1PERLLOCALE(1)          Perl Programmers Reference Guide          PERLLOCALE(1)
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3
4

NAME

6       perllocale - Perl locale handling (internationalization and
7       localization)
8

DESCRIPTION

10       Perl supports language-specific notions of data such as "is this a
11       letter", "what is the uppercase equivalent of this letter", and "which
12       of these letters comes first".  These are important issues, especially
13       for languages other than English--but also for English: it would be
14       naieve to imagine that "A-Za-z" defines all the "letters" needed to
15       write in English. Perl is also aware that some character other than '.'
16       may be preferred as a decimal point, and that output date
17       representations may be language-specific.  The process of making an
18       application take account of its users' preferences in such matters is
19       called internationalization (often abbreviated as i18n); telling such
20       an application about a particular set of preferences is known as
21       localization (l10n).
22
23       Perl can understand language-specific data via the standardized (ISO C,
24       XPG4, POSIX 1.c) method called "the locale system". The locale system
25       is controlled per application using one pragma, one function call, and
26       several environment variables.
27
28       NOTE: This feature is new in Perl 5.004, and does not apply unless an
29       application specifically requests it--see "Backward compatibility".
30       The one exception is that write() now always uses the current locale -
31       see "NOTES".
32

PREPARING TO USE LOCALES

34       If Perl applications are to understand and present your data correctly
35       according a locale of your choice, all of the following must be true:
36
37       ·   Your operating system must support the locale system.  If it does,
38           you should find that the setlocale() function is a documented part
39           of its C library.
40
41       ·   Definitions for locales that you use must be installed.  You, or
42           your system administrator, must make sure that this is the case.
43           The available locales, the location in which they are kept, and the
44           manner in which they are installed all vary from system to system.
45           Some systems provide only a few, hard-wired locales and do not
46           allow more to be added.  Others allow you to add "canned" locales
47           provided by the system supplier.  Still others allow you or the
48           system administrator to define and add arbitrary locales.  (You may
49           have to ask your supplier to provide canned locales that are not
50           delivered with your operating system.)  Read your system
51           documentation for further illumination.
52
53       ·   Perl must believe that the locale system is supported.  If it does,
54           "perl -V:d_setlocale" will say that the value for "d_setlocale" is
55           "define".
56
57       If you want a Perl application to process and present your data
58       according to a particular locale, the application code should include
59       the "use locale" pragma (see "The use locale pragma") where
60       appropriate, and at least one of the following must be true:
61
62       ·   The locale-determining environment variables (see "ENVIRONMENT")
63           must be correctly set up at the time the application is started,
64           either by yourself or by whoever set up your system account.
65
66       ·   The application must set its own locale using the method described
67           in "The setlocale function".
68

USING LOCALES

70   The use locale pragma
71       By default, Perl ignores the current locale.  The "use locale" pragma
72       tells Perl to use the current locale for some operations:
73
74       ·   The comparison operators ("lt", "le", "cmp", "ge", and "gt") and
75           the POSIX string collation functions strcoll() and strxfrm() use
76           "LC_COLLATE".  sort() is also affected if used without an explicit
77           comparison function, because it uses "cmp" by default.
78
79           Note: "eq" and "ne" are unaffected by locale: they always perform a
80           char-by-char comparison of their scalar operands.  What's more, if
81           "cmp" finds that its operands are equal according to the collation
82           sequence specified by the current locale, it goes on to perform a
83           char-by-char comparison, and only returns 0 (equal) if the operands
84           are char-for-char identical.  If you really want to know whether
85           two strings--which "eq" and "cmp" may consider different--are equal
86           as far as collation in the locale is concerned, see the discussion
87           in "Category LC_COLLATE: Collation".
88
89       ·   Regular expressions and case-modification functions (uc(), lc(),
90           ucfirst(), and lcfirst()) use "LC_CTYPE"
91
92       ·   The formatting functions (printf(), sprintf() and write()) use
93           "LC_NUMERIC"
94
95       ·   The POSIX date formatting function (strftime()) uses "LC_TIME".
96
97       "LC_COLLATE", "LC_CTYPE", and so on, are discussed further in "LOCALE
98       CATEGORIES".
99
100       The default behavior is restored with the "no locale" pragma, or upon
101       reaching the end of block enclosing "use locale".
102
103       The string result of any operation that uses locale information is
104       tainted, as it is possible for a locale to be untrustworthy.  See
105       "SECURITY".
106
107   The setlocale function
108       You can switch locales as often as you wish at run time with the
109       POSIX::setlocale() function:
110
111               # This functionality not usable prior to Perl 5.004
112               require 5.004;
113
114               # Import locale-handling tool set from POSIX module.
115               # This example uses: setlocale -- the function call
116               #                    LC_CTYPE -- explained below
117               use POSIX qw(locale_h);
118
119               # query and save the old locale
120               $old_locale = setlocale(LC_CTYPE);
121
122               setlocale(LC_CTYPE, "fr_CA.ISO8859-1");
123               # LC_CTYPE now in locale "French, Canada, codeset ISO 8859-1"
124
125               setlocale(LC_CTYPE, "");
126               # LC_CTYPE now reset to default defined by LC_ALL/LC_CTYPE/LANG
127               # environment variables.  See below for documentation.
128
129               # restore the old locale
130               setlocale(LC_CTYPE, $old_locale);
131
132       The first argument of setlocale() gives the category, the second the
133       locale.  The category tells in what aspect of data processing you want
134       to apply locale-specific rules.  Category names are discussed in
135       "LOCALE CATEGORIES" and "ENVIRONMENT".  The locale is the name of a
136       collection of customization information corresponding to a particular
137       combination of language, country or territory, and codeset.  Read on
138       for hints on the naming of locales: not all systems name locales as in
139       the example.
140
141       If no second argument is provided and the category is something else
142       than LC_ALL, the function returns a string naming the current locale
143       for the category.  You can use this value as the second argument in a
144       subsequent call to setlocale().
145
146       If no second argument is provided and the category is LC_ALL, the
147       result is implementation-dependent.  It may be a string of concatenated
148       locales names (separator also implementation-dependent) or a single
149       locale name.  Please consult your setlocale(3) man page for details.
150
151       If a second argument is given and it corresponds to a valid locale, the
152       locale for the category is set to that value, and the function returns
153       the now-current locale value.  You can then use this in yet another
154       call to setlocale().  (In some implementations, the return value may
155       sometimes differ from the value you gave as the second argument--think
156       of it as an alias for the value you gave.)
157
158       As the example shows, if the second argument is an empty string, the
159       category's locale is returned to the default specified by the
160       corresponding environment variables.  Generally, this results in a
161       return to the default that was in force when Perl started up: changes
162       to the environment made by the application after startup may or may not
163       be noticed, depending on your system's C library.
164
165       If the second argument does not correspond to a valid locale, the
166       locale for the category is not changed, and the function returns undef.
167
168       For further information about the categories, consult setlocale(3).
169
170   Finding locales
171       For locales available in your system, consult also setlocale(3) to see
172       whether it leads to the list of available locales (search for the SEE
173       ALSO section).  If that fails, try the following command lines:
174
175               locale -a
176
177               nlsinfo
178
179               ls /usr/lib/nls/loc
180
181               ls /usr/lib/locale
182
183               ls /usr/lib/nls
184
185               ls /usr/share/locale
186
187       and see whether they list something resembling these
188
189               en_US.ISO8859-1     de_DE.ISO8859-1     ru_RU.ISO8859-5
190               en_US.iso88591      de_DE.iso88591      ru_RU.iso88595
191               en_US               de_DE               ru_RU
192               en                  de                  ru
193               english             german              russian
194               english.iso88591    german.iso88591     russian.iso88595
195               english.roman8                          russian.koi8r
196
197       Sadly, even though the calling interface for setlocale() has been
198       standardized, names of locales and the directories where the
199       configuration resides have not been.  The basic form of the name is
200       language_territory.codeset, but the latter parts after language are not
201       always present.  The language and country are usually from the
202       standards ISO 3166 and ISO 639, the two-letter abbreviations for the
203       countries and the languages of the world, respectively.  The codeset
204       part often mentions some ISO 8859 character set, the Latin codesets.
205       For example, "ISO 8859-1" is the so-called "Western European codeset"
206       that can be used to encode most Western European languages adequately.
207       Again, there are several ways to write even the name of that one
208       standard.  Lamentably.
209
210       Two special locales are worth particular mention: "C" and "POSIX".
211       Currently these are effectively the same locale: the difference is
212       mainly that the first one is defined by the C standard, the second by
213       the POSIX standard.  They define the default locale in which every
214       program starts in the absence of locale information in its environment.
215       (The default default locale, if you will.)  Its language is (American)
216       English and its character codeset ASCII.
217
218       NOTE: Not all systems have the "POSIX" locale (not all systems are
219       POSIX-conformant), so use "C" when you need explicitly to specify this
220       default locale.
221
222   LOCALE PROBLEMS
223       You may encounter the following warning message at Perl startup:
224
225               perl: warning: Setting locale failed.
226               perl: warning: Please check that your locale settings:
227                       LC_ALL = "En_US",
228                       LANG = (unset)
229                   are supported and installed on your system.
230               perl: warning: Falling back to the standard locale ("C").
231
232       This means that your locale settings had LC_ALL set to "En_US" and LANG
233       exists but has no value.  Perl tried to believe you but could not.
234       Instead, Perl gave up and fell back to the "C" locale, the default
235       locale that is supposed to work no matter what.  This usually means
236       your locale settings were wrong, they mention locales your system has
237       never heard of, or the locale installation in your system has problems
238       (for example, some system files are broken or missing).  There are
239       quick and temporary fixes to these problems, as well as more thorough
240       and lasting fixes.
241
242   Temporarily fixing locale problems
243       The two quickest fixes are either to render Perl silent about any
244       locale inconsistencies or to run Perl under the default locale "C".
245
246       Perl's moaning about locale problems can be silenced by setting the
247       environment variable PERL_BADLANG to a zero value, for example "0".
248       This method really just sweeps the problem under the carpet: you tell
249       Perl to shut up even when Perl sees that something is wrong.  Do not be
250       surprised if later something locale-dependent misbehaves.
251
252       Perl can be run under the "C" locale by setting the environment
253       variable LC_ALL to "C".  This method is perhaps a bit more civilized
254       than the PERL_BADLANG approach, but setting LC_ALL (or other locale
255       variables) may affect other programs as well, not just Perl.  In
256       particular, external programs run from within Perl will see these
257       changes.  If you make the new settings permanent (read on), all
258       programs you run see the changes.  See "ENVIRONMENT" for the full list
259       of relevant environment variables and "USING LOCALES" for their effects
260       in Perl.  Effects in other programs are easily deducible.  For example,
261       the variable LC_COLLATE may well affect your sort program (or whatever
262       the program that arranges "records" alphabetically in your system is
263       called).
264
265       You can test out changing these variables temporarily, and if the new
266       settings seem to help, put those settings into your shell startup
267       files.  Consult your local documentation for the exact details.  For in
268       Bourne-like shells (sh, ksh, bash, zsh):
269
270               LC_ALL=en_US.ISO8859-1
271               export LC_ALL
272
273       This assumes that we saw the locale "en_US.ISO8859-1" using the
274       commands discussed above.  We decided to try that instead of the above
275       faulty locale "En_US"--and in Cshish shells (csh, tcsh)
276
277               setenv LC_ALL en_US.ISO8859-1
278
279       or if you have the "env" application you can do in any shell
280
281               env LC_ALL=en_US.ISO8859-1 perl ...
282
283       If you do not know what shell you have, consult your local helpdesk or
284       the equivalent.
285
286   Permanently fixing locale problems
287       The slower but superior fixes are when you may be able to yourself fix
288       the misconfiguration of your own environment variables.  The
289       mis(sing)configuration of the whole system's locales usually requires
290       the help of your friendly system administrator.
291
292       First, see earlier in this document about "Finding locales".  That
293       tells how to find which locales are really supported--and more
294       importantly, installed--on your system.  In our example error message,
295       environment variables affecting the locale are listed in the order of
296       decreasing importance (and unset variables do not matter).  Therefore,
297       having LC_ALL set to "En_US" must have been the bad choice, as shown by
298       the error message.  First try fixing locale settings listed first.
299
300       Second, if using the listed commands you see something exactly (prefix
301       matches do not count and case usually counts) like "En_US" without the
302       quotes, then you should be okay because you are using a locale name
303       that should be installed and available in your system.  In this case,
304       see "Permanently fixing your system's locale configuration".
305
306   Permanently fixing your system's locale configuration
307       This is when you see something like:
308
309               perl: warning: Please check that your locale settings:
310                       LC_ALL = "En_US",
311                       LANG = (unset)
312                   are supported and installed on your system.
313
314       but then cannot see that "En_US" listed by the above-mentioned
315       commands.  You may see things like "en_US.ISO8859-1", but that isn't
316       the same.  In this case, try running under a locale that you can list
317       and which somehow matches what you tried.  The rules for matching
318       locale names are a bit vague because standardization is weak in this
319       area.  See again the "Finding locales" about general rules.
320
321   Fixing system locale configuration
322       Contact a system administrator (preferably your own) and report the
323       exact error message you get, and ask them to read this same
324       documentation you are now reading.  They should be able to check
325       whether there is something wrong with the locale configuration of the
326       system.  The "Finding locales" section is unfortunately a bit vague
327       about the exact commands and places because these things are not that
328       standardized.
329
330   The localeconv function
331       The POSIX::localeconv() function allows you to get particulars of the
332       locale-dependent numeric formatting information specified by the
333       current "LC_NUMERIC" and "LC_MONETARY" locales.  (If you just want the
334       name of the current locale for a particular category, use
335       POSIX::setlocale() with a single parameter--see "The setlocale
336       function".)
337
338               use POSIX qw(locale_h);
339
340               # Get a reference to a hash of locale-dependent info
341               $locale_values = localeconv();
342
343               # Output sorted list of the values
344               for (sort keys %$locale_values) {
345                   printf "%-20s = %s\n", $_, $locale_values->{$_}
346               }
347
348       localeconv() takes no arguments, and returns a reference to a hash.
349       The keys of this hash are variable names for formatting, such as
350       "decimal_point" and "thousands_sep".  The values are the corresponding,
351       er, values.  See "localeconv" in POSIX for a longer example listing the
352       categories an implementation might be expected to provide; some provide
353       more and others fewer.  You don't need an explicit "use locale",
354       because localeconv() always observes the current locale.
355
356       Here's a simple-minded example program that rewrites its command-line
357       parameters as integers correctly formatted in the current locale:
358
359               # See comments in previous example
360               require 5.004;
361               use POSIX qw(locale_h);
362
363               # Get some of locale's numeric formatting parameters
364               my ($thousands_sep, $grouping) =
365                    @{localeconv()}{'thousands_sep', 'grouping'};
366
367               # Apply defaults if values are missing
368               $thousands_sep = ',' unless $thousands_sep;
369
370               # grouping and mon_grouping are packed lists
371               # of small integers (characters) telling the
372               # grouping (thousand_seps and mon_thousand_seps
373               # being the group dividers) of numbers and
374               # monetary quantities.  The integers' meanings:
375               # 255 means no more grouping, 0 means repeat
376               # the previous grouping, 1-254 means use that
377               # as the current grouping.  Grouping goes from
378               # right to left (low to high digits).  In the
379               # below we cheat slightly by never using anything
380               # else than the first grouping (whatever that is).
381               if ($grouping) {
382                   @grouping = unpack("C*", $grouping);
383               } else {
384                   @grouping = (3);
385               }
386
387               # Format command line params for current locale
388               for (@ARGV) {
389                   $_ = int;    # Chop non-integer part
390                   1 while
391                   s/(\d)(\d{$grouping[0]}($|$thousands_sep))/$1$thousands_sep$2/;
392                   print "$_";
393               }
394               print "\n";
395
396   I18N::Langinfo
397       Another interface for querying locale-dependent information is the
398       I18N::Langinfo::langinfo() function, available at least in Unix-like
399       systems and VMS.
400
401       The following example will import the langinfo() function itself and
402       three constants to be used as arguments to langinfo(): a constant for
403       the abbreviated first day of the week (the numbering starts from Sunday
404       = 1) and two more constants for the affirmative and negative answers
405       for a yes/no question in the current locale.
406
407           use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
408
409           my ($abday_1, $yesstr, $nostr) = map { langinfo } qw(ABDAY_1 YESSTR NOSTR);
410
411           print "$abday_1? [$yesstr/$nostr] ";
412
413       In other words, in the "C" (or English) locale the above will probably
414       print something like:
415
416           Sun? [yes/no]
417
418       See I18N::Langinfo for more information.
419

LOCALE CATEGORIES

421       The following subsections describe basic locale categories.  Beyond
422       these, some combination categories allow manipulation of more than one
423       basic category at a time.  See "ENVIRONMENT" for a discussion of these.
424
425   Category LC_COLLATE: Collation
426       In the scope of "use locale", Perl looks to the "LC_COLLATE"
427       environment variable to determine the application's notions on
428       collation (ordering) of characters.  For example, 'b' follows 'a' in
429       Latin alphabets, but where do 'a' and 'aa' belong?  And while 'color'
430       follows 'chocolate' in English, what about in Spanish?
431
432       The following collations all make sense and you may meet any of them if
433       you "use locale".
434
435               A B C D E a b c d e
436               A a B b C c D d E e
437               a A b B c C d D e E
438               a b c d e A B C D E
439
440       Here is a code snippet to tell what "word" characters are in the
441       current locale, in that locale's order:
442
443               use locale;
444               print +(sort grep /\w/, map { chr } 0..255), "\n";
445
446       Compare this with the characters that you see and their order if you
447       state explicitly that the locale should be ignored:
448
449               no locale;
450               print +(sort grep /\w/, map { chr } 0..255), "\n";
451
452       This machine-native collation (which is what you get unless
453       "use locale" has appeared earlier in the same block) must be used for
454       sorting raw binary data, whereas the locale-dependent collation of the
455       first example is useful for natural text.
456
457       As noted in "USING LOCALES", "cmp" compares according to the current
458       collation locale when "use locale" is in effect, but falls back to a
459       char-by-char comparison for strings that the locale says are equal. You
460       can use POSIX::strcoll() if you don't want this fall-back:
461
462               use POSIX qw(strcoll);
463               $equal_in_locale =
464                   !strcoll("space and case ignored", "SpaceAndCaseIgnored");
465
466       $equal_in_locale will be true if the collation locale specifies a
467       dictionary-like ordering that ignores space characters completely and
468       which folds case.
469
470       If you have a single string that you want to check for "equality in
471       locale" against several others, you might think you could gain a little
472       efficiency by using POSIX::strxfrm() in conjunction with "eq":
473
474               use POSIX qw(strxfrm);
475               $xfrm_string = strxfrm("Mixed-case string");
476               print "locale collation ignores spaces\n"
477                   if $xfrm_string eq strxfrm("Mixed-casestring");
478               print "locale collation ignores hyphens\n"
479                   if $xfrm_string eq strxfrm("Mixedcase string");
480               print "locale collation ignores case\n"
481                   if $xfrm_string eq strxfrm("mixed-case string");
482
483       strxfrm() takes a string and maps it into a transformed string for use
484       in char-by-char comparisons against other transformed strings during
485       collation.  "Under the hood", locale-affected Perl comparison operators
486       call strxfrm() for both operands, then do a char-by-char comparison of
487       the transformed strings.  By calling strxfrm() explicitly and using a
488       non locale-affected comparison, the example attempts to save a couple
489       of transformations.  But in fact, it doesn't save anything: Perl magic
490       (see "Magic Variables" in perlguts) creates the transformed version of
491       a string the first time it's needed in a comparison, then keeps this
492       version around in case it's needed again.  An example rewritten the
493       easy way with "cmp" runs just about as fast.  It also copes with null
494       characters embedded in strings; if you call strxfrm() directly, it
495       treats the first null it finds as a terminator.  don't expect the
496       transformed strings it produces to be portable across systems--or even
497       from one revision of your operating system to the next.  In short,
498       don't call strxfrm() directly: let Perl do it for you.
499
500       Note: "use locale" isn't shown in some of these examples because it
501       isn't needed: strcoll() and strxfrm() exist only to generate locale-
502       dependent results, and so always obey the current "LC_COLLATE" locale.
503
504   Category LC_CTYPE: Character Types
505       In the scope of "use locale", Perl obeys the "LC_CTYPE" locale setting.
506       This controls the application's notion of which characters are
507       alphabetic.  This affects Perl's "\w" regular expression metanotation,
508       which stands for alphanumeric characters--that is, alphabetic, numeric,
509       and including other special characters such as the underscore or
510       hyphen.  (Consult perlre for more information about regular
511       expressions.)  Thanks to "LC_CTYPE", depending on your locale setting,
512       characters like 'ae', 'd`', 'ss', and 'o' may be understood as "\w"
513       characters.
514
515       The "LC_CTYPE" locale also provides the map used in transliterating
516       characters between lower and uppercase.  This affects the case-mapping
517       functions--lc(), lcfirst, uc(), and ucfirst(); case-mapping
518       interpolation with "\l", "\L", "\u", or "\U" in double-quoted strings
519       and "s///" substitutions; and case-independent regular expression
520       pattern matching using the "i" modifier.
521
522       Finally, "LC_CTYPE" affects the POSIX character-class test
523       functions--isalpha(), islower(), and so on.  For example, if you move
524       from the "C" locale to a 7-bit Scandinavian one, you may find--possibly
525       to your surprise--that "|" moves from the ispunct() class to isalpha().
526
527       Note: A broken or malicious "LC_CTYPE" locale definition may result in
528       clearly ineligible characters being considered to be alphanumeric by
529       your application.  For strict matching of (mundane) letters and
530       digits--for example, in command strings--locale-aware applications
531       should use "\w" inside a "no locale" block.  See "SECURITY".
532
533   Category LC_NUMERIC: Numeric Formatting
534       After a proper POSIX::setlocale() call, Perl obeys the "LC_NUMERIC"
535       locale information, which controls an application's idea of how numbers
536       should be formatted for human readability by the printf(), sprintf(),
537       and write() functions. String-to-numeric conversion by the
538       POSIX::strtod() function is also affected.  In most implementations the
539       only effect is to change the character used for the decimal
540       point--perhaps from '.'  to ','.  These functions aren't aware of such
541       niceties as thousands separation and so on. (See "The localeconv
542       function" if you care about these things.)
543
544       Output produced by print() is also affected by the current locale: it
545       corresponds to what you'd get from printf() in the "C" locale.  The
546       same is true for Perl's internal conversions between numeric and string
547       formats:
548
549               use POSIX qw(strtod setlocale LC_NUMERIC);
550
551               setlocale LC_NUMERIC, "";
552
553               $n = 5/2;   # Assign numeric 2.5 to $n
554
555               $a = " $n"; # Locale-dependent conversion to string
556
557               print "half five is $n\n";       # Locale-dependent output
558
559               printf "half five is %g\n", $n;  # Locale-dependent output
560
561               print "DECIMAL POINT IS COMMA\n"
562                   if $n == (strtod("2,5"))[0]; # Locale-dependent conversion
563
564       See also I18N::Langinfo and "RADIXCHAR".
565
566   Category LC_MONETARY: Formatting of monetary amounts
567       The C standard defines the "LC_MONETARY" category, but no function that
568       is affected by its contents.  (Those with experience of standards
569       committees will recognize that the working group decided to punt on the
570       issue.)  Consequently, Perl takes no notice of it.  If you really want
571       to use "LC_MONETARY", you can query its contents--see "The localeconv
572       function"--and use the information that it returns in your
573       application's own formatting of currency amounts.  However, you may
574       well find that the information, voluminous and complex though it may
575       be, still does not quite meet your requirements: currency formatting is
576       a hard nut to crack.
577
578       See also I18N::Langinfo and "CRNCYSTR".
579
580   LC_TIME
581       Output produced by POSIX::strftime(), which builds a formatted human-
582       readable date/time string, is affected by the current "LC_TIME" locale.
583       Thus, in a French locale, the output produced by the %B format element
584       (full month name) for the first month of the year would be "janvier".
585       Here's how to get a list of long month names in the current locale:
586
587               use POSIX qw(strftime);
588               for (0..11) {
589                   $long_month_name[$_] =
590                       strftime("%B", 0, 0, 0, 1, $_, 96);
591               }
592
593       Note: "use locale" isn't needed in this example: as a function that
594       exists only to generate locale-dependent results, strftime() always
595       obeys the current "LC_TIME" locale.
596
597       See also I18N::Langinfo and "ABDAY_1".."ABDAY_7", "DAY_1".."DAY_7",
598       "ABMON_1".."ABMON_12", and "ABMON_1".."ABMON_12".
599
600   Other categories
601       The remaining locale category, "LC_MESSAGES" (possibly supplemented by
602       others in particular implementations) is not currently used by
603       Perl--except possibly to affect the behavior of library functions
604       called by extensions outside the standard Perl distribution and by the
605       operating system and its utilities.  Note especially that the string
606       value of $! and the error messages given by external utilities may be
607       changed by "LC_MESSAGES".  If you want to have portable error codes,
608       use "%!".  See Errno.
609

SECURITY

611       Although the main discussion of Perl security issues can be found in
612       perlsec, a discussion of Perl's locale handling would be incomplete if
613       it did not draw your attention to locale-dependent security issues.
614       Locales--particularly on systems that allow unprivileged users to build
615       their own locales--are untrustworthy.  A malicious (or just plain
616       broken) locale can make a locale-aware application give unexpected
617       results.  Here are a few possibilities:
618
619       ·   Regular expression checks for safe file names or mail addresses
620           using "\w" may be spoofed by an "LC_CTYPE" locale that claims that
621           characters such as ">" and "|" are alphanumeric.
622
623       ·   String interpolation with case-mapping, as in, say, "$dest =
624           "C:\U$name.$ext"", may produce dangerous results if a bogus
625           LC_CTYPE case-mapping table is in effect.
626
627       ·   A sneaky "LC_COLLATE" locale could result in the names of students
628           with "D" grades appearing ahead of those with "A"s.
629
630       ·   An application that takes the trouble to use information in
631           "LC_MONETARY" may format debits as if they were credits and vice
632           versa if that locale has been subverted.  Or it might make payments
633           in US dollars instead of Hong Kong dollars.
634
635       ·   The date and day names in dates formatted by strftime() could be
636           manipulated to advantage by a malicious user able to subvert the
637           "LC_DATE" locale.  ("Look--it says I wasn't in the building on
638           Sunday.")
639
640       Such dangers are not peculiar to the locale system: any aspect of an
641       application's environment which may be modified maliciously presents
642       similar challenges.  Similarly, they are not specific to Perl: any
643       programming language that allows you to write programs that take
644       account of their environment exposes you to these issues.
645
646       Perl cannot protect you from all possibilities shown in the
647       examples--there is no substitute for your own vigilance--but, when "use
648       locale" is in effect, Perl uses the tainting mechanism (see perlsec) to
649       mark string results that become locale-dependent, and which may be
650       untrustworthy in consequence.  Here is a summary of the tainting
651       behavior of operators and functions that may be affected by the locale:
652
653       ·   Comparison operators ("lt", "le", "ge", "gt" and "cmp"):
654
655           Scalar true/false (or less/equal/greater) result is never tainted.
656
657       ·   Case-mapping interpolation (with "\l", "\L", "\u" or "\U")
658
659           Result string containing interpolated material is tainted if "use
660           locale" is in effect.
661
662       ·   Matching operator ("m//"):
663
664           Scalar true/false result never tainted.
665
666           Subpatterns, either delivered as a list-context result or as $1
667           etc.  are tainted if "use locale" is in effect, and the subpattern
668           regular expression contains "\w" (to match an alphanumeric
669           character), "\W" (non-alphanumeric character), "\s" (whitespace
670           character), or "\S" (non whitespace character).  The matched-
671           pattern variable, $&, $` (pre-match), $' (post-match), and $+ (last
672           match) are also tainted if "use locale" is in effect and the
673           regular expression contains "\w", "\W", "\s", or "\S".
674
675       ·   Substitution operator ("s///"):
676
677           Has the same behavior as the match operator.  Also, the left
678           operand of "=~" becomes tainted when "use locale" in effect if
679           modified as a result of a substitution based on a regular
680           expression match involving "\w", "\W", "\s", or "\S"; or of case-
681           mapping with "\l", "\L","\u" or "\U".
682
683       ·   Output formatting functions (printf() and write()):
684
685           Results are never tainted because otherwise even output from print,
686           for example "print(1/7)", should be tainted if "use locale" is in
687           effect.
688
689       ·   Case-mapping functions (lc(), lcfirst(), uc(), ucfirst()):
690
691           Results are tainted if "use locale" is in effect.
692
693       ·   POSIX locale-dependent functions (localeconv(), strcoll(),
694           strftime(), strxfrm()):
695
696           Results are never tainted.
697
698       ·   POSIX character class tests (isalnum(), isalpha(), isdigit(),
699           isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(),
700           isxdigit()):
701
702           True/false results are never tainted.
703
704       Three examples illustrate locale-dependent tainting.  The first
705       program, which ignores its locale, won't run: a value taken directly
706       from the command line may not be used to name an output file when taint
707       checks are enabled.
708
709               #/usr/local/bin/perl -T
710               # Run with taint checking
711
712               # Command line sanity check omitted...
713               $tainted_output_file = shift;
714
715               open(F, ">$tainted_output_file")
716                   or warn "Open of $untainted_output_file failed: $!\n";
717
718       The program can be made to run by "laundering" the tainted value
719       through a regular expression: the second example--which still ignores
720       locale information--runs, creating the file named on its command line
721       if it can.
722
723               #/usr/local/bin/perl -T
724
725               $tainted_output_file = shift;
726               $tainted_output_file =~ m%[\w/]+%;
727               $untainted_output_file = $&;
728
729               open(F, ">$untainted_output_file")
730                   or warn "Open of $untainted_output_file failed: $!\n";
731
732       Compare this with a similar but locale-aware program:
733
734               #/usr/local/bin/perl -T
735
736               $tainted_output_file = shift;
737               use locale;
738               $tainted_output_file =~ m%[\w/]+%;
739               $localized_output_file = $&;
740
741               open(F, ">$localized_output_file")
742                   or warn "Open of $localized_output_file failed: $!\n";
743
744       This third program fails to run because $& is tainted: it is the result
745       of a match involving "\w" while "use locale" is in effect.
746

ENVIRONMENT

748       PERL_BADLANG
749                   A string that can suppress Perl's warning about failed
750                   locale settings at startup.  Failure can occur if the
751                   locale support in the operating system is lacking (broken)
752                   in some way--or if you mistyped the name of a locale when
753                   you set up your environment.  If this environment variable
754                   is absent, or has a value that does not evaluate to integer
755                   zero--that is, "0" or ""-- Perl will complain about locale
756                   setting failures.
757
758                   NOTE: PERL_BADLANG only gives you a way to hide the warning
759                   message.  The message tells about some problem in your
760                   system's locale support, and you should investigate what
761                   the problem is.
762
763       The following environment variables are not specific to Perl: They are
764       part of the standardized (ISO C, XPG4, POSIX 1.c) setlocale() method
765       for controlling an application's opinion on data.
766
767       LC_ALL      "LC_ALL" is the "override-all" locale environment variable.
768                   If set, it overrides all the rest of the locale environment
769                   variables.
770
771       LANGUAGE    NOTE: "LANGUAGE" is a GNU extension, it affects you only if
772                   you are using the GNU libc.  This is the case if you are
773                   using e.g. Linux.  If you are using "commercial" Unixes you
774                   are most probably not using GNU libc and you can ignore
775                   "LANGUAGE".
776
777                   However, in the case you are using "LANGUAGE": it affects
778                   the language of informational, warning, and error messages
779                   output by commands (in other words, it's like
780                   "LC_MESSAGES") but it has higher priority than LC_ALL.
781                   Moreover, it's not a single value but instead a "path"
782                   (":"-separated list) of languages (not locales).  See the
783                   GNU "gettext" library documentation for more information.
784
785       LC_CTYPE    In the absence of "LC_ALL", "LC_CTYPE" chooses the
786                   character type locale.  In the absence of both "LC_ALL" and
787                   "LC_CTYPE", "LANG" chooses the character type locale.
788
789       LC_COLLATE  In the absence of "LC_ALL", "LC_COLLATE" chooses the
790                   collation (sorting) locale.  In the absence of both
791                   "LC_ALL" and "LC_COLLATE", "LANG" chooses the collation
792                   locale.
793
794       LC_MONETARY In the absence of "LC_ALL", "LC_MONETARY" chooses the
795                   monetary formatting locale.  In the absence of both
796                   "LC_ALL" and "LC_MONETARY", "LANG" chooses the monetary
797                   formatting locale.
798
799       LC_NUMERIC  In the absence of "LC_ALL", "LC_NUMERIC" chooses the
800                   numeric format locale.  In the absence of both "LC_ALL" and
801                   "LC_NUMERIC", "LANG" chooses the numeric format.
802
803       LC_TIME     In the absence of "LC_ALL", "LC_TIME" chooses the date and
804                   time formatting locale.  In the absence of both "LC_ALL"
805                   and "LC_TIME", "LANG" chooses the date and time formatting
806                   locale.
807
808       LANG        "LANG" is the "catch-all" locale environment variable. If
809                   it is set, it is used as the last resort after the overall
810                   "LC_ALL" and the category-specific "LC_...".
811
812   Examples
813       The LC_NUMERIC controls the numeric output:
814
815               use locale;
816               use POSIX qw(locale_h); # Imports setlocale() and the LC_ constants.
817               setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
818               printf "%g\n", 1.23; # If the "fr_FR" succeeded, probably shows 1,23.
819
820       and also how strings are parsed by POSIX::strtod() as numbers:
821
822               use locale;
823               use POSIX qw(locale_h strtod);
824               setlocale(LC_NUMERIC, "de_DE") or die "Entschuldigung";
825               my $x = strtod("2,34") + 5;
826               print $x, "\n"; # Probably shows 7,34.
827

NOTES

829   Backward compatibility
830       Versions of Perl prior to 5.004 mostly ignored locale information,
831       generally behaving as if something similar to the "C" locale were
832       always in force, even if the program environment suggested otherwise
833       (see "The setlocale function").  By default, Perl still behaves this
834       way for backward compatibility.  If you want a Perl application to pay
835       attention to locale information, you must use the "use locale" pragma
836       (see "The use locale pragma") to instruct it to do so.
837
838       Versions of Perl from 5.002 to 5.003 did use the "LC_CTYPE" information
839       if available; that is, "\w" did understand what were the letters
840       according to the locale environment variables.  The problem was that
841       the user had no control over the feature: if the C library supported
842       locales, Perl used them.
843
844   I18N:Collate obsolete
845       In versions of Perl prior to 5.004, per-locale collation was possible
846       using the "I18N::Collate" library module.  This module is now mildly
847       obsolete and should be avoided in new applications.  The "LC_COLLATE"
848       functionality is now integrated into the Perl core language: One can
849       use locale-specific scalar data completely normally with "use locale",
850       so there is no longer any need to juggle with the scalar references of
851       "I18N::Collate".
852
853   Sort speed and memory use impacts
854       Comparing and sorting by locale is usually slower than the default
855       sorting; slow-downs of two to four times have been observed.  It will
856       also consume more memory: once a Perl scalar variable has participated
857       in any string comparison or sorting operation obeying the locale
858       collation rules, it will take 3-15 times more memory than before.  (The
859       exact multiplier depends on the string's contents, the operating system
860       and the locale.) These downsides are dictated more by the operating
861       system's implementation of the locale system than by Perl.
862
863   write() and LC_NUMERIC
864       Formats are the only part of Perl that unconditionally use information
865       from a program's locale; if a program's environment specifies an
866       LC_NUMERIC locale, it is always used to specify the decimal point
867       character in formatted output.  Formatted output cannot be controlled
868       by "use locale" because the pragma is tied to the block structure of
869       the program, and, for historical reasons, formats exist outside that
870       block structure.
871
872   Freely available locale definitions
873       There is a large collection of locale definitions at:
874
875         http://std.dkuug.dk/i18n/WG15-collection/locales/
876
877       You should be aware that it is unsupported, and is not claimed to be
878       fit for any purpose.  If your system allows installation of arbitrary
879       locales, you may find the definitions useful as they are, or as a basis
880       for the development of your own locales.
881
882   I18n and l10n
883       "Internationalization" is often abbreviated as i18n because its first
884       and last letters are separated by eighteen others.  (You may guess why
885       the internalin ... internaliti ... i18n tends to get abbreviated.)  In
886       the same way, "localization" is often abbreviated to l10n.
887
888   An imperfect standard
889       Internationalization, as defined in the C and POSIX standards, can be
890       criticized as incomplete, ungainly, and having too large a granularity.
891       (Locales apply to a whole process, when it would arguably be more
892       useful to have them apply to a single thread, window group, or
893       whatever.)  They also have a tendency, like standards groups, to divide
894       the world into nations, when we all know that the world can equally
895       well be divided into bankers, bikers, gamers, and so on.  But, for now,
896       it's the only standard we've got.  This may be construed as a bug.
897

Unicode and UTF-8

899       The support of Unicode is new starting from Perl version 5.6, and more
900       fully implemented in the version 5.8.  See perluniintro and perlunicode
901       for more details.
902
903       Usually locale settings and Unicode do not affect each other, but there
904       are exceptions, see "Locales" in perlunicode for examples.
905

BUGS

907   Broken systems
908       In certain systems, the operating system's locale support is broken and
909       cannot be fixed or used by Perl.  Such deficiencies can and will result
910       in mysterious hangs and/or Perl core dumps when the "use locale" is in
911       effect.  When confronted with such a system, please report in
912       excruciating detail to <perlbug@perl.org>, and complain to your vendor:
913       bug fixes may exist for these problems in your operating system.
914       Sometimes such bug fixes are called an operating system upgrade.
915

SEE ALSO

917       I18N::Langinfo, perluniintro, perlunicode, open, "isalnum" in POSIX,
918       "isalpha" in POSIX, "isdigit" in POSIX, "isgraph" in POSIX, "islower"
919       in POSIX, "isprint" in POSIX, "ispunct" in POSIX, "isspace" in POSIX,
920       "isupper" in POSIX, "isxdigit" in POSIX, "localeconv" in POSIX,
921       "setlocale" in POSIX, "strcoll" in POSIX, "strftime" in POSIX, "strtod"
922       in POSIX, "strxfrm" in POSIX.
923

HISTORY

925       Jarkko Hietaniemi's original perli18n.pod heavily hacked by Dominic
926       Dunlop, assisted by the perl5-porters.  Prose worked over a bit by Tom
927       Christiansen.
928
929       Last update: Thu Jun 11 08:44:13 MDT 1998
930
931
932
933perl v5.12.4                      2011-06-07                     PERLLOCALE(1)
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