3 perllocale - Perl locale handling (internationalization and localization)
7 Perl supports language-specific notions of data such as "is this a
8 letter", "what is the upper-case equivalent of this letter", and "which
9 of these letters comes first". These are important issues, especially
10 for languages other than English - but also for English: it would be
11 very naE<iuml>ve to think that C<A-Za-z> defines all the "letters". Perl
12 is also aware that some character other than '.' may be preferred as a
13 decimal point, and that output date representations may be
14 language-specific. The process of making an application take account of
15 its users' preferences in such matters is called B<internationalization>
16 (often abbreviated as B<i18n>); telling such an application about a
17 particular set of preferences is known as B<localization> (B<l10n>).
19 Perl can understand language-specific data via the standardized (ISO C,
20 XPG4, POSIX 1.c) method called "the locale system". The locale system is
21 controlled per application using one pragma, one function call, and
22 several environment variables.
24 B<NOTE>: This feature is new in Perl 5.004, and does not apply unless an
25 application specifically requests it - see L<Backward compatibility>.
26 The one exception is that write() now B<always> uses the current locale
29 =head1 PREPARING TO USE LOCALES
31 If Perl applications are to be able to understand and present your data
32 correctly according a locale of your choice, B<all> of the following
39 B<Your operating system must support the locale system>. If it does,
40 you should find that the setlocale() function is a documented part of
45 B<Definitions for the locales which you use must be installed>. You, or
46 your system administrator, must make sure that this is the case. The
47 available locales, the location in which they are kept, and the manner
48 in which they are installed, vary from system to system. Some systems
49 provide only a few, hard-wired, locales, and do not allow more to be
50 added; others allow you to add "canned" locales provided by the system
51 supplier; still others allow you or the system administrator to define
52 and add arbitrary locales. (You may have to ask your supplier to
53 provide canned locales which are not delivered with your operating
54 system.) Read your system documentation for further illumination.
58 B<Perl must believe that the locale system is supported>. If it does,
59 C<perl -V:d_setlocale> will say that the value for C<d_setlocale> is
64 If you want a Perl application to process and present your data
65 according to a particular locale, the application code should include
66 the S<C<use locale>> pragma (see L<The use locale Pragma>) where
67 appropriate, and B<at least one> of the following must be true:
73 B<The locale-determining environment variables (see L<"ENVIRONMENT">)
74 must be correctly set up>, either by yourself, or by the person who set
75 up your system account, at the time the application is started.
79 B<The application must set its own locale> using the method described in
80 L<The setlocale function>.
86 =head2 The use locale pragma
88 By default, Perl ignores the current locale. The S<C<use locale>>
89 pragma tells Perl to use the current locale for some operations:
95 B<The comparison operators> (C<lt>, C<le>, C<cmp>, C<ge>, and C<gt>) and
96 the POSIX string collation functions strcoll() and strxfrm() use
97 C<LC_COLLATE>. sort() is also affected if it is used without an
98 explicit comparison function because it uses C<cmp> by default.
100 B<Note:> C<eq> and C<ne> are unaffected by the locale: they always
101 perform a byte-by-byte comparison of their scalar operands. What's
102 more, if C<cmp> finds that its operands are equal according to the
103 collation sequence specified by the current locale, it goes on to
104 perform a byte-by-byte comparison, and only returns I<0> (equal) if the
105 operands are bit-for-bit identical. If you really want to know whether
106 two strings - which C<eq> and C<cmp> may consider different - are equal
107 as far as collation in the locale is concerned, see the discussion in
108 L<Category LC_COLLATE: Collation>.
112 B<Regular expressions and case-modification functions> (uc(), lc(),
113 ucfirst(), and lcfirst()) use C<LC_CTYPE>
117 B<The formatting functions> (printf(), sprintf() and write()) use
122 B<The POSIX date formatting function> (strftime()) uses C<LC_TIME>.
126 C<LC_COLLATE>, C<LC_CTYPE>, and so on, are discussed further in L<LOCALE
129 The default behavior returns with S<C<no locale>> or on reaching the
130 end of the enclosing block.
132 Note that the string result of any operation that uses locale
133 information is tainted, as it is possible for a locale to be
134 untrustworthy. See L<"SECURITY">.
136 =head2 The setlocale function
138 You can switch locales as often as you wish at run time with the
139 POSIX::setlocale() function:
141 # This functionality not usable prior to Perl 5.004
144 # Import locale-handling tool set from POSIX module.
145 # This example uses: setlocale -- the function call
146 # LC_CTYPE -- explained below
147 use POSIX qw(locale_h);
149 # query and save the old locale
150 $old_locale = setlocale(LC_CTYPE);
152 setlocale(LC_CTYPE, "fr_CA.ISO8859-1");
153 # LC_CTYPE now in locale "French, Canada, codeset ISO 8859-1"
155 setlocale(LC_CTYPE, "");
156 # LC_CTYPE now reset to default defined by LC_ALL/LC_CTYPE/LANG
157 # environment variables. See below for documentation.
159 # restore the old locale
160 setlocale(LC_CTYPE, $old_locale);
162 The first argument of setlocale() gives the B<category>, the second the
163 B<locale>. The category tells in what aspect of data processing you
164 want to apply locale-specific rules. Category names are discussed in
165 L<LOCALE CATEGORIES> and L<"ENVIRONMENT">. The locale is the name of a
166 collection of customization information corresponding to a particular
167 combination of language, country or territory, and codeset. Read on for
168 hints on the naming of locales: not all systems name locales as in the
171 If no second argument is provided, the function returns a string naming
172 the current locale for the category. You can use this value as the
173 second argument in a subsequent call to setlocale(). If a second
174 argument is given and it corresponds to a valid locale, the locale for
175 the category is set to that value, and the function returns the
176 now-current locale value. You can use this in a subsequent call to
177 setlocale(). (In some implementations, the return value may sometimes
178 differ from the value you gave as the second argument - think of it as
179 an alias for the value that you gave.)
181 As the example shows, if the second argument is an empty string, the
182 category's locale is returned to the default specified by the
183 corresponding environment variables. Generally, this results in a
184 return to the default which was in force when Perl started up: changes
185 to the environment made by the application after start-up may or may not
186 be noticed, depending on the implementation of your system's C library.
188 If the second argument does not correspond to a valid locale, the locale
189 for the category is not changed, and the function returns I<undef>.
191 For further information about the categories, consult L<setlocale(3)>.
192 For the locales available in your system, also consult L<setlocale(3)>
193 and see whether it leads you to the list of the available locales
194 (search for the I<SEE ALSO> section). If that fails, try the following
207 and see whether they list something resembling these
209 en_US.ISO8859-1 de_DE.ISO8859-1 ru_RU.ISO8859-5
212 english german russian
213 english.iso88591 german.iso88591 russian.iso88595
215 Sadly, even though the calling interface for setlocale() has been
216 standardized, the names of the locales and the directories where
217 the configuration is, have not. The basic form of the name is
218 I<language_country/territory>B<.>I<codeset>, but the
219 latter parts are not always present.
221 Two special locales are worth particular mention: "C" and "POSIX".
222 Currently these are effectively the same locale: the difference is
223 mainly that the first one is defined by the C standard and the second by
224 the POSIX standard. What they define is the B<default locale> in which
225 every program starts in the absence of locale information in its
226 environment. (The default default locale, if you will.) Its language
227 is (American) English and its character codeset ASCII.
229 B<NOTE>: Not all systems have the "POSIX" locale (not all systems are
230 POSIX-conformant), so use "C" when you need explicitly to specify this
233 =head2 The localeconv function
235 The POSIX::localeconv() function allows you to get particulars of the
236 locale-dependent numeric formatting information specified by the current
237 C<LC_NUMERIC> and C<LC_MONETARY> locales. (If you just want the name of
238 the current locale for a particular category, use POSIX::setlocale()
239 with a single parameter - see L<The setlocale function>.)
241 use POSIX qw(locale_h);
243 # Get a reference to a hash of locale-dependent info
244 $locale_values = localeconv();
246 # Output sorted list of the values
247 for (sort keys %$locale_values) {
248 printf "%-20s = %s\n", $_, $locale_values->{$_}
251 localeconv() takes no arguments, and returns B<a reference to> a hash.
252 The keys of this hash are formatting variable names such as
253 C<decimal_point> and C<thousands_sep>; the values are the corresponding
254 values. See L<POSIX (3)/localeconv> for a longer example, which lists
255 all the categories an implementation might be expected to provide; some
256 provide more and others fewer, however. Note that you don't need C<use
257 locale>: as a function with the job of querying the locale, localeconv()
258 always observes the current locale.
260 Here's a simple-minded example program which rewrites its command line
261 parameters as integers formatted correctly in the current locale:
263 # See comments in previous example
265 use POSIX qw(locale_h);
267 # Get some of locale's numeric formatting parameters
268 my ($thousands_sep, $grouping) =
269 @{localeconv()}{'thousands_sep', 'grouping'};
271 # Apply defaults if values are missing
272 $thousands_sep = ',' unless $thousands_sep;
273 $grouping = 3 unless $grouping;
275 # Format command line params for current locale
277 $_ = int; # Chop non-integer part
279 s/(\d)(\d{$grouping}($|$thousands_sep))/$1$thousands_sep$2/;
284 =head1 LOCALE CATEGORIES
286 The subsections which follow describe basic locale categories. As well
287 as these, there are some combination categories which allow the
288 manipulation of more than one basic category at a time. See
289 L<"ENVIRONMENT"> for a discussion of these.
291 =head2 Category LC_COLLATE: Collation
293 When in the scope of S<C<use locale>>, Perl looks to the C<LC_COLLATE>
294 environment variable to determine the application's notions on the
295 collation (ordering) of characters. ('b' follows 'a' in Latin
296 alphabets, but where do 'E<aacute>' and 'E<aring>' belong?)
298 Here is a code snippet that will tell you what are the alphanumeric
299 characters in the current locale, in the locale order:
302 print +(sort grep /\w/, map { chr() } 0..255), "\n";
304 Compare this with the characters that you see and their order if you
305 state explicitly that the locale should be ignored:
308 print +(sort grep /\w/, map { chr() } 0..255), "\n";
310 This machine-native collation (which is what you get unless S<C<use
311 locale>> has appeared earlier in the same block) must be used for
312 sorting raw binary data, whereas the locale-dependent collation of the
313 first example is useful for natural text.
315 As noted in L<USING LOCALES>, C<cmp> compares according to the current
316 collation locale when C<use locale> is in effect, but falls back to a
317 byte-by-byte comparison for strings which the locale says are equal. You
318 can use POSIX::strcoll() if you don't want this fall-back:
320 use POSIX qw(strcoll);
322 !strcoll("space and case ignored", "SpaceAndCaseIgnored");
324 $equal_in_locale will be true if the collation locale specifies a
325 dictionary-like ordering which ignores space characters completely, and
326 which folds case. Alternatively, you can use this idiom:
329 $s_a = "space and case ignored";
330 $s_b = "SpaceAndCaseIgnored";
331 $equal_in_locale = $s_a ge $s_b && $s_a le $s_b;
333 which works because neither C<ne> nor C<ge> falls back to doing a
334 byte-by-byte comparison when the operands are equal according to the
335 locale. The idiom may be less efficient than using strcoll(), but,
336 unlike that function, it is not confused by strings containing embedded
339 If you have a single string which you want to check for "equality in
340 locale" against several others, you might think you could gain a little
341 efficiency by using POSIX::strxfrm() in conjunction with C<eq>:
343 use POSIX qw(strxfrm);
344 $xfrm_string = strxfrm("Mixed-case string");
345 print "locale collation ignores spaces\n"
346 if $xfrm_string eq strxfrm("Mixed-casestring");
347 print "locale collation ignores hyphens\n"
348 if $xfrm_string eq strxfrm("Mixedcase string");
349 print "locale collation ignores case\n"
350 if $xfrm_string eq strxfrm("mixed-case string");
352 strxfrm() takes a string and maps it into a transformed string for use
353 in byte-by-byte comparisons against other transformed strings during
354 collation. "Under the hood", locale-affected Perl comparison operators
355 call strxfrm() for both their operands, then do a byte-by-byte
356 comparison of the transformed strings. By calling strxfrm() explicitly,
357 and using a non locale-affected comparison, the example attempts to save
358 a couple of transformations. In fact, it doesn't save anything: Perl
359 magic (see L<perlguts/Magic>) creates the transformed version of a
360 string the first time it's needed in a comparison, then keeps it around
361 in case it's needed again. An example rewritten the easy way with
362 C<cmp> runs just about as fast. It also copes with null characters
363 embedded in strings; if you call strxfrm() directly, it treats the first
364 null it finds as a terminator. And don't expect the transformed strings
365 it produces to be portable across systems - or even from one revision
366 of your operating system to the next. In short, don't call strxfrm()
367 directly: let Perl do it for you.
369 Note: C<use locale> isn't shown in some of these examples, as it isn't
370 needed: strcoll() and strxfrm() exist only to generate locale-dependent
371 results, and so always obey the current C<LC_COLLATE> locale.
373 =head2 Category LC_CTYPE: Character Types
375 When in the scope of S<C<use locale>>, Perl obeys the C<LC_CTYPE> locale
376 setting. This controls the application's notion of which characters are
377 alphabetic. This affects Perl's C<\w> regular expression metanotation,
378 which stands for alphanumeric characters - that is, alphabetic and
379 numeric characters. (Consult L<perlre> for more information about
380 regular expressions.) Thanks to C<LC_CTYPE>, depending on your locale
381 setting, characters like 'E<aelig>', 'E<eth>', 'E<szlig>', and
382 'E<oslash>' may be understood as C<\w> characters.
384 The C<LC_CTYPE> locale also provides the map used in translating
385 characters between lower- and upper-case. This affects the case-mapping
386 functions - lc(), lcfirst, uc() and ucfirst(); case-mapping
387 interpolation with C<\l>, C<\L>, C<\u> or <\U> in double-quoted strings
388 and in C<s///> substitutions; and case-independent regular expression
389 pattern matching using the C<i> modifier.
391 Finally, C<LC_CTYPE> affects the POSIX character-class test functions -
392 isalpha(), islower() and so on. For example, if you move from the "C"
393 locale to a 7-bit Scandinavian one, you may find - possibly to your
394 surprise - that "|" moves from the ispunct() class to isalpha().
396 B<Note:> A broken or malicious C<LC_CTYPE> locale definition may result
397 in clearly ineligible characters being considered to be alphanumeric by
398 your application. For strict matching of (unaccented) letters and
399 digits - for example, in command strings - locale-aware applications
400 should use C<\w> inside a C<no locale> block. See L<"SECURITY">.
402 =head2 Category LC_NUMERIC: Numeric Formatting
404 When in the scope of S<C<use locale>>, Perl obeys the C<LC_NUMERIC>
405 locale information, which controls application's idea of how numbers
406 should be formatted for human readability by the printf(), sprintf(),
407 and write() functions. String to numeric conversion by the
408 POSIX::strtod() function is also affected. In most implementations the
409 only effect is to change the character used for the decimal point -
410 perhaps from '.' to ',': these functions aren't aware of such niceties
411 as thousands separation and so on. (See L<The localeconv function> if
412 you care about these things.)
414 Note that output produced by print() is B<never> affected by the
415 current locale: it is independent of whether C<use locale> or C<no
416 locale> is in effect, and corresponds to what you'd get from printf()
417 in the "C" locale. The same is true for Perl's internal conversions
418 between numeric and string formats:
420 use POSIX qw(strtod);
423 $n = 5/2; # Assign numeric 2.5 to $n
425 $a = " $n"; # Locale-independent conversion to string
427 print "half five is $n\n"; # Locale-independent output
429 printf "half five is %g\n", $n; # Locale-dependent output
431 print "DECIMAL POINT IS COMMA\n"
432 if $n == (strtod("2,5"))[0]; # Locale-dependent conversion
434 =head2 Category LC_MONETARY: Formatting of monetary amounts
436 The C standard defines the C<LC_MONETARY> category, but no function that
437 is affected by its contents. (Those with experience of standards
438 committees will recognize that the working group decided to punt on the
439 issue.) Consequently, Perl takes no notice of it. If you really want
440 to use C<LC_MONETARY>, you can query its contents - see L<The localeconv
441 function> - and use the information that it returns in your
442 application's own formatting of currency amounts. However, you may well
443 find that the information, though voluminous and complex, does not quite
444 meet your requirements: currency formatting is a hard nut to crack.
448 The output produced by POSIX::strftime(), which builds a formatted
449 human-readable date/time string, is affected by the current C<LC_TIME>
450 locale. Thus, in a French locale, the output produced by the C<%B>
451 format element (full month name) for the first month of the year would
452 be "janvier". Here's how to get a list of the long month names in the
455 use POSIX qw(strftime);
457 $long_month_name[$_] =
458 strftime("%B", 0, 0, 0, 1, $_, 96);
461 Note: C<use locale> isn't needed in this example: as a function which
462 exists only to generate locale-dependent results, strftime() always
463 obeys the current C<LC_TIME> locale.
465 =head2 Other categories
467 The remaining locale category, C<LC_MESSAGES> (possibly supplemented by
468 others in particular implementations) is not currently used by Perl -
469 except possibly to affect the behavior of library functions called by
470 extensions which are not part of the standard Perl distribution.
474 While the main discussion of Perl security issues can be found in
475 L<perlsec>, a discussion of Perl's locale handling would be incomplete
476 if it did not draw your attention to locale-dependent security issues.
477 Locales - particularly on systems which allow unprivileged users to
478 build their own locales - are untrustworthy. A malicious (or just plain
479 broken) locale can make a locale-aware application give unexpected
480 results. Here are a few possibilities:
486 Regular expression checks for safe file names or mail addresses using
487 C<\w> may be spoofed by an C<LC_CTYPE> locale which claims that
488 characters such as "E<gt>" and "|" are alphanumeric.
492 String interpolation with case-mapping, as in, say, C<$dest =
493 "C:\U$name.$ext">, may produce dangerous results if a bogus LC_CTYPE
494 case-mapping table is in effect.
498 If the decimal point character in the C<LC_NUMERIC> locale is
499 surreptitiously changed from a dot to a comma, C<sprintf("%g",
500 0.123456e3)> produces a string result of "123,456". Many people would
501 interpret this as one hundred and twenty-three thousand, four hundred
506 A sneaky C<LC_COLLATE> locale could result in the names of students with
507 "D" grades appearing ahead of those with "A"s.
511 An application which takes the trouble to use the information in
512 C<LC_MONETARY> may format debits as if they were credits and vice versa
513 if that locale has been subverted. Or it make may make payments in US
514 dollars instead of Hong Kong dollars.
518 The date and day names in dates formatted by strftime() could be
519 manipulated to advantage by a malicious user able to subvert the
520 C<LC_DATE> locale. ("Look - it says I wasn't in the building on
525 Such dangers are not peculiar to the locale system: any aspect of an
526 application's environment which may maliciously be modified presents
527 similar challenges. Similarly, they are not specific to Perl: any
528 programming language which allows you to write programs which take
529 account of their environment exposes you to these issues.
531 Perl cannot protect you from all of the possibilities shown in the
532 examples - there is no substitute for your own vigilance - but, when
533 C<use locale> is in effect, Perl uses the tainting mechanism (see
534 L<perlsec>) to mark string results which become locale-dependent, and
535 which may be untrustworthy in consequence. Here is a summary of the
536 tainting behavior of operators and functions which may be affected by
541 =item B<Comparison operators> (C<lt>, C<le>, C<ge>, C<gt> and C<cmp>):
543 Scalar true/false (or less/equal/greater) result is never tainted.
545 =item B<Case-mapping interpolation> (with C<\l>, C<\L>, C<\u> or <\U>)
547 Result string containing interpolated material is tainted if
548 C<use locale> is in effect.
550 =item B<Matching operator> (C<m//>):
552 Scalar true/false result never tainted.
554 Subpatterns, either delivered as an array-context result, or as $1 etc.
555 are tainted if C<use locale> is in effect, and the subpattern regular
556 expression contains C<\w> (to match an alphanumeric character), C<\W>
557 (non-alphanumeric character), C<\s> (white-space character), or C<\S>
558 (non white-space character). The matched pattern variable, $&, $`
559 (pre-match), $' (post-match), and $+ (last match) are also tainted if
560 C<use locale> is in effect and the regular expression contains C<\w>,
561 C<\W>, C<\s>, or C<\S>.
563 =item B<Substitution operator> (C<s///>):
565 Has the same behavior as the match operator. Also, the left
566 operand of C<=~> becomes tainted when C<use locale> in effect,
567 if it is modified as a result of a substitution based on a regular
568 expression match involving C<\w>, C<\W>, C<\s>, or C<\S>; or of
569 case-mapping with C<\l>, C<\L>,C<\u> or <\U>.
571 =item B<In-memory formatting function> (sprintf()):
573 Result is tainted if "use locale" is in effect.
575 =item B<Output formatting functions> (printf() and write()):
577 Success/failure result is never tainted.
579 =item B<Case-mapping functions> (lc(), lcfirst(), uc(), ucfirst()):
581 Results are tainted if C<use locale> is in effect.
583 =item B<POSIX locale-dependent functions> (localeconv(), strcoll(),
584 strftime(), strxfrm()):
586 Results are never tainted.
588 =item B<POSIX character class tests> (isalnum(), isalpha(), isdigit(),
589 isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(),
592 True/false results are never tainted.
596 Three examples illustrate locale-dependent tainting.
597 The first program, which ignores its locale, won't run: a value taken
598 directly from the command-line may not be used to name an output file
599 when taint checks are enabled.
601 #/usr/local/bin/perl -T
602 # Run with taint checking
604 # Command-line sanity check omitted...
605 $tainted_output_file = shift;
607 open(F, ">$tainted_output_file")
608 or warn "Open of $untainted_output_file failed: $!\n";
610 The program can be made to run by "laundering" the tainted value through
611 a regular expression: the second example - which still ignores locale
612 information - runs, creating the file named on its command-line
615 #/usr/local/bin/perl -T
617 $tainted_output_file = shift;
618 $tainted_output_file =~ m%[\w/]+%;
619 $untainted_output_file = $&;
621 open(F, ">$untainted_output_file")
622 or warn "Open of $untainted_output_file failed: $!\n";
624 Compare this with a very similar program which is locale-aware:
626 #/usr/local/bin/perl -T
628 $tainted_output_file = shift;
630 $tainted_output_file =~ m%[\w/]+%;
631 $localized_output_file = $&;
633 open(F, ">$localized_output_file")
634 or warn "Open of $localized_output_file failed: $!\n";
636 This third program fails to run because $& is tainted: it is the result
637 of a match involving C<\w> when C<use locale> is in effect.
645 A string that can suppress Perl's warning about failed locale settings
646 at start-up. Failure can occur if the locale support in the operating
647 system is lacking (broken) is some way - or if you mistyped the name of
648 a locale when you set up your environment. If this environment variable
649 is absent, or has a value which does not evaluate to integer zero - that
650 is "0" or "" - Perl will complain about locale setting failures.
652 B<NOTE>: PERL_BADLANG only gives you a way to hide the warning message.
653 The message tells about some problem in your system's locale support,
654 and you should investigate what the problem is.
658 The following environment variables are not specific to Perl: They are
659 part of the standardized (ISO C, XPG4, POSIX 1.c) setlocale() method
660 for controlling an application's opinion on data.
666 C<LC_ALL> is the "override-all" locale environment variable. If it is
667 set, it overrides all the rest of the locale environment variables.
671 In the absence of C<LC_ALL>, C<LC_CTYPE> chooses the character type
672 locale. In the absence of both C<LC_ALL> and C<LC_CTYPE>, C<LANG>
673 chooses the character type locale.
677 In the absence of C<LC_ALL>, C<LC_COLLATE> chooses the collation
678 (sorting) locale. In the absence of both C<LC_ALL> and C<LC_COLLATE>,
679 C<LANG> chooses the collation locale.
683 In the absence of C<LC_ALL>, C<LC_MONETARY> chooses the monetary
684 formatting locale. In the absence of both C<LC_ALL> and C<LC_MONETARY>,
685 C<LANG> chooses the monetary formatting locale.
689 In the absence of C<LC_ALL>, C<LC_NUMERIC> chooses the numeric format
690 locale. In the absence of both C<LC_ALL> and C<LC_NUMERIC>, C<LANG>
691 chooses the numeric format.
695 In the absence of C<LC_ALL>, C<LC_TIME> chooses the date and time
696 formatting locale. In the absence of both C<LC_ALL> and C<LC_TIME>,
697 C<LANG> chooses the date and time formatting locale.
701 C<LANG> is the "catch-all" locale environment variable. If it is set, it
702 is used as the last resort after the overall C<LC_ALL> and the
703 category-specific C<LC_...>.
709 =head2 Backward compatibility
711 Versions of Perl prior to 5.004 B<mostly> ignored locale information,
712 generally behaving as if something similar to the C<"C"> locale (see
713 L<The setlocale function>) was always in force, even if the program
714 environment suggested otherwise. By default, Perl still behaves this
715 way so as to maintain backward compatibility. If you want a Perl
716 application to pay attention to locale information, you B<must> use
717 the S<C<use locale>> pragma (see L<The S<C<use locale>> Pragma>) to
718 instruct it to do so.
720 Versions of Perl from 5.002 to 5.003 did use the C<LC_CTYPE>
721 information if that was available, that is, C<\w> did understand what
722 are the letters according to the locale environment variables.
723 The problem was that the user had no control over the feature:
724 if the C library supported locales, Perl used them.
726 =head2 I18N:Collate obsolete
728 In versions of Perl prior to 5.004 per-locale collation was possible
729 using the C<I18N::Collate> library module. This module is now mildly
730 obsolete and should be avoided in new applications. The C<LC_COLLATE>
731 functionality is now integrated into the Perl core language: One can
732 use locale-specific scalar data completely normally with C<use locale>,
733 so there is no longer any need to juggle with the scalar references of
736 =head2 Sort speed and memory use impacts
738 Comparing and sorting by locale is usually slower than the default
739 sorting; slow-downs of two to four times have been observed. It will
740 also consume more memory: once a Perl scalar variable has participated
741 in any string comparison or sorting operation obeying the locale
742 collation rules, it will take 3-15 times more memory than before. (The
743 exact multiplier depends on the string's contents, the operating system
744 and the locale.) These downsides are dictated more by the operating
745 system's implementation of the locale system than by Perl.
747 =head2 write() and LC_NUMERIC
749 Formats are the only part of Perl which unconditionally use information
750 from a program's locale; if a program's environment specifies an
751 LC_NUMERIC locale, it is always used to specify the decimal point
752 character in formatted output. Formatted output cannot be controlled by
753 C<use locale> because the pragma is tied to the block structure of the
754 program, and, for historical reasons, formats exist outside that block
757 =head2 Freely available locale definitions
759 There is a large collection of locale definitions at
760 C<ftp://dkuug.dk/i18n/WG15-collection>. You should be aware that it is
761 unsupported, and is not claimed to be fit for any purpose. If your
762 system allows the installation of arbitrary locales, you may find the
763 definitions useful as they are, or as a basis for the development of
768 "Internationalization" is often abbreviated as B<i18n> because its first
769 and last letters are separated by eighteen others. (You may guess why
770 the internalin ... internaliti ... i18n tends to get abbreviated.) In
771 the same way, "localization" is often abbreviated to B<l10n>.
773 =head2 An imperfect standard
775 Internationalization, as defined in the C and POSIX standards, can be
776 criticized as incomplete, ungainly, and having too large a granularity.
777 (Locales apply to a whole process, when it would arguably be more useful
778 to have them apply to a single thread, window group, or whatever.) They
779 also have a tendency, like standards groups, to divide the world into
780 nations, when we all know that the world can equally well be divided
781 into bankers, bikers, gamers, and so on. But, for now, it's the only
782 standard we've got. This may be construed as a bug.
786 =head2 Broken systems
788 In certain system environments the operating system's locale support
789 is broken and cannot be fixed or used by Perl. Such deficiencies can
790 and will result in mysterious hangs and/or Perl core dumps when the
791 C<use locale> is in effect. When confronted with such a system,
792 please report in excruciating detail to C<perlbug@perl.com>, and
793 complain to your vendor: maybe some bug fixes exist for these problems
794 in your operating system. Sometimes such bug fixes are called an
795 operating system upgrade.
799 L<POSIX (3)/isalnum>, L<POSIX (3)/isalpha>, L<POSIX (3)/isdigit>,
800 L<POSIX (3)/isgraph>, L<POSIX (3)/islower>, L<POSIX (3)/isprint>,
801 L<POSIX (3)/ispunct>, L<POSIX (3)/isspace>, L<POSIX (3)/isupper>,
802 L<POSIX (3)/isxdigit>, L<POSIX (3)/localeconv>, L<POSIX (3)/setlocale>,
803 L<POSIX (3)/strcoll>, L<POSIX (3)/strftime>, L<POSIX (3)/strtod>,
808 Jarkko Hietaniemi's original F<perli18n.pod> heavily hacked by Dominic
809 Dunlop, assisted by the perl5-porters.
811 Last update: Tue Dec 31 01:30:55 EST 1996