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1=encoding utf8
2
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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
185initialized to the C locale (mentioned under L<Finding locales>).
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186If there is no valid environment, the current locale is whatever the
187system default has been set to. It is likely, but not necessarily, the
188"C" locale.
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189
190The operations that are affected by locale are:
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191
192=over 4
193
4c9b78f4 194=item B<Not within the scope of any C<"use locale"> variant>
b960a36e 195
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196Only operations originating outside Perl should be affected.
197
198The variable L<$!|perlvar/$ERRNO> (and its synonyms C<$ERRNO> and
199C<$OS_ERROR>) when used as strings always are in terms of the current
200locale.
201
202The current locale is also used when going outside of Perl with
203operations like L<system()|perlfunc/system LIST> or
204L<qxE<sol>E<sol>|perlop/qxE<sol>STRINGE<sol>>, if those operations are
205locale-sensitive.
206
207Also Perl gives access to various C library functions through the
208L<POSIX> module. Some of those functions are always affected by the
209current locale. For example, C<POSIX::strftime()> uses C<LC_TIME>;
210C<POSIX::strtod()> uses C<LC_NUMERIC>; C<POSIX::strcoll()> and
211C<POSIX::strxfrm()> use C<LC_COLLATE>; and character classification
212functions like C<POSIX::isalnum()> use C<LC_CTYPE>. All such functions
213will behave according to the current underlying locale, even if that
214isn't exposed to Perl space.
215
216And, certain Perl operations that are set-up within the scope of a
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217C<use locale> variant retain that effect even outside the scope.
218These include:
219
220=over 4
221
222=item *
223
224The output format of a L<write()|perlfunc/write> is determined by an
225earlier format declaration (L<perlfunc/format>), so whether or not the
226output is affected by locale is determined by if the C<format()> is
227within the scope of a C<use locale> variant, not whether the C<write()>
228is.
229
230=item *
231
232Regular expression patterns can be compiled using
233L<qrE<sol>E<sol>|perlop/qrE<sol>STRINGE<sol>msixpodual> with actual
234matching deferred to later. Again, it is whether or not the compilation
235was done within the scope of C<use locale> that determines the match
236behavior, not if the matches are done within such a scope or not.
237
238=back
239
4c9b78f4 240=item B<Under C<"use locale ':not_characters';">>
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241
242=over 4
243
244=item *
245
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246All the non-Perl operations.
247
248=item *
249
250B<Format declarations> (L<perlfunc/format>) and hence any subsequent
251C<write()>s use C<LC_NUMERIC>.
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252
253=item *
254
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255B<stringification and output> use C<LC_NUMERIC>.
256These include the results of
257C<print()>,
258C<printf()>,
259C<say()>,
260and
261C<sprintf()>.
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262
263=back
264
265=for comment
266The nbsp below makes this look better
267
268E<160>
269
4c9b78f4 270=item B<Under just plain C<"use locale";>>
66cbab2c 271
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272=over 4
273
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274=item *
275
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276All the above operations
277
278=item *
279
280B<The comparison operators> (C<lt>, C<le>, C<cmp>, C<ge>, and C<gt>) use
39332f68 281C<LC_COLLATE>. C<sort()> is also affected if used without an
5a964f20 282explicit comparison function, because it uses C<cmp> by default.
14280422 283
5a964f20 284B<Note:> C<eq> and C<ne> are unaffected by locale: they always
de108802 285perform a char-by-char comparison of their scalar operands. What's
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286more, if C<cmp> finds that its operands are equal according to the
287collation sequence specified by the current locale, it goes on to
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288perform a char-by-char comparison, and only returns I<0> (equal) if the
289operands are char-for-char identical. If you really want to know whether
5a964f20 290two strings--which C<eq> and C<cmp> may consider different--are equal
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291as far as collation in the locale is concerned, see the discussion in
292L<Category LC_COLLATE: Collation>.
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293
294=item *
295
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296B<Regular expressions and case-modification functions> (C<uc()>, C<lc()>,
297C<ucfirst()>, and C<lcfirst()>) use C<LC_CTYPE>
5f05dabc 298
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299=back
300
66cbab2c 301=back
5f05dabc 302
5a964f20 303The default behavior is restored with the S<C<no locale>> pragma, or
ef3087ec 304upon reaching the end of the block enclosing C<use locale>.
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305Note that C<use locale> and C<use locale ':not_characters'> may be
306nested, and that what is in effect within an inner scope will revert to
307the outer scope's rules at the end of the inner scope.
5f05dabc 308
5a964f20 309The string result of any operation that uses locale
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310information is tainted, as it is possible for a locale to be
311untrustworthy. See L<"SECURITY">.
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312
313=head2 The setlocale function
314
14280422 315You can switch locales as often as you wish at run time with the
39332f68 316C<POSIX::setlocale()> function:
5f05dabc 317
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318 # Import locale-handling tool set from POSIX module.
319 # This example uses: setlocale -- the function call
320 # LC_CTYPE -- explained below
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321 # (Showing the testing for success/failure of operations is
322 # omitted in these examples to avoid distracting from the main
dfcc8045 323 # point
6ea81ccf 324
5f05dabc 325 use POSIX qw(locale_h);
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326 use locale;
327 my $old_locale;
5f05dabc 328
14280422 329 # query and save the old locale
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330 $old_locale = setlocale(LC_CTYPE);
331
332 setlocale(LC_CTYPE, "fr_CA.ISO8859-1");
333 # LC_CTYPE now in locale "French, Canada, codeset ISO 8859-1"
334
335 setlocale(LC_CTYPE, "");
336 # LC_CTYPE now reset to default defined by LC_ALL/LC_CTYPE/LANG
337 # environment variables. See below for documentation.
338
339 # restore the old locale
340 setlocale(LC_CTYPE, $old_locale);
341
39332f68 342The first argument of C<setlocale()> gives the B<category>, the second the
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343B<locale>. The category tells in what aspect of data processing you
344want to apply locale-specific rules. Category names are discussed in
66cbab2c 345L</LOCALE CATEGORIES> and L</"ENVIRONMENT">. The locale is the name of a
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346collection of customization information corresponding to a particular
347combination of language, country or territory, and codeset. Read on for
348hints on the naming of locales: not all systems name locales as in the
349example.
350
39332f68 351If no second argument is provided and the category is something other
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352than LC_ALL, the function returns a string naming the current locale
353for the category. You can use this value as the second argument in a
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354subsequent call to C<setlocale()>, B<but> on some platforms the string
355is opaque, not something that most people would be able to decipher as
356to what locale it means.
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357
358If no second argument is provided and the category is LC_ALL, the
359result is implementation-dependent. It may be a string of
c052850d 360concatenated locale names (separator also implementation-dependent)
39332f68 361or a single locale name. Please consult your L<setlocale(3)> man page for
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362details.
363
364If a second argument is given and it corresponds to a valid locale,
365the locale for the category is set to that value, and the function
366returns the now-current locale value. You can then use this in yet
39332f68 367another call to C<setlocale()>. (In some implementations, the return
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368value may sometimes differ from the value you gave as the second
369argument--think of it as an alias for the value you gave.)
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370
371As the example shows, if the second argument is an empty string, the
372category's locale is returned to the default specified by the
373corresponding environment variables. Generally, this results in a
5a964f20 374return to the default that was in force when Perl started up: changes
54310121 375to the environment made by the application after startup may or may not
5a964f20 376be noticed, depending on your system's C library.
5f05dabc 377
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378Note that Perl ignores the current C<LC_CTYPE> and C<LC_COLLATE> locales
379within the scope of a C<use locale ':not_characters'>.
380
f170b852 381If C<set_locale()> fails for some reason (for example, an attempt to set
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382to a locale unknown to the system), the locale for the category is not
383changed, and the function returns C<undef>.
384
2619d284 385
39332f68 386For further information about the categories, consult L<setlocale(3)>.
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387
388=head2 Finding locales
389
39332f68 390For locales available in your system, consult also L<setlocale(3)> to
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391see whether it leads to the list of available locales (search for the
392I<SEE ALSO> section). If that fails, try the following command lines:
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393
394 locale -a
395
396 nlsinfo
397
398 ls /usr/lib/nls/loc
399
400 ls /usr/lib/locale
401
402 ls /usr/lib/nls
403
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404 ls /usr/share/locale
405
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406and see whether they list something resembling these
407
2bdf8add 408 en_US.ISO8859-1 de_DE.ISO8859-1 ru_RU.ISO8859-5
502a173a 409 en_US.iso88591 de_DE.iso88591 ru_RU.iso88595
2bdf8add 410 en_US de_DE ru_RU
14280422 411 en de ru
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412 english german russian
413 english.iso88591 german.iso88591 russian.iso88595
502a173a 414 english.roman8 russian.koi8r
5f05dabc 415
39332f68 416Sadly, even though the calling interface for C<setlocale()> has been
528d65ad 417standardized, names of locales and the directories where the
5a964f20 418configuration resides have not been. The basic form of the name is
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419I<language_territory>B<.>I<codeset>, but the latter parts after
420I<language> are not always present. The I<language> and I<country>
421are usually from the standards B<ISO 3166> and B<ISO 639>, the
422two-letter abbreviations for the countries and the languages of the
423world, respectively. The I<codeset> part often mentions some B<ISO
4248859> character set, the Latin codesets. For example, C<ISO 8859-1>
425is the so-called "Western European codeset" that can be used to encode
426most Western European languages adequately. Again, there are several
427ways to write even the name of that one standard. Lamentably.
5f05dabc 428
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429Two special locales are worth particular mention: "C" and "POSIX".
430Currently these are effectively the same locale: the difference is
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431mainly that the first one is defined by the C standard, the second by
432the POSIX standard. They define the B<default locale> in which
14280422 433every program starts in the absence of locale information in its
5a964f20 434environment. (The I<default> default locale, if you will.) Its language
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435is (American) English and its character codeset ASCII or, rarely, a
436superset thereof (such as the "DEC Multinational Character Set
437(DEC-MCS)"). B<Warning>. The C locale delivered by some vendors
438may not actually exactly match what the C standard calls for. So
439beware.
5f05dabc 440
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441B<NOTE>: Not all systems have the "POSIX" locale (not all systems are
442POSIX-conformant), so use "C" when you need explicitly to specify this
443default locale.
5f05dabc 444
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445=head2 LOCALE PROBLEMS
446
5a964f20 447You may encounter the following warning message at Perl startup:
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448
449 perl: warning: Setting locale failed.
450 perl: warning: Please check that your locale settings:
451 LC_ALL = "En_US",
452 LANG = (unset)
453 are supported and installed on your system.
454 perl: warning: Falling back to the standard locale ("C").
455
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456This means that your locale settings had LC_ALL set to "En_US" and
457LANG exists but has no value. Perl tried to believe you but could not.
458Instead, Perl gave up and fell back to the "C" locale, the default locale
459that is supposed to work no matter what. This usually means your locale
460settings were wrong, they mention locales your system has never heard
461of, or the locale installation in your system has problems (for example,
462some system files are broken or missing). There are quick and temporary
463fixes to these problems, as well as more thorough and lasting fixes.
3e6e419a 464
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465=head2 Testing for broken locales
466
467If you are building Perl from source, the Perl test suite file
468F<lib/locale.t> can be used to test the locales on your system.
469Setting the environment variable C<PERL_DEBUG_FULL_TEST> to 1
470will cause it to output detailed results. For example, on Linux, you
471could say
472
473 PERL_DEBUG_FULL_TEST=1 ./perl -T lib/locale.t > locale.log 2>&1
474
475Besides many other tests, it will test every locale it finds on your
476system to see if they conform to the POSIX standard. If any have
477errors, it will include a summary near the end of the output of which
478locales passed all its tests, and which failed, and why.
479
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480=head2 Temporarily fixing locale problems
481
5a964f20 482The two quickest fixes are either to render Perl silent about any
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483locale inconsistencies or to run Perl under the default locale "C".
484
485Perl's moaning about locale problems can be silenced by setting the
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486environment variable PERL_BADLANG to a zero value, for example "0".
487This method really just sweeps the problem under the carpet: you tell
488Perl to shut up even when Perl sees that something is wrong. Do not
489be surprised if later something locale-dependent misbehaves.
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490
491Perl can be run under the "C" locale by setting the environment
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492variable LC_ALL to "C". This method is perhaps a bit more civilized
493than the PERL_BADLANG approach, but setting LC_ALL (or
494other locale variables) may affect other programs as well, not just
495Perl. In particular, external programs run from within Perl will see
3e6e419a 496these changes. If you make the new settings permanent (read on), all
f979aebc 497programs you run see the changes. See L<"ENVIRONMENT"> for
5a964f20 498the full list of relevant environment variables and L<USING LOCALES>
e05ffc7d 499for their effects in Perl. Effects in other programs are
5a964f20 500easily deducible. For example, the variable LC_COLLATE may well affect
b432a672 501your B<sort> program (or whatever the program that arranges "records"
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502alphabetically in your system is called).
503
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504You can test out changing these variables temporarily, and if the
505new settings seem to help, put those settings into your shell startup
506files. Consult your local documentation for the exact details. For in
507Bourne-like shells (B<sh>, B<ksh>, B<bash>, B<zsh>):
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508
509 LC_ALL=en_US.ISO8859-1
510 export LC_ALL
511
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512This assumes that we saw the locale "en_US.ISO8859-1" using the commands
513discussed above. We decided to try that instead of the above faulty
514locale "En_US"--and in Cshish shells (B<csh>, B<tcsh>)
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515
516 setenv LC_ALL en_US.ISO8859-1
c47ff5f1 517
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518or if you have the "env" application you can do in any shell
519
520 env LC_ALL=en_US.ISO8859-1 perl ...
521
5a964f20 522If you do not know what shell you have, consult your local
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523helpdesk or the equivalent.
524
525=head2 Permanently fixing locale problems
526
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527The slower but superior fixes are when you may be able to yourself
528fix the misconfiguration of your own environment variables. The
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529mis(sing)configuration of the whole system's locales usually requires
530the help of your friendly system administrator.
531
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532First, see earlier in this document about L<Finding locales>. That tells
533how to find which locales are really supported--and more importantly,
534installed--on your system. In our example error message, environment
535variables affecting the locale are listed in the order of decreasing
536importance (and unset variables do not matter). Therefore, having
537LC_ALL set to "En_US" must have been the bad choice, as shown by the
538error message. First try fixing locale settings listed first.
3e6e419a 539
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540Second, if using the listed commands you see something B<exactly>
541(prefix matches do not count and case usually counts) like "En_US"
542without the quotes, then you should be okay because you are using a
543locale name that should be installed and available in your system.
4a4eefd0 544In this case, see L<Permanently fixing your system's locale configuration>.
3e6e419a 545
4a4eefd0 546=head2 Permanently fixing your system's locale configuration
3e6e419a 547
5a964f20 548This is when you see something like:
3e6e419a
JH
549
550 perl: warning: Please check that your locale settings:
551 LC_ALL = "En_US",
552 LANG = (unset)
553 are supported and installed on your system.
554
555but then cannot see that "En_US" listed by the above-mentioned
5a964f20
TC
556commands. You may see things like "en_US.ISO8859-1", but that isn't
557the same. In this case, try running under a locale
558that you can list and which somehow matches what you tried. The
3e6e419a 559rules for matching locale names are a bit vague because
e05ffc7d 560standardization is weak in this area. See again the
13a2d996 561L<Finding locales> about general rules.
3e6e419a 562
b687b08b 563=head2 Fixing system locale configuration
3e6e419a 564
5a964f20
TC
565Contact a system administrator (preferably your own) and report the exact
566error message you get, and ask them to read this same documentation you
567are now reading. They should be able to check whether there is something
568wrong with the locale configuration of the system. The L<Finding locales>
569section is unfortunately a bit vague about the exact commands and places
570because these things are not that standardized.
3e6e419a 571
5f05dabc
PP
572=head2 The localeconv function
573
39332f68 574The C<POSIX::localeconv()> function allows you to get particulars of the
14280422
DD
575locale-dependent numeric formatting information specified by the current
576C<LC_NUMERIC> and C<LC_MONETARY> locales. (If you just want the name of
39332f68 577the current locale for a particular category, use C<POSIX::setlocale()>
5a964f20 578with a single parameter--see L<The setlocale function>.)
5f05dabc
PP
579
580 use POSIX qw(locale_h);
5f05dabc
PP
581
582 # Get a reference to a hash of locale-dependent info
583 $locale_values = localeconv();
584
585 # Output sorted list of the values
586 for (sort keys %$locale_values) {
14280422 587 printf "%-20s = %s\n", $_, $locale_values->{$_}
5f05dabc
PP
588 }
589
39332f68 590C<localeconv()> takes no arguments, and returns B<a reference to> a hash.
5a964f20 591The keys of this hash are variable names for formatting, such as
502a173a 592C<decimal_point> and C<thousands_sep>. The values are the
cea6626f 593corresponding, er, values. See L<POSIX/localeconv> for a longer
502a173a
JH
594example listing the categories an implementation might be expected to
595provide; some provide more and others fewer. You don't need an
39332f68 596explicit C<use locale>, because C<localeconv()> always observes the
502a173a 597current locale.
5f05dabc 598
5a964f20
TC
599Here's a simple-minded example program that rewrites its command-line
600parameters as integers correctly formatted in the current locale:
5f05dabc 601
ef3087ec
KW
602 use POSIX qw(locale_h);
603
604 # Get some of locale's numeric formatting parameters
605 my ($thousands_sep, $grouping) =
606 @{localeconv()}{'thousands_sep', 'grouping'};
607
608 # Apply defaults if values are missing
609 $thousands_sep = ',' unless $thousands_sep;
610
611 # grouping and mon_grouping are packed lists
612 # of small integers (characters) telling the
613 # grouping (thousand_seps and mon_thousand_seps
614 # being the group dividers) of numbers and
615 # monetary quantities. The integers' meanings:
616 # 255 means no more grouping, 0 means repeat
617 # the previous grouping, 1-254 means use that
618 # as the current grouping. Grouping goes from
619 # right to left (low to high digits). In the
620 # below we cheat slightly by never using anything
621 # else than the first grouping (whatever that is).
622 if ($grouping) {
623 @grouping = unpack("C*", $grouping);
624 } else {
625 @grouping = (3);
626 }
627
628 # Format command line params for current locale
629 for (@ARGV) {
630 $_ = int; # Chop non-integer part
631 1 while
632 s/(\d)(\d{$grouping[0]}($|$thousands_sep))/$1$thousands_sep$2/;
633 print "$_";
634 }
635 print "\n";
5f05dabc 636
74c76037 637=head2 I18N::Langinfo
4bbcc6e8
JH
638
639Another interface for querying locale-dependent information is the
39332f68 640C<I18N::Langinfo::langinfo()> function, available at least in Unix-like
4bbcc6e8
JH
641systems and VMS.
642
39332f68
KW
643The following example will import the C<langinfo()> function itself and
644three constants to be used as arguments to C<langinfo()>: a constant for
74c76037
JH
645the abbreviated first day of the week (the numbering starts from
646Sunday = 1) and two more constants for the affirmative and negative
647answers for a yes/no question in the current locale.
4bbcc6e8 648
74c76037 649 use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
4bbcc6e8 650
ef3087ec
KW
651 my ($abday_1, $yesstr, $nostr)
652 = map { langinfo } qw(ABDAY_1 YESSTR NOSTR);
4bbcc6e8 653
74c76037 654 print "$abday_1? [$yesstr/$nostr] ";
4bbcc6e8 655
74c76037
JH
656In other words, in the "C" (or English) locale the above will probably
657print something like:
658
e05ffc7d 659 Sun? [yes/no]
4bbcc6e8
JH
660
661See L<I18N::Langinfo> for more information.
662
5f05dabc
PP
663=head1 LOCALE CATEGORIES
664
5a964f20
TC
665The following subsections describe basic locale categories. Beyond these,
666some combination categories allow manipulation of more than one
667basic category at a time. See L<"ENVIRONMENT"> for a discussion of these.
5f05dabc
PP
668
669=head2 Category LC_COLLATE: Collation
670
66cbab2c
KW
671In the scope of S<C<use locale>> (but not a
672C<use locale ':not_characters'>), Perl looks to the C<LC_COLLATE>
5a964f20 673environment variable to determine the application's notions on collation
b4ffc3db
TC
674(ordering) of characters. For example, "b" follows "a" in Latin
675alphabets, but where do "E<aacute>" and "E<aring>" belong? And while
f87fa335 676"color" follows "chocolate" in English, what about in traditional Spanish?
5f05dabc 677
60f0fa02
JH
678The following collations all make sense and you may meet any of them
679if you "use locale".
680
681 A B C D E a b c d e
35316ca3 682 A a B b C c D d E e
60f0fa02
JH
683 a A b B c C d D e E
684 a b c d e A B C D E
685
f1cbbd6e 686Here is a code snippet to tell what "word"
5a964f20 687characters are in the current locale, in that locale's order:
5f05dabc
PP
688
689 use locale;
35316ca3 690 print +(sort grep /\w/, map { chr } 0..255), "\n";
5f05dabc 691
14280422
DD
692Compare this with the characters that you see and their order if you
693state explicitly that the locale should be ignored:
5f05dabc
PP
694
695 no locale;
35316ca3 696 print +(sort grep /\w/, map { chr } 0..255), "\n";
5f05dabc
PP
697
698This machine-native collation (which is what you get unless S<C<use
699locale>> has appeared earlier in the same block) must be used for
700sorting raw binary data, whereas the locale-dependent collation of the
b0c42ed9 701first example is useful for natural text.
5f05dabc 702
14280422
DD
703As noted in L<USING LOCALES>, C<cmp> compares according to the current
704collation locale when C<use locale> is in effect, but falls back to a
de108802 705char-by-char comparison for strings that the locale says are equal. You
39332f68 706can use C<POSIX::strcoll()> if you don't want this fall-back:
14280422
DD
707
708 use POSIX qw(strcoll);
709 $equal_in_locale =
710 !strcoll("space and case ignored", "SpaceAndCaseIgnored");
711
39332f68 712C<$equal_in_locale> will be true if the collation locale specifies a
5a964f20 713dictionary-like ordering that ignores space characters completely and
9e3a2af8 714which folds case.
14280422 715
5a964f20 716If you have a single string that you want to check for "equality in
14280422 717locale" against several others, you might think you could gain a little
39332f68 718efficiency by using C<POSIX::strxfrm()> in conjunction with C<eq>:
14280422
DD
719
720 use POSIX qw(strxfrm);
721 $xfrm_string = strxfrm("Mixed-case string");
722 print "locale collation ignores spaces\n"
723 if $xfrm_string eq strxfrm("Mixed-casestring");
724 print "locale collation ignores hyphens\n"
725 if $xfrm_string eq strxfrm("Mixedcase string");
726 print "locale collation ignores case\n"
727 if $xfrm_string eq strxfrm("mixed-case string");
728
39332f68 729C<strxfrm()> takes a string and maps it into a transformed string for use
de108802 730in char-by-char comparisons against other transformed strings during
14280422 731collation. "Under the hood", locale-affected Perl comparison operators
39332f68
KW
732call C<strxfrm()> for both operands, then do a char-by-char
733comparison of the transformed strings. By calling C<strxfrm()> explicitly
14280422 734and using a non locale-affected comparison, the example attempts to save
5a964f20 735a couple of transformations. But in fact, it doesn't save anything: Perl
2ae324a7 736magic (see L<perlguts/Magic Variables>) creates the transformed version of a
5a964f20 737string the first time it's needed in a comparison, then keeps this version around
14280422 738in case it's needed again. An example rewritten the easy way with
e38874e2 739C<cmp> runs just about as fast. It also copes with null characters
39332f68 740embedded in strings; if you call C<strxfrm()> directly, it treats the first
5a964f20
TC
741null it finds as a terminator. don't expect the transformed strings
742it produces to be portable across systems--or even from one revision
39332f68 743of your operating system to the next. In short, don't call C<strxfrm()>
e38874e2 744directly: let Perl do it for you.
14280422 745
5a964f20 746Note: C<use locale> isn't shown in some of these examples because it isn't
dfcc8045
KW
747needed: C<strcoll()> and C<strxfrm()> are POSIX functions
748which use the standard system-supplied C<libc> functions that
749always obey the current C<LC_COLLATE> locale.
5f05dabc
PP
750
751=head2 Category LC_CTYPE: Character Types
752
66cbab2c
KW
753In the scope of S<C<use locale>> (but not a
754C<use locale ':not_characters'>), Perl obeys the C<LC_CTYPE> locale
14280422
DD
755setting. This controls the application's notion of which characters are
756alphabetic. This affects Perl's C<\w> regular expression metanotation,
f1cbbd6e
GS
757which stands for alphanumeric characters--that is, alphabetic,
758numeric, and including other special characters such as the underscore or
759hyphen. (Consult L<perlre> for more information about
14280422 760regular expressions.) Thanks to C<LC_CTYPE>, depending on your locale
b4ffc3db
TC
761setting, characters like "E<aelig>", "E<eth>", "E<szlig>", and
762"E<oslash>" may be understood as C<\w> characters.
5f05dabc 763
2c268ad5 764The C<LC_CTYPE> locale also provides the map used in transliterating
68dc0745 765characters between lower and uppercase. This affects the case-mapping
39332f68 766functions--C<fc()>, C<lc()>, C<lcfirst()>, C<uc()>, and C<ucfirst()>; case-mapping
b9cc4f69
KW
767interpolation with C<\F>, C<\l>, C<\L>, C<\u>, or C<\U> in double-quoted
768strings and C<s///> substitutions; and case-independent regular expression
e38874e2
DD
769pattern matching using the C<i> modifier.
770
5a964f20 771Finally, C<LC_CTYPE> affects the POSIX character-class test
39332f68 772functions--C<isalpha()>, C<islower()>, and so on. For example, if you move
5a964f20 773from the "C" locale to a 7-bit Scandinavian one, you may find--possibly
39332f68 774to your surprise--that "|" moves from the C<ispunct()> class to C<isalpha()>.
ef3087ec
KW
775Unfortunately, this creates big problems for regular expressions. "|" still
776means alternation even though it matches C<\w>.
5f05dabc 777
5d63e270
KW
778Note that there are quite a few things that are unaffected by the
779current locale. All the escape sequences for particular characters,
780C<\n> for example, always mean the platform's native one. This means,
781for example, that C<\N> in regular expressions (every character
782but new-line) work on the platform character set.
783
14280422
DD
784B<Note:> A broken or malicious C<LC_CTYPE> locale definition may result
785in clearly ineligible characters being considered to be alphanumeric by
e199995e 786your application. For strict matching of (mundane) ASCII letters and
5a964f20 787digits--for example, in command strings--locale-aware applications
e199995e 788should use C<\w> with the C</a> regular expression modifier. See L<"SECURITY">.
5f05dabc
PP
789
790=head2 Category LC_NUMERIC: Numeric Formatting
791
b960a36e
KW
792After a proper C<POSIX::setlocale()> call, and within the scope of one
793of the C<use locale> variants, Perl obeys the C<LC_NUMERIC>
2095dafa 794locale information, which controls an application's idea of how numbers
b960a36e
KW
795should be formatted for human readability.
796In most implementations the only effect is to
b4ffc3db 797change the character used for the decimal point--perhaps from "." to ",".
b960a36e 798The functions aren't aware of such niceties as thousands separation and
2095dafa 799so on. (See L<The localeconv function> if you care about these things.)
5a964f20 800
b960a36e
KW
801 use POSIX qw(strtod setlocale LC_NUMERIC);
802 use locale;
5f05dabc 803
b960a36e 804 setlocale LC_NUMERIC, "";
14280422 805
b960a36e 806 $n = 5/2; # Assign numeric 2.5 to $n
5f05dabc 807
b960a36e 808 $a = " $n"; # Locale-dependent conversion to string
5f05dabc 809
b960a36e 810 print "half five is $n\n"; # Locale-dependent output
5f05dabc 811
b960a36e 812 printf "half five is %g\n", $n; # Locale-dependent output
5f05dabc 813
b960a36e
KW
814 print "DECIMAL POINT IS COMMA\n"
815 if $n == (strtod("2,5"))[0]; # Locale-dependent conversion
5f05dabc 816
4bbcc6e8
JH
817See also L<I18N::Langinfo> and C<RADIXCHAR>.
818
5f05dabc
PP
819=head2 Category LC_MONETARY: Formatting of monetary amounts
820
e199995e 821The C standard defines the C<LC_MONETARY> category, but not a function
5a964f20 822that is affected by its contents. (Those with experience of standards
b0c42ed9 823committees will recognize that the working group decided to punt on the
fa9b773e
KW
824issue.) Consequently, Perl essentially takes no notice of it. If you
825really want to use C<LC_MONETARY>, you can query its contents--see
e05ffc7d
KW
826L<The localeconv function>--and use the information that it returns in your
827application's own formatting of currency amounts. However, you may well
828find that the information, voluminous and complex though it may be, still
829does not quite meet your requirements: currency formatting is a hard nut
13a2d996 830to crack.
5f05dabc 831
4bbcc6e8
JH
832See also L<I18N::Langinfo> and C<CRNCYSTR>.
833
5f05dabc
PP
834=head2 LC_TIME
835
39332f68 836Output produced by C<POSIX::strftime()>, which builds a formatted
5f05dabc
PP
837human-readable date/time string, is affected by the current C<LC_TIME>
838locale. Thus, in a French locale, the output produced by the C<%B>
839format element (full month name) for the first month of the year would
5a964f20 840be "janvier". Here's how to get a list of long month names in the
5f05dabc
PP
841current locale:
842
843 use POSIX qw(strftime);
14280422
DD
844 for (0..11) {
845 $long_month_name[$_] =
846 strftime("%B", 0, 0, 0, 1, $_, 96);
5f05dabc
PP
847 }
848
2619d284
KW
849Note: C<use locale> isn't needed in this example: C<strftime()> is a POSIX
850function which uses the standard system-supplied C<libc> function that
851always obeys the current C<LC_TIME> locale.
5f05dabc 852
4bbcc6e8 853See also L<I18N::Langinfo> and C<ABDAY_1>..C<ABDAY_7>, C<DAY_1>..C<DAY_7>,
2a2bf5f4 854C<ABMON_1>..C<ABMON_12>, and C<ABMON_1>..C<ABMON_12>.
4bbcc6e8 855
5f05dabc
PP
856=head2 Other categories
857
2619d284
KW
858The remaining locale categories are not currently used by Perl itself.
859But again note that things Perl interacts with may use these, including
860extensions outside the standard Perl distribution, and by the
98a6f11e 861operating system and its utilities. Note especially that the string
862value of C<$!> and the error messages given by external utilities may
863be changed by C<LC_MESSAGES>. If you want to have portable error
265f5c4a 864codes, use C<%!>. See L<Errno>.
14280422
DD
865
866=head1 SECURITY
867
5a964f20 868Although the main discussion of Perl security issues can be found in
14280422
DD
869L<perlsec>, a discussion of Perl's locale handling would be incomplete
870if it did not draw your attention to locale-dependent security issues.
5a964f20
TC
871Locales--particularly on systems that allow unprivileged users to
872build their own locales--are untrustworthy. A malicious (or just plain
14280422
DD
873broken) locale can make a locale-aware application give unexpected
874results. Here are a few possibilities:
875
876=over 4
877
878=item *
879
880Regular expression checks for safe file names or mail addresses using
5a964f20 881C<\w> may be spoofed by an C<LC_CTYPE> locale that claims that
14280422
DD
882characters such as "E<gt>" and "|" are alphanumeric.
883
884=item *
885
e38874e2
DD
886String interpolation with case-mapping, as in, say, C<$dest =
887"C:\U$name.$ext">, may produce dangerous results if a bogus LC_CTYPE
888case-mapping table is in effect.
889
890=item *
891
14280422
DD
892A sneaky C<LC_COLLATE> locale could result in the names of students with
893"D" grades appearing ahead of those with "A"s.
894
895=item *
896
5a964f20 897An application that takes the trouble to use information in
14280422 898C<LC_MONETARY> may format debits as if they were credits and vice versa
5a964f20 899if that locale has been subverted. Or it might make payments in US
14280422
DD
900dollars instead of Hong Kong dollars.
901
902=item *
903
39332f68 904The date and day names in dates formatted by C<strftime()> could be
14280422 905manipulated to advantage by a malicious user able to subvert the
5a964f20 906C<LC_DATE> locale. ("Look--it says I wasn't in the building on
14280422
DD
907Sunday.")
908
909=back
910
911Such dangers are not peculiar to the locale system: any aspect of an
5a964f20 912application's environment which may be modified maliciously presents
14280422 913similar challenges. Similarly, they are not specific to Perl: any
5a964f20 914programming language that allows you to write programs that take
14280422
DD
915account of their environment exposes you to these issues.
916
5a964f20
TC
917Perl cannot protect you from all possibilities shown in the
918examples--there is no substitute for your own vigilance--but, when
14280422 919C<use locale> is in effect, Perl uses the tainting mechanism (see
5a964f20 920L<perlsec>) to mark string results that become locale-dependent, and
14280422 921which may be untrustworthy in consequence. Here is a summary of the
5a964f20 922tainting behavior of operators and functions that may be affected by
14280422
DD
923the locale:
924
925=over 4
926
551e1d92
RB
927=item *
928
929B<Comparison operators> (C<lt>, C<le>, C<ge>, C<gt> and C<cmp>):
14280422
DD
930
931Scalar true/false (or less/equal/greater) result is never tainted.
932
551e1d92
RB
933=item *
934
935B<Case-mapping interpolation> (with C<\l>, C<\L>, C<\u> or C<\U>)
e38874e2
DD
936
937Result string containing interpolated material is tainted if
66cbab2c 938C<use locale> (but not S<C<use locale ':not_characters'>>) is in effect.
e38874e2 939
551e1d92
RB
940=item *
941
942B<Matching operator> (C<m//>):
14280422
DD
943
944Scalar true/false result never tainted.
945
9fc477bf 946All subpatterns, either delivered as a list-context result or as $1 etc.
66cbab2c
KW
947are tainted if C<use locale> (but not S<C<use locale ':not_characters'>>)
948is in effect, and the subpattern regular
e38874e2 949expression contains C<\w> (to match an alphanumeric character), C<\W>
6b0ac556
OK
950(non-alphanumeric character), C<\s> (whitespace character), or C<\S>
951(non whitespace character). The matched-pattern variable, $&, $`
e38874e2
DD
952(pre-match), $' (post-match), and $+ (last match) are also tainted if
953C<use locale> is in effect and the regular expression contains C<\w>,
954C<\W>, C<\s>, or C<\S>.
14280422 955
551e1d92
RB
956=item *
957
958B<Substitution operator> (C<s///>):
14280422 959
e38874e2 960Has the same behavior as the match operator. Also, the left
66cbab2c
KW
961operand of C<=~> becomes tainted when C<use locale>
962(but not S<C<use locale ':not_characters'>>) is in effect if modified as
963a result of a substitution based on a regular
e38874e2 964expression match involving C<\w>, C<\W>, C<\s>, or C<\S>; or of
7b8d334a 965case-mapping with C<\l>, C<\L>,C<\u> or C<\U>.
14280422 966
551e1d92
RB
967=item *
968
39332f68 969B<Output formatting functions> (C<printf()> and C<write()>):
14280422 970
3cf03d68
JH
971Results are never tainted because otherwise even output from print,
972for example C<print(1/7)>, should be tainted if C<use locale> is in
973effect.
14280422 974
551e1d92
RB
975=item *
976
39332f68 977B<Case-mapping functions> (C<lc()>, C<lcfirst()>, C<uc()>, C<ucfirst()>):
14280422 978
66cbab2c
KW
979Results are tainted if C<use locale> (but not
980S<C<use locale ':not_characters'>>) is in effect.
14280422 981
551e1d92
RB
982=item *
983
39332f68
KW
984B<POSIX locale-dependent functions> (C<localeconv()>, C<strcoll()>,
985C<strftime()>, C<strxfrm()>):
14280422
DD
986
987Results are never tainted.
988
551e1d92
RB
989=item *
990
39332f68
KW
991B<POSIX character class tests> (C<isalnum()>, C<isalpha()>, C<isdigit()>,
992C<isgraph()>, C<islower()>, C<isprint()>, C<ispunct()>, C<isspace()>, C<isupper()>,
993C<isxdigit()>):
14280422
DD
994
995True/false results are never tainted.
996
997=back
998
999Three examples illustrate locale-dependent tainting.
1000The first program, which ignores its locale, won't run: a value taken
54310121 1001directly from the command line may not be used to name an output file
14280422
DD
1002when taint checks are enabled.
1003
1004 #/usr/local/bin/perl -T
1005 # Run with taint checking
1006
54310121 1007 # Command line sanity check omitted...
14280422
DD
1008 $tainted_output_file = shift;
1009
1010 open(F, ">$tainted_output_file")
3183d96c 1011 or warn "Open of $tainted_output_file failed: $!\n";
14280422
DD
1012
1013The program can be made to run by "laundering" the tainted value through
5a964f20
TC
1014a regular expression: the second example--which still ignores locale
1015information--runs, creating the file named on its command line
14280422
DD
1016if it can.
1017
1018 #/usr/local/bin/perl -T
1019
1020 $tainted_output_file = shift;
1021 $tainted_output_file =~ m%[\w/]+%;
1022 $untainted_output_file = $&;
1023
1024 open(F, ">$untainted_output_file")
1025 or warn "Open of $untainted_output_file failed: $!\n";
1026
5a964f20 1027Compare this with a similar but locale-aware program:
14280422
DD
1028
1029 #/usr/local/bin/perl -T
1030
1031 $tainted_output_file = shift;
1032 use locale;
1033 $tainted_output_file =~ m%[\w/]+%;
1034 $localized_output_file = $&;
1035
1036 open(F, ">$localized_output_file")
1037 or warn "Open of $localized_output_file failed: $!\n";
1038
1039This third program fails to run because $& is tainted: it is the result
5a964f20 1040of a match involving C<\w> while C<use locale> is in effect.
5f05dabc
PP
1041
1042=head1 ENVIRONMENT
1043
1044=over 12
1045
1046=item PERL_BADLANG
1047
14280422 1048A string that can suppress Perl's warning about failed locale settings
54310121 1049at startup. Failure can occur if the locale support in the operating
5a964f20 1050system is lacking (broken) in some way--or if you mistyped the name of
900bd440
JH
1051a locale when you set up your environment. If this environment
1052variable is absent, or has a value that does not evaluate to integer
1053zero--that is, "0" or ""-- Perl will complain about locale setting
1054failures.
5f05dabc 1055
14280422
DD
1056B<NOTE>: PERL_BADLANG only gives you a way to hide the warning message.
1057The message tells about some problem in your system's locale support,
1058and you should investigate what the problem is.
5f05dabc
PP
1059
1060=back
1061
1062The following environment variables are not specific to Perl: They are
39332f68 1063part of the standardized (ISO C, XPG4, POSIX 1.c) C<setlocale()> method
14280422 1064for controlling an application's opinion on data.
5f05dabc
PP
1065
1066=over 12
1067
1068=item LC_ALL
1069
5a964f20 1070C<LC_ALL> is the "override-all" locale environment variable. If
5f05dabc
PP
1071set, it overrides all the rest of the locale environment variables.
1072
528d65ad
JH
1073=item LANGUAGE
1074
1075B<NOTE>: C<LANGUAGE> is a GNU extension, it affects you only if you
1076are using the GNU libc. This is the case if you are using e.g. Linux.
e1020413 1077If you are using "commercial" Unixes you are most probably I<not>
22b6f60d
JH
1078using GNU libc and you can ignore C<LANGUAGE>.
1079
1080However, in the case you are using C<LANGUAGE>: it affects the
1081language of informational, warning, and error messages output by
1082commands (in other words, it's like C<LC_MESSAGES>) but it has higher
96090e4f 1083priority than C<LC_ALL>. Moreover, it's not a single value but
22b6f60d
JH
1084instead a "path" (":"-separated list) of I<languages> (not locales).
1085See the GNU C<gettext> library documentation for more information.
528d65ad 1086
5f05dabc
PP
1087=item LC_CTYPE
1088
1089In the absence of C<LC_ALL>, C<LC_CTYPE> chooses the character type
1090locale. In the absence of both C<LC_ALL> and C<LC_CTYPE>, C<LANG>
1091chooses the character type locale.
1092
1093=item LC_COLLATE
1094
14280422
DD
1095In the absence of C<LC_ALL>, C<LC_COLLATE> chooses the collation
1096(sorting) locale. In the absence of both C<LC_ALL> and C<LC_COLLATE>,
1097C<LANG> chooses the collation locale.
5f05dabc
PP
1098
1099=item LC_MONETARY
1100
14280422
DD
1101In the absence of C<LC_ALL>, C<LC_MONETARY> chooses the monetary
1102formatting locale. In the absence of both C<LC_ALL> and C<LC_MONETARY>,
1103C<LANG> chooses the monetary formatting locale.
5f05dabc
PP
1104
1105=item LC_NUMERIC
1106
1107In the absence of C<LC_ALL>, C<LC_NUMERIC> chooses the numeric format
1108locale. In the absence of both C<LC_ALL> and C<LC_NUMERIC>, C<LANG>
1109chooses the numeric format.
1110
1111=item LC_TIME
1112
14280422
DD
1113In the absence of C<LC_ALL>, C<LC_TIME> chooses the date and time
1114formatting locale. In the absence of both C<LC_ALL> and C<LC_TIME>,
1115C<LANG> chooses the date and time formatting locale.
5f05dabc
PP
1116
1117=item LANG
1118
14280422
DD
1119C<LANG> is the "catch-all" locale environment variable. If it is set, it
1120is used as the last resort after the overall C<LC_ALL> and the
5f05dabc
PP
1121category-specific C<LC_...>.
1122
1123=back
1124
7e4353e9
RGS
1125=head2 Examples
1126
1127The LC_NUMERIC controls the numeric output:
1128
ef3087ec
KW
1129 use locale;
1130 use POSIX qw(locale_h); # Imports setlocale() and the LC_ constants.
1131 setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
1132 printf "%g\n", 1.23; # If the "fr_FR" succeeded, probably shows 1,23.
7e4353e9 1133
39332f68 1134and also how strings are parsed by C<POSIX::strtod()> as numbers:
7e4353e9 1135
ef3087ec
KW
1136 use locale;
1137 use POSIX qw(locale_h strtod);
1138 setlocale(LC_NUMERIC, "de_DE") or die "Entschuldigung";
1139 my $x = strtod("2,34") + 5;
1140 print $x, "\n"; # Probably shows 7,34.
7e4353e9 1141
5f05dabc
PP
1142=head1 NOTES
1143
b960a36e
KW
1144=head2 String C<eval> and C<LC_NUMERIC>
1145
1146A string L<eval|perlfunc/eval EXPR> parses its expression as standard
1147Perl. It is therefore expecting the decimal point to be a dot. If
1148C<LC_NUMERIC> is set to have this be a comma instead, the parsing will
1149be confused, perhaps silently.
1150
1151 use locale;
1152 use POSIX qw(locale_h);
1153 setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
1154 my $a = 1.2;
1155 print eval "$a + 1.5";
1156 print "\n";
1157
1158prints C<13,5>. This is because in that locale, the comma is the
1159decimal point character. The C<eval> thus expands to:
1160
1161 eval "1,2 + 1.5"
1162
1163and the result is not what you likely expected. No warnings are
1164generated. If you do string C<eval>'s within the scope of
1165S<C<use locale>>, you should instead change the C<eval> line to do
1166something like:
1167
1168 print eval "no locale; $a + 1.5";
1169
1170This prints C<2.7>.
1171
5f05dabc
PP
1172=head2 Backward compatibility
1173
b0c42ed9 1174Versions of Perl prior to 5.004 B<mostly> ignored locale information,
5a964f20
TC
1175generally behaving as if something similar to the C<"C"> locale were
1176always in force, even if the program environment suggested otherwise
1177(see L<The setlocale function>). By default, Perl still behaves this
1178way for backward compatibility. If you want a Perl application to pay
1179attention to locale information, you B<must> use the S<C<use locale>>
062ca197
KW
1180pragma (see L<The use locale pragma>) or, in the unlikely event
1181that you want to do so for just pattern matching, the
70709c68
KW
1182C</l> regular expression modifier (see L<perlre/Character set
1183modifiers>) to instruct it to do so.
b0c42ed9
JH
1184
1185Versions of Perl from 5.002 to 5.003 did use the C<LC_CTYPE>
5a964f20
TC
1186information if available; that is, C<\w> did understand what
1187were the letters according to the locale environment variables.
b0c42ed9
JH
1188The problem was that the user had no control over the feature:
1189if the C library supported locales, Perl used them.
1190
1191=head2 I18N:Collate obsolete
1192
5a964f20 1193In versions of Perl prior to 5.004, per-locale collation was possible
b0c42ed9
JH
1194using the C<I18N::Collate> library module. This module is now mildly
1195obsolete and should be avoided in new applications. The C<LC_COLLATE>
1196functionality is now integrated into the Perl core language: One can
1197use locale-specific scalar data completely normally with C<use locale>,
1198so there is no longer any need to juggle with the scalar references of
1199C<I18N::Collate>.
5f05dabc 1200
14280422 1201=head2 Sort speed and memory use impacts
5f05dabc
PP
1202
1203Comparing and sorting by locale is usually slower than the default
14280422
DD
1204sorting; slow-downs of two to four times have been observed. It will
1205also consume more memory: once a Perl scalar variable has participated
1206in any string comparison or sorting operation obeying the locale
1207collation rules, it will take 3-15 times more memory than before. (The
1208exact multiplier depends on the string's contents, the operating system
1209and the locale.) These downsides are dictated more by the operating
1210system's implementation of the locale system than by Perl.
5f05dabc 1211
5f05dabc
PP
1212=head2 Freely available locale definitions
1213
66cbab2c
KW
1214The Unicode CLDR project extracts the POSIX portion of many of its
1215locales, available at
1216
1217 http://unicode.org/Public/cldr/latest/
1218
08d7a6b2
LB
1219There is a large collection of locale definitions at:
1220
1221 http://std.dkuug.dk/i18n/WG15-collection/locales/
1222
1223You should be aware that it is
14280422 1224unsupported, and is not claimed to be fit for any purpose. If your
5a964f20 1225system allows installation of arbitrary locales, you may find the
14280422
DD
1226definitions useful as they are, or as a basis for the development of
1227your own locales.
5f05dabc 1228
14280422 1229=head2 I18n and l10n
5f05dabc 1230
b0c42ed9
JH
1231"Internationalization" is often abbreviated as B<i18n> because its first
1232and last letters are separated by eighteen others. (You may guess why
1233the internalin ... internaliti ... i18n tends to get abbreviated.) In
1234the same way, "localization" is often abbreviated to B<l10n>.
14280422
DD
1235
1236=head2 An imperfect standard
1237
1238Internationalization, as defined in the C and POSIX standards, can be
1239criticized as incomplete, ungainly, and having too large a granularity.
1240(Locales apply to a whole process, when it would arguably be more useful
1241to have them apply to a single thread, window group, or whatever.) They
1242also have a tendency, like standards groups, to divide the world into
1243nations, when we all know that the world can equally well be divided
e199995e 1244into bankers, bikers, gamers, and so on.
5f05dabc 1245
b310b053
JH
1246=head1 Unicode and UTF-8
1247
7ee2ae1e
KW
1248The support of Unicode is new starting from Perl version v5.6, and more fully
1249implemented in version v5.8 and later. See L<perluniintro>. It is
66cbab2c 1250strongly recommended that when combining Unicode and locale (starting in
7ee2ae1e 1251v5.16), you use
66cbab2c
KW
1252
1253 use locale ':not_characters';
1254
1255When this form of the pragma is used, only the non-character portions of
1256locales are used by Perl, for example C<LC_NUMERIC>. Perl assumes that
1257you have translated all the characters it is to operate on into Unicode
1258(actually the platform's native character set (ASCII or EBCDIC) plus
1259Unicode). For data in files, this can conveniently be done by also
1260specifying
1261
1262 use open ':locale';
1263
1264This pragma arranges for all inputs from files to be translated into
1265Unicode from the current locale as specified in the environment (see
1266L</ENVIRONMENT>), and all outputs to files to be translated back
1267into the locale. (See L<open>). On a per-filehandle basis, you can
1268instead use the L<PerlIO::locale> module, or the L<Encode::Locale>
1269module, both available from CPAN. The latter module also has methods to
1270ease the handling of C<ARGV> and environment variables, and can be used
1271on individual strings. Also, if you know that all your locales will be
1272UTF-8, as many are these days, you can use the L<B<-C>|perlrun/-C>
1273command line switch.
1274
1275This form of the pragma allows essentially seamless handling of locales
1276with Unicode. The collation order will be Unicode's. It is strongly
1277recommended that when you need to order and sort strings that you use
1278the standard module L<Unicode::Collate> which gives much better results
1279in many instances than you can get with the old-style locale handling.
1280
7ee2ae1e 1281For pre-v5.16 Perls, or if you use the locale pragma without the
66cbab2c
KW
1282C<:not_characters> parameter, Perl tries to work with both Unicode and
1283locales--but there are problems.
1284
1285Perl does not handle multi-byte locales in this case, such as have been
1286used for various
dc4bfc4b
KW
1287Asian languages, such as Big5 or Shift JIS. However, the increasingly
1288common multi-byte UTF-8 locales, if properly implemented, may work
1289reasonably well (depending on your C library implementation) in this
1290form of the locale pragma, simply because both
1291they and Perl store characters that take up multiple bytes the same way.
1292However, some, if not most, C library implementations may not process
1293the characters in the upper half of the Latin-1 range (128 - 255)
1294properly under LC_CTYPE. To see if a character is a particular type
1295under a locale, Perl uses the functions like C<isalnum()>. Your C
1296library may not work for UTF-8 locales with those functions, instead
1297only working under the newer wide library functions like C<iswalnum()>.
e199995e
KW
1298
1299Perl generally takes the tack to use locale rules on code points that can fit
66cbab2c
KW
1300in a single byte, and Unicode rules for those that can't (though this
1301isn't uniformly applied, see the note at the end of this section). This
1302prevents many problems in locales that aren't UTF-8. Suppose the locale
1303is ISO8859-7, Greek. The character at 0xD7 there is a capital Chi. But
1304in the ISO8859-1 locale, Latin1, it is a multiplication sign. The POSIX
1305regular expression character class C<[[:alpha:]]> will magically match
13060xD7 in the Greek locale but not in the Latin one.
e199995e
KW
1307
1308However, there are places where this breaks down. Certain constructs are
b4ffc3db
TC
1309for Unicode only, such as C<\p{Alpha}>. They assume that 0xD7 always has its
1310Unicode meaning (or the equivalent on EBCDIC platforms). Since Latin1 is a
1311subset of Unicode and 0xD7 is the multiplication sign in both Latin1 and
1312Unicode, C<\p{Alpha}> will never match it, regardless of locale. A similar
1313issue occurs with C<\N{...}>. It is therefore a bad idea to use C<\p{}> or
66cbab2c
KW
1314C<\N{}> under plain C<use locale>--I<unless> you can guarantee that the
1315locale will be a ISO8859-1. Use POSIX character classes instead.
1316
1317Another problem with this approach is that operations that cross the
1318single byte/multiple byte boundary are not well-defined, and so are
1319disallowed. (This boundary is between the codepoints at 255/256.).
1320For example, lower casing LATIN CAPITAL LETTER Y WITH DIAERESIS (U+0178)
1321should return LATIN SMALL LETTER Y WITH DIAERESIS (U+00FF). But in the
1322Greek locale, for example, there is no character at 0xFF, and Perl
1323has no way of knowing what the character at 0xFF is really supposed to
1324represent. Thus it disallows the operation. In this mode, the
1325lowercase of U+0178 is itself.
1326
1327The same problems ensue if you enable automatic UTF-8-ification of your
e199995e 1328standard file handles, default C<open()> layer, and C<@ARGV> on non-ISO8859-1,
b4ffc3db
TC
1329non-UTF-8 locales (by using either the B<-C> command line switch or the
1330C<PERL_UNICODE> environment variable; see L<perlrun>).
1331Things are read in as UTF-8, which would normally imply a Unicode
1332interpretation, but the presence of a locale causes them to be interpreted
1333in that locale instead. For example, a 0xD7 code point in the Unicode
1334input, which should mean the multiplication sign, won't be interpreted by
66cbab2c 1335Perl that way under the Greek locale. This is not a problem
b4ffc3db 1336I<provided> you make certain that all locales will always and only be either
66cbab2c 1337an ISO8859-1, or, if you don't have a deficient C library, a UTF-8 locale.
b4ffc3db
TC
1338
1339Vendor locales are notoriously buggy, and it is difficult for Perl to test
1340its locale-handling code because this interacts with code that Perl has no
1341control over; therefore the locale-handling code in Perl may be buggy as
66cbab2c
KW
1342well. (However, the Unicode-supplied locales should be better, and
1343there is a feed back mechanism to correct any problems. See
1344L</Freely available locale definitions>.)
1345
7ee2ae1e 1346If you have Perl v5.16, the problems mentioned above go away if you use
66cbab2c 1347the C<:not_characters> parameter to the locale pragma (except for vendor
7ee2ae1e 1348bugs in the non-character portions). If you don't have v5.16, and you
66cbab2c
KW
1349I<do> have locales that work, using them may be worthwhile for certain
1350specific purposes, as long as you keep in mind the gotchas already
1351mentioned. For example, if the collation for your locales works, it
1352runs faster under locales than under L<Unicode::Collate>; and you gain
1353access to such things as the local currency symbol and the names of the
7ee2ae1e 1354months and days of the week. (But to hammer home the point, in v5.16,
66cbab2c
KW
1355you get this access without the downsides of locales by using the
1356C<:not_characters> form of the pragma.)
1357
1358Note: The policy of using locale rules for code points that can fit in a
1359byte, and Unicode rules for those that can't is not uniformly applied.
7ee2ae1e 1360Pre-v5.12, it was somewhat haphazard; in v5.12 it was applied fairly
66cbab2c 1361consistently to regular expression matching except for bracketed
7ee2ae1e
KW
1362character classes; in v5.14 it was extended to all regex matches; and in
1363v5.16 to the casing operations such as C<"\L"> and C<uc()>. For
66cbab2c
KW
1364collation, in all releases, the system's C<strxfrm()> function is called,
1365and whatever it does is what you get.
b310b053 1366
5f05dabc
PP
1367=head1 BUGS
1368
1369=head2 Broken systems
1370
5a964f20 1371In certain systems, the operating system's locale support
2bdf8add 1372is broken and cannot be fixed or used by Perl. Such deficiencies can
b4ffc3db 1373and will result in mysterious hangs and/or Perl core dumps when
2bdf8add 1374C<use locale> is in effect. When confronted with such a system,
7f2de2d2 1375please report in excruciating detail to <F<perlbug@perl.org>>, and
b4ffc3db 1376also contact your vendor: bug fixes may exist for these problems
2bdf8add 1377in your operating system. Sometimes such bug fixes are called an
83fb1bf0
KW
1378operating system upgrade. If you have the source for Perl, include in
1379the perlbug email the output of the test described above in L</Testing
1380for broken locales>.
5f05dabc
PP
1381
1382=head1 SEE ALSO
1383
b310b053
JH
1384L<I18N::Langinfo>, L<perluniintro>, L<perlunicode>, L<open>,
1385L<POSIX/isalnum>, L<POSIX/isalpha>,
4bbcc6e8
JH
1386L<POSIX/isdigit>, L<POSIX/isgraph>, L<POSIX/islower>,
1387L<POSIX/isprint>, L<POSIX/ispunct>, L<POSIX/isspace>,
1388L<POSIX/isupper>, L<POSIX/isxdigit>, L<POSIX/localeconv>,
1389L<POSIX/setlocale>, L<POSIX/strcoll>, L<POSIX/strftime>,
1390L<POSIX/strtod>, L<POSIX/strxfrm>.
5f05dabc 1391
ccd65d51
KW
1392For special considerations when Perl is embedded in a C program,
1393see L<perlembed/Using embedded Perl with POSIX locales>.
1394
5f05dabc
PP
1395=head1 HISTORY
1396
b0c42ed9 1397Jarkko Hietaniemi's original F<perli18n.pod> heavily hacked by Dominic
5a964f20 1398Dunlop, assisted by the perl5-porters. Prose worked over a bit by
c052850d 1399Tom Christiansen, and updated by Perl 5 porters.