C<use locale> and C<use locale ':not_characters'> may be
237 nested, and that what is in effect within an inner scope will revert to
238 the outer scope's rules at the end of the inner scope.
240 The string result of any operation that uses locale
241 information is tainted, as it is possible for a locale to be
242 untrustworthy. See L<"SECURITY">.
244 =head2 The setlocale function
246 You can switch locales as often as you wish at run time with the
247 POSIX::setlocale() function:
249 # Import locale-handling tool set from POSIX module.
250 # This example uses: setlocale -- the function call
251 # LC_CTYPE -- explained below
252 use POSIX qw(locale_h);
254 # query and save the old locale
255 $old_locale = setlocale(LC_CTYPE);
257 setlocale(LC_CTYPE, "fr_CA.ISO8859-1");
258 # LC_CTYPE now in locale "French, Canada, codeset ISO 8859-1"
260 setlocale(LC_CTYPE, "");
261 # LC_CTYPE now reset to default defined by LC_ALL/LC_CTYPE/LANG
262 # environment variables. See below for documentation.
264 # restore the old locale
265 setlocale(LC_CTYPE, $old_locale);
267 The first argument of setlocale() gives the B<category>, the second the
268 B<locale>. The category tells in what aspect of data processing you
269 want to apply locale-specific rules. Category names are discussed in
270 L</LOCALE CATEGORIES> and L</"ENVIRONMENT">. The locale is the name of a
271 collection of customization information corresponding to a particular
272 combination of language, country or territory, and codeset. Read on for
273 hints on the naming of locales: not all systems name locales as in the
276 If no second argument is provided and the category is something else
277 than LC_ALL, the function returns a string naming the current locale
278 for the category. You can use this value as the second argument in a
279 subsequent call to setlocale().
281 If no second argument is provided and the category is LC_ALL, the
282 result is implementation-dependent. It may be a string of
283 concatenated locale names (separator also implementation-dependent)
284 or a single locale name. Please consult your setlocale(3) man page for
287 If a second argument is given and it corresponds to a valid locale,
288 the locale for the category is set to that value, and the function
289 returns the now-current locale value. You can then use this in yet
290 another call to setlocale(). (In some implementations, the return
291 value may sometimes differ from the value you gave as the second
292 argument--think of it as an alias for the value you gave.)
294 As the example shows, if the second argument is an empty string, the
295 category's locale is returned to the default specified by the
296 corresponding environment variables. Generally, this results in a
297 return to the default that was in force when Perl started up: changes
298 to the environment made by the application after startup may or may not
299 be noticed, depending on your system's C library.
301 If the second argument does not correspond to a valid locale, the locale
302 for the category is not changed, and the function returns I<undef>.
304 Note that Perl ignores the current C<LC_CTYPE> and C<LC_COLLATE> locales
305 within the scope of a C<use locale ':not_characters'>.
307 For further information about the categories, consult setlocale(3).
309 =head2 Finding locales
311 For locales available in your system, consult also setlocale(3) to
312 see whether it leads to the list of available locales (search for the
313 I<SEE ALSO> section). If that fails, try the following command lines:
327 and see whether they list something resembling these
329 en_US.ISO8859-1 de_DE.ISO8859-1 ru_RU.ISO8859-5
330 en_US.iso88591 de_DE.iso88591 ru_RU.iso88595
333 english german russian
334 english.iso88591 german.iso88591 russian.iso88595
335 english.roman8 russian.koi8r
337 Sadly, even though the calling interface for setlocale() has been
338 standardized, names of locales and the directories where the
339 configuration resides have not been. The basic form of the name is
340 I<language_territory>B<.>I<codeset>, but the latter parts after
341 I<language> are not always present. The I<language> and I<country>
342 are usually from the standards B<ISO 3166> and B<ISO 639>, the
343 two-letter abbreviations for the countries and the languages of the
344 world, respectively. The I<codeset> part often mentions some B<ISO
345 8859> character set, the Latin codesets. For example, C<ISO 8859-1>
346 is the so-called "Western European codeset" that can be used to encode
347 most Western European languages adequately. Again, there are several
348 ways to write even the name of that one standard. Lamentably.
350 Two special locales are worth particular mention: "C" and "POSIX".
351 Currently these are effectively the same locale: the difference is
352 mainly that the first one is defined by the C standard, the second by
353 the POSIX standard. They define the B<default locale> in which
354 every program starts in the absence of locale information in its
355 environment. (The I<default> default locale, if you will.) Its language
356 is (American) English and its character codeset ASCII.
357 B<Warning>. The C locale delivered by some vendors may not
358 actually exactly match what the C standard calls for. So beware.
360 B<NOTE>: Not all systems have the "POSIX" locale (not all systems are
361 POSIX-conformant), so use "C" when you need explicitly to specify this
364 =head2 LOCALE PROBLEMS
366 You may encounter the following warning message at Perl startup:
368 perl: warning: Setting locale failed.
369 perl: warning: Please check that your locale settings:
372 are supported and installed on your system.
373 perl: warning: Falling back to the standard locale ("C").
375 This means that your locale settings had LC_ALL set to "En_US" and
376 LANG exists but has no value. Perl tried to believe you but could not.
377 Instead, Perl gave up and fell back to the "C" locale, the default locale
378 that is supposed to work no matter what. This usually means your locale
379 settings were wrong, they mention locales your system has never heard
380 of, or the locale installation in your system has problems (for example,
381 some system files are broken or missing). There are quick and temporary
382 fixes to these problems, as well as more thorough and lasting fixes.
384 =head2 Temporarily fixing locale problems
386 The two quickest fixes are either to render Perl silent about any
387 locale inconsistencies or to run Perl under the default locale "C".
389 Perl's moaning about locale problems can be silenced by setting the
390 environment variable PERL_BADLANG to a zero value, for example "0".
391 This method really just sweeps the problem under the carpet: you tell
392 Perl to shut up even when Perl sees that something is wrong. Do not
393 be surprised if later something locale-dependent misbehaves.
395 Perl can be run under the "C" locale by setting the environment
396 variable LC_ALL to "C". This method is perhaps a bit more civilized
397 than the PERL_BADLANG approach, but setting LC_ALL (or
398 other locale variables) may affect other programs as well, not just
399 Perl. In particular, external programs run from within Perl will see
400 these changes. If you make the new settings permanent (read on), all
401 programs you run see the changes. See L<"ENVIRONMENT"> for
402 the full list of relevant environment variables and L<USING LOCALES>
403 for their effects in Perl. Effects in other programs are
404 easily deducible. For example, the variable LC_COLLATE may well affect
405 your B<sort> program (or whatever the program that arranges "records"
406 alphabetically in your system is called).
408 You can test out changing these variables temporarily, and if the
409 new settings seem to help, put those settings into your shell startup
410 files. Consult your local documentation for the exact details. For in
411 Bourne-like shells (B<sh>, B<ksh>, B<bash>, B<zsh>):
413 LC_ALL=en_US.ISO8859-1
416 This assumes that we saw the locale "en_US.ISO8859-1" using the commands
417 discussed above. We decided to try that instead of the above faulty
418 locale "En_US"--and in Cshish shells (B<csh>, B<tcsh>)
420 setenv LC_ALL en_US.ISO8859-1
422 or if you have the "env" application you can do in any shell
424 env LC_ALL=en_US.ISO8859-1 perl ...
426 If you do not know what shell you have, consult your local
427 helpdesk or the equivalent.
429 =head2 Permanently fixing locale problems
431 The slower but superior fixes are when you may be able to yourself
432 fix the misconfiguration of your own environment variables. The
433 mis(sing)configuration of the whole system's locales usually requires
434 the help of your friendly system administrator.
436 First, see earlier in this document about L<Finding locales>. That tells
437 how to find which locales are really supported--and more importantly,
438 installed--on your system. In our example error message, environment
439 variables affecting the locale are listed in the order of decreasing
440 importance (and unset variables do not matter). Therefore, having
441 LC_ALL set to "En_US" must have been the bad choice, as shown by the
442 error message. First try fixing locale settings listed first.
444 Second, if using the listed commands you see something B<exactly>
445 (prefix matches do not count and case usually counts) like "En_US"
446 without the quotes, then you should be okay because you are using a
447 locale name that should be installed and available in your system.
448 In this case, see L<Permanently fixing your system's locale configuration>.
450 =head2 Permanently fixing your system's locale configuration
452 This is when you see something like:
454 perl: warning: Please check that your locale settings:
457 are supported and installed on your system.
459 but then cannot see that "En_US" listed by the above-mentioned
460 commands. You may see things like "en_US.ISO8859-1", but that isn't
461 the same. In this case, try running under a locale
462 that you can list and which somehow matches what you tried. The
463 rules for matching locale names are a bit vague because
464 standardization is weak in this area. See again the
465 L<Finding locales> about general rules.
467 =head2 Fixing system locale configuration
469 Contact a system administrator (preferably your own) and report the exact
470 error message you get, and ask them to read this same documentation you
471 are now reading. They should be able to check whether there is something
472 wrong with the locale configuration of the system. The L<Finding locales>
473 section is unfortunately a bit vague about the exact commands and places
474 because these things are not that standardized.
476 =head2 The localeconv function
478 The POSIX::localeconv() function allows you to get particulars of the
479 locale-dependent numeric formatting information specified by the current
480 C<LC_NUMERIC> and C<LC_MONETARY> locales. (If you just want the name of
481 the current locale for a particular category, use POSIX::setlocale()
482 with a single parameter--see L<The setlocale function>.)
484 use POSIX qw(locale_h);
486 # Get a reference to a hash of locale-dependent info
487 $locale_values = localeconv();
489 # Output sorted list of the values
490 for (sort keys %$locale_values) {
491 printf "%-20s = %s\n", $_, $locale_values->{$_}
494 localeconv() takes no arguments, and returns B<a reference to> a hash.
495 The keys of this hash are variable names for formatting, such as
496 C<decimal_point> and C<thousands_sep>. The values are the
497 corresponding, er, values. See L<POSIX/localeconv> for a longer
498 example listing the categories an implementation might be expected to
499 provide; some provide more and others fewer. You don't need an
500 explicit C<use locale>, because localeconv() always observes the
503 Here's a simple-minded example program that rewrites its command-line
504 parameters as integers correctly formatted in the current locale:
506 use POSIX qw(locale_h);
508 # Get some of locale's numeric formatting parameters
509 my ($thousands_sep, $grouping) =
510 @{localeconv()}{'thousands_sep', 'grouping'};
512 # Apply defaults if values are missing
513 $thousands_sep = ',' unless $thousands_sep;
515 # grouping and mon_grouping are packed lists
516 # of small integers (characters) telling the
517 # grouping (thousand_seps and mon_thousand_seps
518 # being the group dividers) of numbers and
519 # monetary quantities. The integers' meanings:
520 # 255 means no more grouping, 0 means repeat
521 # the previous grouping, 1-254 means use that
522 # as the current grouping. Grouping goes from
523 # right to left (low to high digits). In the
524 # below we cheat slightly by never using anything
525 # else than the first grouping (whatever that is).
527 @grouping = unpack("C*", $grouping);
532 # Format command line params for current locale
534 $_ = int; # Chop non-integer part
536 s/(\d)(\d{$grouping[0]}($|$thousands_sep))/$1$thousands_sep$2/;
541 =head2 I18N::Langinfo
543 Another interface for querying locale-dependent information is the
544 I18N::Langinfo::langinfo() function, available at least in Unix-like
547 The following example will import the langinfo() function itself and
548 three constants to be used as arguments to langinfo(): a constant for
549 the abbreviated first day of the week (the numbering starts from
550 Sunday = 1) and two more constants for the affirmative and negative
551 answers for a yes/no question in the current locale.
553 use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
555 my ($abday_1, $yesstr, $nostr)
556 = map { langinfo } qw(ABDAY_1 YESSTR NOSTR);
558 print "$abday_1? [$yesstr/$nostr] ";
560 In other words, in the "C" (or English) locale the above will probably
561 print something like:
565 See L<I18N::Langinfo> for more information.
567 =head1 LOCALE CATEGORIES
569 The following subsections describe basic locale categories. Beyond these,
570 some combination categories allow manipulation of more than one
571 basic category at a time. See L<"ENVIRONMENT"> for a discussion of these.
573 =head2 Category LC_COLLATE: Collation
575 In the scope of S<C<use locale>> (but not a
576 C<use locale ':not_characters'>), Perl looks to the C<LC_COLLATE>
577 environment variable to determine the application's notions on collation
578 (ordering) of characters. For example, "b" follows "a" in Latin
579 alphabets, but where do "E<aacute>" and "E<aring>" belong? And while
580 "color" follows "chocolate" in English, what about in traditional Spanish?
582 The following collations all make sense and you may meet any of them
590 Here is a code snippet to tell what "word"
591 characters are in the current locale, in that locale's order:
594 print +(sort grep /\w/, map { chr } 0..255), "\n";
596 Compare this with the characters that you see and their order if you
597 state explicitly that the locale should be ignored:
600 print +(sort grep /\w/, map { chr } 0..255), "\n";
602 This machine-native collation (which is what you get unless S<C<use
603 locale>> has appeared earlier in the same block) must be used for
604 sorting raw binary data, whereas the locale-dependent collation of the
605 first example is useful for natural text.
607 As noted in L<USING LOCALES>, C<cmp> compares according to the current
608 collation locale when C<use locale> is in effect, but falls back to a
609 char-by-char comparison for strings that the locale says are equal. You
610 can use POSIX::strcoll() if you don't want this fall-back:
612 use POSIX qw(strcoll);
614 !strcoll("space and case ignored", "SpaceAndCaseIgnored");
616 $equal_in_locale will be true if the collation locale specifies a
617 dictionary-like ordering that ignores space characters completely and
620 If you have a single string that you want to check for "equality in
621 locale" against several others, you might think you could gain a little
622 efficiency by using POSIX::strxfrm() in conjunction with C<eq>:
624 use POSIX qw(strxfrm);
625 $xfrm_string = strxfrm("Mixed-case string");
626 print "locale collation ignores spaces\n"
627 if $xfrm_string eq strxfrm("Mixed-casestring");
628 print "locale collation ignores hyphens\n"
629 if $xfrm_string eq strxfrm("Mixedcase string");
630 print "locale collation ignores case\n"
631 if $xfrm_string eq strxfrm("mixed-case string");
633 strxfrm() takes a string and maps it into a transformed string for use
634 in char-by-char comparisons against other transformed strings during
635 collation. "Under the hood", locale-affected Perl comparison operators
636 call strxfrm() for both operands, then do a char-by-char
637 comparison of the transformed strings. By calling strxfrm() explicitly
638 and using a non locale-affected comparison, the example attempts to save
639 a couple of transformations. But in fact, it doesn't save anything: Perl
640 magic (see L<perlguts/Magic Variables>) creates the transformed version of a
641 string the first time it's needed in a comparison, then keeps this version around
642 in case it's needed again. An example rewritten the easy way with
643 C<cmp> runs just about as fast. It also copes with null characters
644 embedded in strings; if you call strxfrm() directly, it treats the first
645 null it finds as a terminator. don't expect the transformed strings
646 it produces to be portable across systems--or even from one revision
647 of your operating system to the next. In short, don't call strxfrm()
648 directly: let Perl do it for you.
650 Note: C<use locale> isn't shown in some of these examples because it isn't
651 needed: strcoll() and strxfrm() exist only to generate locale-dependent
652 results, and so always obey the current C<LC_COLLATE> locale.
654 =head2 Category LC_CTYPE: Character Types
656 In the scope of S<C<use locale>> (but not a
657 C<use locale ':not_characters'>), Perl obeys the C<LC_CTYPE> locale
658 setting. This controls the application's notion of which characters are
659 alphabetic. This affects Perl's C<\w> regular expression metanotation,
660 which stands for alphanumeric characters--that is, alphabetic,
661 numeric, and including other special characters such as the underscore or
662 hyphen. (Consult L<perlre> for more information about
663 regular expressions.) Thanks to C<LC_CTYPE>, depending on your locale
664 setting, characters like "E<aelig>", "E<eth>", "E<szlig>", and
665 "E<oslash>" may be understood as C<\w> characters.
667 The C<LC_CTYPE> locale also provides the map used in transliterating
668 characters between lower and uppercase. This affects the case-mapping
669 functions--lc(), lcfirst, uc(), and ucfirst(); case-mapping
670 interpolation with C<\l>, C<\L>, C<\u>, or C<\U> in double-quoted strings
671 and C<s///> substitutions; and case-independent regular expression
672 pattern matching using the C<i> modifier.
674 Finally, C<LC_CTYPE> affects the POSIX character-class test
675 functions--isalpha(), islower(), and so on. For example, if you move
676 from the "C" locale to a 7-bit Scandinavian one, you may find--possibly
677 to your surprise--that "|" moves from the ispunct() class to isalpha().
678 Unfortunately, this creates big problems for regular expressions. "|" still
679 means alternation even though it matches C<\w>.
681 B<Note:> A broken or malicious C<LC_CTYPE> locale definition may result
682 in clearly ineligible characters being considered to be alphanumeric by
683 your application. For strict matching of (mundane) ASCII letters and
684 digits--for example, in command strings--locale-aware applications
685 should use C<\w> with the C</a> regular expression modifier. See L<"SECURITY">.
687 =head2 Category LC_NUMERIC: Numeric Formatting
689 After a proper POSIX::setlocale() call, Perl obeys the C<LC_NUMERIC>
690 locale information, which controls an application's idea of how numbers
691 should be formatted for human readability by the printf(), sprintf(), and
692 write() functions. String-to-numeric conversion by the POSIX::strtod()
693 function is also affected. In most implementations the only effect is to
694 change the character used for the decimal point--perhaps from "." to ",".
695 These functions aren't aware of such niceties as thousands separation and
696 so on. (See L<The localeconv function> if you care about these things.)
698 Output produced by print() is also affected by the current locale: it
699 corresponds to what you'd get from printf() in the "C" locale. The
700 same is true for Perl's internal conversions between numeric and
703 use POSIX qw(strtod setlocale LC_NUMERIC);
705 setlocale LC_NUMERIC, "";
707 $n = 5/2; # Assign numeric 2.5 to $n
709 $a = " $n"; # Locale-dependent conversion to string
711 print "half five is $n\n"; # Locale-dependent output
713 printf "half five is %g\n", $n; # Locale-dependent output
715 print "DECIMAL POINT IS COMMA\n"
716 if $n == (strtod("2,5"))[0]; # Locale-dependent conversion
718 See also L<I18N::Langinfo> and C<RADIXCHAR>.
720 =head2 Category LC_MONETARY: Formatting of monetary amounts
722 The C standard defines the C<LC_MONETARY> category, but not a function
723 that is affected by its contents. (Those with experience of standards
724 committees will recognize that the working group decided to punt on the
725 issue.) Consequently, Perl takes no notice of it. If you really want
726 to use C<LC_MONETARY>, you can query its contents--see
727 L<The localeconv function>--and use the information that it returns in your
728 application's own formatting of currency amounts. However, you may well
729 find that the information, voluminous and complex though it may be, still
730 does not quite meet your requirements: currency formatting is a hard nut
733 See also L<I18N::Langinfo> and C<CRNCYSTR>.
737 Output produced by POSIX::strftime(), which builds a formatted
738 human-readable date/time string, is affected by the current C<LC_TIME>
739 locale. Thus, in a French locale, the output produced by the C<%B>
740 format element (full month name) for the first month of the year would
741 be "janvier". Here's how to get a list of long month names in the
744 use POSIX qw(strftime);
746 $long_month_name[$_] =
747 strftime("%B", 0, 0, 0, 1, $_, 96);
750 Note: C<use locale> isn't needed in this example: as a function that
751 exists only to generate locale-dependent results, strftime() always
752 obeys the current C<LC_TIME> locale.
754 See also L<I18N::Langinfo> and C<ABDAY_1>..C<ABDAY_7>, C<DAY_1>..C<DAY_7>,
755 C<ABMON_1>..C<ABMON_12>, and C<ABMON_1>..C<ABMON_12>.
757 =head2 Other categories
759 The remaining locale category, C<LC_MESSAGES> (possibly supplemented
760 by others in particular implementations) is not currently used by
761 Perl--except possibly to affect the behavior of library functions
762 called by extensions outside the standard Perl distribution and by the
763 operating system and its utilities. Note especially that the string
764 value of C<$!> and the error messages given by external utilities may
765 be changed by C<LC_MESSAGES>. If you want to have portable error
766 codes, use C<%!>. See L<Errno>.
770 Although the main discussion of Perl security issues can be found in
771 L<perlsec>, a discussion of Perl's locale handling would be incomplete
772 if it did not draw your attention to locale-dependent security issues.
773 Locales--particularly on systems that allow unprivileged users to
774 build their own locales--are untrustworthy. A malicious (or just plain
775 broken) locale can make a locale-aware application give unexpected
776 results. Here are a few possibilities:
782 Regular expression checks for safe file names or mail addresses using
783 C<\w> may be spoofed by an C<LC_CTYPE> locale that claims that
784 characters such as "E<gt>" and "|" are alphanumeric.
788 String interpolation with case-mapping, as in, say, C<$dest =
789 "C:\U$name.$ext">, may produce dangerous results if a bogus LC_CTYPE
790 case-mapping table is in effect.
794 A sneaky C<LC_COLLATE> locale could result in the names of students with
795 "D" grades appearing ahead of those with "A"s.
799 An application that takes the trouble to use information in
800 C<LC_MONETARY> may format debits as if they were credits and vice versa
801 if that locale has been subverted. Or it might make payments in US
802 dollars instead of Hong Kong dollars.
806 The date and day names in dates formatted by strftime() could be
807 manipulated to advantage by a malicious user able to subvert the
808 C<LC_DATE> locale. ("Look--it says I wasn't in the building on
813 Such dangers are not peculiar to the locale system: any aspect of an
814 application's environment which may be modified maliciously presents
815 similar challenges. Similarly, they are not specific to Perl: any
816 programming language that allows you to write programs that take
817 account of their environment exposes you to these issues.
819 Perl cannot protect you from all possibilities shown in the
820 examples--there is no substitute for your own vigilance--but, when
821 C<use locale> is in effect, Perl uses the tainting mechanism (see
822 L<perlsec>) to mark string results that become locale-dependent, and
823 which may be untrustworthy in consequence. Here is a summary of the
824 tainting behavior of operators and functions that may be affected by
831 B<Comparison operators> (C<lt>, C<le>, C<ge>, C<gt> and C<cmp>):
833 Scalar true/false (or less/equal/greater) result is never tainted.
837 B<Case-mapping interpolation> (with C<\l>, C<\L>, C<\u> or C<\U>)
839 Result string containing interpolated material is tainted if
840 C<use locale> (but not S<C<use locale ':not_characters'>>) is in effect.
844 B<Matching operator> (C<m//>):
846 Scalar true/false result never tainted.
848 Subpatterns, either delivered as a list-context result or as $1 etc.
849 are tainted if C<use locale> (but not S<C<use locale ':not_characters'>>)
850 is in effect, and the subpattern regular
851 expression contains C<\w> (to match an alphanumeric character), C<\W>
852 (non-alphanumeric character), C<\s> (whitespace character), or C<\S>
853 (non whitespace character). The matched-pattern variable, $&, $`
854 (pre-match), $' (post-match), and $+ (last match) are also tainted if
855 C<use locale> is in effect and the regular expression contains C<\w>,
856 C<\W>, C<\s>, or C<\S>.
860 B<Substitution operator> (C<s///>):
862 Has the same behavior as the match operator. Also, the left
863 operand of C<=~> becomes tainted when C<use locale>
864 (but not S<C<use locale ':not_characters'>>) is in effect if modified as
865 a result of a substitution based on a regular
866 expression match involving C<\w>, C<\W>, C<\s>, or C<\S>; or of
867 case-mapping with C<\l>, C<\L>,C<\u> or C<\U>.
871 B<Output formatting functions> (printf() and write()):
873 Results are never tainted because otherwise even output from print,
874 for example C<print(1/7)>, should be tainted if C<use locale> is in
879 B<Case-mapping functions> (lc(), lcfirst(), uc(), ucfirst()):
881 Results are tainted if C<use locale> (but not
882 S<C<use locale ':not_characters'>>) is in effect.
886 B<POSIX locale-dependent functions> (localeconv(), strcoll(),
887 strftime(), strxfrm()):
889 Results are never tainted.
893 B<POSIX character class tests> (isalnum(), isalpha(), isdigit(),
894 isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(),
897 True/false results are never tainted.
901 Three examples illustrate locale-dependent tainting.
902 The first program, which ignores its locale, won't run: a value taken
903 directly from the command line may not be used to name an output file
904 when taint checks are enabled.
906 #/usr/local/bin/perl -T
907 # Run with taint checking
909 # Command line sanity check omitted...
910 $tainted_output_file = shift;
912 open(F, ">$tainted_output_file")
913 or warn "Open of $tainted_output_file failed: $!\n";
915 The program can be made to run by "laundering" the tainted value through
916 a regular expression: the second example--which still ignores locale
917 information--runs, creating the file named on its command line
920 #/usr/local/bin/perl -T
922 $tainted_output_file = shift;
923 $tainted_output_file =~ m%[\w/]+%;
924 $untainted_output_file = $&;
926 open(F, ">$untainted_output_file")
927 or warn "Open of $untainted_output_file failed: $!\n";
929 Compare this with a similar but locale-aware program:
931 #/usr/local/bin/perl -T
933 $tainted_output_file = shift;
935 $tainted_output_file =~ m%[\w/]+%;
936 $localized_output_file = $&;
938 open(F, ">$localized_output_file")
939 or warn "Open of $localized_output_file failed: $!\n";
941 This third program fails to run because $& is tainted: it is the result
942 of a match involving C<\w> while C<use locale> is in effect.
950 A string that can suppress Perl's warning about failed locale settings
951 at startup. Failure can occur if the locale support in the operating
952 system is lacking (broken) in some way--or if you mistyped the name of
953 a locale when you set up your environment. If this environment
954 variable is absent, or has a value that does not evaluate to integer
955 zero--that is, "0" or ""-- Perl will complain about locale setting
958 B<NOTE>: PERL_BADLANG only gives you a way to hide the warning message.
959 The message tells about some problem in your system's locale support,
960 and you should investigate what the problem is.
964 The following environment variables are not specific to Perl: They are
965 part of the standardized (ISO C, XPG4, POSIX 1.c) setlocale() method
966 for controlling an application's opinion on data.
972 C<LC_ALL> is the "override-all" locale environment variable. If
973 set, it overrides all the rest of the locale environment variables.
977 B<NOTE>: C<LANGUAGE> is a GNU extension, it affects you only if you
978 are using the GNU libc. This is the case if you are using e.g. Linux.
979 If you are using "commercial" Unixes you are most probably I<not>
980 using GNU libc and you can ignore C<LANGUAGE>.
982 However, in the case you are using C<LANGUAGE>: it affects the
983 language of informational, warning, and error messages output by
984 commands (in other words, it's like C<LC_MESSAGES>) but it has higher
985 priority than C<LC_ALL>. Moreover, it's not a single value but
986 instead a "path" (":"-separated list) of I<languages> (not locales).
987 See the GNU C<gettext> library documentation for more information.
991 In the absence of C<LC_ALL>, C<LC_CTYPE> chooses the character type
992 locale. In the absence of both C<LC_ALL> and C<LC_CTYPE>, C<LANG>
993 chooses the character type locale.
997 In the absence of C<LC_ALL>, C<LC_COLLATE> chooses the collation
998 (sorting) locale. In the absence of both C<LC_ALL> and C<LC_COLLATE>,
999 C<LANG> chooses the collation locale.
1003 In the absence of C<LC_ALL>, C<LC_MONETARY> chooses the monetary
1004 formatting locale. In the absence of both C<LC_ALL> and C<LC_MONETARY>,
1005 C<LANG> chooses the monetary formatting locale.
1009 In the absence of C<LC_ALL>, C<LC_NUMERIC> chooses the numeric format
1010 locale. In the absence of both C<LC_ALL> and C<LC_NUMERIC>, C<LANG>
1011 chooses the numeric format.
1015 In the absence of C<LC_ALL>, C<LC_TIME> chooses the date and time
1016 formatting locale. In the absence of both C<LC_ALL> and C<LC_TIME>,
1017 C<LANG> chooses the date and time formatting locale.
1021 C<LANG> is the "catch-all" locale environment variable. If it is set, it
1022 is used as the last resort after the overall C<LC_ALL> and the
1023 category-specific C<LC_...>.
1029 The LC_NUMERIC controls the numeric output:
1032 use POSIX qw(locale_h); # Imports setlocale() and the LC_ constants.
1033 setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
1034 printf "%g\n", 1.23; # If the "fr_FR" succeeded, probably shows 1,23.
1036 and also how strings are parsed by POSIX::strtod() as numbers:
1039 use POSIX qw(locale_h strtod);
1040 setlocale(LC_NUMERIC, "de_DE") or die "Entschuldigung";
1041 my $x = strtod("2,34") + 5;
1042 print $x, "\n"; # Probably shows 7,34.
1046 =head2 Backward compatibility
1048 Versions of Perl prior to 5.004 B<mostly> ignored locale information,
1049 generally behaving as if something similar to the C<"C"> locale were
1050 always in force, even if the program environment suggested otherwise
1051 (see L<The setlocale function>). By default, Perl still behaves this
1052 way for backward compatibility. If you want a Perl application to pay
1053 attention to locale information, you B<must> use the S<C<use locale>>
1054 pragma (see L<The use locale pragma>) or, in the unlikely event
1055 that you want to do so for just pattern matching, the
1056 C</l> regular expression modifier (see L<perlre/Character set
1057 modifiers>) to instruct it to do so.
1059 Versions of Perl from 5.002 to 5.003 did use the C<LC_CTYPE>
1060 information if available; that is, C<\w> did understand what
1061 were the letters according to the locale environment variables.
1062 The problem was that the user had no control over the feature:
1063 if the C library supported locales, Perl used them.
1065 =head2 I18N:Collate obsolete
1067 In versions of Perl prior to 5.004, per-locale collation was possible
1068 using the C<I18N::Collate> library module. This module is now mildly
1069 obsolete and should be avoided in new applications. The C<LC_COLLATE>
1070 functionality is now integrated into the Perl core language: One can
1071 use locale-specific scalar data completely normally with C<use locale>,
1072 so there is no longer any need to juggle with the scalar references of
1075 =head2 Sort speed and memory use impacts
1077 Comparing and sorting by locale is usually slower than the default
1078 sorting; slow-downs of two to four times have been observed. It will
1079 also consume more memory: once a Perl scalar variable has participated
1080 in any string comparison or sorting operation obeying the locale
1081 collation rules, it will take 3-15 times more memory than before. (The
1082 exact multiplier depends on the string's contents, the operating system
1083 and the locale.) These downsides are dictated more by the operating
1084 system's implementation of the locale system than by Perl.
1086 =head2 write() and LC_NUMERIC
1088 If a program's environment specifies an LC_NUMERIC locale and C<use
1089 locale> is in effect when the format is declared, the locale is used
1090 to specify the decimal point character in formatted output. Formatted
1091 output cannot be controlled by C<use locale> at the time when write()
1094 =head2 Freely available locale definitions
1096 The Unicode CLDR project extracts the POSIX portion of many of its
1097 locales, available at
1099 http://unicode.org/Public/cldr/latest/
1101 There is a large collection of locale definitions at:
1103 http://std.dkuug.dk/i18n/WG15-collection/locales/
1105 You should be aware that it is
1106 unsupported, and is not claimed to be fit for any purpose. If your
1107 system allows installation of arbitrary locales, you may find the
1108 definitions useful as they are, or as a basis for the development of
1111 =head2 I18n and l10n
1113 "Internationalization" is often abbreviated as B<i18n> because its first
1114 and last letters are separated by eighteen others. (You may guess why
1115 the internalin ... internaliti ... i18n tends to get abbreviated.) In
1116 the same way, "localization" is often abbreviated to B<l10n>.
1118 =head2 An imperfect standard
1120 Internationalization, as defined in the C and POSIX standards, can be
1121 criticized as incomplete, ungainly, and having too large a granularity.
1122 (Locales apply to a whole process, when it would arguably be more useful
1123 to have them apply to a single thread, window group, or whatever.) They
1124 also have a tendency, like standards groups, to divide the world into
1125 nations, when we all know that the world can equally well be divided
1126 into bankers, bikers, gamers, and so on.
1128 =head1 Unicode and UTF-8
1130 The support of Unicode is new starting from Perl version v5.6, and more fully
1131 implemented in version v5.8 and later. See L<perluniintro>. It is
1132 strongly recommended that when combining Unicode and locale (starting in
1135 use locale ':not_characters';
1137 When this form of the pragma is used, only the non-character portions of
1138 locales are used by Perl, for example C<LC_NUMERIC>. Perl assumes that
1139 you have translated all the characters it is to operate on into Unicode
1140 (actually the platform's native character set (ASCII or EBCDIC) plus
1141 Unicode). For data in files, this can conveniently be done by also
1146 This pragma arranges for all inputs from files to be translated into
1147 Unicode from the current locale as specified in the environment (see
1148 L</ENVIRONMENT>), and all outputs to files to be translated back
1149 into the locale. (See L<open>). On a per-filehandle basis, you can
1150 instead use the L<PerlIO::locale> module, or the L<Encode::Locale>
1151 module, both available from CPAN. The latter module also has methods to
1152 ease the handling of C<ARGV> and environment variables, and can be used
1153 on individual strings. Also, if you know that all your locales will be
1154 UTF-8, as many are these days, you can use the L<B<-C>|perlrun/-C>
1155 command line switch.
1157 This form of the pragma allows essentially seamless handling of locales
1158 with Unicode. The collation order will be Unicode's. It is strongly
1159 recommended that when you need to order and sort strings that you use
1160 the standard module L<Unicode::Collate> which gives much better results
1161 in many instances than you can get with the old-style locale handling.
1163 For pre-v5.16 Perls, or if you use the locale pragma without the
1164 C<:not_characters> parameter, Perl tries to work with both Unicode and
1165 locales--but there are problems.
1167 Perl does not handle multi-byte locales in this case, such as have been
1169 Asian languages, such as Big5 or Shift JIS. However, the increasingly
1170 common multi-byte UTF-8 locales, if properly implemented, may work
1171 reasonably well (depending on your C library implementation) in this
1172 form of the locale pragma, simply because both
1173 they and Perl store characters that take up multiple bytes the same way.
1174 However, some, if not most, C library implementations may not process
1175 the characters in the upper half of the Latin-1 range (128 - 255)
1176 properly under LC_CTYPE. To see if a character is a particular type
1177 under a locale, Perl uses the functions like C<isalnum()>. Your C
1178 library may not work for UTF-8 locales with those functions, instead
1179 only working under the newer wide library functions like C<iswalnum()>.
1181 Perl generally takes the tack to use locale rules on code points that can fit
1182 in a single byte, and Unicode rules for those that can't (though this
1183 isn't uniformly applied, see the note at the end of this section). This
1184 prevents many problems in locales that aren't UTF-8. Suppose the locale
1185 is ISO8859-7, Greek. The character at 0xD7 there is a capital Chi. But
1186 in the ISO8859-1 locale, Latin1, it is a multiplication sign. The POSIX
1187 regular expression character class C<[[:alpha:]]> will magically match
1188 0xD7 in the Greek locale but not in the Latin one.
1190 However, there are places where this breaks down. Certain constructs are
1191 for Unicode only, such as C<\p{Alpha}>. They assume that 0xD7 always has its
1192 Unicode meaning (or the equivalent on EBCDIC platforms). Since Latin1 is a
1193 subset of Unicode and 0xD7 is the multiplication sign in both Latin1 and
1194 Unicode, C<\p{Alpha}> will never match it, regardless of locale. A similar
1195 issue occurs with C<\N{...}>. It is therefore a bad idea to use C<\p{}> or
1196 C<\N{}> under plain C<use locale>--I<unless> you can guarantee that the
1197 locale will be a ISO8859-1. Use POSIX character classes instead.
1199 Another problem with this approach is that operations that cross the
1200 single byte/multiple byte boundary are not well-defined, and so are
1201 disallowed. (This boundary is between the codepoints at 255/256.).
1202 For example, lower casing LATIN CAPITAL LETTER Y WITH DIAERESIS (U+0178)
1203 should return LATIN SMALL LETTER Y WITH DIAERESIS (U+00FF). But in the
1204 Greek locale, for example, there is no character at 0xFF, and Perl
1205 has no way of knowing what the character at 0xFF is really supposed to
1206 represent. Thus it disallows the operation. In this mode, the
1207 lowercase of U+0178 is itself.
1209 The same problems ensue if you enable automatic UTF-8-ification of your
1210 standard file handles, default C<open()> layer, and C<@ARGV> on non-ISO8859-1,
1211 non-UTF-8 locales (by using either the B<-C> command line switch or the
1212 C<PERL_UNICODE> environment variable; see L<perlrun>).
1213 Things are read in as UTF-8, which would normally imply a Unicode
1214 interpretation, but the presence of a locale causes them to be interpreted
1215 in that locale instead. For example, a 0xD7 code point in the Unicode
1216 input, which should mean the multiplication sign, won't be interpreted by
1217 Perl that way under the Greek locale. This is not a problem
1218 I<provided> you make certain that all locales will always and only be either
1219 an ISO8859-1, or, if you don't have a deficient C library, a UTF-8 locale.
1221 Vendor locales are notoriously buggy, and it is difficult for Perl to test
1222 its locale-handling code because this interacts with code that Perl has no
1223 control over; therefore the locale-handling code in Perl may be buggy as
1224 well. (However, the Unicode-supplied locales should be better, and
1225 there is a feed back mechanism to correct any problems. See
1226 L</Freely available locale definitions>.)
1228 If you have Perl v5.16, the problems mentioned above go away if you use
1229 the C<:not_characters> parameter to the locale pragma (except for vendor
1230 bugs in the non-character portions). If you don't have v5.16, and you
1231 I<do> have locales that work, using them may be worthwhile for certain
1232 specific purposes, as long as you keep in mind the gotchas already
1233 mentioned. For example, if the collation for your locales works, it
1234 runs faster under locales than under L<Unicode::Collate>; and you gain
1235 access to such things as the local currency symbol and the names of the
1236 months and days of the week. (But to hammer home the point, in v5.16,
1237 you get this access without the downsides of locales by using the
1238 C<:not_characters> form of the pragma.)
1240 Note: The policy of using locale rules for code points that can fit in a
1241 byte, and Unicode rules for those that can't is not uniformly applied.
1242 Pre-v5.12, it was somewhat haphazard; in v5.12 it was applied fairly
1243 consistently to regular expression matching except for bracketed
1244 character classes; in v5.14 it was extended to all regex matches; and in
1245 v5.16 to the casing operations such as C<"\L"> and C<uc()>. For
1246 collation, in all releases, the system's C<strxfrm()> function is called,
1247 and whatever it does is what you get.
1251 =head2 Broken systems
1253 In certain systems, the operating system's locale support
1254 is broken and cannot be fixed or used by Perl. Such deficiencies can
1255 and will result in mysterious hangs and/or Perl core dumps when
1256 C<use locale> is in effect. When confronted with such a system,
1257 please report in excruciating detail to <F<perlbug@perl.org>>, and
1258 also contact your vendor: bug fixes may exist for these problems
1259 in your operating system. Sometimes such bug fixes are called an
1260 operating system upgrade.
1264 L<I18N::Langinfo>, L<perluniintro>, L<perlunicode>, L<open>,
1265 L<POSIX/isalnum>, L<POSIX/isalpha>,
1266 L<POSIX/isdigit>, L<POSIX/isgraph>, L<POSIX/islower>,
1267 L<POSIX/isprint>, L<POSIX/ispunct>, L<POSIX/isspace>,
1268 L<POSIX/isupper>, L<POSIX/isxdigit>, L<POSIX/localeconv>,
1269 L<POSIX/setlocale>, L<POSIX/strcoll>, L<POSIX/strftime>,
1270 L<POSIX/strtod>, L<POSIX/strxfrm>.
1274 Jarkko Hietaniemi's original F<perli18n.pod> heavily hacked by Dominic
1275 Dunlop, assisted by the perl5-porters. Prose worked over a bit by
1276 Tom Christiansen, and updated by Perl 5 porters.