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1=encoding utf8
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3=head1 NAME
4
b0c42ed9 5perllocale - Perl locale handling (internationalization and localization)
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6
7=head1 DESCRIPTION
8
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9In the beginning there was ASCII, the "American Standard Code for
10Information Interchange", which works quite well for Americans with
11their English alphabet and dollar-denominated currency. But it doesn't
12work so well even for other English speakers, who may use different
13currencies, such as the pound sterling (as the symbol for that currency
14is not in ASCII); and it's hopelessly inadequate for many of the
15thousands of the world's other languages.
16
17To address these deficiencies, the concept of locales was invented
18(formally the ISO C, XPG4, POSIX 1.c "locale system"). And applications
19were and are being written that use the locale mechanism. The process of
20making such an application take account of its users' preferences in
21these kinds of matters is called B<internationalization> (often
22abbreviated as B<i18n>); telling such an application about a particular
23set of preferences is known as B<localization> (B<l10n>).
24
39332f68 25Perl has been extended to support the locale system. This
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26is controlled per application by using one pragma, one function call,
27and several environment variables.
28
29Unfortunately, there are quite a few deficiencies with the design (and
30often, the implementations) of locales, and their use for character sets
31has mostly been supplanted by Unicode (see L<perlunitut> for an
32introduction to that, and keep on reading here for how Unicode interacts
33with locales in Perl).
34
7ee2ae1e 35Perl continues to support the old locale system, and starting in v5.16,
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36provides a hybrid way to use the Unicode character set, along with the
37other portions of locales that may not be so problematic.
38(Unicode is also creating C<CLDR>, the "Common Locale Data Repository",
39L<http://cldr.unicode.org/> which includes more types of information than
40are available in the POSIX locale system. At the time of this writing,
41there was no CPAN module that provides access to this XML-encoded data.
42However, many of its locales have the POSIX-only data extracted, and are
43available at L<http://unicode.org/Public/cldr/latest/>.)
44
45=head1 WHAT IS A LOCALE
46
47A locale is a set of data that describes various aspects of how various
48communities in the world categorize their world. These categories are
49broken down into the following types (some of which include a brief
50note here):
51
52=over
53
54=item Category LC_NUMERIC: Numeric formatting
55
56This indicates how numbers should be formatted for human readability,
57for example the character used as the decimal point.
58
59=item Category LC_MONETARY: Formatting of monetary amounts
60
61=for comment
62The nbsp below makes this look better
63
64E<160>
65
66=item Category LC_TIME: Date/Time formatting
67
68=for comment
69The nbsp below makes this look better
70
71E<160>
72
73=item Category LC_MESSAGES: Error and other messages
74
2619d284 75This is used by Perl itself only for accessing operating system error
03c702c5 76messages via L<$!|perlvar/$ERRNO> and L<$^E|perlvar/$EXTENDED_OS_ERROR>.
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77
78=item Category LC_COLLATE: Collation
79
76073c88 80This indicates the ordering of letters for comparison and sorting.
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81In Latin alphabets, for example, "b", generally follows "a".
82
83=item Category LC_CTYPE: Character Types
84
85This indicates, for example if a character is an uppercase letter.
86
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87=item Other categories
88
89Some platforms have other categories, dealing with such things as
90measurement units and paper sizes. None of these are used directly by
91Perl, but outside operations that Perl interacts with may use
4c9b78f4 92these. See L</Not within the scope of any "use locale" variant> below.
2619d284 93
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94=back
95
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96More details on the categories used by Perl are given below in L</LOCALE
97CATEGORIES>.
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98
99Together, these categories go a long way towards being able to customize
100a single program to run in many different locations. But there are
101deficiencies, so keep reading.
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102
103=head1 PREPARING TO USE LOCALES
104
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105Perl itself will not use locales unless specifically requested to (but
106again note that Perl may interact with code that does use them). Even
107if there is such a request, B<all> of the following must be true
b960a36e 108for it to work properly:
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109
110=over 4
111
112=item *
113
114B<Your operating system must support the locale system>. If it does,
39332f68 115you should find that the C<setlocale()> function is a documented part of
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116its C library.
117
118=item *
119
5a964f20 120B<Definitions for locales that you use must be installed>. You, or
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121your system administrator, must make sure that this is the case. The
122available locales, the location in which they are kept, and the manner
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123in which they are installed all vary from system to system. Some systems
124provide only a few, hard-wired locales and do not allow more to be
125added. Others allow you to add "canned" locales provided by the system
126supplier. Still others allow you or the system administrator to define
14280422 127and add arbitrary locales. (You may have to ask your supplier to
5a964f20 128provide canned locales that are not delivered with your operating
14280422 129system.) Read your system documentation for further illumination.
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130
131=item *
132
133B<Perl must believe that the locale system is supported>. If it does,
134C<perl -V:d_setlocale> will say that the value for C<d_setlocale> is
135C<define>.
136
137=back
138
139If you want a Perl application to process and present your data
140according to a particular locale, the application code should include
2ae324a7 141the S<C<use locale>> pragma (see L<The use locale pragma>) where
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142appropriate, and B<at least one> of the following must be true:
143
144=over 4
145
c052850d 146=item 1
5f05dabc 147
66cbab2c 148B<The locale-determining environment variables (see L</"ENVIRONMENT">)
5a964f20 149must be correctly set up> at the time the application is started, either
ef3087ec 150by yourself or by whomever set up your system account; or
5f05dabc 151
c052850d 152=item 2
5f05dabc 153
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154B<The application must set its own locale> using the method described in
155L<The setlocale function>.
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156
157=back
158
159=head1 USING LOCALES
160
161=head2 The use locale pragma
162
2619d284 163By default, Perl itself ignores the current locale. The S<C<use locale>>
66cbab2c 164pragma tells Perl to use the current locale for some operations.
7ee2ae1e 165Starting in v5.16, there is an optional parameter to this pragma:
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166
167 use locale ':not_characters';
168
169This parameter allows better mixing of locales and Unicode, and is
170described fully in L</Unicode and UTF-8>, but briefly, it tells Perl to
171not use the character portions of the locale definition, that is
172the C<LC_CTYPE> and C<LC_COLLATE> categories. Instead it will use the
2619d284 173native character set (extended by Unicode). When using this parameter,
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174you are responsible for getting the external character set translated
175into the native/Unicode one (which it already will be if it is one of
176the increasingly popular UTF-8 locales). There are convenient ways of
177doing this, as described in L</Unicode and UTF-8>.
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178
179The current locale is set at execution time by
180L<setlocale()|/The setlocale function> described below. If that function
181hasn't yet been called in the course of the program's execution, the
66cbab2c 182current locale is that which was determined by the L</"ENVIRONMENT"> in
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183effect at the start of the program, except that
184C<L<LC_NUMERIC|/Category LC_NUMERIC: Numeric Formatting>> is always
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185initialized to the C locale (the C locale is mentioned under L<Finding
186locales>).
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187If there is no valid environment, the current locale is whatever the
188system default has been set to. It is likely, but not necessarily, the
189"C" locale.
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190
191The operations that are affected by locale are:
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192
193=over 4
194
4c9b78f4 195=item B<Not within the scope of any C<"use locale"> variant>
b960a36e 196
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197Only operations originating outside Perl should be affected, as follows:
198
199=over 4
200
201=item *
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202
203The variable L<$!|perlvar/$ERRNO> (and its synonyms C<$ERRNO> and
204C<$OS_ERROR>) when used as strings always are in terms of the current
205locale.
206
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207=item *
208
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209The current locale is also used when going outside of Perl with
210operations like L<system()|perlfunc/system LIST> or
211L<qxE<sol>E<sol>|perlop/qxE<sol>STRINGE<sol>>, if those operations are
212locale-sensitive.
213
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214=item *
215
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216Also Perl gives access to various C library functions through the
217L<POSIX> module. Some of those functions are always affected by the
218current locale. For example, C<POSIX::strftime()> uses C<LC_TIME>;
219C<POSIX::strtod()> uses C<LC_NUMERIC>; C<POSIX::strcoll()> and
220C<POSIX::strxfrm()> use C<LC_COLLATE>; and character classification
221functions like C<POSIX::isalnum()> use C<LC_CTYPE>. All such functions
222will behave according to the current underlying locale, even if that
1d2ab946 223locale isn't exposed to Perl space.
2619d284 224
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225=item *
226
227Perl also provides lite wrappers for XS modules to use some C library
228C<printf> functions. These wrappers don't do anything with the locale,
229and the underlying C library function is affected by the locale in
230effect at the time of the wrapper call.
231The affected functions are
232L<perlapi/my_sprintf>,
233L<perlapi/my_snprintf>,
234and
235L<perlapi/my_vsnprintf>.
236
237=back
238
239=item Lingering effects of C<S<use locale>>
240
241Certain Perl operations that are set-up within the scope of a
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242C<use locale> variant retain that effect even outside the scope.
243These include:
244
245=over 4
246
247=item *
248
249The output format of a L<write()|perlfunc/write> is determined by an
250earlier format declaration (L<perlfunc/format>), so whether or not the
251output is affected by locale is determined by if the C<format()> is
252within the scope of a C<use locale> variant, not whether the C<write()>
253is.
254
255=item *
256
257Regular expression patterns can be compiled using
258L<qrE<sol>E<sol>|perlop/qrE<sol>STRINGE<sol>msixpodual> with actual
259matching deferred to later. Again, it is whether or not the compilation
260was done within the scope of C<use locale> that determines the match
261behavior, not if the matches are done within such a scope or not.
262
263=back
264
4c9b78f4 265=item B<Under C<"use locale ':not_characters';">>
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266
267=over 4
268
269=item *
270
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271All the non-Perl operations.
272
273=item *
274
275B<Format declarations> (L<perlfunc/format>) and hence any subsequent
276C<write()>s use C<LC_NUMERIC>.
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277
278=item *
279
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280B<stringification and output> use C<LC_NUMERIC>.
281These include the results of
282C<print()>,
283C<printf()>,
284C<say()>,
285and
286C<sprintf()>.
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287
288=back
289
290=for comment
291The nbsp below makes this look better
292
293E<160>
294
4c9b78f4 295=item B<Under just plain C<"use locale";>>
66cbab2c 296
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297=over 4
298
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299=item *
300
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301All the above operations
302
303=item *
304
305B<The comparison operators> (C<lt>, C<le>, C<cmp>, C<ge>, and C<gt>) use
39332f68 306C<LC_COLLATE>. C<sort()> is also affected if used without an
5a964f20 307explicit comparison function, because it uses C<cmp> by default.
14280422 308
5a964f20 309B<Note:> C<eq> and C<ne> are unaffected by locale: they always
de108802 310perform a char-by-char comparison of their scalar operands. What's
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311more, if C<cmp> finds that its operands are equal according to the
312collation sequence specified by the current locale, it goes on to
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313perform a char-by-char comparison, and only returns I<0> (equal) if the
314operands are char-for-char identical. If you really want to know whether
5a964f20 315two strings--which C<eq> and C<cmp> may consider different--are equal
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316as far as collation in the locale is concerned, see the discussion in
317L<Category LC_COLLATE: Collation>.
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318
319=item *
320
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321B<Regular expressions and case-modification functions> (C<uc()>, C<lc()>,
322C<ucfirst()>, and C<lcfirst()>) use C<LC_CTYPE>
5f05dabc 323
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324=back
325
66cbab2c 326=back
5f05dabc 327
5a964f20 328The default behavior is restored with the S<C<no locale>> pragma, or
ef3087ec 329upon reaching the end of the block enclosing C<use locale>.
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330Note that C<use locale> and C<use locale ':not_characters'> may be
331nested, and that what is in effect within an inner scope will revert to
332the outer scope's rules at the end of the inner scope.
5f05dabc 333
5a964f20 334The string result of any operation that uses locale
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335information is tainted, as it is possible for a locale to be
336untrustworthy. See L<"SECURITY">.
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337
338=head2 The setlocale function
339
14280422 340You can switch locales as often as you wish at run time with the
39332f68 341C<POSIX::setlocale()> function:
5f05dabc 342
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343 # Import locale-handling tool set from POSIX module.
344 # This example uses: setlocale -- the function call
345 # LC_CTYPE -- explained below
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346 # (Showing the testing for success/failure of operations is
347 # omitted in these examples to avoid distracting from the main
dfcc8045 348 # point
6ea81ccf 349
5f05dabc 350 use POSIX qw(locale_h);
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351 use locale;
352 my $old_locale;
5f05dabc 353
14280422 354 # query and save the old locale
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355 $old_locale = setlocale(LC_CTYPE);
356
357 setlocale(LC_CTYPE, "fr_CA.ISO8859-1");
358 # LC_CTYPE now in locale "French, Canada, codeset ISO 8859-1"
359
360 setlocale(LC_CTYPE, "");
361 # LC_CTYPE now reset to default defined by LC_ALL/LC_CTYPE/LANG
362 # environment variables. See below for documentation.
363
364 # restore the old locale
365 setlocale(LC_CTYPE, $old_locale);
366
39332f68 367The first argument of C<setlocale()> gives the B<category>, the second the
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368B<locale>. The category tells in what aspect of data processing you
369want to apply locale-specific rules. Category names are discussed in
66cbab2c 370L</LOCALE CATEGORIES> and L</"ENVIRONMENT">. The locale is the name of a
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371collection of customization information corresponding to a particular
372combination of language, country or territory, and codeset. Read on for
373hints on the naming of locales: not all systems name locales as in the
374example.
375
39332f68 376If no second argument is provided and the category is something other
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377than LC_ALL, the function returns a string naming the current locale
378for the category. You can use this value as the second argument in a
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379subsequent call to C<setlocale()>, B<but> on some platforms the string
380is opaque, not something that most people would be able to decipher as
381to what locale it means.
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382
383If no second argument is provided and the category is LC_ALL, the
384result is implementation-dependent. It may be a string of
c052850d 385concatenated locale names (separator also implementation-dependent)
39332f68 386or a single locale name. Please consult your L<setlocale(3)> man page for
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387details.
388
389If a second argument is given and it corresponds to a valid locale,
390the locale for the category is set to that value, and the function
391returns the now-current locale value. You can then use this in yet
39332f68 392another call to C<setlocale()>. (In some implementations, the return
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393value may sometimes differ from the value you gave as the second
394argument--think of it as an alias for the value you gave.)
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395
396As the example shows, if the second argument is an empty string, the
397category's locale is returned to the default specified by the
398corresponding environment variables. Generally, this results in a
5a964f20 399return to the default that was in force when Perl started up: changes
54310121 400to the environment made by the application after startup may or may not
5a964f20 401be noticed, depending on your system's C library.
5f05dabc 402
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403Note that Perl ignores the current C<LC_CTYPE> and C<LC_COLLATE> locales
404within the scope of a C<use locale ':not_characters'>.
405
f170b852 406If C<set_locale()> fails for some reason (for example, an attempt to set
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407to a locale unknown to the system), the locale for the category is not
408changed, and the function returns C<undef>.
409
2619d284 410
39332f68 411For further information about the categories, consult L<setlocale(3)>.
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412
413=head2 Finding locales
414
39332f68 415For locales available in your system, consult also L<setlocale(3)> to
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416see whether it leads to the list of available locales (search for the
417I<SEE ALSO> section). If that fails, try the following command lines:
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418
419 locale -a
420
421 nlsinfo
422
423 ls /usr/lib/nls/loc
424
425 ls /usr/lib/locale
426
427 ls /usr/lib/nls
428
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429 ls /usr/share/locale
430
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431and see whether they list something resembling these
432
2bdf8add 433 en_US.ISO8859-1 de_DE.ISO8859-1 ru_RU.ISO8859-5
502a173a 434 en_US.iso88591 de_DE.iso88591 ru_RU.iso88595
2bdf8add 435 en_US de_DE ru_RU
14280422 436 en de ru
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437 english german russian
438 english.iso88591 german.iso88591 russian.iso88595
502a173a 439 english.roman8 russian.koi8r
5f05dabc 440
39332f68 441Sadly, even though the calling interface for C<setlocale()> has been
528d65ad 442standardized, names of locales and the directories where the
5a964f20 443configuration resides have not been. The basic form of the name is
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444I<language_territory>B<.>I<codeset>, but the latter parts after
445I<language> are not always present. The I<language> and I<country>
446are usually from the standards B<ISO 3166> and B<ISO 639>, the
447two-letter abbreviations for the countries and the languages of the
448world, respectively. The I<codeset> part often mentions some B<ISO
4498859> character set, the Latin codesets. For example, C<ISO 8859-1>
450is the so-called "Western European codeset" that can be used to encode
451most Western European languages adequately. Again, there are several
452ways to write even the name of that one standard. Lamentably.
5f05dabc 453
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454Two special locales are worth particular mention: "C" and "POSIX".
455Currently these are effectively the same locale: the difference is
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456mainly that the first one is defined by the C standard, the second by
457the POSIX standard. They define the B<default locale> in which
14280422 458every program starts in the absence of locale information in its
5a964f20 459environment. (The I<default> default locale, if you will.) Its language
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460is (American) English and its character codeset ASCII or, rarely, a
461superset thereof (such as the "DEC Multinational Character Set
462(DEC-MCS)"). B<Warning>. The C locale delivered by some vendors
463may not actually exactly match what the C standard calls for. So
464beware.
5f05dabc 465
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466B<NOTE>: Not all systems have the "POSIX" locale (not all systems are
467POSIX-conformant), so use "C" when you need explicitly to specify this
468default locale.
5f05dabc 469
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470=head2 LOCALE PROBLEMS
471
5a964f20 472You may encounter the following warning message at Perl startup:
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473
474 perl: warning: Setting locale failed.
475 perl: warning: Please check that your locale settings:
476 LC_ALL = "En_US",
477 LANG = (unset)
478 are supported and installed on your system.
479 perl: warning: Falling back to the standard locale ("C").
480
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481This means that your locale settings had LC_ALL set to "En_US" and
482LANG exists but has no value. Perl tried to believe you but could not.
483Instead, Perl gave up and fell back to the "C" locale, the default locale
484that is supposed to work no matter what. This usually means your locale
485settings were wrong, they mention locales your system has never heard
486of, or the locale installation in your system has problems (for example,
487some system files are broken or missing). There are quick and temporary
488fixes to these problems, as well as more thorough and lasting fixes.
3e6e419a 489
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490=head2 Testing for broken locales
491
492If you are building Perl from source, the Perl test suite file
493F<lib/locale.t> can be used to test the locales on your system.
494Setting the environment variable C<PERL_DEBUG_FULL_TEST> to 1
495will cause it to output detailed results. For example, on Linux, you
496could say
497
1d2ab946 498 PERL_DEBUG_FULL_TEST=1 ./perl -T -Ilib lib/locale.t > locale.log 2>&1
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499
500Besides many other tests, it will test every locale it finds on your
501system to see if they conform to the POSIX standard. If any have
502errors, it will include a summary near the end of the output of which
503locales passed all its tests, and which failed, and why.
504
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505=head2 Temporarily fixing locale problems
506
5a964f20 507The two quickest fixes are either to render Perl silent about any
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508locale inconsistencies or to run Perl under the default locale "C".
509
510Perl's moaning about locale problems can be silenced by setting the
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511environment variable PERL_BADLANG to a zero value, for example "0".
512This method really just sweeps the problem under the carpet: you tell
513Perl to shut up even when Perl sees that something is wrong. Do not
514be surprised if later something locale-dependent misbehaves.
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515
516Perl can be run under the "C" locale by setting the environment
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517variable LC_ALL to "C". This method is perhaps a bit more civilized
518than the PERL_BADLANG approach, but setting LC_ALL (or
519other locale variables) may affect other programs as well, not just
520Perl. In particular, external programs run from within Perl will see
3e6e419a 521these changes. If you make the new settings permanent (read on), all
f979aebc 522programs you run see the changes. See L<"ENVIRONMENT"> for
5a964f20 523the full list of relevant environment variables and L<USING LOCALES>
e05ffc7d 524for their effects in Perl. Effects in other programs are
5a964f20 525easily deducible. For example, the variable LC_COLLATE may well affect
b432a672 526your B<sort> program (or whatever the program that arranges "records"
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527alphabetically in your system is called).
528
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529You can test out changing these variables temporarily, and if the
530new settings seem to help, put those settings into your shell startup
531files. Consult your local documentation for the exact details. For in
532Bourne-like shells (B<sh>, B<ksh>, B<bash>, B<zsh>):
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533
534 LC_ALL=en_US.ISO8859-1
535 export LC_ALL
536
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537This assumes that we saw the locale "en_US.ISO8859-1" using the commands
538discussed above. We decided to try that instead of the above faulty
539locale "En_US"--and in Cshish shells (B<csh>, B<tcsh>)
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540
541 setenv LC_ALL en_US.ISO8859-1
c47ff5f1 542
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543or if you have the "env" application you can do in any shell
544
545 env LC_ALL=en_US.ISO8859-1 perl ...
546
5a964f20 547If you do not know what shell you have, consult your local
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548helpdesk or the equivalent.
549
550=head2 Permanently fixing locale problems
551
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552The slower but superior fixes are when you may be able to yourself
553fix the misconfiguration of your own environment variables. The
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554mis(sing)configuration of the whole system's locales usually requires
555the help of your friendly system administrator.
556
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557First, see earlier in this document about L<Finding locales>. That tells
558how to find which locales are really supported--and more importantly,
559installed--on your system. In our example error message, environment
560variables affecting the locale are listed in the order of decreasing
561importance (and unset variables do not matter). Therefore, having
562LC_ALL set to "En_US" must have been the bad choice, as shown by the
563error message. First try fixing locale settings listed first.
3e6e419a 564
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565Second, if using the listed commands you see something B<exactly>
566(prefix matches do not count and case usually counts) like "En_US"
567without the quotes, then you should be okay because you are using a
568locale name that should be installed and available in your system.
4a4eefd0 569In this case, see L<Permanently fixing your system's locale configuration>.
3e6e419a 570
4a4eefd0 571=head2 Permanently fixing your system's locale configuration
3e6e419a 572
5a964f20 573This is when you see something like:
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574
575 perl: warning: Please check that your locale settings:
576 LC_ALL = "En_US",
577 LANG = (unset)
578 are supported and installed on your system.
579
580but then cannot see that "En_US" listed by the above-mentioned
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581commands. You may see things like "en_US.ISO8859-1", but that isn't
582the same. In this case, try running under a locale
583that you can list and which somehow matches what you tried. The
3e6e419a 584rules for matching locale names are a bit vague because
e05ffc7d 585standardization is weak in this area. See again the
13a2d996 586L<Finding locales> about general rules.
3e6e419a 587
b687b08b 588=head2 Fixing system locale configuration
3e6e419a 589
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590Contact a system administrator (preferably your own) and report the exact
591error message you get, and ask them to read this same documentation you
592are now reading. They should be able to check whether there is something
593wrong with the locale configuration of the system. The L<Finding locales>
594section is unfortunately a bit vague about the exact commands and places
595because these things are not that standardized.
3e6e419a 596
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597=head2 The localeconv function
598
39332f68 599The C<POSIX::localeconv()> function allows you to get particulars of the
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600locale-dependent numeric formatting information specified by the current
601C<LC_NUMERIC> and C<LC_MONETARY> locales. (If you just want the name of
39332f68 602the current locale for a particular category, use C<POSIX::setlocale()>
5a964f20 603with a single parameter--see L<The setlocale function>.)
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604
605 use POSIX qw(locale_h);
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606
607 # Get a reference to a hash of locale-dependent info
608 $locale_values = localeconv();
609
610 # Output sorted list of the values
611 for (sort keys %$locale_values) {
14280422 612 printf "%-20s = %s\n", $_, $locale_values->{$_}
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613 }
614
39332f68 615C<localeconv()> takes no arguments, and returns B<a reference to> a hash.
5a964f20 616The keys of this hash are variable names for formatting, such as
502a173a 617C<decimal_point> and C<thousands_sep>. The values are the
cea6626f 618corresponding, er, values. See L<POSIX/localeconv> for a longer
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619example listing the categories an implementation might be expected to
620provide; some provide more and others fewer. You don't need an
39332f68 621explicit C<use locale>, because C<localeconv()> always observes the
502a173a 622current locale.
5f05dabc 623
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624Here's a simple-minded example program that rewrites its command-line
625parameters as integers correctly formatted in the current locale:
5f05dabc 626
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627 use POSIX qw(locale_h);
628
629 # Get some of locale's numeric formatting parameters
630 my ($thousands_sep, $grouping) =
631 @{localeconv()}{'thousands_sep', 'grouping'};
632
633 # Apply defaults if values are missing
634 $thousands_sep = ',' unless $thousands_sep;
635
636 # grouping and mon_grouping are packed lists
637 # of small integers (characters) telling the
638 # grouping (thousand_seps and mon_thousand_seps
639 # being the group dividers) of numbers and
640 # monetary quantities. The integers' meanings:
641 # 255 means no more grouping, 0 means repeat
642 # the previous grouping, 1-254 means use that
643 # as the current grouping. Grouping goes from
644 # right to left (low to high digits). In the
645 # below we cheat slightly by never using anything
646 # else than the first grouping (whatever that is).
647 if ($grouping) {
648 @grouping = unpack("C*", $grouping);
649 } else {
650 @grouping = (3);
651 }
652
653 # Format command line params for current locale
654 for (@ARGV) {
655 $_ = int; # Chop non-integer part
656 1 while
657 s/(\d)(\d{$grouping[0]}($|$thousands_sep))/$1$thousands_sep$2/;
658 print "$_";
659 }
660 print "\n";
5f05dabc 661
74c76037 662=head2 I18N::Langinfo
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663
664Another interface for querying locale-dependent information is the
39332f68 665C<I18N::Langinfo::langinfo()> function, available at least in Unix-like
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666systems and VMS.
667
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668The following example will import the C<langinfo()> function itself and
669three constants to be used as arguments to C<langinfo()>: a constant for
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670the abbreviated first day of the week (the numbering starts from
671Sunday = 1) and two more constants for the affirmative and negative
672answers for a yes/no question in the current locale.
4bbcc6e8 673
74c76037 674 use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
4bbcc6e8 675
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676 my ($abday_1, $yesstr, $nostr)
677 = map { langinfo } qw(ABDAY_1 YESSTR NOSTR);
4bbcc6e8 678
74c76037 679 print "$abday_1? [$yesstr/$nostr] ";
4bbcc6e8 680
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681In other words, in the "C" (or English) locale the above will probably
682print something like:
683
e05ffc7d 684 Sun? [yes/no]
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685
686See L<I18N::Langinfo> for more information.
687
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688=head1 LOCALE CATEGORIES
689
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690The following subsections describe basic locale categories. Beyond these,
691some combination categories allow manipulation of more than one
692basic category at a time. See L<"ENVIRONMENT"> for a discussion of these.
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693
694=head2 Category LC_COLLATE: Collation
695
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696In the scope of S<C<use locale>> (but not a
697C<use locale ':not_characters'>), Perl looks to the C<LC_COLLATE>
5a964f20 698environment variable to determine the application's notions on collation
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699(ordering) of characters. For example, "b" follows "a" in Latin
700alphabets, but where do "E<aacute>" and "E<aring>" belong? And while
f87fa335 701"color" follows "chocolate" in English, what about in traditional Spanish?
5f05dabc 702
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703The following collations all make sense and you may meet any of them
704if you "use locale".
705
706 A B C D E a b c d e
35316ca3 707 A a B b C c D d E e
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708 a A b B c C d D e E
709 a b c d e A B C D E
710
f1cbbd6e 711Here is a code snippet to tell what "word"
5a964f20 712characters are in the current locale, in that locale's order:
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713
714 use locale;
35316ca3 715 print +(sort grep /\w/, map { chr } 0..255), "\n";
5f05dabc 716
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717Compare this with the characters that you see and their order if you
718state explicitly that the locale should be ignored:
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719
720 no locale;
35316ca3 721 print +(sort grep /\w/, map { chr } 0..255), "\n";
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722
723This machine-native collation (which is what you get unless S<C<use
724locale>> has appeared earlier in the same block) must be used for
725sorting raw binary data, whereas the locale-dependent collation of the
b0c42ed9 726first example is useful for natural text.
5f05dabc 727
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728As noted in L<USING LOCALES>, C<cmp> compares according to the current
729collation locale when C<use locale> is in effect, but falls back to a
de108802 730char-by-char comparison for strings that the locale says are equal. You
39332f68 731can use C<POSIX::strcoll()> if you don't want this fall-back:
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732
733 use POSIX qw(strcoll);
734 $equal_in_locale =
735 !strcoll("space and case ignored", "SpaceAndCaseIgnored");
736
39332f68 737C<$equal_in_locale> will be true if the collation locale specifies a
5a964f20 738dictionary-like ordering that ignores space characters completely and
9e3a2af8 739which folds case.
14280422 740
5a964f20 741If you have a single string that you want to check for "equality in
14280422 742locale" against several others, you might think you could gain a little
39332f68 743efficiency by using C<POSIX::strxfrm()> in conjunction with C<eq>:
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744
745 use POSIX qw(strxfrm);
746 $xfrm_string = strxfrm("Mixed-case string");
747 print "locale collation ignores spaces\n"
748 if $xfrm_string eq strxfrm("Mixed-casestring");
749 print "locale collation ignores hyphens\n"
750 if $xfrm_string eq strxfrm("Mixedcase string");
751 print "locale collation ignores case\n"
752 if $xfrm_string eq strxfrm("mixed-case string");
753
39332f68 754C<strxfrm()> takes a string and maps it into a transformed string for use
de108802 755in char-by-char comparisons against other transformed strings during
14280422 756collation. "Under the hood", locale-affected Perl comparison operators
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757call C<strxfrm()> for both operands, then do a char-by-char
758comparison of the transformed strings. By calling C<strxfrm()> explicitly
14280422 759and using a non locale-affected comparison, the example attempts to save
5a964f20 760a couple of transformations. But in fact, it doesn't save anything: Perl
2ae324a7 761magic (see L<perlguts/Magic Variables>) creates the transformed version of a
5a964f20 762string the first time it's needed in a comparison, then keeps this version around
14280422 763in case it's needed again. An example rewritten the easy way with
e38874e2 764C<cmp> runs just about as fast. It also copes with null characters
39332f68 765embedded in strings; if you call C<strxfrm()> directly, it treats the first
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766null it finds as a terminator. don't expect the transformed strings
767it produces to be portable across systems--or even from one revision
39332f68 768of your operating system to the next. In short, don't call C<strxfrm()>
e38874e2 769directly: let Perl do it for you.
14280422 770
5a964f20 771Note: C<use locale> isn't shown in some of these examples because it isn't
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772needed: C<strcoll()> and C<strxfrm()> are POSIX functions
773which use the standard system-supplied C<libc> functions that
774always obey the current C<LC_COLLATE> locale.
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775
776=head2 Category LC_CTYPE: Character Types
777
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778In the scope of S<C<use locale>> (but not a
779C<use locale ':not_characters'>), Perl obeys the C<LC_CTYPE> locale
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780setting. This controls the application's notion of which characters are
781alphabetic. This affects Perl's C<\w> regular expression metanotation,
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782which stands for alphanumeric characters--that is, alphabetic,
783numeric, and including other special characters such as the underscore or
784hyphen. (Consult L<perlre> for more information about
14280422 785regular expressions.) Thanks to C<LC_CTYPE>, depending on your locale
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786setting, characters like "E<aelig>", "E<eth>", "E<szlig>", and
787"E<oslash>" may be understood as C<\w> characters.
5f05dabc 788
2c268ad5 789The C<LC_CTYPE> locale also provides the map used in transliterating
68dc0745 790characters between lower and uppercase. This affects the case-mapping
39332f68 791functions--C<fc()>, C<lc()>, C<lcfirst()>, C<uc()>, and C<ucfirst()>; case-mapping
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792interpolation with C<\F>, C<\l>, C<\L>, C<\u>, or C<\U> in double-quoted
793strings and C<s///> substitutions; and case-independent regular expression
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794pattern matching using the C<i> modifier.
795
5a964f20 796Finally, C<LC_CTYPE> affects the POSIX character-class test
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797functions--C<POSIX::isalpha()>, C<POSIX::islower()>, and so on. For
798example, if you move from the "C" locale to a 7-bit Scandinavian one,
799you may find--possibly to your surprise--that "|" moves from the
800C<POSIX::ispunct()> class to C<POSIX::isalpha()>.
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801Unfortunately, this creates big problems for regular expressions. "|" still
802means alternation even though it matches C<\w>.
5f05dabc 803
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804Note that there are quite a few things that are unaffected by the
805current locale. All the escape sequences for particular characters,
806C<\n> for example, always mean the platform's native one. This means,
807for example, that C<\N> in regular expressions (every character
1d2ab946 808but new-line) works on the platform character set.
5d63e270 809
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810B<Note:> A broken or malicious C<LC_CTYPE> locale definition may result
811in clearly ineligible characters being considered to be alphanumeric by
e199995e 812your application. For strict matching of (mundane) ASCII letters and
5a964f20 813digits--for example, in command strings--locale-aware applications
e199995e 814should use C<\w> with the C</a> regular expression modifier. See L<"SECURITY">.
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815
816=head2 Category LC_NUMERIC: Numeric Formatting
817
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818After a proper C<POSIX::setlocale()> call, and within the scope of one
819of the C<use locale> variants, Perl obeys the C<LC_NUMERIC>
2095dafa 820locale information, which controls an application's idea of how numbers
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821should be formatted for human readability.
822In most implementations the only effect is to
b4ffc3db 823change the character used for the decimal point--perhaps from "." to ",".
b960a36e 824The functions aren't aware of such niceties as thousands separation and
2095dafa 825so on. (See L<The localeconv function> if you care about these things.)
5a964f20 826
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827 use POSIX qw(strtod setlocale LC_NUMERIC);
828 use locale;
5f05dabc 829
b960a36e 830 setlocale LC_NUMERIC, "";
14280422 831
b960a36e 832 $n = 5/2; # Assign numeric 2.5 to $n
5f05dabc 833
b960a36e 834 $a = " $n"; # Locale-dependent conversion to string
5f05dabc 835
b960a36e 836 print "half five is $n\n"; # Locale-dependent output
5f05dabc 837
b960a36e 838 printf "half five is %g\n", $n; # Locale-dependent output
5f05dabc 839
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840 print "DECIMAL POINT IS COMMA\n"
841 if $n == (strtod("2,5"))[0]; # Locale-dependent conversion
5f05dabc 842
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843See also L<I18N::Langinfo> and C<RADIXCHAR>.
844
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845=head2 Category LC_MONETARY: Formatting of monetary amounts
846
e199995e 847The C standard defines the C<LC_MONETARY> category, but not a function
5a964f20 848that is affected by its contents. (Those with experience of standards
b0c42ed9 849committees will recognize that the working group decided to punt on the
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850issue.) Consequently, Perl essentially takes no notice of it. If you
851really want to use C<LC_MONETARY>, you can query its contents--see
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852L<The localeconv function>--and use the information that it returns in your
853application's own formatting of currency amounts. However, you may well
854find that the information, voluminous and complex though it may be, still
855does not quite meet your requirements: currency formatting is a hard nut
13a2d996 856to crack.
5f05dabc 857
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858See also L<I18N::Langinfo> and C<CRNCYSTR>.
859
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860=head2 LC_TIME
861
39332f68 862Output produced by C<POSIX::strftime()>, which builds a formatted
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863human-readable date/time string, is affected by the current C<LC_TIME>
864locale. Thus, in a French locale, the output produced by the C<%B>
865format element (full month name) for the first month of the year would
5a964f20 866be "janvier". Here's how to get a list of long month names in the
5f05dabc
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867current locale:
868
869 use POSIX qw(strftime);
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870 for (0..11) {
871 $long_month_name[$_] =
872 strftime("%B", 0, 0, 0, 1, $_, 96);
5f05dabc
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873 }
874
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KW
875Note: C<use locale> isn't needed in this example: C<strftime()> is a POSIX
876function which uses the standard system-supplied C<libc> function that
877always obeys the current C<LC_TIME> locale.
5f05dabc 878
4bbcc6e8 879See also L<I18N::Langinfo> and C<ABDAY_1>..C<ABDAY_7>, C<DAY_1>..C<DAY_7>,
2a2bf5f4 880C<ABMON_1>..C<ABMON_12>, and C<ABMON_1>..C<ABMON_12>.
4bbcc6e8 881
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882=head2 Other categories
883
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884The remaining locale categories are not currently used by Perl itself.
885But again note that things Perl interacts with may use these, including
886extensions outside the standard Perl distribution, and by the
98a6f11e 887operating system and its utilities. Note especially that the string
888value of C<$!> and the error messages given by external utilities may
889be changed by C<LC_MESSAGES>. If you want to have portable error
265f5c4a 890codes, use C<%!>. See L<Errno>.
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891
892=head1 SECURITY
893
5a964f20 894Although the main discussion of Perl security issues can be found in
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895L<perlsec>, a discussion of Perl's locale handling would be incomplete
896if it did not draw your attention to locale-dependent security issues.
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897Locales--particularly on systems that allow unprivileged users to
898build their own locales--are untrustworthy. A malicious (or just plain
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899broken) locale can make a locale-aware application give unexpected
900results. Here are a few possibilities:
901
902=over 4
903
904=item *
905
906Regular expression checks for safe file names or mail addresses using
5a964f20 907C<\w> may be spoofed by an C<LC_CTYPE> locale that claims that
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908characters such as "E<gt>" and "|" are alphanumeric.
909
910=item *
911
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912String interpolation with case-mapping, as in, say, C<$dest =
913"C:\U$name.$ext">, may produce dangerous results if a bogus LC_CTYPE
914case-mapping table is in effect.
915
916=item *
917
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918A sneaky C<LC_COLLATE> locale could result in the names of students with
919"D" grades appearing ahead of those with "A"s.
920
921=item *
922
5a964f20 923An application that takes the trouble to use information in
14280422 924C<LC_MONETARY> may format debits as if they were credits and vice versa
5a964f20 925if that locale has been subverted. Or it might make payments in US
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926dollars instead of Hong Kong dollars.
927
928=item *
929
39332f68 930The date and day names in dates formatted by C<strftime()> could be
14280422 931manipulated to advantage by a malicious user able to subvert the
5a964f20 932C<LC_DATE> locale. ("Look--it says I wasn't in the building on
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933Sunday.")
934
935=back
936
937Such dangers are not peculiar to the locale system: any aspect of an
5a964f20 938application's environment which may be modified maliciously presents
14280422 939similar challenges. Similarly, they are not specific to Perl: any
5a964f20 940programming language that allows you to write programs that take
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941account of their environment exposes you to these issues.
942
5a964f20
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943Perl cannot protect you from all possibilities shown in the
944examples--there is no substitute for your own vigilance--but, when
14280422 945C<use locale> is in effect, Perl uses the tainting mechanism (see
5a964f20 946L<perlsec>) to mark string results that become locale-dependent, and
14280422 947which may be untrustworthy in consequence. Here is a summary of the
5a964f20 948tainting behavior of operators and functions that may be affected by
14280422
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949the locale:
950
951=over 4
952
551e1d92
RB
953=item *
954
955B<Comparison operators> (C<lt>, C<le>, C<ge>, C<gt> and C<cmp>):
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956
957Scalar true/false (or less/equal/greater) result is never tainted.
958
551e1d92
RB
959=item *
960
1d2ab946 961B<Case-mapping interpolation> (with C<\l>, C<\L>, C<\u>, C<\U>, or C<\F>)
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962
963Result string containing interpolated material is tainted if
66cbab2c 964C<use locale> (but not S<C<use locale ':not_characters'>>) is in effect.
e38874e2 965
551e1d92
RB
966=item *
967
968B<Matching operator> (C<m//>):
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969
970Scalar true/false result never tainted.
971
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972All subpatterns, either delivered as a list-context result or as C<$1>
973I<etc>., are tainted if C<use locale> (but not
974S<C<use locale ':not_characters'>>) is in effect, and the subpattern
975regular expression is matched case-insensitively (C</i>) or contains a
976locale-dependent construct. These constructs include C<\w>
977(to match an alphanumeric character), C<\W> (non-alphanumeric
978character), C<\s> (whitespace character), C<\S> (non whitespace
979character), and the POSIX character classes, such as C<[:alpha:]> (see
980L<perlrecharclass/POSIX Character Classes>).
981The matched-pattern variables, C<$&>, C<$`> (pre-match), C<$'>
982(post-match), and C<$+> (last match) also are tainted.
983(Note that currently there are some bugs where not everything that
984should be tainted gets tainted in all circumstances.)
14280422 985
551e1d92
RB
986=item *
987
988B<Substitution operator> (C<s///>):
14280422 989
e38874e2 990Has the same behavior as the match operator. Also, the left
66cbab2c
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991operand of C<=~> becomes tainted when C<use locale>
992(but not S<C<use locale ':not_characters'>>) is in effect if modified as
993a result of a substitution based on a regular
1d2ab946
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994expression match involving any of the things mentioned in the previous
995item, or of case-mapping, such as C<\l>, C<\L>,C<\u>, C<\U>, or C<\F>.
14280422 996
551e1d92
RB
997=item *
998
39332f68 999B<Output formatting functions> (C<printf()> and C<write()>):
14280422 1000
3cf03d68
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1001Results are never tainted because otherwise even output from print,
1002for example C<print(1/7)>, should be tainted if C<use locale> is in
1003effect.
14280422 1004
551e1d92
RB
1005=item *
1006
39332f68 1007B<Case-mapping functions> (C<lc()>, C<lcfirst()>, C<uc()>, C<ucfirst()>):
14280422 1008
66cbab2c
KW
1009Results are tainted if C<use locale> (but not
1010S<C<use locale ':not_characters'>>) is in effect.
14280422 1011
551e1d92
RB
1012=item *
1013
39332f68
KW
1014B<POSIX locale-dependent functions> (C<localeconv()>, C<strcoll()>,
1015C<strftime()>, C<strxfrm()>):
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1016
1017Results are never tainted.
1018
551e1d92
RB
1019=item *
1020
1d2ab946
KW
1021B<POSIX character class tests> (C<POSIX::isalnum()>,
1022C<POSIX::isalpha()>, C<POSIX::isdigit()>, C<POSIX::isgraph()>,
1023C<POSIX::islower()>, C<POSIX::isprint()>, C<POSIX::ispunct()>,
1024C<POSIX::isspace()>, C<POSIX::isupper()>, C<POSIX::isxdigit()>):
14280422
DD
1025
1026True/false results are never tainted.
1027
1028=back
1029
1030Three examples illustrate locale-dependent tainting.
1031The first program, which ignores its locale, won't run: a value taken
54310121 1032directly from the command line may not be used to name an output file
14280422
DD
1033when taint checks are enabled.
1034
1035 #/usr/local/bin/perl -T
1036 # Run with taint checking
1037
54310121 1038 # Command line sanity check omitted...
14280422
DD
1039 $tainted_output_file = shift;
1040
1041 open(F, ">$tainted_output_file")
3183d96c 1042 or warn "Open of $tainted_output_file failed: $!\n";
14280422
DD
1043
1044The program can be made to run by "laundering" the tainted value through
5a964f20
TC
1045a regular expression: the second example--which still ignores locale
1046information--runs, creating the file named on its command line
14280422
DD
1047if it can.
1048
1049 #/usr/local/bin/perl -T
1050
1051 $tainted_output_file = shift;
1052 $tainted_output_file =~ m%[\w/]+%;
1053 $untainted_output_file = $&;
1054
1055 open(F, ">$untainted_output_file")
1056 or warn "Open of $untainted_output_file failed: $!\n";
1057
5a964f20 1058Compare this with a similar but locale-aware program:
14280422
DD
1059
1060 #/usr/local/bin/perl -T
1061
1062 $tainted_output_file = shift;
1063 use locale;
1064 $tainted_output_file =~ m%[\w/]+%;
1065 $localized_output_file = $&;
1066
1067 open(F, ">$localized_output_file")
1068 or warn "Open of $localized_output_file failed: $!\n";
1069
1d2ab946 1070This third program fails to run because C<$&> is tainted: it is the result
5a964f20 1071of a match involving C<\w> while C<use locale> is in effect.
5f05dabc
PP
1072
1073=head1 ENVIRONMENT
1074
1075=over 12
1076
1077=item PERL_BADLANG
1078
14280422 1079A string that can suppress Perl's warning about failed locale settings
54310121 1080at startup. Failure can occur if the locale support in the operating
5a964f20 1081system is lacking (broken) in some way--or if you mistyped the name of
900bd440
JH
1082a locale when you set up your environment. If this environment
1083variable is absent, or has a value that does not evaluate to integer
1084zero--that is, "0" or ""-- Perl will complain about locale setting
1085failures.
5f05dabc 1086
14280422
DD
1087B<NOTE>: PERL_BADLANG only gives you a way to hide the warning message.
1088The message tells about some problem in your system's locale support,
1089and you should investigate what the problem is.
5f05dabc
PP
1090
1091=back
1092
1093The following environment variables are not specific to Perl: They are
39332f68 1094part of the standardized (ISO C, XPG4, POSIX 1.c) C<setlocale()> method
14280422 1095for controlling an application's opinion on data.
5f05dabc
PP
1096
1097=over 12
1098
1099=item LC_ALL
1100
5a964f20 1101C<LC_ALL> is the "override-all" locale environment variable. If
5f05dabc
PP
1102set, it overrides all the rest of the locale environment variables.
1103
528d65ad
JH
1104=item LANGUAGE
1105
1106B<NOTE>: C<LANGUAGE> is a GNU extension, it affects you only if you
1107are using the GNU libc. This is the case if you are using e.g. Linux.
e1020413 1108If you are using "commercial" Unixes you are most probably I<not>
22b6f60d
JH
1109using GNU libc and you can ignore C<LANGUAGE>.
1110
1111However, in the case you are using C<LANGUAGE>: it affects the
1112language of informational, warning, and error messages output by
1113commands (in other words, it's like C<LC_MESSAGES>) but it has higher
96090e4f 1114priority than C<LC_ALL>. Moreover, it's not a single value but
22b6f60d
JH
1115instead a "path" (":"-separated list) of I<languages> (not locales).
1116See the GNU C<gettext> library documentation for more information.
528d65ad 1117
5f05dabc
PP
1118=item LC_CTYPE
1119
1120In the absence of C<LC_ALL>, C<LC_CTYPE> chooses the character type
1121locale. In the absence of both C<LC_ALL> and C<LC_CTYPE>, C<LANG>
1122chooses the character type locale.
1123
1124=item LC_COLLATE
1125
14280422
DD
1126In the absence of C<LC_ALL>, C<LC_COLLATE> chooses the collation
1127(sorting) locale. In the absence of both C<LC_ALL> and C<LC_COLLATE>,
1128C<LANG> chooses the collation locale.
5f05dabc
PP
1129
1130=item LC_MONETARY
1131
14280422
DD
1132In the absence of C<LC_ALL>, C<LC_MONETARY> chooses the monetary
1133formatting locale. In the absence of both C<LC_ALL> and C<LC_MONETARY>,
1134C<LANG> chooses the monetary formatting locale.
5f05dabc
PP
1135
1136=item LC_NUMERIC
1137
1138In the absence of C<LC_ALL>, C<LC_NUMERIC> chooses the numeric format
1139locale. In the absence of both C<LC_ALL> and C<LC_NUMERIC>, C<LANG>
1140chooses the numeric format.
1141
1142=item LC_TIME
1143
14280422
DD
1144In the absence of C<LC_ALL>, C<LC_TIME> chooses the date and time
1145formatting locale. In the absence of both C<LC_ALL> and C<LC_TIME>,
1146C<LANG> chooses the date and time formatting locale.
5f05dabc
PP
1147
1148=item LANG
1149
14280422
DD
1150C<LANG> is the "catch-all" locale environment variable. If it is set, it
1151is used as the last resort after the overall C<LC_ALL> and the
5f05dabc
PP
1152category-specific C<LC_...>.
1153
1154=back
1155
7e4353e9
RGS
1156=head2 Examples
1157
1158The LC_NUMERIC controls the numeric output:
1159
ef3087ec
KW
1160 use locale;
1161 use POSIX qw(locale_h); # Imports setlocale() and the LC_ constants.
1162 setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
1163 printf "%g\n", 1.23; # If the "fr_FR" succeeded, probably shows 1,23.
7e4353e9 1164
39332f68 1165and also how strings are parsed by C<POSIX::strtod()> as numbers:
7e4353e9 1166
ef3087ec
KW
1167 use locale;
1168 use POSIX qw(locale_h strtod);
1169 setlocale(LC_NUMERIC, "de_DE") or die "Entschuldigung";
1170 my $x = strtod("2,34") + 5;
1171 print $x, "\n"; # Probably shows 7,34.
7e4353e9 1172
5f05dabc
PP
1173=head1 NOTES
1174
b960a36e
KW
1175=head2 String C<eval> and C<LC_NUMERIC>
1176
1177A string L<eval|perlfunc/eval EXPR> parses its expression as standard
1178Perl. It is therefore expecting the decimal point to be a dot. If
1179C<LC_NUMERIC> is set to have this be a comma instead, the parsing will
1180be confused, perhaps silently.
1181
1182 use locale;
1183 use POSIX qw(locale_h);
1184 setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
1185 my $a = 1.2;
1186 print eval "$a + 1.5";
1187 print "\n";
1188
1189prints C<13,5>. This is because in that locale, the comma is the
1190decimal point character. The C<eval> thus expands to:
1191
1192 eval "1,2 + 1.5"
1193
1194and the result is not what you likely expected. No warnings are
1195generated. If you do string C<eval>'s within the scope of
1196S<C<use locale>>, you should instead change the C<eval> line to do
1197something like:
1198
1199 print eval "no locale; $a + 1.5";
1200
1201This prints C<2.7>.
1202
5f05dabc
PP
1203=head2 Backward compatibility
1204
b0c42ed9 1205Versions of Perl prior to 5.004 B<mostly> ignored locale information,
5a964f20
TC
1206generally behaving as if something similar to the C<"C"> locale were
1207always in force, even if the program environment suggested otherwise
1208(see L<The setlocale function>). By default, Perl still behaves this
1209way for backward compatibility. If you want a Perl application to pay
1210attention to locale information, you B<must> use the S<C<use locale>>
062ca197
KW
1211pragma (see L<The use locale pragma>) or, in the unlikely event
1212that you want to do so for just pattern matching, the
70709c68
KW
1213C</l> regular expression modifier (see L<perlre/Character set
1214modifiers>) to instruct it to do so.
b0c42ed9
JH
1215
1216Versions of Perl from 5.002 to 5.003 did use the C<LC_CTYPE>
5a964f20
TC
1217information if available; that is, C<\w> did understand what
1218were the letters according to the locale environment variables.
b0c42ed9
JH
1219The problem was that the user had no control over the feature:
1220if the C library supported locales, Perl used them.
1221
1222=head2 I18N:Collate obsolete
1223
5a964f20 1224In versions of Perl prior to 5.004, per-locale collation was possible
b0c42ed9
JH
1225using the C<I18N::Collate> library module. This module is now mildly
1226obsolete and should be avoided in new applications. The C<LC_COLLATE>
1227functionality is now integrated into the Perl core language: One can
1228use locale-specific scalar data completely normally with C<use locale>,
1229so there is no longer any need to juggle with the scalar references of
1230C<I18N::Collate>.
5f05dabc 1231
14280422 1232=head2 Sort speed and memory use impacts
5f05dabc
PP
1233
1234Comparing and sorting by locale is usually slower than the default
14280422
DD
1235sorting; slow-downs of two to four times have been observed. It will
1236also consume more memory: once a Perl scalar variable has participated
1237in any string comparison or sorting operation obeying the locale
1238collation rules, it will take 3-15 times more memory than before. (The
1239exact multiplier depends on the string's contents, the operating system
1240and the locale.) These downsides are dictated more by the operating
1241system's implementation of the locale system than by Perl.
5f05dabc 1242
5f05dabc
PP
1243=head2 Freely available locale definitions
1244
66cbab2c
KW
1245The Unicode CLDR project extracts the POSIX portion of many of its
1246locales, available at
1247
1248 http://unicode.org/Public/cldr/latest/
1249
08d7a6b2
LB
1250There is a large collection of locale definitions at:
1251
1252 http://std.dkuug.dk/i18n/WG15-collection/locales/
1253
1254You should be aware that it is
14280422 1255unsupported, and is not claimed to be fit for any purpose. If your
5a964f20 1256system allows installation of arbitrary locales, you may find the
14280422
DD
1257definitions useful as they are, or as a basis for the development of
1258your own locales.
5f05dabc 1259
14280422 1260=head2 I18n and l10n
5f05dabc 1261
b0c42ed9
JH
1262"Internationalization" is often abbreviated as B<i18n> because its first
1263and last letters are separated by eighteen others. (You may guess why
1264the internalin ... internaliti ... i18n tends to get abbreviated.) In
1265the same way, "localization" is often abbreviated to B<l10n>.
14280422
DD
1266
1267=head2 An imperfect standard
1268
1269Internationalization, as defined in the C and POSIX standards, can be
1270criticized as incomplete, ungainly, and having too large a granularity.
1271(Locales apply to a whole process, when it would arguably be more useful
1272to have them apply to a single thread, window group, or whatever.) They
1273also have a tendency, like standards groups, to divide the world into
1274nations, when we all know that the world can equally well be divided
e199995e 1275into bankers, bikers, gamers, and so on.
5f05dabc 1276
b310b053
JH
1277=head1 Unicode and UTF-8
1278
7ee2ae1e 1279The support of Unicode is new starting from Perl version v5.6, and more fully
1d2ab946 1280implemented in versions v5.8 and later. See L<perluniintro>. It is
66cbab2c 1281strongly recommended that when combining Unicode and locale (starting in
7ee2ae1e 1282v5.16), you use
66cbab2c
KW
1283
1284 use locale ':not_characters';
1285
1286When this form of the pragma is used, only the non-character portions of
1287locales are used by Perl, for example C<LC_NUMERIC>. Perl assumes that
1288you have translated all the characters it is to operate on into Unicode
1289(actually the platform's native character set (ASCII or EBCDIC) plus
1290Unicode). For data in files, this can conveniently be done by also
1291specifying
1292
1293 use open ':locale';
1294
1295This pragma arranges for all inputs from files to be translated into
1296Unicode from the current locale as specified in the environment (see
1297L</ENVIRONMENT>), and all outputs to files to be translated back
1298into the locale. (See L<open>). On a per-filehandle basis, you can
1299instead use the L<PerlIO::locale> module, or the L<Encode::Locale>
1300module, both available from CPAN. The latter module also has methods to
1301ease the handling of C<ARGV> and environment variables, and can be used
1302on individual strings. Also, if you know that all your locales will be
1303UTF-8, as many are these days, you can use the L<B<-C>|perlrun/-C>
1304command line switch.
1305
1306This form of the pragma allows essentially seamless handling of locales
1307with Unicode. The collation order will be Unicode's. It is strongly
1308recommended that when you need to order and sort strings that you use
1309the standard module L<Unicode::Collate> which gives much better results
1310in many instances than you can get with the old-style locale handling.
1311
7ee2ae1e 1312For pre-v5.16 Perls, or if you use the locale pragma without the
66cbab2c
KW
1313C<:not_characters> parameter, Perl tries to work with both Unicode and
1314locales--but there are problems.
1315
1316Perl does not handle multi-byte locales in this case, such as have been
1317used for various
dc4bfc4b
KW
1318Asian languages, such as Big5 or Shift JIS. However, the increasingly
1319common multi-byte UTF-8 locales, if properly implemented, may work
1320reasonably well (depending on your C library implementation) in this
1321form of the locale pragma, simply because both
1322they and Perl store characters that take up multiple bytes the same way.
1323However, some, if not most, C library implementations may not process
1324the characters in the upper half of the Latin-1 range (128 - 255)
1325properly under LC_CTYPE. To see if a character is a particular type
1326under a locale, Perl uses the functions like C<isalnum()>. Your C
1327library may not work for UTF-8 locales with those functions, instead
1328only working under the newer wide library functions like C<iswalnum()>.
e199995e
KW
1329
1330Perl generally takes the tack to use locale rules on code points that can fit
66cbab2c
KW
1331in a single byte, and Unicode rules for those that can't (though this
1332isn't uniformly applied, see the note at the end of this section). This
1333prevents many problems in locales that aren't UTF-8. Suppose the locale
1334is ISO8859-7, Greek. The character at 0xD7 there is a capital Chi. But
1335in the ISO8859-1 locale, Latin1, it is a multiplication sign. The POSIX
1336regular expression character class C<[[:alpha:]]> will magically match
13370xD7 in the Greek locale but not in the Latin one.
e199995e 1338
1d2ab946 1339However, there are places where this breaks down. Certain Perl constructs are
b4ffc3db
TC
1340for Unicode only, such as C<\p{Alpha}>. They assume that 0xD7 always has its
1341Unicode meaning (or the equivalent on EBCDIC platforms). Since Latin1 is a
1342subset of Unicode and 0xD7 is the multiplication sign in both Latin1 and
1343Unicode, C<\p{Alpha}> will never match it, regardless of locale. A similar
1344issue occurs with C<\N{...}>. It is therefore a bad idea to use C<\p{}> or
66cbab2c
KW
1345C<\N{}> under plain C<use locale>--I<unless> you can guarantee that the
1346locale will be a ISO8859-1. Use POSIX character classes instead.
1347
1348Another problem with this approach is that operations that cross the
1349single byte/multiple byte boundary are not well-defined, and so are
1350disallowed. (This boundary is between the codepoints at 255/256.).
1351For example, lower casing LATIN CAPITAL LETTER Y WITH DIAERESIS (U+0178)
1352should return LATIN SMALL LETTER Y WITH DIAERESIS (U+00FF). But in the
1353Greek locale, for example, there is no character at 0xFF, and Perl
1354has no way of knowing what the character at 0xFF is really supposed to
1355represent. Thus it disallows the operation. In this mode, the
1356lowercase of U+0178 is itself.
1357
1358The same problems ensue if you enable automatic UTF-8-ification of your
e199995e 1359standard file handles, default C<open()> layer, and C<@ARGV> on non-ISO8859-1,
b4ffc3db
TC
1360non-UTF-8 locales (by using either the B<-C> command line switch or the
1361C<PERL_UNICODE> environment variable; see L<perlrun>).
1362Things are read in as UTF-8, which would normally imply a Unicode
1363interpretation, but the presence of a locale causes them to be interpreted
1364in that locale instead. For example, a 0xD7 code point in the Unicode
1365input, which should mean the multiplication sign, won't be interpreted by
66cbab2c 1366Perl that way under the Greek locale. This is not a problem
b4ffc3db 1367I<provided> you make certain that all locales will always and only be either
66cbab2c 1368an ISO8859-1, or, if you don't have a deficient C library, a UTF-8 locale.
b4ffc3db 1369
1d2ab946
KW
1370Still another problem is that this approach can lead to two code
1371points meaning the same character. Thus in a Greek locale, both U+03A7
1372and U+00D7 are GREEK CAPITAL LETTER CHI.
1373
b4ffc3db
TC
1374Vendor locales are notoriously buggy, and it is difficult for Perl to test
1375its locale-handling code because this interacts with code that Perl has no
1376control over; therefore the locale-handling code in Perl may be buggy as
66cbab2c
KW
1377well. (However, the Unicode-supplied locales should be better, and
1378there is a feed back mechanism to correct any problems. See
1379L</Freely available locale definitions>.)
1380
7ee2ae1e 1381If you have Perl v5.16, the problems mentioned above go away if you use
66cbab2c 1382the C<:not_characters> parameter to the locale pragma (except for vendor
7ee2ae1e 1383bugs in the non-character portions). If you don't have v5.16, and you
66cbab2c
KW
1384I<do> have locales that work, using them may be worthwhile for certain
1385specific purposes, as long as you keep in mind the gotchas already
1386mentioned. For example, if the collation for your locales works, it
1387runs faster under locales than under L<Unicode::Collate>; and you gain
1388access to such things as the local currency symbol and the names of the
7ee2ae1e 1389months and days of the week. (But to hammer home the point, in v5.16,
66cbab2c
KW
1390you get this access without the downsides of locales by using the
1391C<:not_characters> form of the pragma.)
1392
1393Note: The policy of using locale rules for code points that can fit in a
1394byte, and Unicode rules for those that can't is not uniformly applied.
7ee2ae1e 1395Pre-v5.12, it was somewhat haphazard; in v5.12 it was applied fairly
66cbab2c 1396consistently to regular expression matching except for bracketed
7ee2ae1e
KW
1397character classes; in v5.14 it was extended to all regex matches; and in
1398v5.16 to the casing operations such as C<"\L"> and C<uc()>. For
66cbab2c
KW
1399collation, in all releases, the system's C<strxfrm()> function is called,
1400and whatever it does is what you get.
b310b053 1401
5f05dabc
PP
1402=head1 BUGS
1403
1404=head2 Broken systems
1405
5a964f20 1406In certain systems, the operating system's locale support
2bdf8add 1407is broken and cannot be fixed or used by Perl. Such deficiencies can
b4ffc3db 1408and will result in mysterious hangs and/or Perl core dumps when
2bdf8add 1409C<use locale> is in effect. When confronted with such a system,
7f2de2d2 1410please report in excruciating detail to <F<perlbug@perl.org>>, and
b4ffc3db 1411also contact your vendor: bug fixes may exist for these problems
2bdf8add 1412in your operating system. Sometimes such bug fixes are called an
83fb1bf0
KW
1413operating system upgrade. If you have the source for Perl, include in
1414the perlbug email the output of the test described above in L</Testing
1415for broken locales>.
5f05dabc
PP
1416
1417=head1 SEE ALSO
1418
b310b053
JH
1419L<I18N::Langinfo>, L<perluniintro>, L<perlunicode>, L<open>,
1420L<POSIX/isalnum>, L<POSIX/isalpha>,
4bbcc6e8
JH
1421L<POSIX/isdigit>, L<POSIX/isgraph>, L<POSIX/islower>,
1422L<POSIX/isprint>, L<POSIX/ispunct>, L<POSIX/isspace>,
1423L<POSIX/isupper>, L<POSIX/isxdigit>, L<POSIX/localeconv>,
1424L<POSIX/setlocale>, L<POSIX/strcoll>, L<POSIX/strftime>,
1425L<POSIX/strtod>, L<POSIX/strxfrm>.
5f05dabc 1426
ccd65d51
KW
1427For special considerations when Perl is embedded in a C program,
1428see L<perlembed/Using embedded Perl with POSIX locales>.
1429
5f05dabc
PP
1430=head1 HISTORY
1431
b0c42ed9 1432Jarkko Hietaniemi's original F<perli18n.pod> heavily hacked by Dominic
5a964f20 1433Dunlop, assisted by the perl5-porters. Prose worked over a bit by
c052850d 1434Tom Christiansen, and updated by Perl 5 porters.