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       In the beginning there was ASCII, the "American Standard Code for
11       Information Interchange", which works quite well for Americans with
12       their English alphabet and dollar-denominated currency.  But it doesn't
13       work so well even for other English speakers, who may use different
14       currencies, such as the pound sterling (as the symbol for that currency
15       is not in ASCII); and it's hopelessly inadequate for many of the
16       thousands of the world's other languages.
17
18       To address these deficiencies, the concept of locales was invented
19       (formally the ISO C, XPG4, POSIX 1.c "locale system").  And
20       applications were and are being written that use the locale mechanism.
21       The process of making such an application take account of its users'
22       preferences in these kinds of matters is called internationalization
23       (often abbreviated as i18n); telling such an application about a
24       particular set of preferences is known as localization (l10n).
25
26       Perl has been extended to support certain types of locales available in
27       the locale system.  This is controlled per application by using one
28       pragma, one function call, and several environment variables.
29
30       Perl supports single-byte locales that are supersets of ASCII, such as
31       the ISO 8859 ones, and one multi-byte-type locale, UTF-8 ones,
32       described in the next paragraph.  Perl doesn't support any other multi-
33       byte locales, such as the ones for East Asian languages.
34
35       Unfortunately, there are quite a few deficiencies with the design (and
36       often, the implementations) of locales.  Unicode was invented (see
37       perlunitut for an introduction to that) in part to address these design
38       deficiencies, and nowadays, there is a series of "UTF-8 locales", based
39       on Unicode.  These are locales whose character set is Unicode, encoded
40       in UTF-8.  Starting in v5.20, Perl fully supports UTF-8 locales, except
41       for sorting and string comparisons like "lt" and "ge".  Starting in
42       v5.26, Perl can handle these reasonably as well, depending on the
43       platform's implementation.  However, for earlier releases or for better
44       control, use Unicode::Collate.  There are actually two slightly
45       different types of UTF-8 locales: one for Turkic languages and one for
46       everything else.
47
48       Starting in Perl v5.30, Perl detects Turkic locales by their behaviour,
49       and seamlessly handles both types; previously only the non-Turkic one
50       was supported.  The name of the locale is ignored, if your system has a
51       "tr_TR.UTF-8" locale and it doesn't behave like a Turkic locale, perl
52       will treat it like a non-Turkic locale.
53
54       Perl continues to support the old non UTF-8 locales as well.  There are
55       currently no UTF-8 locales for EBCDIC platforms.
56
57       (Unicode is also creating "CLDR", the "Common Locale Data Repository",
58       <http://cldr.unicode.org/> which includes more types of information
59       than are available in the POSIX locale system.  At the time of this
60       writing, there was no CPAN module that provides access to this XML-
61       encoded data.  However, it is possible to compute the POSIX locale data
62       from them, and earlier CLDR versions had these already extracted for
63       you as UTF-8 locales <http://unicode.org/Public/cldr/2.0.1/>.)
64

WHAT IS A LOCALE

66       A locale is a set of data that describes various aspects of how various
67       communities in the world categorize their world.  These categories are
68       broken down into the following types (some of which include a brief
69       note here):
70
71       Category "LC_NUMERIC": Numeric formatting
72           This indicates how numbers should be formatted for human
73           readability, for example the character used as the decimal point.
74
75       Category "LC_MONETARY": Formatting of monetary amounts
76
77
78       Category "LC_TIME": Date/Time formatting
79
80
81       Category "LC_MESSAGES": Error and other messages
82           This is used by Perl itself only for accessing operating system
83           error messages via $! and $^E.
84
85       Category "LC_COLLATE": Collation
86           This indicates the ordering of letters for comparison and sorting.
87           In Latin alphabets, for example, "b", generally follows "a".
88
89       Category "LC_CTYPE": Character Types
90           This indicates, for example if a character is an uppercase letter.
91
92       Other categories
93           Some platforms have other categories, dealing with such things as
94           measurement units and paper sizes.  None of these are used directly
95           by Perl, but outside operations that Perl interacts with may use
96           these.  See "Not within the scope of "use locale"" below.
97
98       More details on the categories used by Perl are given below in "LOCALE
99       CATEGORIES".
100
101       Together, these categories go a long way towards being able to
102       customize a single program to run in many different locations.  But
103       there are deficiencies, so keep reading.
104

PREPARING TO USE LOCALES

106       Perl itself (outside the POSIX module) will not use locales unless
107       specifically requested to (but again note that Perl may interact with
108       code that does use them).  Even if there is such a request, all of the
109       following must be true for it to work properly:
110
111Your operating system must support the locale system.  If it does,
112           you should find that the "setlocale()" function is a documented
113           part of its C library.
114
115Definitions for locales that you use must be installed.  You, or
116           your system administrator, must make sure that this is the case.
117           The available locales, the location in which they are kept, and the
118           manner in which they are installed all vary from system to system.
119           Some systems provide only a few, hard-wired locales and do not
120           allow more to be added.  Others allow you to add "canned" locales
121           provided by the system supplier.  Still others allow you or the
122           system administrator to define and add arbitrary locales.  (You may
123           have to ask your supplier to provide canned locales that are not
124           delivered with your operating system.)  Read your system
125           documentation for further illumination.
126
127Perl must believe that the locale system is supported.  If it does,
128           "perl -V:d_setlocale" will say that the value for "d_setlocale" is
129           "define".
130
131       If you want a Perl application to process and present your data
132       according to a particular locale, the application code should include
133       the "use locale" pragma (see "The "use locale" pragma") where
134       appropriate, and at least one of the following must be true:
135
136       1.  The locale-determining environment variables (see "ENVIRONMENT")
137           must be correctly set up at the time the application is started,
138           either by yourself or by whomever set up your system account; or
139
140       2.  The application must set its own locale using the method described
141           in "The setlocale function".
142

USING LOCALES

144   The "use locale" pragma
145       Starting in Perl 5.28, this pragma may be used in multi-threaded
146       applications on systems that have thread-safe locale ability.  Some
147       caveats apply, see "Multi-threaded" below.  On systems without this
148       capability, or in earlier Perls, do NOT use this pragma in scripts that
149       have multiple threads active.  The locale in these cases is not local
150       to a single thread.  Another thread may change the locale at any time,
151       which could cause at a minimum that a given thread is operating in a
152       locale it isn't expecting to be in.  On some platforms, segfaults can
153       also occur.  The locale change need not be explicit; some operations
154       cause perl to change the locale itself.  You are vulnerable simply by
155       having done a "use locale".
156
157       By default, Perl itself (outside the POSIX module) ignores the current
158       locale.  The "use locale" pragma tells Perl to use the current locale
159       for some operations.  Starting in v5.16, there are optional parameters
160       to this pragma, described below, which restrict which operations are
161       affected by it.
162
163       The current locale is set at execution time by setlocale() described
164       below.  If that function hasn't yet been called in the course of the
165       program's execution, the current locale is that which was determined by
166       the "ENVIRONMENT" in effect at the start of the program.  If there is
167       no valid environment, the current locale is whatever the system default
168       has been set to.   On POSIX systems, it is likely, but not necessarily,
169       the "C" locale.  On Windows, the default is set via the computer's
170       "Control Panel->Regional and Language Options" (or its current
171       equivalent).
172
173       The operations that are affected by locale are:
174
175       Not within the scope of "use locale"
176           Only certain operations (all originating outside Perl) should be
177           affected, as follows:
178
179           •   The current locale is used when going outside of Perl with
180               operations like system() or qx//, if those operations are
181               locale-sensitive.
182
183           •   Also Perl gives access to various C library functions through
184               the POSIX module.  Some of those functions are always affected
185               by the current locale.  For example, "POSIX::strftime()" uses
186               "LC_TIME"; "POSIX::strtod()" uses "LC_NUMERIC";
187               "POSIX::strcoll()" and "POSIX::strxfrm()" use "LC_COLLATE".
188               All such functions will behave according to the current
189               underlying locale, even if that locale isn't exposed to Perl
190               space.
191
192               This applies as well to I18N::Langinfo.
193
194           •   XS modules for all categories but "LC_NUMERIC" get the
195               underlying locale, and hence any C library functions they call
196               will use that underlying locale.  For more discussion, see
197               "CAVEATS" in perlxs.
198
199           Note that all C programs (including the perl interpreter, which is
200           written in C) always have an underlying locale.  That locale is the
201           "C" locale unless changed by a call to setlocale().  When Perl
202           starts up, it changes the underlying locale to the one which is
203           indicated by the "ENVIRONMENT".  When using the POSIX module or
204           writing XS code, it is important to keep in mind that the
205           underlying locale may be something other than "C", even if the
206           program hasn't explicitly changed it.
207
208
209
210       Lingering effects of "use locale"
211           Certain Perl operations that are set-up within the scope of a "use
212           locale" retain that effect even outside the scope.  These include:
213
214           •   The output format of a write() is determined by an earlier
215               format declaration ("format" in perlfunc), so whether or not
216               the output is affected by locale is determined by if the
217               "format()" is within the scope of a "use locale", not whether
218               the "write()" is.
219
220           •   Regular expression patterns can be compiled using qr// with
221               actual matching deferred to later.  Again, it is whether or not
222               the compilation was done within the scope of "use locale" that
223               determines the match behavior, not if the matches are done
224               within such a scope or not.
225
226
227
228       Under ""use locale";"
229           •   All the above operations
230
231Format declarations ("format" in perlfunc) and hence any
232               subsequent "write()"s use "LC_NUMERIC".
233
234stringification and output use "LC_NUMERIC".  These include the
235               results of "print()", "printf()", "say()", and "sprintf()".
236
237The comparison operators ("lt", "le", "cmp", "ge", and "gt")
238               use "LC_COLLATE".  "sort()" is also affected if used without an
239               explicit comparison function, because it uses "cmp" by default.
240
241               Note: "eq" and "ne" are unaffected by locale: they always
242               perform a char-by-char comparison of their scalar operands.
243               What's more, if "cmp" finds that its operands are equal
244               according to the collation sequence specified by the current
245               locale, it goes on to perform a char-by-char comparison, and
246               only returns 0 (equal) if the operands are char-for-char
247               identical.  If you really want to know whether two
248               strings--which "eq" and "cmp" may consider different--are equal
249               as far as collation in the locale is concerned, see the
250               discussion in "Category "LC_COLLATE": Collation".
251
252Regular expressions and case-modification functions ("uc()",
253               "lc()", "ucfirst()", and "lcfirst()") use "LC_CTYPE"
254
255The variables $! (and its synonyms $ERRNO and $OS_ERROR) and
256               $^E (and its synonym $EXTENDED_OS_ERROR) when used as strings
257               use "LC_MESSAGES".
258
259       The default behavior is restored with the "no locale" pragma, or upon
260       reaching the end of the block enclosing "use locale".  Note that "use
261       locale" calls may be nested, and that what is in effect within an inner
262       scope will revert to the outer scope's rules at the end of the inner
263       scope.
264
265       The string result of any operation that uses locale information is
266       tainted, as it is possible for a locale to be untrustworthy.  See
267       "SECURITY".
268
269       Starting in Perl v5.16 in a very limited way, and more generally in
270       v5.22, you can restrict which category or categories are enabled by
271       this particular instance of the pragma by adding parameters to it.  For
272       example,
273
274        use locale qw(:ctype :numeric);
275
276       enables locale awareness within its scope of only those operations
277       (listed above) that are affected by "LC_CTYPE" and "LC_NUMERIC".
278
279       The possible categories are: ":collate", ":ctype", ":messages",
280       ":monetary", ":numeric", ":time", and the pseudo category ":characters"
281       (described below).
282
283       Thus you can say
284
285        use locale ':messages';
286
287       and only $! and $^E will be locale aware.  Everything else is
288       unaffected.
289
290       Since Perl doesn't currently do anything with the "LC_MONETARY"
291       category, specifying ":monetary" does effectively nothing.  Some
292       systems have other categories, such as "LC_PAPER", but Perl also
293       doesn't do anything with them, and there is no way to specify them in
294       this pragma's arguments.
295
296       You can also easily say to use all categories but one, by either, for
297       example,
298
299        use locale ':!ctype';
300        use locale ':not_ctype';
301
302       both of which mean to enable locale awarness of all categories but
303       "LC_CTYPE".  Only one category argument may be specified in a
304       "use locale" if it is of the negated form.
305
306       Prior to v5.22 only one form of the pragma with arguments is available:
307
308        use locale ':not_characters';
309
310       (and you have to say "not_"; you can't use the bang "!" form).  This
311       pseudo category is a shorthand for specifying both ":collate" and
312       ":ctype".  Hence, in the negated form, it is nearly the same thing as
313       saying
314
315        use locale qw(:messages :monetary :numeric :time);
316
317       We use the term "nearly", because ":not_characters" also turns on
318       "use feature 'unicode_strings'" within its scope.  This form is less
319       useful in v5.20 and later, and is described fully in "Unicode and
320       UTF-8", but briefly, it tells Perl to not use the character portions of
321       the locale definition, that is the "LC_CTYPE" and "LC_COLLATE"
322       categories.  Instead it will use the native character set (extended by
323       Unicode).  When using this parameter, you are responsible for getting
324       the external character set translated into the native/Unicode one
325       (which it already will be if it is one of the increasingly popular
326       UTF-8 locales).  There are convenient ways of doing this, as described
327       in "Unicode and UTF-8".
328
329   The setlocale function
330       WARNING!  Prior to Perl 5.28 or on a system that does not support
331       thread-safe locale operations, do NOT use this function in a thread.
332       The locale will change in all other threads at the same time, and
333       should your thread get paused by the operating system, and another
334       started, that thread will not have the locale it is expecting.  On some
335       platforms, there can be a race leading to segfaults if two threads call
336       this function nearly simultaneously.  This warning does not apply on
337       unthreaded builds, or on perls where "${^SAFE_LOCALES}" exists and is
338       non-zero; namely Perl 5.28 and later unthreaded or compiled to be
339       locale-thread-safe.
340
341       You can switch locales as often as you wish at run time with the
342       "POSIX::setlocale()" function:
343
344               # Import locale-handling tool set from POSIX module.
345               # This example uses: setlocale -- the function call
346               #                    LC_CTYPE -- explained below
347               # (Showing the testing for success/failure of operations is
348               # omitted in these examples to avoid distracting from the main
349               # point)
350
351               use POSIX qw(locale_h);
352               use locale;
353               my $old_locale;
354
355               # query and save the old locale
356               $old_locale = setlocale(LC_CTYPE);
357
358               setlocale(LC_CTYPE, "fr_CA.ISO8859-1");
359               # LC_CTYPE now in locale "French, Canada, codeset ISO 8859-1"
360
361               setlocale(LC_CTYPE, "");
362               # LC_CTYPE now reset to the default defined by the
363               # LC_ALL/LC_CTYPE/LANG environment variables, or to the system
364               # default.  See below for documentation.
365
366               # restore the old locale
367               setlocale(LC_CTYPE, $old_locale);
368
369       The first argument of "setlocale()" gives the category, the second the
370       locale.  The category tells in what aspect of data processing you want
371       to apply locale-specific rules.  Category names are discussed in
372       "LOCALE CATEGORIES" and "ENVIRONMENT".  The locale is the name of a
373       collection of customization information corresponding to a particular
374       combination of language, country or territory, and codeset.  Read on
375       for hints on the naming of locales: not all systems name locales as in
376       the example.
377
378       If no second argument is provided and the category is something other
379       than "LC_ALL", the function returns a string naming the current locale
380       for the category.  You can use this value as the second argument in a
381       subsequent call to "setlocale()", but on some platforms the string is
382       opaque, not something that most people would be able to decipher as to
383       what locale it means.
384
385       If no second argument is provided and the category is "LC_ALL", the
386       result is implementation-dependent.  It may be a string of concatenated
387       locale names (separator also implementation-dependent) or a single
388       locale name.  Please consult your setlocale(3) man page for details.
389
390       If a second argument is given and it corresponds to a valid locale, the
391       locale for the category is set to that value, and the function returns
392       the now-current locale value.  You can then use this in yet another
393       call to "setlocale()".  (In some implementations, the return value may
394       sometimes differ from the value you gave as the second argument--think
395       of it as an alias for the value you gave.)
396
397       As the example shows, if the second argument is an empty string, the
398       category's locale is returned to the default specified by the
399       corresponding environment variables.  Generally, this results in a
400       return to the default that was in force when Perl started up: changes
401       to the environment made by the application after startup may or may not
402       be noticed, depending on your system's C library.
403
404       Note that when a form of "use locale" that doesn't include all
405       categories is specified, Perl ignores the excluded categories.
406
407       If "setlocale()" fails for some reason (for example, an attempt to set
408       to a locale unknown to the system), the locale for the category is not
409       changed, and the function returns "undef".
410
411       Starting in Perl 5.28, on multi-threaded perls compiled on systems that
412       implement POSIX 2008 thread-safe locale operations, this function
413       doesn't actually call the system "setlocale".  Instead those thread-
414       safe operations are used to emulate the "setlocale" function, but in a
415       thread-safe manner.
416
417       You can force the thread-safe locale operations to always be used (if
418       available) by recompiling perl with
419
420        -Accflags='-DUSE_THREAD_SAFE_LOCALE'
421
422       added to your call to Configure.
423
424       For further information about the categories, consult setlocale(3).
425
426   Multi-threaded operation
427       Beginning in Perl 5.28, multi-threaded locale operation is supported on
428       systems that implement either the POSIX 2008 or Windows-specific
429       thread-safe locale operations.  Many modern systems, such as various
430       Unix variants and Darwin do have this.
431
432       You can tell if using locales is safe on your system by looking at the
433       read-only boolean variable "${^SAFE_LOCALES}".  The value is 1 if the
434       perl is not threaded, or if it is using thread-safe locale operations.
435
436       Thread-safe operations are supported in Windows starting in Visual
437       Studio 2005, and in systems compatible with POSIX 2008.  Some platforms
438       claim to support POSIX 2008, but have buggy implementations, so that
439       the hints files for compiling to run on them turn off attempting to use
440       thread-safety.  "${^SAFE_LOCALES}" will be 0 on them.
441
442       Be aware that writing a multi-threaded application will not be portable
443       to a platform which lacks the native thread-safe locale support.  On
444       systems that do have it, you automatically get this behavior for
445       threaded perls, without having to do anything.  If for some reason, you
446       don't want to use this capability (perhaps the POSIX 2008 support is
447       buggy on your system), you can manually compile Perl to use the old
448       non-thread-safe implementation by passing the argument
449       "-Accflags='-DNO_THREAD_SAFE_LOCALE'" to Configure.  Except on Windows,
450       this will continue to use certain of the POSIX 2008 functions in some
451       situations.  If these are buggy, you can pass the following to
452       Configure instead or additionally:
453       "-Accflags='-DNO_POSIX_2008_LOCALE'".  This will also keep the code
454       from using thread-safe locales.  "${^SAFE_LOCALES}" will be 0 on
455       systems that turn off the thread-safe operations.
456
457       Normally on unthreaded builds, the traditional "setlocale()" is used
458       and not the thread-safe locale functions.  You can force the use of
459       these on systems that have them by adding the
460       "-Accflags='-DUSE_THREAD_SAFE_LOCALE'" to Configure.
461
462       The initial program is started up using the locale specified from the
463       environment, as currently, described in "ENVIRONMENT".   All newly
464       created threads start with "LC_ALL" set to "C">.  Each thread may use
465       "POSIX::setlocale()" to query or switch its locale at any time, without
466       affecting any other thread.  All locale-dependent operations
467       automatically use their thread's locale.
468
469       This should be completely transparent to any applications written
470       entirely in Perl (minus a few rarely encountered caveats given in the
471       "Multi-threaded" section).  Information for XS module writers is given
472       in "Locale-aware XS code" in perlxs.
473
474   Finding locales
475       For locales available in your system, consult also setlocale(3) to see
476       whether it leads to the list of available locales (search for the SEE
477       ALSO section).  If that fails, try the following command lines:
478
479               locale -a
480
481               nlsinfo
482
483               ls /usr/lib/nls/loc
484
485               ls /usr/lib/locale
486
487               ls /usr/lib/nls
488
489               ls /usr/share/locale
490
491       and see whether they list something resembling these
492
493               en_US.ISO8859-1     de_DE.ISO8859-1     ru_RU.ISO8859-5
494               en_US.iso88591      de_DE.iso88591      ru_RU.iso88595
495               en_US               de_DE               ru_RU
496               en                  de                  ru
497               english             german              russian
498               english.iso88591    german.iso88591     russian.iso88595
499               english.roman8                          russian.koi8r
500
501       Sadly, even though the calling interface for "setlocale()" has been
502       standardized, names of locales and the directories where the
503       configuration resides have not been.  The basic form of the name is
504       language_territory.codeset, but the latter parts after language are not
505       always present.  The language and country are usually from the
506       standards ISO 3166 and ISO 639, the two-letter abbreviations for the
507       countries and the languages of the world, respectively.  The codeset
508       part often mentions some ISO 8859 character set, the Latin codesets.
509       For example, "ISO 8859-1" is the so-called "Western European codeset"
510       that can be used to encode most Western European languages adequately.
511       Again, there are several ways to write even the name of that one
512       standard.  Lamentably.
513
514       Two special locales are worth particular mention: "C" and "POSIX".
515       Currently these are effectively the same locale: the difference is
516       mainly that the first one is defined by the C standard, the second by
517       the POSIX standard.  They define the default locale in which every
518       program starts in the absence of locale information in its environment.
519       (The default default locale, if you will.)  Its language is (American)
520       English and its character codeset ASCII or, rarely, a superset thereof
521       (such as the "DEC Multinational Character Set (DEC-MCS)").  Warning.
522       The C locale delivered by some vendors may not actually exactly match
523       what the C standard calls for.  So beware.
524
525       NOTE: Not all systems have the "POSIX" locale (not all systems are
526       POSIX-conformant), so use "C" when you need explicitly to specify this
527       default locale.
528
529   LOCALE PROBLEMS
530       You may encounter the following warning message at Perl startup:
531
532               perl: warning: Setting locale failed.
533               perl: warning: Please check that your locale settings:
534                       LC_ALL = "En_US",
535                       LANG = (unset)
536                   are supported and installed on your system.
537               perl: warning: Falling back to the standard locale ("C").
538
539       This means that your locale settings had "LC_ALL" set to "En_US" and
540       LANG exists but has no value.  Perl tried to believe you but could not.
541       Instead, Perl gave up and fell back to the "C" locale, the default
542       locale that is supposed to work no matter what.  (On Windows, it first
543       tries falling back to the system default locale.)  This usually means
544       your locale settings were wrong, they mention locales your system has
545       never heard of, or the locale installation in your system has problems
546       (for example, some system files are broken or missing).  There are
547       quick and temporary fixes to these problems, as well as more thorough
548       and lasting fixes.
549
550   Testing for broken locales
551       If you are building Perl from source, the Perl test suite file
552       lib/locale.t can be used to test the locales on your system.  Setting
553       the environment variable "PERL_DEBUG_FULL_TEST" to 1 will cause it to
554       output detailed results.  For example, on Linux, you could say
555
556        PERL_DEBUG_FULL_TEST=1 ./perl -T -Ilib lib/locale.t > locale.log 2>&1
557
558       Besides many other tests, it will test every locale it finds on your
559       system to see if they conform to the POSIX standard.  If any have
560       errors, it will include a summary near the end of the output of which
561       locales passed all its tests, and which failed, and why.
562
563   Temporarily fixing locale problems
564       The two quickest fixes are either to render Perl silent about any
565       locale inconsistencies or to run Perl under the default locale "C".
566
567       Perl's moaning about locale problems can be silenced by setting the
568       environment variable "PERL_BADLANG" to "0" or "".  This method really
569       just sweeps the problem under the carpet: you tell Perl to shut up even
570       when Perl sees that something is wrong.  Do not be surprised if later
571       something locale-dependent misbehaves.
572
573       Perl can be run under the "C" locale by setting the environment
574       variable "LC_ALL" to "C".  This method is perhaps a bit more civilized
575       than the "PERL_BADLANG" approach, but setting "LC_ALL" (or other locale
576       variables) may affect other programs as well, not just Perl.  In
577       particular, external programs run from within Perl will see these
578       changes.  If you make the new settings permanent (read on), all
579       programs you run see the changes.  See "ENVIRONMENT" for the full list
580       of relevant environment variables and "USING LOCALES" for their effects
581       in Perl.  Effects in other programs are easily deducible.  For example,
582       the variable "LC_COLLATE" may well affect your sort program (or
583       whatever the program that arranges "records" alphabetically in your
584       system is called).
585
586       You can test out changing these variables temporarily, and if the new
587       settings seem to help, put those settings into your shell startup
588       files.  Consult your local documentation for the exact details.  For
589       Bourne-like shells (sh, ksh, bash, zsh):
590
591               LC_ALL=en_US.ISO8859-1
592               export LC_ALL
593
594       This assumes that we saw the locale "en_US.ISO8859-1" using the
595       commands discussed above.  We decided to try that instead of the above
596       faulty locale "En_US"--and in Cshish shells (csh, tcsh)
597
598               setenv LC_ALL en_US.ISO8859-1
599
600       or if you have the "env" application you can do (in any shell)
601
602               env LC_ALL=en_US.ISO8859-1 perl ...
603
604       If you do not know what shell you have, consult your local helpdesk or
605       the equivalent.
606
607   Permanently fixing locale problems
608       The slower but superior fixes are when you may be able to yourself fix
609       the misconfiguration of your own environment variables.  The
610       mis(sing)configuration of the whole system's locales usually requires
611       the help of your friendly system administrator.
612
613       First, see earlier in this document about "Finding locales".  That
614       tells how to find which locales are really supported--and more
615       importantly, installed--on your system.  In our example error message,
616       environment variables affecting the locale are listed in the order of
617       decreasing importance (and unset variables do not matter).  Therefore,
618       having LC_ALL set to "En_US" must have been the bad choice, as shown by
619       the error message.  First try fixing locale settings listed first.
620
621       Second, if using the listed commands you see something exactly (prefix
622       matches do not count and case usually counts) like "En_US" without the
623       quotes, then you should be okay because you are using a locale name
624       that should be installed and available in your system.  In this case,
625       see "Permanently fixing your system's locale configuration".
626
627   Permanently fixing your system's locale configuration
628       This is when you see something like:
629
630               perl: warning: Please check that your locale settings:
631                       LC_ALL = "En_US",
632                       LANG = (unset)
633                   are supported and installed on your system.
634
635       but then cannot see that "En_US" listed by the above-mentioned
636       commands.  You may see things like "en_US.ISO8859-1", but that isn't
637       the same.  In this case, try running under a locale that you can list
638       and which somehow matches what you tried.  The rules for matching
639       locale names are a bit vague because standardization is weak in this
640       area.  See again the "Finding locales" about general rules.
641
642   Fixing system locale configuration
643       Contact a system administrator (preferably your own) and report the
644       exact error message you get, and ask them to read this same
645       documentation you are now reading.  They should be able to check
646       whether there is something wrong with the locale configuration of the
647       system.  The "Finding locales" section is unfortunately a bit vague
648       about the exact commands and places because these things are not that
649       standardized.
650
651   The localeconv function
652       The "POSIX::localeconv()" function allows you to get particulars of the
653       locale-dependent numeric formatting information specified by the
654       current underlying "LC_NUMERIC" and "LC_MONETARY" locales (regardless
655       of whether called from within the scope of "use locale" or not).  (If
656       you just want the name of the current locale for a particular category,
657       use "POSIX::setlocale()" with a single parameter--see "The setlocale
658       function".)
659
660               use POSIX qw(locale_h);
661
662               # Get a reference to a hash of locale-dependent info
663               $locale_values = localeconv();
664
665               # Output sorted list of the values
666               for (sort keys %$locale_values) {
667                   printf "%-20s = %s\n", $_, $locale_values->{$_}
668               }
669
670       "localeconv()" takes no arguments, and returns a reference to a hash.
671       The keys of this hash are variable names for formatting, such as
672       "decimal_point" and "thousands_sep".  The values are the corresponding,
673       er, values.  See "localeconv" in POSIX for a longer example listing the
674       categories an implementation might be expected to provide; some provide
675       more and others fewer.  You don't need an explicit "use locale",
676       because "localeconv()" always observes the current locale.
677
678       Here's a simple-minded example program that rewrites its command-line
679       parameters as integers correctly formatted in the current locale:
680
681           use POSIX qw(locale_h);
682
683           # Get some of locale's numeric formatting parameters
684           my ($thousands_sep, $grouping) =
685                   @{localeconv()}{'thousands_sep', 'grouping'};
686
687           # Apply defaults if values are missing
688           $thousands_sep = ',' unless $thousands_sep;
689
690           # grouping and mon_grouping are packed lists
691           # of small integers (characters) telling the
692           # grouping (thousand_seps and mon_thousand_seps
693           # being the group dividers) of numbers and
694           # monetary quantities.  The integers' meanings:
695           # 255 means no more grouping, 0 means repeat
696           # the previous grouping, 1-254 means use that
697           # as the current grouping.  Grouping goes from
698           # right to left (low to high digits).  In the
699           # below we cheat slightly by never using anything
700           # else than the first grouping (whatever that is).
701           if ($grouping) {
702               @grouping = unpack("C*", $grouping);
703           } else {
704               @grouping = (3);
705           }
706
707           # Format command line params for current locale
708           for (@ARGV) {
709               $_ = int;    # Chop non-integer part
710               1 while
711               s/(\d)(\d{$grouping[0]}($|$thousands_sep))/$1$thousands_sep$2/;
712               print "$_";
713           }
714           print "\n";
715
716       Note that if the platform doesn't have "LC_NUMERIC" and/or
717       "LC_MONETARY" available or enabled, the corresponding elements of the
718       hash will be missing.
719
720   I18N::Langinfo
721       Another interface for querying locale-dependent information is the
722       "I18N::Langinfo::langinfo()" function.
723
724       The following example will import the "langinfo()" function itself and
725       three constants to be used as arguments to "langinfo()": a constant for
726       the abbreviated first day of the week (the numbering starts from Sunday
727       = 1) and two more constants for the affirmative and negative answers
728       for a yes/no question in the current locale.
729
730           use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
731
732           my ($abday_1, $yesstr, $nostr)
733                       = map { langinfo } qw(ABDAY_1 YESSTR NOSTR);
734
735           print "$abday_1? [$yesstr/$nostr] ";
736
737       In other words, in the "C" (or English) locale the above will probably
738       print something like:
739
740           Sun? [yes/no]
741
742       See I18N::Langinfo for more information.
743

LOCALE CATEGORIES

745       The following subsections describe basic locale categories.  Beyond
746       these, some combination categories allow manipulation of more than one
747       basic category at a time.  See "ENVIRONMENT" for a discussion of these.
748
749   Category "LC_COLLATE": Collation: Text Comparisons and Sorting
750       In the scope of a "use locale" form that includes collation, Perl looks
751       to the "LC_COLLATE" environment variable to determine the application's
752       notions on collation (ordering) of characters.  For example, "b"
753       follows "a" in Latin alphabets, but where do "a" and "aa" belong?  And
754       while "color" follows "chocolate" in English, what about in traditional
755       Spanish?
756
757       The following collations all make sense and you may meet any of them if
758       you "use locale".
759
760               A B C D E a b c d e
761               A a B b C c D d E e
762               a A b B c C d D e E
763               a b c d e A B C D E
764
765       Here is a code snippet to tell what "word" characters are in the
766       current locale, in that locale's order:
767
768               use locale;
769               print +(sort grep /\w/, map { chr } 0..255), "\n";
770
771       Compare this with the characters that you see and their order if you
772       state explicitly that the locale should be ignored:
773
774               no locale;
775               print +(sort grep /\w/, map { chr } 0..255), "\n";
776
777       This machine-native collation (which is what you get unless
778       "use locale" has appeared earlier in the same block) must be used for
779       sorting raw binary data, whereas the locale-dependent collation of the
780       first example is useful for natural text.
781
782       As noted in "USING LOCALES", "cmp" compares according to the current
783       collation locale when "use locale" is in effect, but falls back to a
784       char-by-char comparison for strings that the locale says are equal. You
785       can use "POSIX::strcoll()" if you don't want this fall-back:
786
787               use POSIX qw(strcoll);
788               $equal_in_locale =
789                   !strcoll("space and case ignored", "SpaceAndCaseIgnored");
790
791       $equal_in_locale will be true if the collation locale specifies a
792       dictionary-like ordering that ignores space characters completely and
793       which folds case.
794
795       Perl uses the platform's C library collation functions "strcoll()" and
796       "strxfrm()".  That means you get whatever they give.  On some
797       platforms, these functions work well on UTF-8 locales, giving a
798       reasonable default collation for the code points that are important in
799       that locale.  (And if they aren't working well, the problem may only be
800       that the locale definition is deficient, so can be fixed by using a
801       better definition file.  Unicode's definitions (see "Freely available
802       locale definitions") provide reasonable UTF-8 locale collation
803       definitions.)  Starting in Perl v5.26, Perl's use of these functions
804       has been made more seamless.  This may be sufficient for your needs.
805       For more control, and to make sure strings containing any code point
806       (not just the ones important in the locale) collate properly, the
807       Unicode::Collate module is suggested.
808
809       In non-UTF-8 locales (hence single byte), code points above 0xFF are
810       technically invalid.  But if present, again starting in v5.26, they
811       will collate to the same position as the highest valid code point does.
812       This generally gives good results, but the collation order may be
813       skewed if the valid code point gets special treatment when it forms
814       particular sequences with other characters as defined by the locale.
815       When two strings collate identically, the code point order is used as a
816       tie breaker.
817
818       If Perl detects that there are problems with the locale collation
819       order, it reverts to using non-locale collation rules for that locale.
820
821       If you have a single string that you want to check for "equality in
822       locale" against several others, you might think you could gain a little
823       efficiency by using "POSIX::strxfrm()" in conjunction with "eq":
824
825               use POSIX qw(strxfrm);
826               $xfrm_string = strxfrm("Mixed-case string");
827               print "locale collation ignores spaces\n"
828                   if $xfrm_string eq strxfrm("Mixed-casestring");
829               print "locale collation ignores hyphens\n"
830                   if $xfrm_string eq strxfrm("Mixedcase string");
831               print "locale collation ignores case\n"
832                   if $xfrm_string eq strxfrm("mixed-case string");
833
834       "strxfrm()" takes a string and maps it into a transformed string for
835       use in char-by-char comparisons against other transformed strings
836       during collation.  "Under the hood", locale-affected Perl comparison
837       operators call "strxfrm()" for both operands, then do a char-by-char
838       comparison of the transformed strings.  By calling "strxfrm()"
839       explicitly and using a non locale-affected comparison, the example
840       attempts to save a couple of transformations.  But in fact, it doesn't
841       save anything: Perl magic (see "Magic Variables" in perlguts) creates
842       the transformed version of a string the first time it's needed in a
843       comparison, then keeps this version around in case it's needed again.
844       An example rewritten the easy way with "cmp" runs just about as fast.
845       It also copes with null characters embedded in strings; if you call
846       "strxfrm()" directly, it treats the first null it finds as a
847       terminator.  Don't expect the transformed strings it produces to be
848       portable across systems--or even from one revision of your operating
849       system to the next.  In short, don't call "strxfrm()" directly: let
850       Perl do it for you.
851
852       Note: "use locale" isn't shown in some of these examples because it
853       isn't needed: "strcoll()" and "strxfrm()" are POSIX functions which use
854       the standard system-supplied "libc" functions that always obey the
855       current "LC_COLLATE" locale.
856
857   Category "LC_CTYPE": Character Types
858       In the scope of a "use locale" form that includes "LC_CTYPE", Perl
859       obeys the "LC_CTYPE" locale setting.  This controls the application's
860       notion of which characters are alphabetic, numeric, punctuation, etc.
861       This affects Perl's "\w" regular expression metanotation, which stands
862       for alphanumeric characters--that is, alphabetic, numeric, and the
863       platform's native underscore.  (Consult perlre for more information
864       about regular expressions.)  Thanks to "LC_CTYPE", depending on your
865       locale setting, characters like "ae", "d`", "ss", and "o" may be
866       understood as "\w" characters.  It also affects things like "\s", "\D",
867       and the POSIX character classes, like "[[:graph:]]".  (See
868       perlrecharclass for more information on all these.)
869
870       The "LC_CTYPE" locale also provides the map used in transliterating
871       characters between lower and uppercase.  This affects the case-mapping
872       functions--"fc()", "lc()", "lcfirst()", "uc()", and "ucfirst()"; case-
873       mapping interpolation with "\F", "\l", "\L", "\u", or "\U" in double-
874       quoted strings and "s///" substitutions; and case-insensitive regular
875       expression pattern matching using the "i" modifier.
876
877       Starting in v5.20, Perl supports UTF-8 locales for "LC_CTYPE", but
878       otherwise Perl only supports single-byte locales, such as the ISO 8859
879       series.  This means that wide character locales, for example for Asian
880       languages, are not well-supported.  Use of these locales may cause core
881       dumps.  If the platform has the capability for Perl to detect such a
882       locale, starting in Perl v5.22, Perl will warn, default enabled, using
883       the "locale" warning category, whenever such a locale is switched into.
884       The UTF-8 locale support is actually a superset of POSIX locales,
885       because it is really full Unicode behavior as if no "LC_CTYPE" locale
886       were in effect at all (except for tainting; see "SECURITY").  POSIX
887       locales, even UTF-8 ones, are lacking certain concepts in Unicode, such
888       as the idea that changing the case of a character could expand to be
889       more than one character.  Perl in a UTF-8 locale, will give you that
890       expansion.  Prior to v5.20, Perl treated a UTF-8 locale on some
891       platforms like an ISO 8859-1 one, with some restrictions, and on other
892       platforms more like the "C" locale.  For releases v5.16 and v5.18,
893       "use locale 'not_characters" could be used as a workaround for this
894       (see "Unicode and UTF-8").
895
896       Note that there are quite a few things that are unaffected by the
897       current locale.  Any literal character is the native character for the
898       given platform.  Hence 'A' means the character at code point 65 on
899       ASCII platforms, and 193 on EBCDIC.  That may or may not be an 'A' in
900       the current locale, if that locale even has an 'A'.  Similarly, all the
901       escape sequences for particular characters, "\n" for example, always
902       mean the platform's native one.  This means, for example, that "\N" in
903       regular expressions (every character but new-line) works on the
904       platform character set.
905
906       Starting in v5.22, Perl will by default warn when switching into a
907       locale that redefines any ASCII printable character (plus "\t" and
908       "\n") into a different class than expected.  This is likely to happen
909       on modern locales only on EBCDIC platforms, where, for example, a CCSID
910       0037 locale on a CCSID 1047 machine moves "[", but it can happen on
911       ASCII platforms with the ISO 646 and other 7-bit locales that are
912       essentially obsolete.  Things may still work, depending on what
913       features of Perl are used by the program.  For example, in the example
914       from above where "|" becomes a "\w", and there are no regular
915       expressions where this matters, the program may still work properly.
916       The warning lists all the characters that it can determine could be
917       adversely affected.
918
919       Note: A broken or malicious "LC_CTYPE" locale definition may result in
920       clearly ineligible characters being considered to be alphanumeric by
921       your application.  For strict matching of (mundane) ASCII letters and
922       digits--for example, in command strings--locale-aware applications
923       should use "\w" with the "/a" regular expression modifier.  See
924       "SECURITY".
925
926   Category "LC_NUMERIC": Numeric Formatting
927       After a proper "POSIX::setlocale()" call, and within the scope of a
928       "use locale" form that includes numerics, Perl obeys the "LC_NUMERIC"
929       locale information, which controls an application's idea of how numbers
930       should be formatted for human readability.  In most implementations the
931       only effect is to change the character used for the decimal
932       point--perhaps from "."  to ",".  The functions aren't aware of such
933       niceties as thousands separation and so on. (See "The localeconv
934       function" if you care about these things.)
935
936        use POSIX qw(strtod setlocale LC_NUMERIC);
937        use locale;
938
939        setlocale LC_NUMERIC, "";
940
941        $n = 5/2;   # Assign numeric 2.5 to $n
942
943        $a = " $n"; # Locale-dependent conversion to string
944
945        print "half five is $n\n";       # Locale-dependent output
946
947        printf "half five is %g\n", $n;  # Locale-dependent output
948
949        print "DECIMAL POINT IS COMMA\n"
950                 if $n == (strtod("2,5"))[0]; # Locale-dependent conversion
951
952       See also I18N::Langinfo and "RADIXCHAR".
953
954   Category "LC_MONETARY": Formatting of monetary amounts
955       The C standard defines the "LC_MONETARY" category, but not a function
956       that is affected by its contents.  (Those with experience of standards
957       committees will recognize that the working group decided to punt on the
958       issue.)  Consequently, Perl essentially takes no notice of it.  If you
959       really want to use "LC_MONETARY", you can query its contents--see "The
960       localeconv function"--and use the information that it returns in your
961       application's own formatting of currency amounts.  However, you may
962       well find that the information, voluminous and complex though it may
963       be, still does not quite meet your requirements: currency formatting is
964       a hard nut to crack.
965
966       See also I18N::Langinfo and "CRNCYSTR".
967
968   Category "LC_TIME": Respresentation of time
969       Output produced by "POSIX::strftime()", which builds a formatted human-
970       readable date/time string, is affected by the current "LC_TIME" locale.
971       Thus, in a French locale, the output produced by the %B format element
972       (full month name) for the first month of the year would be "janvier".
973       Here's how to get a list of long month names in the current locale:
974
975               use POSIX qw(strftime);
976               for (0..11) {
977                   $long_month_name[$_] =
978                       strftime("%B", 0, 0, 0, 1, $_, 96);
979               }
980
981       Note: "use locale" isn't needed in this example: "strftime()" is a
982       POSIX function which uses the standard system-supplied "libc" function
983       that always obeys the current "LC_TIME" locale.
984
985       See also I18N::Langinfo and "ABDAY_1".."ABDAY_7", "DAY_1".."DAY_7",
986       "ABMON_1".."ABMON_12", and "ABMON_1".."ABMON_12".
987
988   Other categories
989       The remaining locale categories are not currently used by Perl itself.
990       But again note that things Perl interacts with may use these, including
991       extensions outside the standard Perl distribution, and by the operating
992       system and its utilities.  Note especially that the string value of $!
993       and the error messages given by external utilities may be changed by
994       "LC_MESSAGES".  If you want to have portable error codes, use "%!".
995       See Errno.
996

SECURITY

998       Although the main discussion of Perl security issues can be found in
999       perlsec, a discussion of Perl's locale handling would be incomplete if
1000       it did not draw your attention to locale-dependent security issues.
1001       Locales--particularly on systems that allow unprivileged users to build
1002       their own locales--are untrustworthy.  A malicious (or just plain
1003       broken) locale can make a locale-aware application give unexpected
1004       results.  Here are a few possibilities:
1005
1006       •   Regular expression checks for safe file names or mail addresses
1007           using "\w" may be spoofed by an "LC_CTYPE" locale that claims that
1008           characters such as ">" and "|" are alphanumeric.
1009
1010       •   String interpolation with case-mapping, as in, say, "$dest =
1011           "C:\U$name.$ext"", may produce dangerous results if a bogus
1012           "LC_CTYPE" case-mapping table is in effect.
1013
1014       •   A sneaky "LC_COLLATE" locale could result in the names of students
1015           with "D" grades appearing ahead of those with "A"s.
1016
1017       •   An application that takes the trouble to use information in
1018           "LC_MONETARY" may format debits as if they were credits and vice
1019           versa if that locale has been subverted.  Or it might make payments
1020           in US dollars instead of Hong Kong dollars.
1021
1022       •   The date and day names in dates formatted by "strftime()" could be
1023           manipulated to advantage by a malicious user able to subvert the
1024           "LC_DATE" locale.  ("Look--it says I wasn't in the building on
1025           Sunday.")
1026
1027       Such dangers are not peculiar to the locale system: any aspect of an
1028       application's environment which may be modified maliciously presents
1029       similar challenges.  Similarly, they are not specific to Perl: any
1030       programming language that allows you to write programs that take
1031       account of their environment exposes you to these issues.
1032
1033       Perl cannot protect you from all possibilities shown in the
1034       examples--there is no substitute for your own vigilance--but, when "use
1035       locale" is in effect, Perl uses the tainting mechanism (see perlsec) to
1036       mark string results that become locale-dependent, and which may be
1037       untrustworthy in consequence.  Here is a summary of the tainting
1038       behavior of operators and functions that may be affected by the locale:
1039
1040Comparison operators ("lt", "le", "ge", "gt" and "cmp"):
1041
1042           Scalar true/false (or less/equal/greater) result is never tainted.
1043
1044Case-mapping interpolation (with "\l", "\L", "\u", "\U", or "\F")
1045
1046           The result string containing interpolated material is tainted if a
1047           "use locale" form that includes "LC_CTYPE" is in effect.
1048
1049Matching operator ("m//"):
1050
1051           Scalar true/false result never tainted.
1052
1053           All subpatterns, either delivered as a list-context result or as $1
1054           etc., are tainted if a "use locale" form that includes "LC_CTYPE"
1055           is in effect, and the subpattern regular expression contains a
1056           locale-dependent construct.  These constructs include "\w" (to
1057           match an alphanumeric character), "\W" (non-alphanumeric
1058           character), "\b" and "\B" (word-boundary and non-boundardy, which
1059           depend on what "\w" and "\W" match), "\s" (whitespace character),
1060           "\S" (non whitespace character), "\d" and "\D" (digits and non-
1061           digits), and the POSIX character classes, such as "[:alpha:]" (see
1062           "POSIX Character Classes" in perlrecharclass).
1063
1064           Tainting is also likely if the pattern is to be matched case-
1065           insensitively (via "/i").  The exception is if all the code points
1066           to be matched this way are above 255 and do not have folds under
1067           Unicode rules to below 256.  Tainting is not done for these because
1068           Perl only uses Unicode rules for such code points, and those rules
1069           are the same no matter what the current locale.
1070
1071           The matched-pattern variables, $&, "$`" (pre-match), "$'" (post-
1072           match), and $+ (last match) also are tainted.
1073
1074Substitution operator ("s///"):
1075
1076           Has the same behavior as the match operator.  Also, the left
1077           operand of "=~" becomes tainted when a "use locale" form that
1078           includes "LC_CTYPE" is in effect, if modified as a result of a
1079           substitution based on a regular expression match involving any of
1080           the things mentioned in the previous item, or of case-mapping, such
1081           as "\l", "\L","\u", "\U", or "\F".
1082
1083Output formatting functions ("printf()" and "write()"):
1084
1085           Results are never tainted because otherwise even output from print,
1086           for example "print(1/7)", should be tainted if "use locale" is in
1087           effect.
1088
1089Case-mapping functions ("lc()", "lcfirst()", "uc()", "ucfirst()"):
1090
1091           Results are tainted if a "use locale" form that includes "LC_CTYPE"
1092           is in effect.
1093
1094POSIX locale-dependent functions ("localeconv()", "strcoll()",
1095           "strftime()", "strxfrm()"):
1096
1097           Results are never tainted.
1098
1099       Three examples illustrate locale-dependent tainting.  The first
1100       program, which ignores its locale, won't run: a value taken directly
1101       from the command line may not be used to name an output file when taint
1102       checks are enabled.
1103
1104               #/usr/local/bin/perl -T
1105               # Run with taint checking
1106
1107               # Command line sanity check omitted...
1108               $tainted_output_file = shift;
1109
1110               open(F, ">$tainted_output_file")
1111                   or warn "Open of $tainted_output_file failed: $!\n";
1112
1113       The program can be made to run by "laundering" the tainted value
1114       through a regular expression: the second example--which still ignores
1115       locale information--runs, creating the file named on its command line
1116       if it can.
1117
1118               #/usr/local/bin/perl -T
1119
1120               $tainted_output_file = shift;
1121               $tainted_output_file =~ m%[\w/]+%;
1122               $untainted_output_file = $&;
1123
1124               open(F, ">$untainted_output_file")
1125                   or warn "Open of $untainted_output_file failed: $!\n";
1126
1127       Compare this with a similar but locale-aware program:
1128
1129               #/usr/local/bin/perl -T
1130
1131               $tainted_output_file = shift;
1132               use locale;
1133               $tainted_output_file =~ m%[\w/]+%;
1134               $localized_output_file = $&;
1135
1136               open(F, ">$localized_output_file")
1137                   or warn "Open of $localized_output_file failed: $!\n";
1138
1139       This third program fails to run because $& is tainted: it is the result
1140       of a match involving "\w" while "use locale" is in effect.
1141

ENVIRONMENT

1143       PERL_SKIP_LOCALE_INIT
1144                   This environment variable, available starting in Perl
1145                   v5.20, if set (to any value), tells Perl to not use the
1146                   rest of the environment variables to initialize with.
1147                   Instead, Perl uses whatever the current locale settings
1148                   are.  This is particularly useful in embedded environments,
1149                   see "Using embedded Perl with POSIX locales" in perlembed.
1150
1151       PERL_BADLANG
1152                   A string that can suppress Perl's warning about failed
1153                   locale settings at startup.  Failure can occur if the
1154                   locale support in the operating system is lacking (broken)
1155                   in some way--or if you mistyped the name of a locale when
1156                   you set up your environment.  If this environment variable
1157                   is absent, or has a value other than "0" or "", Perl will
1158                   complain about locale setting failures.
1159
1160                   NOTE: "PERL_BADLANG" only gives you a way to hide the
1161                   warning message.  The message tells about some problem in
1162                   your system's locale support, and you should investigate
1163                   what the problem is.
1164
1165       The following environment variables are not specific to Perl: They are
1166       part of the standardized (ISO C, XPG4, POSIX 1.c) "setlocale()" method
1167       for controlling an application's opinion on data.  Windows is non-
1168       POSIX, but Perl arranges for the following to work as described anyway.
1169       If the locale given by an environment variable is not valid, Perl tries
1170       the next lower one in priority.  If none are valid, on Windows, the
1171       system default locale is then tried.  If all else fails, the "C" locale
1172       is used.  If even that doesn't work, something is badly broken, but
1173       Perl tries to forge ahead with whatever the locale settings might be.
1174
1175       "LC_ALL"    "LC_ALL" is the "override-all" locale environment variable.
1176                   If set, it overrides all the rest of the locale environment
1177                   variables.
1178
1179       "LANGUAGE"  NOTE: "LANGUAGE" is a GNU extension, it affects you only if
1180                   you are using the GNU libc.  This is the case if you are
1181                   using e.g. Linux.  If you are using "commercial" Unixes you
1182                   are most probably not using GNU libc and you can ignore
1183                   "LANGUAGE".
1184
1185                   However, in the case you are using "LANGUAGE": it affects
1186                   the language of informational, warning, and error messages
1187                   output by commands (in other words, it's like
1188                   "LC_MESSAGES") but it has higher priority than "LC_ALL".
1189                   Moreover, it's not a single value but instead a "path"
1190                   (":"-separated list) of languages (not locales).  See the
1191                   GNU "gettext" library documentation for more information.
1192
1193       "LC_CTYPE"  In the absence of "LC_ALL", "LC_CTYPE" chooses the
1194                   character type locale.  In the absence of both "LC_ALL" and
1195                   "LC_CTYPE", "LANG" chooses the character type locale.
1196
1197       "LC_COLLATE"
1198                   In the absence of "LC_ALL", "LC_COLLATE" chooses the
1199                   collation (sorting) locale.  In the absence of both
1200                   "LC_ALL" and "LC_COLLATE", "LANG" chooses the collation
1201                   locale.
1202
1203       "LC_MONETARY"
1204                   In the absence of "LC_ALL", "LC_MONETARY" chooses the
1205                   monetary formatting locale.  In the absence of both
1206                   "LC_ALL" and "LC_MONETARY", "LANG" chooses the monetary
1207                   formatting locale.
1208
1209       "LC_NUMERIC"
1210                   In the absence of "LC_ALL", "LC_NUMERIC" chooses the
1211                   numeric format locale.  In the absence of both "LC_ALL" and
1212                   "LC_NUMERIC", "LANG" chooses the numeric format.
1213
1214       "LC_TIME"   In the absence of "LC_ALL", "LC_TIME" chooses the date and
1215                   time formatting locale.  In the absence of both "LC_ALL"
1216                   and "LC_TIME", "LANG" chooses the date and time formatting
1217                   locale.
1218
1219       "LANG"      "LANG" is the "catch-all" locale environment variable. If
1220                   it is set, it is used as the last resort after the overall
1221                   "LC_ALL" and the category-specific "LC_foo".
1222
1223   Examples
1224       The "LC_NUMERIC" controls the numeric output:
1225
1226          use locale;
1227          use POSIX qw(locale_h); # Imports setlocale() and the LC_ constants.
1228          setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
1229          printf "%g\n", 1.23; # If the "fr_FR" succeeded, probably shows 1,23.
1230
1231       and also how strings are parsed by "POSIX::strtod()" as numbers:
1232
1233          use locale;
1234          use POSIX qw(locale_h strtod);
1235          setlocale(LC_NUMERIC, "de_DE") or die "Entschuldigung";
1236          my $x = strtod("2,34") + 5;
1237          print $x, "\n"; # Probably shows 7,34.
1238

NOTES

1240   String "eval" and "LC_NUMERIC"
1241       A string eval parses its expression as standard Perl.  It is therefore
1242       expecting the decimal point to be a dot.  If "LC_NUMERIC" is set to
1243       have this be a comma instead, the parsing will be confused, perhaps
1244       silently.
1245
1246        use locale;
1247        use POSIX qw(locale_h);
1248        setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
1249        my $a = 1.2;
1250        print eval "$a + 1.5";
1251        print "\n";
1252
1253       prints "13,5".  This is because in that locale, the comma is the
1254       decimal point character.  The "eval" thus expands to:
1255
1256        eval "1,2 + 1.5"
1257
1258       and the result is not what you likely expected.  No warnings are
1259       generated.  If you do string "eval"'s within the scope of "use locale",
1260       you should instead change the "eval" line to do something like:
1261
1262        print eval "no locale; $a + 1.5";
1263
1264       This prints 2.7.
1265
1266       You could also exclude "LC_NUMERIC", if you don't need it, by
1267
1268        use locale ':!numeric';
1269
1270   Backward compatibility
1271       Versions of Perl prior to 5.004 mostly ignored locale information,
1272       generally behaving as if something similar to the "C" locale were
1273       always in force, even if the program environment suggested otherwise
1274       (see "The setlocale function").  By default, Perl still behaves this
1275       way for backward compatibility.  If you want a Perl application to pay
1276       attention to locale information, you must use the "use locale" pragma
1277       (see "The "use locale" pragma") or, in the unlikely event that you want
1278       to do so for just pattern matching, the "/l" regular expression
1279       modifier (see "Character set modifiers" in perlre) to instruct it to do
1280       so.
1281
1282       Versions of Perl from 5.002 to 5.003 did use the "LC_CTYPE" information
1283       if available; that is, "\w" did understand what were the letters
1284       according to the locale environment variables.  The problem was that
1285       the user had no control over the feature: if the C library supported
1286       locales, Perl used them.
1287
1288   I18N:Collate obsolete
1289       In versions of Perl prior to 5.004, per-locale collation was possible
1290       using the "I18N::Collate" library module.  This module is now mildly
1291       obsolete and should be avoided in new applications.  The "LC_COLLATE"
1292       functionality is now integrated into the Perl core language: One can
1293       use locale-specific scalar data completely normally with "use locale",
1294       so there is no longer any need to juggle with the scalar references of
1295       "I18N::Collate".
1296
1297   Sort speed and memory use impacts
1298       Comparing and sorting by locale is usually slower than the default
1299       sorting; slow-downs of two to four times have been observed.  It will
1300       also consume more memory: once a Perl scalar variable has participated
1301       in any string comparison or sorting operation obeying the locale
1302       collation rules, it will take 3-15 times more memory than before.  (The
1303       exact multiplier depends on the string's contents, the operating system
1304       and the locale.) These downsides are dictated more by the operating
1305       system's implementation of the locale system than by Perl.
1306
1307   Freely available locale definitions
1308       The Unicode CLDR project extracts the POSIX portion of many of its
1309       locales, available at
1310
1311         https://unicode.org/Public/cldr/2.0.1/
1312
1313       (Newer versions of CLDR require you to compute the POSIX data yourself.
1314       See <http://unicode.org/Public/cldr/latest/>.)
1315
1316       There is a large collection of locale definitions at:
1317
1318         http://std.dkuug.dk/i18n/WG15-collection/locales/
1319
1320       You should be aware that it is unsupported, and is not claimed to be
1321       fit for any purpose.  If your system allows installation of arbitrary
1322       locales, you may find the definitions useful as they are, or as a basis
1323       for the development of your own locales.
1324
1325   I18n and l10n
1326       "Internationalization" is often abbreviated as i18n because its first
1327       and last letters are separated by eighteen others.  (You may guess why
1328       the internalin ... internaliti ... i18n tends to get abbreviated.)  In
1329       the same way, "localization" is often abbreviated to l10n.
1330
1331   An imperfect standard
1332       Internationalization, as defined in the C and POSIX standards, can be
1333       criticized as incomplete and ungainly.  They also have a tendency, like
1334       standards groups, to divide the world into nations, when we all know
1335       that the world can equally well be divided into bankers, bikers,
1336       gamers, and so on.
1337

Unicode and UTF-8

1339       The support of Unicode is new starting from Perl version v5.6, and more
1340       fully implemented in versions v5.8 and later.  See perluniintro.
1341
1342       Starting in Perl v5.20, UTF-8 locales are supported in Perl, except
1343       "LC_COLLATE" is only partially supported; collation support is improved
1344       in Perl v5.26 to a level that may be sufficient for your needs (see
1345       "Category "LC_COLLATE": Collation: Text Comparisons and Sorting").
1346
1347       If you have Perl v5.16 or v5.18 and can't upgrade, you can use
1348
1349           use locale ':not_characters';
1350
1351       When this form of the pragma is used, only the non-character portions
1352       of locales are used by Perl, for example "LC_NUMERIC".  Perl assumes
1353       that you have translated all the characters it is to operate on into
1354       Unicode (actually the platform's native character set (ASCII or EBCDIC)
1355       plus Unicode).  For data in files, this can conveniently be done by
1356       also specifying
1357
1358           use open ':locale';
1359
1360       This pragma arranges for all inputs from files to be translated into
1361       Unicode from the current locale as specified in the environment (see
1362       "ENVIRONMENT"), and all outputs to files to be translated back into the
1363       locale.  (See open).  On a per-filehandle basis, you can instead use
1364       the PerlIO::locale module, or the Encode::Locale module, both available
1365       from CPAN.  The latter module also has methods to ease the handling of
1366       "ARGV" and environment variables, and can be used on individual
1367       strings.  If you know that all your locales will be UTF-8, as many are
1368       these days, you can use the -C command line switch.
1369
1370       This form of the pragma allows essentially seamless handling of locales
1371       with Unicode.  The collation order will be by Unicode code point order.
1372       Unicode::Collate can be used to get Unicode rules collation.
1373
1374       All the modules and switches just described can be used in v5.20 with
1375       just plain "use locale", and, should the input locales not be UTF-8,
1376       you'll get the less than ideal behavior, described below, that you get
1377       with pre-v5.16 Perls, or when you use the locale pragma without the
1378       ":not_characters" parameter in v5.16 and v5.18.  If you are using
1379       exclusively UTF-8 locales in v5.20 and higher, the rest of this section
1380       does not apply to you.
1381
1382       There are two cases, multi-byte and single-byte locales.  First multi-
1383       byte:
1384
1385       The only multi-byte (or wide character) locale that Perl is ever likely
1386       to support is UTF-8.  This is due to the difficulty of implementation,
1387       the fact that high quality UTF-8 locales are now published for every
1388       area of the world (<https://unicode.org/Public/cldr/2.0.1/> for ones
1389       that are already set-up, but from an earlier version;
1390       <https://unicode.org/Public/cldr/latest/> for the most up-to-date, but
1391       you have to extract the POSIX information yourself), and that failing
1392       all that you can use the Encode module to translate to/from your
1393       locale.  So, you'll have to do one of those things if you're using one
1394       of these locales, such as Big5 or Shift JIS.  For UTF-8 locales, in
1395       Perls (pre v5.20) that don't have full UTF-8 locale support, they may
1396       work reasonably well (depending on your C library implementation)
1397       simply because both they and Perl store characters that take up
1398       multiple bytes the same way.  However, some, if not most, C library
1399       implementations may not process the characters in the upper half of the
1400       Latin-1 range (128 - 255) properly under "LC_CTYPE".  To see if a
1401       character is a particular type under a locale, Perl uses the functions
1402       like "isalnum()".  Your C library may not work for UTF-8 locales with
1403       those functions, instead only working under the newer wide library
1404       functions like "iswalnum()", which Perl does not use.  These multi-byte
1405       locales are treated like single-byte locales, and will have the
1406       restrictions described below.  Starting in Perl v5.22 a warning message
1407       is raised when Perl detects a multi-byte locale that it doesn't fully
1408       support.
1409
1410       For single-byte locales, Perl generally takes the tack to use locale
1411       rules on code points that can fit in a single byte, and Unicode rules
1412       for those that can't (though this isn't uniformly applied, see the note
1413       at the end of this section).  This prevents many problems in locales
1414       that aren't UTF-8.  Suppose the locale is ISO8859-7, Greek.  The
1415       character at 0xD7 there is a capital Chi. But in the ISO8859-1 locale,
1416       Latin1, it is a multiplication sign.  The POSIX regular expression
1417       character class "[[:alpha:]]" will magically match 0xD7 in the Greek
1418       locale but not in the Latin one.
1419
1420       However, there are places where this breaks down.  Certain Perl
1421       constructs are for Unicode only, such as "\p{Alpha}".  They assume that
1422       0xD7 always has its Unicode meaning (or the equivalent on EBCDIC
1423       platforms).  Since Latin1 is a subset of Unicode and 0xD7 is the
1424       multiplication sign in both Latin1 and Unicode, "\p{Alpha}" will never
1425       match it, regardless of locale.  A similar issue occurs with "\N{...}".
1426       Prior to v5.20, it is therefore a bad idea to use "\p{}" or "\N{}"
1427       under plain "use locale"--unless you can guarantee that the locale will
1428       be ISO8859-1.  Use POSIX character classes instead.
1429
1430       Another problem with this approach is that operations that cross the
1431       single byte/multiple byte boundary are not well-defined, and so are
1432       disallowed.  (This boundary is between the codepoints at 255/256.)  For
1433       example, lower casing LATIN CAPITAL LETTER Y WITH DIAERESIS (U+0178)
1434       should return LATIN SMALL LETTER Y WITH DIAERESIS (U+00FF).  But in the
1435       Greek locale, for example, there is no character at 0xFF, and Perl has
1436       no way of knowing what the character at 0xFF is really supposed to
1437       represent.  Thus it disallows the operation.  In this mode, the
1438       lowercase of U+0178 is itself.
1439
1440       The same problems ensue if you enable automatic UTF-8-ification of your
1441       standard file handles, default "open()" layer, and @ARGV on
1442       non-ISO8859-1, non-UTF-8 locales (by using either the -C command line
1443       switch or the "PERL_UNICODE" environment variable; see perlrun).
1444       Things are read in as UTF-8, which would normally imply a Unicode
1445       interpretation, but the presence of a locale causes them to be
1446       interpreted in that locale instead.  For example, a 0xD7 code point in
1447       the Unicode input, which should mean the multiplication sign, won't be
1448       interpreted by Perl that way under the Greek locale.  This is not a
1449       problem provided you make certain that all locales will always and only
1450       be either an ISO8859-1, or, if you don't have a deficient C library, a
1451       UTF-8 locale.
1452
1453       Still another problem is that this approach can lead to two code points
1454       meaning the same character.  Thus in a Greek locale, both U+03A7 and
1455       U+00D7 are GREEK CAPITAL LETTER CHI.
1456
1457       Because of all these problems, starting in v5.22, Perl will raise a
1458       warning if a multi-byte (hence Unicode) code point is used when a
1459       single-byte locale is in effect.  (Although it doesn't check for this
1460       if doing so would unreasonably slow execution down.)
1461
1462       Vendor locales are notoriously buggy, and it is difficult for Perl to
1463       test its locale-handling code because this interacts with code that
1464       Perl has no control over; therefore the locale-handling code in Perl
1465       may be buggy as well.  (However, the Unicode-supplied locales should be
1466       better, and there is a feed back mechanism to correct any problems.
1467       See "Freely available locale definitions".)
1468
1469       If you have Perl v5.16, the problems mentioned above go away if you use
1470       the ":not_characters" parameter to the locale pragma (except for vendor
1471       bugs in the non-character portions).  If you don't have v5.16, and you
1472       do have locales that work, using them may be worthwhile for certain
1473       specific purposes, as long as you keep in mind the gotchas already
1474       mentioned.  For example, if the collation for your locales works, it
1475       runs faster under locales than under Unicode::Collate; and you gain
1476       access to such things as the local currency symbol and the names of the
1477       months and days of the week.  (But to hammer home the point, in v5.16,
1478       you get this access without the downsides of locales by using the
1479       ":not_characters" form of the pragma.)
1480
1481       Note: The policy of using locale rules for code points that can fit in
1482       a byte, and Unicode rules for those that can't is not uniformly
1483       applied.  Pre-v5.12, it was somewhat haphazard; in v5.12 it was applied
1484       fairly consistently to regular expression matching except for bracketed
1485       character classes; in v5.14 it was extended to all regex matches; and
1486       in v5.16 to the casing operations such as "\L" and "uc()".  For
1487       collation, in all releases so far, the system's "strxfrm()" function is
1488       called, and whatever it does is what you get.  Starting in v5.26,
1489       various bugs are fixed with the way perl uses this function.
1490

BUGS

1492   Collation of strings containing embedded "NUL" characters
1493       "NUL" characters will sort the same as the lowest collating control
1494       character does, or to "\001" in the unlikely event that there are no
1495       control characters at all in the locale.  In cases where the strings
1496       don't contain this non-"NUL" control, the results will be correct, and
1497       in many locales, this control, whatever it might be, will rarely be
1498       encountered.  But there are cases where a "NUL" should sort before this
1499       control, but doesn't.  If two strings do collate identically, the one
1500       containing the "NUL" will sort to earlier.  Prior to 5.26, there were
1501       more bugs.
1502
1503   Multi-threaded
1504       XS code or C-language libraries called from it that use the system
1505       setlocale(3) function (except on Windows) likely will not work from a
1506       multi-threaded application without changes.  See "Locale-aware XS code"
1507       in perlxs.
1508
1509       An XS module that is locale-dependent could have been written under the
1510       assumption that it will never be called in a multi-threaded
1511       environment, and so uses other non-locale constructs that aren't multi-
1512       thread-safe.  See "Thread-aware system interfaces" in perlxs.
1513
1514       POSIX does not define a way to get the name of the current per-thread
1515       locale.  Some systems, such as Darwin and NetBSD do implement a
1516       function, querylocale(3) to do this.  On non-Windows systems without
1517       it, such as Linux, there are some additional caveats:
1518
1519       •   An embedded perl needs to be started up while the global locale is
1520           in effect.  See "Using embedded Perl with POSIX locales" in
1521           perlembed.
1522
1523       •   It becomes more important for perl to know about all the possible
1524           locale categories on the platform, even if they aren't apparently
1525           used in your program.  Perl knows all of the Linux ones.  If your
1526           platform has others, you can submit an issue at
1527           <https://github.com/Perl/perl5/issues> for inclusion of it in the
1528           next release.  In the meantime, it is possible to edit the Perl
1529           source to teach it about the category, and then recompile.  Search
1530           for instances of, say, "LC_PAPER" in the source, and use that as a
1531           template to add the omitted one.
1532
1533       •   It is possible, though hard to do, to call "POSIX::setlocale" with
1534           a locale that it doesn't recognize as syntactically legal, but
1535           actually is legal on that system.  This should happen only with
1536           embedded perls, or if you hand-craft a locale name yourself.
1537
1538   Broken systems
1539       In certain systems, the operating system's locale support is broken and
1540       cannot be fixed or used by Perl.  Such deficiencies can and will result
1541       in mysterious hangs and/or Perl core dumps when "use locale" is in
1542       effect.  When confronted with such a system, please report in
1543       excruciating detail to <<https://github.com/Perl/perl5/issues>>, and
1544       also contact your vendor: bug fixes may exist for these problems in
1545       your operating system.  Sometimes such bug fixes are called an
1546       operating system upgrade.  If you have the source for Perl, include in
1547       the bug report the output of the test described above in "Testing for
1548       broken locales".
1549

SEE ALSO

1551       I18N::Langinfo, perluniintro, perlunicode, open, "localeconv" in POSIX,
1552       "setlocale" in POSIX, "strcoll" in POSIX, "strftime" in POSIX, "strtod"
1553       in POSIX, "strxfrm" in POSIX.
1554
1555       For special considerations when Perl is embedded in a C program, see
1556       "Using embedded Perl with POSIX locales" in perlembed.
1557

HISTORY

1559       Jarkko Hietaniemi's original perli18n.pod heavily hacked by Dominic
1560       Dunlop, assisted by the perl5-porters.  Prose worked over a bit by Tom
1561       Christiansen, and now maintained by Perl 5 porters.
1562
1563
1564
1565perl v5.32.1                      2021-05-31                     PERLLOCALE(1)
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