3 perllocale - Perl locale handling (internationalization and localization)
7 Perl supports language-specific notions of data such as "is this
8 a letter", "what is the uppercase equivalent of this letter", and
9 "which of these letters comes first". These are important issues,
10 especially for languages other than English--but also for English: it
11 would be naE<iuml>ve to imagine that C<A-Za-z> defines all the "letters"
12 needed to write in English. Perl is also aware that some character other
13 than '.' may be preferred as a decimal point, and that output date
14 representations may be language-specific. The process of making an
15 application take account of its users' preferences in such matters is
16 called B<internationalization> (often abbreviated as B<i18n>); telling
17 such an application about a particular set of preferences is known as
18 B<localization> (B<l10n>).
20 Perl can understand language-specific data via the standardized (ISO C,
21 XPG4, POSIX 1.c) method called "the locale system". The locale system is
22 controlled per application using one pragma, one function call, and
23 several environment variables.
25 B<NOTE>: This feature is new in Perl 5.004, and does not apply unless an
26 application specifically requests it--see L<Backward compatibility>.
27 The one exception is that write() now B<always> uses the current locale
30 =head1 PREPARING TO USE LOCALES
32 If Perl applications are to understand and present your data
33 correctly according a locale of your choice, B<all> of the following
40 B<Your operating system must support the locale system>. If it does,
41 you should find that the setlocale() function is a documented part of
46 B<Definitions for locales that you use must be installed>. You, or
47 your system administrator, must make sure that this is the case. The
48 available locales, the location in which they are kept, and the manner
49 in which they are installed all vary from system to system. Some systems
50 provide only a few, hard-wired locales and do not allow more to be
51 added. Others allow you to add "canned" locales provided by the system
52 supplier. Still others allow you or the system administrator to define
53 and add arbitrary locales. (You may have to ask your supplier to
54 provide canned locales that are not delivered with your operating
55 system.) Read your system documentation for further illumination.
59 B<Perl must believe that the locale system is supported>. If it does,
60 C<perl -V:d_setlocale> will say that the value for C<d_setlocale> is
65 If you want a Perl application to process and present your data
66 according to a particular locale, the application code should include
67 the S<C<use locale>> pragma (see L<The use locale pragma>) where
68 appropriate, and B<at least one> of the following must be true:
74 B<The locale-determining environment variables (see L<"ENVIRONMENT">)
75 must be correctly set up> at the time the application is started, either
76 by yourself or by whoever set up your system account.
80 B<The application must set its own locale> using the method described in
81 L<The setlocale function>.
87 =head2 The use locale pragma
89 By default, Perl ignores the current locale. The S<C<use locale>>
90 pragma tells Perl to use the current locale for some operations:
96 B<The comparison operators> (C<lt>, C<le>, C<cmp>, C<ge>, and C<gt>) and
97 the POSIX string collation functions strcoll() and strxfrm() use
98 C<LC_COLLATE>. sort() is also affected if used without an
99 explicit comparison function, because it uses C<cmp> by default.
101 B<Note:> C<eq> and C<ne> are unaffected by locale: they always
102 perform a byte-by-byte comparison of their scalar operands. What's
103 more, if C<cmp> finds that its operands are equal according to the
104 collation sequence specified by the current locale, it goes on to
105 perform a byte-by-byte comparison, and only returns I<0> (equal) if the
106 operands are bit-for-bit identical. If you really want to know whether
107 two strings--which C<eq> and C<cmp> may consider different--are equal
108 as far as collation in the locale is concerned, see the discussion in
109 L<Category LC_COLLATE: Collation>.
113 B<Regular expressions and case-modification functions> (uc(), lc(),
114 ucfirst(), and lcfirst()) use C<LC_CTYPE>
118 B<The formatting functions> (printf(), sprintf() and write()) use
123 B<The POSIX date formatting function> (strftime()) uses C<LC_TIME>.
127 C<LC_COLLATE>, C<LC_CTYPE>, and so on, are discussed further in
128 L<LOCALE CATEGORIES>.
130 The default behavior is restored with the S<C<no locale>> pragma, or
131 upon reaching the end of block enclosing C<use locale>.
133 The string result of any operation that uses locale
134 information is tainted, as it is possible for a locale to be
135 untrustworthy. See L<"SECURITY">.
137 =head2 The setlocale function
139 You can switch locales as often as you wish at run time with the
140 POSIX::setlocale() function:
142 # This functionality not usable prior to Perl 5.004
145 # Import locale-handling tool set from POSIX module.
146 # This example uses: setlocale -- the function call
147 # LC_CTYPE -- explained below
148 use POSIX qw(locale_h);
150 # query and save the old locale
151 $old_locale = setlocale(LC_CTYPE);
153 setlocale(LC_CTYPE, "fr_CA.ISO8859-1");
154 # LC_CTYPE now in locale "French, Canada, codeset ISO 8859-1"
156 setlocale(LC_CTYPE, "");
157 # LC_CTYPE now reset to default defined by LC_ALL/LC_CTYPE/LANG
158 # environment variables. See below for documentation.
160 # restore the old locale
161 setlocale(LC_CTYPE, $old_locale);
163 The first argument of setlocale() gives the B<category>, the second the
164 B<locale>. The category tells in what aspect of data processing you
165 want to apply locale-specific rules. Category names are discussed in
166 L<LOCALE CATEGORIES> and L<"ENVIRONMENT">. The locale is the name of a
167 collection of customization information corresponding to a particular
168 combination of language, country or territory, and codeset. Read on for
169 hints on the naming of locales: not all systems name locales as in the
172 If no second argument is provided and the category is something else
173 than LC_ALL, the function returns a string naming the current locale
174 for the category. You can use this value as the second argument in a
175 subsequent call to setlocale().
177 If no second argument is provided and the category is LC_ALL, the
178 result is implementation-dependent. It may be a string of
179 concatenated locales names (separator also implementation-dependent)
180 or a single locale name. Please consult your L<setlocale(3)> for
183 If a second argument is given and it corresponds to a valid locale,
184 the locale for the category is set to that value, and the function
185 returns the now-current locale value. You can then use this in yet
186 another call to setlocale(). (In some implementations, the return
187 value may sometimes differ from the value you gave as the second
188 argument--think of it as an alias for the value you gave.)
190 As the example shows, if the second argument is an empty string, the
191 category's locale is returned to the default specified by the
192 corresponding environment variables. Generally, this results in a
193 return to the default that was in force when Perl started up: changes
194 to the environment made by the application after startup may or may not
195 be noticed, depending on your system's C library.
197 If the second argument does not correspond to a valid locale, the locale
198 for the category is not changed, and the function returns I<undef>.
200 For further information about the categories, consult L<setlocale(3)>.
202 =head2 Finding locales
204 For locales available in your system, consult also L<setlocale(3)> to
205 see whether it leads to the list of available locales (search for the
206 I<SEE ALSO> section). If that fails, try the following command lines:
220 and see whether they list something resembling these
222 en_US.ISO8859-1 de_DE.ISO8859-1 ru_RU.ISO8859-5
223 en_US.iso88591 de_DE.iso88591 ru_RU.iso88595
226 english german russian
227 english.iso88591 german.iso88591 russian.iso88595
228 english.roman8 russian.koi8r
230 Sadly, even though the calling interface for setlocale() has been
231 standardized, names of locales and the directories where the
232 configuration resides have not been. The basic form of the name is
233 I<language_territory>B<.>I<codeset>, but the latter parts after
234 I<language> are not always present. The I<language> and I<country>
235 are usually from the standards B<ISO 3166> and B<ISO 639>, the
236 two-letter abbreviations for the countries and the languages of the
237 world, respectively. The I<codeset> part often mentions some B<ISO
238 8859> character set, the Latin codesets. For example, C<ISO 8859-1>
239 is the so-called "Western European codeset" that can be used to encode
240 most Western European languages adequately. Again, there are several
241 ways to write even the name of that one standard. Lamentably.
243 Two special locales are worth particular mention: "C" and "POSIX".
244 Currently these are effectively the same locale: the difference is
245 mainly that the first one is defined by the C standard, the second by
246 the POSIX standard. They define the B<default locale> in which
247 every program starts in the absence of locale information in its
248 environment. (The I<default> default locale, if you will.) Its language
249 is (American) English and its character codeset ASCII.
251 B<NOTE>: Not all systems have the "POSIX" locale (not all systems are
252 POSIX-conformant), so use "C" when you need explicitly to specify this
255 =head2 LOCALE PROBLEMS
257 You may encounter the following warning message at Perl startup:
259 perl: warning: Setting locale failed.
260 perl: warning: Please check that your locale settings:
263 are supported and installed on your system.
264 perl: warning: Falling back to the standard locale ("C").
266 This means that your locale settings had LC_ALL set to "En_US" and
267 LANG exists but has no value. Perl tried to believe you but could not.
268 Instead, Perl gave up and fell back to the "C" locale, the default locale
269 that is supposed to work no matter what. This usually means your locale
270 settings were wrong, they mention locales your system has never heard
271 of, or the locale installation in your system has problems (for example,
272 some system files are broken or missing). There are quick and temporary
273 fixes to these problems, as well as more thorough and lasting fixes.
275 =head2 Temporarily fixing locale problems
277 The two quickest fixes are either to render Perl silent about any
278 locale inconsistencies or to run Perl under the default locale "C".
280 Perl's moaning about locale problems can be silenced by setting the
281 environment variable PERL_BADLANG to a zero value, for example "0".
282 This method really just sweeps the problem under the carpet: you tell
283 Perl to shut up even when Perl sees that something is wrong. Do not
284 be surprised if later something locale-dependent misbehaves.
286 Perl can be run under the "C" locale by setting the environment
287 variable LC_ALL to "C". This method is perhaps a bit more civilized
288 than the PERL_BADLANG approach, but setting LC_ALL (or
289 other locale variables) may affect other programs as well, not just
290 Perl. In particular, external programs run from within Perl will see
291 these changes. If you make the new settings permanent (read on), all
292 programs you run see the changes. See L<ENVIRONMENT> for
293 the full list of relevant environment variables and L<USING LOCALES>
294 for their effects in Perl. Effects in other programs are
295 easily deducible. For example, the variable LC_COLLATE may well affect
296 your B<sort> program (or whatever the program that arranges `records'
297 alphabetically in your system is called).
299 You can test out changing these variables temporarily, and if the
300 new settings seem to help, put those settings into your shell startup
301 files. Consult your local documentation for the exact details. For in
302 Bourne-like shells (B<sh>, B<ksh>, B<bash>, B<zsh>):
304 LC_ALL=en_US.ISO8859-1
307 This assumes that we saw the locale "en_US.ISO8859-1" using the commands
308 discussed above. We decided to try that instead of the above faulty
309 locale "En_US"--and in Cshish shells (B<csh>, B<tcsh>)
311 setenv LC_ALL en_US.ISO8859-1
313 If you do not know what shell you have, consult your local
314 helpdesk or the equivalent.
316 =head2 Permanently fixing locale problems
318 The slower but superior fixes are when you may be able to yourself
319 fix the misconfiguration of your own environment variables. The
320 mis(sing)configuration of the whole system's locales usually requires
321 the help of your friendly system administrator.
323 First, see earlier in this document about L<Finding locales>. That tells
324 how to find which locales are really supported--and more importantly,
325 installed--on your system. In our example error message, environment
326 variables affecting the locale are listed in the order of decreasing
327 importance (and unset variables do not matter). Therefore, having
328 LC_ALL set to "En_US" must have been the bad choice, as shown by the
329 error message. First try fixing locale settings listed first.
331 Second, if using the listed commands you see something B<exactly>
332 (prefix matches do not count and case usually counts) like "En_US"
333 without the quotes, then you should be okay because you are using a
334 locale name that should be installed and available in your system.
335 In this case, see L<Permanently fixing your system's locale configuration>.
337 =head2 Permanently fixing your system's locale configuration
339 This is when you see something like:
341 perl: warning: Please check that your locale settings:
344 are supported and installed on your system.
346 but then cannot see that "En_US" listed by the above-mentioned
347 commands. You may see things like "en_US.ISO8859-1", but that isn't
348 the same. In this case, try running under a locale
349 that you can list and which somehow matches what you tried. The
350 rules for matching locale names are a bit vague because
351 standardization is weak in this area. See again the
352 L<Finding locales> about general rules.
354 =head2 Fixing system locale configuration
356 Contact a system administrator (preferably your own) and report the exact
357 error message you get, and ask them to read this same documentation you
358 are now reading. They should be able to check whether there is something
359 wrong with the locale configuration of the system. The L<Finding locales>
360 section is unfortunately a bit vague about the exact commands and places
361 because these things are not that standardized.
363 =head2 The localeconv function
365 The POSIX::localeconv() function allows you to get particulars of the
366 locale-dependent numeric formatting information specified by the current
367 C<LC_NUMERIC> and C<LC_MONETARY> locales. (If you just want the name of
368 the current locale for a particular category, use POSIX::setlocale()
369 with a single parameter--see L<The setlocale function>.)
371 use POSIX qw(locale_h);
373 # Get a reference to a hash of locale-dependent info
374 $locale_values = localeconv();
376 # Output sorted list of the values
377 for (sort keys %$locale_values) {
378 printf "%-20s = %s\n", $_, $locale_values->{$_}
381 localeconv() takes no arguments, and returns B<a reference to> a hash.
382 The keys of this hash are variable names for formatting, such as
383 C<decimal_point> and C<thousands_sep>. The values are the
384 corresponding, er, values. See L<POSIX/localeconv> for a longer
385 example listing the categories an implementation might be expected to
386 provide; some provide more and others fewer. You don't need an
387 explicit C<use locale>, because localeconv() always observes the
390 Here's a simple-minded example program that rewrites its command-line
391 parameters as integers correctly formatted in the current locale:
393 # See comments in previous example
395 use POSIX qw(locale_h);
397 # Get some of locale's numeric formatting parameters
398 my ($thousands_sep, $grouping) =
399 @{localeconv()}{'thousands_sep', 'grouping'};
401 # Apply defaults if values are missing
402 $thousands_sep = ',' unless $thousands_sep;
404 # grouping and mon_grouping are packed lists
405 # of small integers (characters) telling the
406 # grouping (thousand_seps and mon_thousand_seps
407 # being the group dividers) of numbers and
408 # monetary quantities. The integers' meanings:
409 # 255 means no more grouping, 0 means repeat
410 # the previous grouping, 1-254 means use that
411 # as the current grouping. Grouping goes from
412 # right to left (low to high digits). In the
413 # below we cheat slightly by never using anything
414 # else than the first grouping (whatever that is).
416 @grouping = unpack("C*", $grouping);
421 # Format command line params for current locale
423 $_ = int; # Chop non-integer part
425 s/(\d)(\d{$grouping[0]}($|$thousands_sep))/$1$thousands_sep$2/;
430 =head2 I18N::Langinfo
432 Another interface for querying locale-dependent information is the
433 I18N::Langinfo::langinfo() function, available at least in UNIX-like
436 The following example will import the langinfo() function itself and
437 three constants to be used as arguments to langinfo(): a constant for
438 the abbreviated first day of the week (the numbering starts from
439 Sunday = 1) and two more constants for the affirmative and negative
440 answers for a yes/no question in the current locale.
442 use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
444 my ($abday_1, $yesstr, $nostr) = map { langinfo } qw(ABDAY_1 YESSTR NOSTR);
446 print "$abday_1? [$yesstr/$nostr] ";
448 In other words, in the "C" (or English) locale the above will probably
449 print something like:
453 See L<I18N::Langinfo> for more information.
455 =head1 LOCALE CATEGORIES
457 The following subsections describe basic locale categories. Beyond these,
458 some combination categories allow manipulation of more than one
459 basic category at a time. See L<"ENVIRONMENT"> for a discussion of these.
461 =head2 Category LC_COLLATE: Collation
463 In the scope of S<C<use locale>>, Perl looks to the C<LC_COLLATE>
464 environment variable to determine the application's notions on collation
465 (ordering) of characters. For example, 'b' follows 'a' in Latin
466 alphabets, but where do 'E<aacute>' and 'E<aring>' belong? And while
467 'color' follows 'chocolate' in English, what about in Spanish?
469 The following collations all make sense and you may meet any of them
477 Here is a code snippet to tell what "word"
478 characters are in the current locale, in that locale's order:
481 print +(sort grep /\w/, map { chr } 0..255), "\n";
483 Compare this with the characters that you see and their order if you
484 state explicitly that the locale should be ignored:
487 print +(sort grep /\w/, map { chr } 0..255), "\n";
489 This machine-native collation (which is what you get unless S<C<use
490 locale>> has appeared earlier in the same block) must be used for
491 sorting raw binary data, whereas the locale-dependent collation of the
492 first example is useful for natural text.
494 As noted in L<USING LOCALES>, C<cmp> compares according to the current
495 collation locale when C<use locale> is in effect, but falls back to a
496 byte-by-byte comparison for strings that the locale says are equal. You
497 can use POSIX::strcoll() if you don't want this fall-back:
499 use POSIX qw(strcoll);
501 !strcoll("space and case ignored", "SpaceAndCaseIgnored");
503 $equal_in_locale will be true if the collation locale specifies a
504 dictionary-like ordering that ignores space characters completely and
507 If you have a single string that you want to check for "equality in
508 locale" against several others, you might think you could gain a little
509 efficiency by using POSIX::strxfrm() in conjunction with C<eq>:
511 use POSIX qw(strxfrm);
512 $xfrm_string = strxfrm("Mixed-case string");
513 print "locale collation ignores spaces\n"
514 if $xfrm_string eq strxfrm("Mixed-casestring");
515 print "locale collation ignores hyphens\n"
516 if $xfrm_string eq strxfrm("Mixedcase string");
517 print "locale collation ignores case\n"
518 if $xfrm_string eq strxfrm("mixed-case string");
520 strxfrm() takes a string and maps it into a transformed string for use
521 in byte-by-byte comparisons against other transformed strings during
522 collation. "Under the hood", locale-affected Perl comparison operators
523 call strxfrm() for both operands, then do a byte-by-byte
524 comparison of the transformed strings. By calling strxfrm() explicitly
525 and using a non locale-affected comparison, the example attempts to save
526 a couple of transformations. But in fact, it doesn't save anything: Perl
527 magic (see L<perlguts/Magic Variables>) creates the transformed version of a
528 string the first time it's needed in a comparison, then keeps this version around
529 in case it's needed again. An example rewritten the easy way with
530 C<cmp> runs just about as fast. It also copes with null characters
531 embedded in strings; if you call strxfrm() directly, it treats the first
532 null it finds as a terminator. don't expect the transformed strings
533 it produces to be portable across systems--or even from one revision
534 of your operating system to the next. In short, don't call strxfrm()
535 directly: let Perl do it for you.
537 Note: C<use locale> isn't shown in some of these examples because it isn't
538 needed: strcoll() and strxfrm() exist only to generate locale-dependent
539 results, and so always obey the current C<LC_COLLATE> locale.
541 =head2 Category LC_CTYPE: Character Types
543 In the scope of S<C<use locale>>, Perl obeys the C<LC_CTYPE> locale
544 setting. This controls the application's notion of which characters are
545 alphabetic. This affects Perl's C<\w> regular expression metanotation,
546 which stands for alphanumeric characters--that is, alphabetic,
547 numeric, and including other special characters such as the underscore or
548 hyphen. (Consult L<perlre> for more information about
549 regular expressions.) Thanks to C<LC_CTYPE>, depending on your locale
550 setting, characters like 'E<aelig>', 'E<eth>', 'E<szlig>', and
551 'E<oslash>' may be understood as C<\w> characters.
553 The C<LC_CTYPE> locale also provides the map used in transliterating
554 characters between lower and uppercase. This affects the case-mapping
555 functions--lc(), lcfirst, uc(), and ucfirst(); case-mapping
556 interpolation with C<\l>, C<\L>, C<\u>, or C<\U> in double-quoted strings
557 and C<s///> substitutions; and case-independent regular expression
558 pattern matching using the C<i> modifier.
560 Finally, C<LC_CTYPE> affects the POSIX character-class test
561 functions--isalpha(), islower(), and so on. For example, if you move
562 from the "C" locale to a 7-bit Scandinavian one, you may find--possibly
563 to your surprise--that "|" moves from the ispunct() class to isalpha().
565 B<Note:> A broken or malicious C<LC_CTYPE> locale definition may result
566 in clearly ineligible characters being considered to be alphanumeric by
567 your application. For strict matching of (mundane) letters and
568 digits--for example, in command strings--locale-aware applications
569 should use C<\w> inside a C<no locale> block. See L<"SECURITY">.
571 =head2 Category LC_NUMERIC: Numeric Formatting
573 In the scope of S<C<use locale>>, Perl obeys the C<LC_NUMERIC> locale
574 information, which controls an application's idea of how numbers should
575 be formatted for human readability by the printf(), sprintf(), and
576 write() functions. String-to-numeric conversion by the POSIX::strtod()
577 function is also affected. In most implementations the only effect is to
578 change the character used for the decimal point--perhaps from '.' to ','.
579 These functions aren't aware of such niceties as thousands separation and
580 so on. (See L<The localeconv function> if you care about these things.)
582 Output produced by print() is also affected by the current locale: it
583 depends on whether C<use locale> or C<no locale> is in effect, and
584 corresponds to what you'd get from printf() in the "C" locale. The
585 same is true for Perl's internal conversions between numeric and
588 use POSIX qw(strtod);
591 $n = 5/2; # Assign numeric 2.5 to $n
593 $a = " $n"; # Locale-dependent conversion to string
595 print "half five is $n\n"; # Locale-dependent output
597 printf "half five is %g\n", $n; # Locale-dependent output
599 print "DECIMAL POINT IS COMMA\n"
600 if $n == (strtod("2,5"))[0]; # Locale-dependent conversion
602 See also L<I18N::Langinfo> and C<RADIXCHAR>.
604 =head2 Category LC_MONETARY: Formatting of monetary amounts
606 The C standard defines the C<LC_MONETARY> category, but no function
607 that is affected by its contents. (Those with experience of standards
608 committees will recognize that the working group decided to punt on the
609 issue.) Consequently, Perl takes no notice of it. If you really want
610 to use C<LC_MONETARY>, you can query its contents--see
611 L<The localeconv function>--and use the information that it returns in your
612 application's own formatting of currency amounts. However, you may well
613 find that the information, voluminous and complex though it may be, still
614 does not quite meet your requirements: currency formatting is a hard nut
617 See also L<I18N::Langinfo> and C<CRNCYSTR>.
621 Output produced by POSIX::strftime(), which builds a formatted
622 human-readable date/time string, is affected by the current C<LC_TIME>
623 locale. Thus, in a French locale, the output produced by the C<%B>
624 format element (full month name) for the first month of the year would
625 be "janvier". Here's how to get a list of long month names in the
628 use POSIX qw(strftime);
630 $long_month_name[$_] =
631 strftime("%B", 0, 0, 0, 1, $_, 96);
634 Note: C<use locale> isn't needed in this example: as a function that
635 exists only to generate locale-dependent results, strftime() always
636 obeys the current C<LC_TIME> locale.
638 See also L<I18N::Langinfo> and C<ABDAY_1>..C<ABDAY_7>, C<DAY_1>..C<DAY_7>,
639 C<ABMON_1>..C<ABMON_12>, and C<ABMON_1>..C<ABMON_12>.
641 =head2 Other categories
643 The remaining locale category, C<LC_MESSAGES> (possibly supplemented
644 by others in particular implementations) is not currently used by
645 Perl--except possibly to affect the behavior of library functions
646 called by extensions outside the standard Perl distribution and by the
647 operating system and its utilities. Note especially that the string
648 value of C<$!> and the error messages given by external utilities may
649 be changed by C<LC_MESSAGES>. If you want to have portable error
650 codes, use C<%!>. See L<Errno>.
654 Although the main discussion of Perl security issues can be found in
655 L<perlsec>, a discussion of Perl's locale handling would be incomplete
656 if it did not draw your attention to locale-dependent security issues.
657 Locales--particularly on systems that allow unprivileged users to
658 build their own locales--are untrustworthy. A malicious (or just plain
659 broken) locale can make a locale-aware application give unexpected
660 results. Here are a few possibilities:
666 Regular expression checks for safe file names or mail addresses using
667 C<\w> may be spoofed by an C<LC_CTYPE> locale that claims that
668 characters such as "E<gt>" and "|" are alphanumeric.
672 String interpolation with case-mapping, as in, say, C<$dest =
673 "C:\U$name.$ext">, may produce dangerous results if a bogus LC_CTYPE
674 case-mapping table is in effect.
678 A sneaky C<LC_COLLATE> locale could result in the names of students with
679 "D" grades appearing ahead of those with "A"s.
683 An application that takes the trouble to use information in
684 C<LC_MONETARY> may format debits as if they were credits and vice versa
685 if that locale has been subverted. Or it might make payments in US
686 dollars instead of Hong Kong dollars.
690 The date and day names in dates formatted by strftime() could be
691 manipulated to advantage by a malicious user able to subvert the
692 C<LC_DATE> locale. ("Look--it says I wasn't in the building on
697 Such dangers are not peculiar to the locale system: any aspect of an
698 application's environment which may be modified maliciously presents
699 similar challenges. Similarly, they are not specific to Perl: any
700 programming language that allows you to write programs that take
701 account of their environment exposes you to these issues.
703 Perl cannot protect you from all possibilities shown in the
704 examples--there is no substitute for your own vigilance--but, when
705 C<use locale> is in effect, Perl uses the tainting mechanism (see
706 L<perlsec>) to mark string results that become locale-dependent, and
707 which may be untrustworthy in consequence. Here is a summary of the
708 tainting behavior of operators and functions that may be affected by
715 B<Comparison operators> (C<lt>, C<le>, C<ge>, C<gt> and C<cmp>):
717 Scalar true/false (or less/equal/greater) result is never tainted.
721 B<Case-mapping interpolation> (with C<\l>, C<\L>, C<\u> or C<\U>)
723 Result string containing interpolated material is tainted if
724 C<use locale> is in effect.
728 B<Matching operator> (C<m//>):
730 Scalar true/false result never tainted.
732 Subpatterns, either delivered as a list-context result or as $1 etc.
733 are tainted if C<use locale> is in effect, and the subpattern regular
734 expression contains C<\w> (to match an alphanumeric character), C<\W>
735 (non-alphanumeric character), C<\s> (white-space character), or C<\S>
736 (non white-space character). The matched-pattern variable, $&, $`
737 (pre-match), $' (post-match), and $+ (last match) are also tainted if
738 C<use locale> is in effect and the regular expression contains C<\w>,
739 C<\W>, C<\s>, or C<\S>.
743 B<Substitution operator> (C<s///>):
745 Has the same behavior as the match operator. Also, the left
746 operand of C<=~> becomes tainted when C<use locale> in effect
747 if modified as a result of a substitution based on a regular
748 expression match involving C<\w>, C<\W>, C<\s>, or C<\S>; or of
749 case-mapping with C<\l>, C<\L>,C<\u> or C<\U>.
753 B<Output formatting functions> (printf() and write()):
755 Results are never tainted because otherwise even output from print,
756 for example C<print(1/7)>, should be tainted if C<use locale> is in
761 B<Case-mapping functions> (lc(), lcfirst(), uc(), ucfirst()):
763 Results are tainted if C<use locale> is in effect.
767 B<POSIX locale-dependent functions> (localeconv(), strcoll(),
768 strftime(), strxfrm()):
770 Results are never tainted.
774 B<POSIX character class tests> (isalnum(), isalpha(), isdigit(),
775 isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(),
778 True/false results are never tainted.
782 Three examples illustrate locale-dependent tainting.
783 The first program, which ignores its locale, won't run: a value taken
784 directly from the command line may not be used to name an output file
785 when taint checks are enabled.
787 #/usr/local/bin/perl -T
788 # Run with taint checking
790 # Command line sanity check omitted...
791 $tainted_output_file = shift;
793 open(F, ">$tainted_output_file")
794 or warn "Open of $untainted_output_file failed: $!\n";
796 The program can be made to run by "laundering" the tainted value through
797 a regular expression: the second example--which still ignores locale
798 information--runs, creating the file named on its command line
801 #/usr/local/bin/perl -T
803 $tainted_output_file = shift;
804 $tainted_output_file =~ m%[\w/]+%;
805 $untainted_output_file = $&;
807 open(F, ">$untainted_output_file")
808 or warn "Open of $untainted_output_file failed: $!\n";
810 Compare this with a similar but locale-aware program:
812 #/usr/local/bin/perl -T
814 $tainted_output_file = shift;
816 $tainted_output_file =~ m%[\w/]+%;
817 $localized_output_file = $&;
819 open(F, ">$localized_output_file")
820 or warn "Open of $localized_output_file failed: $!\n";
822 This third program fails to run because $& is tainted: it is the result
823 of a match involving C<\w> while C<use locale> is in effect.
831 A string that can suppress Perl's warning about failed locale settings
832 at startup. Failure can occur if the locale support in the operating
833 system is lacking (broken) in some way--or if you mistyped the name of
834 a locale when you set up your environment. If this environment
835 variable is absent, or has a value that does not evaluate to integer
836 zero--that is, "0" or ""-- Perl will complain about locale setting
839 B<NOTE>: PERL_BADLANG only gives you a way to hide the warning message.
840 The message tells about some problem in your system's locale support,
841 and you should investigate what the problem is.
845 The following environment variables are not specific to Perl: They are
846 part of the standardized (ISO C, XPG4, POSIX 1.c) setlocale() method
847 for controlling an application's opinion on data.
853 C<LC_ALL> is the "override-all" locale environment variable. If
854 set, it overrides all the rest of the locale environment variables.
858 B<NOTE>: C<LANGUAGE> is a GNU extension, it affects you only if you
859 are using the GNU libc. This is the case if you are using e.g. Linux.
860 If you are using "commercial" UNIXes you are most probably I<not>
861 using GNU libc and you can ignore C<LANGUAGE>.
863 However, in the case you are using C<LANGUAGE>: it affects the
864 language of informational, warning, and error messages output by
865 commands (in other words, it's like C<LC_MESSAGES>) but it has higher
866 priority than L<LC_ALL>. Moreover, it's not a single value but
867 instead a "path" (":"-separated list) of I<languages> (not locales).
868 See the GNU C<gettext> library documentation for more information.
872 In the absence of C<LC_ALL>, C<LC_CTYPE> chooses the character type
873 locale. In the absence of both C<LC_ALL> and C<LC_CTYPE>, C<LANG>
874 chooses the character type locale.
878 In the absence of C<LC_ALL>, C<LC_COLLATE> chooses the collation
879 (sorting) locale. In the absence of both C<LC_ALL> and C<LC_COLLATE>,
880 C<LANG> chooses the collation locale.
884 In the absence of C<LC_ALL>, C<LC_MONETARY> chooses the monetary
885 formatting locale. In the absence of both C<LC_ALL> and C<LC_MONETARY>,
886 C<LANG> chooses the monetary formatting locale.
890 In the absence of C<LC_ALL>, C<LC_NUMERIC> chooses the numeric format
891 locale. In the absence of both C<LC_ALL> and C<LC_NUMERIC>, C<LANG>
892 chooses the numeric format.
896 In the absence of C<LC_ALL>, C<LC_TIME> chooses the date and time
897 formatting locale. In the absence of both C<LC_ALL> and C<LC_TIME>,
898 C<LANG> chooses the date and time formatting locale.
902 C<LANG> is the "catch-all" locale environment variable. If it is set, it
903 is used as the last resort after the overall C<LC_ALL> and the
904 category-specific C<LC_...>.
910 =head2 Backward compatibility
912 Versions of Perl prior to 5.004 B<mostly> ignored locale information,
913 generally behaving as if something similar to the C<"C"> locale were
914 always in force, even if the program environment suggested otherwise
915 (see L<The setlocale function>). By default, Perl still behaves this
916 way for backward compatibility. If you want a Perl application to pay
917 attention to locale information, you B<must> use the S<C<use locale>>
918 pragma (see L<The use locale pragma>) to instruct it to do so.
920 Versions of Perl from 5.002 to 5.003 did use the C<LC_CTYPE>
921 information if available; that is, C<\w> did understand what
922 were the letters according to the locale environment variables.
923 The problem was that the user had no control over the feature:
924 if the C library supported locales, Perl used them.
926 =head2 I18N:Collate obsolete
928 In versions of Perl prior to 5.004, per-locale collation was possible
929 using the C<I18N::Collate> library module. This module is now mildly
930 obsolete and should be avoided in new applications. The C<LC_COLLATE>
931 functionality is now integrated into the Perl core language: One can
932 use locale-specific scalar data completely normally with C<use locale>,
933 so there is no longer any need to juggle with the scalar references of
936 =head2 Sort speed and memory use impacts
938 Comparing and sorting by locale is usually slower than the default
939 sorting; slow-downs of two to four times have been observed. It will
940 also consume more memory: once a Perl scalar variable has participated
941 in any string comparison or sorting operation obeying the locale
942 collation rules, it will take 3-15 times more memory than before. (The
943 exact multiplier depends on the string's contents, the operating system
944 and the locale.) These downsides are dictated more by the operating
945 system's implementation of the locale system than by Perl.
947 =head2 write() and LC_NUMERIC
949 Formats are the only part of Perl that unconditionally use information
950 from a program's locale; if a program's environment specifies an
951 LC_NUMERIC locale, it is always used to specify the decimal point
952 character in formatted output. Formatted output cannot be controlled by
953 C<use locale> because the pragma is tied to the block structure of the
954 program, and, for historical reasons, formats exist outside that block
957 =head2 Freely available locale definitions
959 There is a large collection of locale definitions at
960 C<ftp://dkuug.dk/i18n/WG15-collection>. You should be aware that it is
961 unsupported, and is not claimed to be fit for any purpose. If your
962 system allows installation of arbitrary locales, you may find the
963 definitions useful as they are, or as a basis for the development of
968 "Internationalization" is often abbreviated as B<i18n> because its first
969 and last letters are separated by eighteen others. (You may guess why
970 the internalin ... internaliti ... i18n tends to get abbreviated.) In
971 the same way, "localization" is often abbreviated to B<l10n>.
973 =head2 An imperfect standard
975 Internationalization, as defined in the C and POSIX standards, can be
976 criticized as incomplete, ungainly, and having too large a granularity.
977 (Locales apply to a whole process, when it would arguably be more useful
978 to have them apply to a single thread, window group, or whatever.) They
979 also have a tendency, like standards groups, to divide the world into
980 nations, when we all know that the world can equally well be divided
981 into bankers, bikers, gamers, and so on. But, for now, it's the only
982 standard we've got. This may be construed as a bug.
986 =head2 Broken systems
988 In certain systems, the operating system's locale support
989 is broken and cannot be fixed or used by Perl. Such deficiencies can
990 and will result in mysterious hangs and/or Perl core dumps when the
991 C<use locale> is in effect. When confronted with such a system,
992 please report in excruciating detail to <F<perlbug@perl.org>>, and
993 complain to your vendor: bug fixes may exist for these problems
994 in your operating system. Sometimes such bug fixes are called an
995 operating system upgrade.
999 L<I18N::Langinfo>, L<POSIX/isalnum>, L<POSIX/isalpha>,
1000 L<POSIX/isdigit>, L<POSIX/isgraph>, L<POSIX/islower>,
1001 L<POSIX/isprint>, L<POSIX/ispunct>, L<POSIX/isspace>,
1002 L<POSIX/isupper>, L<POSIX/isxdigit>, L<POSIX/localeconv>,
1003 L<POSIX/setlocale>, L<POSIX/strcoll>, L<POSIX/strftime>,
1004 L<POSIX/strtod>, L<POSIX/strxfrm>.
1008 Jarkko Hietaniemi's original F<perli18n.pod> heavily hacked by Dominic
1009 Dunlop, assisted by the perl5-porters. Prose worked over a bit by
1012 Last update: Thu Jun 11 08:44:13 MDT 1998