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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
25Perl was extended, starting in 5.04, to support the locale system. This
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
35Perl continues to support the old locale system, and starting in 5.16,
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
75This for the most part is beyond the scope of Perl
76
77=item Category LC_COLLATE: Collation
78
79This indicates the ordering of letters for comparision and sorting.
80In Latin alphabets, for example, "b", generally follows "a".
81
82=item Category LC_CTYPE: Character Types
83
84This indicates, for example if a character is an uppercase letter.
85
86=back
87
88More details on the categories are given below in L</LOCALE CATEGORIES>.
89
90Together, these categories go a long way towards being able to customize
91a single program to run in many different locations. But there are
92deficiencies, so keep reading.
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93
94=head1 PREPARING TO USE LOCALES
95
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96Perl will not use locales unless specifically requested to (see L</NOTES> below
97for the partial exception of C<write()>). But even if there is such a
98request, B<all> of the following must be true for it to work properly:
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99
100=over 4
101
102=item *
103
104B<Your operating system must support the locale system>. If it does,
14280422 105you should find that the setlocale() function is a documented part of
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106its C library.
107
108=item *
109
5a964f20 110B<Definitions for locales that you use must be installed>. You, or
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111your system administrator, must make sure that this is the case. The
112available locales, the location in which they are kept, and the manner
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113in which they are installed all vary from system to system. Some systems
114provide only a few, hard-wired locales and do not allow more to be
115added. Others allow you to add "canned" locales provided by the system
116supplier. Still others allow you or the system administrator to define
14280422 117and add arbitrary locales. (You may have to ask your supplier to
5a964f20 118provide canned locales that are not delivered with your operating
14280422 119system.) Read your system documentation for further illumination.
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120
121=item *
122
123B<Perl must believe that the locale system is supported>. If it does,
124C<perl -V:d_setlocale> will say that the value for C<d_setlocale> is
125C<define>.
126
127=back
128
129If you want a Perl application to process and present your data
130according to a particular locale, the application code should include
2ae324a7 131the S<C<use locale>> pragma (see L<The use locale pragma>) where
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132appropriate, and B<at least one> of the following must be true:
133
134=over 4
135
c052850d 136=item 1
5f05dabc 137
66cbab2c 138B<The locale-determining environment variables (see L</"ENVIRONMENT">)
5a964f20 139must be correctly set up> at the time the application is started, either
ef3087ec 140by yourself or by whomever set up your system account; or
5f05dabc 141
c052850d 142=item 2
5f05dabc 143
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144B<The application must set its own locale> using the method described in
145L<The setlocale function>.
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146
147=back
148
149=head1 USING LOCALES
150
151=head2 The use locale pragma
152
14280422 153By default, Perl ignores the current locale. The S<C<use locale>>
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154pragma tells Perl to use the current locale for some operations.
155Starting in 5.15, there is an optional parameter to this pragma:
156
157 use locale ':not_characters';
158
159This parameter allows better mixing of locales and Unicode, and is
160described fully in L</Unicode and UTF-8>, but briefly, it tells Perl to
161not use the character portions of the locale definition, that is
162the C<LC_CTYPE> and C<LC_COLLATE> categories. Instead it will use the
163native (extended by Unicode) character set. When using this parameter,
164you are responsible for getting the external character set translated
165into the native/Unicode one (which it already will be if it is one of
166the increasingly popular UTF-8 locales). There are convenient ways of
167doing this, as described in L</Unicode and UTF-8>.
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168
169The current locale is set at execution time by
170L<setlocale()|/The setlocale function> described below. If that function
171hasn't yet been called in the course of the program's execution, the
66cbab2c 172current locale is that which was determined by the L</"ENVIRONMENT"> in
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173effect at the start of the program, except that
174C<L<LC_NUMERIC|/Category LC_NUMERIC: Numeric Formatting>> is always
175initialized to the C locale (mentioned under L<Finding locales>).
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176If there is no valid environment, the current locale is undefined. It
177is likely, but not necessarily, the "C" locale.
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178
179The operations that are affected by locale are:
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180
181=over 4
182
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183=item B<Under C<use locale ':not_characters';>>
184
185=over 4
186
187=item *
188
189B<Format declarations> (format()) use C<LC_NUMERIC>
190
191=item *
192
193B<The POSIX date formatting function> (strftime()) uses C<LC_TIME>.
194
195=back
196
197=for comment
198The nbsp below makes this look better
199
200E<160>
201
202=item B<Under just plain C<use locale;>>
203
204The above operations are affected, as well as the following:
205
206=over 4
207
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208=item *
209
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210B<The comparison operators> (C<lt>, C<le>, C<cmp>, C<ge>, and C<gt>) and
211the POSIX string collation functions strcoll() and strxfrm() use
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212C<LC_COLLATE>. sort() is also affected if used without an
213explicit comparison function, because it uses C<cmp> by default.
14280422 214
5a964f20 215B<Note:> C<eq> and C<ne> are unaffected by locale: they always
de108802 216perform a char-by-char comparison of their scalar operands. What's
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217more, if C<cmp> finds that its operands are equal according to the
218collation sequence specified by the current locale, it goes on to
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219perform a char-by-char comparison, and only returns I<0> (equal) if the
220operands are char-for-char identical. If you really want to know whether
5a964f20 221two strings--which C<eq> and C<cmp> may consider different--are equal
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222as far as collation in the locale is concerned, see the discussion in
223L<Category LC_COLLATE: Collation>.
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224
225=item *
226
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227B<Regular expressions and case-modification functions> (uc(), lc(),
228ucfirst(), and lcfirst()) use C<LC_CTYPE>
5f05dabc 229
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230=back
231
66cbab2c 232=back
5f05dabc 233
5a964f20 234The default behavior is restored with the S<C<no locale>> pragma, or
ef3087ec 235upon reaching the end of the block enclosing C<use locale>.
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236Note that C<use locale> and C<use locale ':not_characters'> may be
237nested, and that what is in effect within an inner scope will revert to
238the outer scope's rules at the end of the inner scope.
5f05dabc 239
5a964f20 240The string result of any operation that uses locale
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241information is tainted, as it is possible for a locale to be
242untrustworthy. See L<"SECURITY">.
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243
244=head2 The setlocale function
245
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246You can switch locales as often as you wish at run time with the
247POSIX::setlocale() function:
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248
249 # This functionality not usable prior to Perl 5.004
250 require 5.004;
251
252 # Import locale-handling tool set from POSIX module.
253 # This example uses: setlocale -- the function call
254 # LC_CTYPE -- explained below
255 use POSIX qw(locale_h);
256
14280422 257 # query and save the old locale
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258 $old_locale = setlocale(LC_CTYPE);
259
260 setlocale(LC_CTYPE, "fr_CA.ISO8859-1");
261 # LC_CTYPE now in locale "French, Canada, codeset ISO 8859-1"
262
263 setlocale(LC_CTYPE, "");
264 # LC_CTYPE now reset to default defined by LC_ALL/LC_CTYPE/LANG
265 # environment variables. See below for documentation.
266
267 # restore the old locale
268 setlocale(LC_CTYPE, $old_locale);
269
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270The first argument of setlocale() gives the B<category>, the second the
271B<locale>. The category tells in what aspect of data processing you
272want to apply locale-specific rules. Category names are discussed in
66cbab2c 273L</LOCALE CATEGORIES> and L</"ENVIRONMENT">. The locale is the name of a
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274collection of customization information corresponding to a particular
275combination of language, country or territory, and codeset. Read on for
276hints on the naming of locales: not all systems name locales as in the
277example.
278
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279If no second argument is provided and the category is something else
280than LC_ALL, the function returns a string naming the current locale
281for the category. You can use this value as the second argument in a
282subsequent call to setlocale().
283
284If no second argument is provided and the category is LC_ALL, the
285result is implementation-dependent. It may be a string of
c052850d 286concatenated locale names (separator also implementation-dependent)
f979aebc 287or a single locale name. Please consult your setlocale(3) man page for
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288details.
289
290If a second argument is given and it corresponds to a valid locale,
291the locale for the category is set to that value, and the function
292returns the now-current locale value. You can then use this in yet
293another call to setlocale(). (In some implementations, the return
294value may sometimes differ from the value you gave as the second
295argument--think of it as an alias for the value you gave.)
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296
297As the example shows, if the second argument is an empty string, the
298category's locale is returned to the default specified by the
299corresponding environment variables. Generally, this results in a
5a964f20 300return to the default that was in force when Perl started up: changes
54310121 301to the environment made by the application after startup may or may not
5a964f20 302be noticed, depending on your system's C library.
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304If the second argument does not correspond to a valid locale, the locale
305for the category is not changed, and the function returns I<undef>.
5f05dabc 306
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307Note that Perl ignores the current C<LC_CTYPE> and C<LC_COLLATE> locales
308within the scope of a C<use locale ':not_characters'>.
309
f979aebc 310For further information about the categories, consult setlocale(3).
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311
312=head2 Finding locales
313
f979aebc 314For locales available in your system, consult also setlocale(3) to
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315see whether it leads to the list of available locales (search for the
316I<SEE ALSO> section). If that fails, try the following command lines:
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317
318 locale -a
319
320 nlsinfo
321
322 ls /usr/lib/nls/loc
323
324 ls /usr/lib/locale
325
326 ls /usr/lib/nls
327
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328 ls /usr/share/locale
329
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330and see whether they list something resembling these
331
2bdf8add 332 en_US.ISO8859-1 de_DE.ISO8859-1 ru_RU.ISO8859-5
502a173a 333 en_US.iso88591 de_DE.iso88591 ru_RU.iso88595
2bdf8add 334 en_US de_DE ru_RU
14280422 335 en de ru
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336 english german russian
337 english.iso88591 german.iso88591 russian.iso88595
502a173a 338 english.roman8 russian.koi8r
5f05dabc 339
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340Sadly, even though the calling interface for setlocale() has been
341standardized, names of locales and the directories where the
5a964f20 342configuration resides have not been. The basic form of the name is
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343I<language_territory>B<.>I<codeset>, but the latter parts after
344I<language> are not always present. The I<language> and I<country>
345are usually from the standards B<ISO 3166> and B<ISO 639>, the
346two-letter abbreviations for the countries and the languages of the
347world, respectively. The I<codeset> part often mentions some B<ISO
3488859> character set, the Latin codesets. For example, C<ISO 8859-1>
349is the so-called "Western European codeset" that can be used to encode
350most Western European languages adequately. Again, there are several
351ways to write even the name of that one standard. Lamentably.
5f05dabc 352
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353Two special locales are worth particular mention: "C" and "POSIX".
354Currently these are effectively the same locale: the difference is
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355mainly that the first one is defined by the C standard, the second by
356the POSIX standard. They define the B<default locale> in which
14280422 357every program starts in the absence of locale information in its
5a964f20 358environment. (The I<default> default locale, if you will.) Its language
14280422 359is (American) English and its character codeset ASCII.
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360B<Warning>. The C locale delivered by some vendors may not
361actually exactly match what the C standard calls for. So beware.
5f05dabc 362
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363B<NOTE>: Not all systems have the "POSIX" locale (not all systems are
364POSIX-conformant), so use "C" when you need explicitly to specify this
365default locale.
5f05dabc 366
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367=head2 LOCALE PROBLEMS
368
5a964f20 369You may encounter the following warning message at Perl startup:
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370
371 perl: warning: Setting locale failed.
372 perl: warning: Please check that your locale settings:
373 LC_ALL = "En_US",
374 LANG = (unset)
375 are supported and installed on your system.
376 perl: warning: Falling back to the standard locale ("C").
377
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378This means that your locale settings had LC_ALL set to "En_US" and
379LANG exists but has no value. Perl tried to believe you but could not.
380Instead, Perl gave up and fell back to the "C" locale, the default locale
381that is supposed to work no matter what. This usually means your locale
382settings were wrong, they mention locales your system has never heard
383of, or the locale installation in your system has problems (for example,
384some system files are broken or missing). There are quick and temporary
385fixes to these problems, as well as more thorough and lasting fixes.
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386
387=head2 Temporarily fixing locale problems
388
5a964f20 389The two quickest fixes are either to render Perl silent about any
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390locale inconsistencies or to run Perl under the default locale "C".
391
392Perl's moaning about locale problems can be silenced by setting the
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393environment variable PERL_BADLANG to a zero value, for example "0".
394This method really just sweeps the problem under the carpet: you tell
395Perl to shut up even when Perl sees that something is wrong. Do not
396be surprised if later something locale-dependent misbehaves.
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397
398Perl can be run under the "C" locale by setting the environment
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399variable LC_ALL to "C". This method is perhaps a bit more civilized
400than the PERL_BADLANG approach, but setting LC_ALL (or
401other locale variables) may affect other programs as well, not just
402Perl. In particular, external programs run from within Perl will see
3e6e419a 403these changes. If you make the new settings permanent (read on), all
f979aebc 404programs you run see the changes. See L<"ENVIRONMENT"> for
5a964f20 405the full list of relevant environment variables and L<USING LOCALES>
e05ffc7d 406for their effects in Perl. Effects in other programs are
5a964f20 407easily deducible. For example, the variable LC_COLLATE may well affect
b432a672 408your B<sort> program (or whatever the program that arranges "records"
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409alphabetically in your system is called).
410
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411You can test out changing these variables temporarily, and if the
412new settings seem to help, put those settings into your shell startup
413files. Consult your local documentation for the exact details. For in
414Bourne-like shells (B<sh>, B<ksh>, B<bash>, B<zsh>):
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415
416 LC_ALL=en_US.ISO8859-1
417 export LC_ALL
418
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419This assumes that we saw the locale "en_US.ISO8859-1" using the commands
420discussed above. We decided to try that instead of the above faulty
421locale "En_US"--and in Cshish shells (B<csh>, B<tcsh>)
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422
423 setenv LC_ALL en_US.ISO8859-1
c47ff5f1 424
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425or if you have the "env" application you can do in any shell
426
427 env LC_ALL=en_US.ISO8859-1 perl ...
428
5a964f20 429If you do not know what shell you have, consult your local
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430helpdesk or the equivalent.
431
432=head2 Permanently fixing locale problems
433
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434The slower but superior fixes are when you may be able to yourself
435fix the misconfiguration of your own environment variables. The
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436mis(sing)configuration of the whole system's locales usually requires
437the help of your friendly system administrator.
438
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439First, see earlier in this document about L<Finding locales>. That tells
440how to find which locales are really supported--and more importantly,
441installed--on your system. In our example error message, environment
442variables affecting the locale are listed in the order of decreasing
443importance (and unset variables do not matter). Therefore, having
444LC_ALL set to "En_US" must have been the bad choice, as shown by the
445error message. First try fixing locale settings listed first.
3e6e419a 446
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447Second, if using the listed commands you see something B<exactly>
448(prefix matches do not count and case usually counts) like "En_US"
449without the quotes, then you should be okay because you are using a
450locale name that should be installed and available in your system.
4a4eefd0 451In this case, see L<Permanently fixing your system's locale configuration>.
3e6e419a 452
4a4eefd0 453=head2 Permanently fixing your system's locale configuration
3e6e419a 454
5a964f20 455This is when you see something like:
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456
457 perl: warning: Please check that your locale settings:
458 LC_ALL = "En_US",
459 LANG = (unset)
460 are supported and installed on your system.
461
462but then cannot see that "En_US" listed by the above-mentioned
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463commands. You may see things like "en_US.ISO8859-1", but that isn't
464the same. In this case, try running under a locale
465that you can list and which somehow matches what you tried. The
3e6e419a 466rules for matching locale names are a bit vague because
e05ffc7d 467standardization is weak in this area. See again the
13a2d996 468L<Finding locales> about general rules.
3e6e419a 469
b687b08b 470=head2 Fixing system locale configuration
3e6e419a 471
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472Contact a system administrator (preferably your own) and report the exact
473error message you get, and ask them to read this same documentation you
474are now reading. They should be able to check whether there is something
475wrong with the locale configuration of the system. The L<Finding locales>
476section is unfortunately a bit vague about the exact commands and places
477because these things are not that standardized.
3e6e419a 478
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479=head2 The localeconv function
480
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481The POSIX::localeconv() function allows you to get particulars of the
482locale-dependent numeric formatting information specified by the current
483C<LC_NUMERIC> and C<LC_MONETARY> locales. (If you just want the name of
484the current locale for a particular category, use POSIX::setlocale()
5a964f20 485with a single parameter--see L<The setlocale function>.)
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486
487 use POSIX qw(locale_h);
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488
489 # Get a reference to a hash of locale-dependent info
490 $locale_values = localeconv();
491
492 # Output sorted list of the values
493 for (sort keys %$locale_values) {
14280422 494 printf "%-20s = %s\n", $_, $locale_values->{$_}
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495 }
496
14280422 497localeconv() takes no arguments, and returns B<a reference to> a hash.
5a964f20 498The keys of this hash are variable names for formatting, such as
502a173a 499C<decimal_point> and C<thousands_sep>. The values are the
cea6626f 500corresponding, er, values. See L<POSIX/localeconv> for a longer
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501example listing the categories an implementation might be expected to
502provide; some provide more and others fewer. You don't need an
503explicit C<use locale>, because localeconv() always observes the
504current locale.
5f05dabc 505
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506Here's a simple-minded example program that rewrites its command-line
507parameters as integers correctly formatted in the current locale:
5f05dabc 508
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509 # See comments in previous example
510 require 5.004;
511 use POSIX qw(locale_h);
512
513 # Get some of locale's numeric formatting parameters
514 my ($thousands_sep, $grouping) =
515 @{localeconv()}{'thousands_sep', 'grouping'};
516
517 # Apply defaults if values are missing
518 $thousands_sep = ',' unless $thousands_sep;
519
520 # grouping and mon_grouping are packed lists
521 # of small integers (characters) telling the
522 # grouping (thousand_seps and mon_thousand_seps
523 # being the group dividers) of numbers and
524 # monetary quantities. The integers' meanings:
525 # 255 means no more grouping, 0 means repeat
526 # the previous grouping, 1-254 means use that
527 # as the current grouping. Grouping goes from
528 # right to left (low to high digits). In the
529 # below we cheat slightly by never using anything
530 # else than the first grouping (whatever that is).
531 if ($grouping) {
532 @grouping = unpack("C*", $grouping);
533 } else {
534 @grouping = (3);
535 }
536
537 # Format command line params for current locale
538 for (@ARGV) {
539 $_ = int; # Chop non-integer part
540 1 while
541 s/(\d)(\d{$grouping[0]}($|$thousands_sep))/$1$thousands_sep$2/;
542 print "$_";
543 }
544 print "\n";
5f05dabc 545
74c76037 546=head2 I18N::Langinfo
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547
548Another interface for querying locale-dependent information is the
e1020413 549I18N::Langinfo::langinfo() function, available at least in Unix-like
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550systems and VMS.
551
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552The following example will import the langinfo() function itself and
553three constants to be used as arguments to langinfo(): a constant for
554the abbreviated first day of the week (the numbering starts from
555Sunday = 1) and two more constants for the affirmative and negative
556answers for a yes/no question in the current locale.
4bbcc6e8 557
74c76037 558 use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
4bbcc6e8 559
ef3087ec
KW
560 my ($abday_1, $yesstr, $nostr)
561 = map { langinfo } qw(ABDAY_1 YESSTR NOSTR);
4bbcc6e8 562
74c76037 563 print "$abday_1? [$yesstr/$nostr] ";
4bbcc6e8 564
74c76037
JH
565In other words, in the "C" (or English) locale the above will probably
566print something like:
567
e05ffc7d 568 Sun? [yes/no]
4bbcc6e8
JH
569
570See L<I18N::Langinfo> for more information.
571
5f05dabc
PP
572=head1 LOCALE CATEGORIES
573
5a964f20
TC
574The following subsections describe basic locale categories. Beyond these,
575some combination categories allow manipulation of more than one
576basic category at a time. See L<"ENVIRONMENT"> for a discussion of these.
5f05dabc
PP
577
578=head2 Category LC_COLLATE: Collation
579
66cbab2c
KW
580In the scope of S<C<use locale>> (but not a
581C<use locale ':not_characters'>), Perl looks to the C<LC_COLLATE>
5a964f20 582environment variable to determine the application's notions on collation
b4ffc3db
TC
583(ordering) of characters. For example, "b" follows "a" in Latin
584alphabets, but where do "E<aacute>" and "E<aring>" belong? And while
585"color" follows "chocolate" in English, what about in Spanish?
5f05dabc 586
60f0fa02
JH
587The following collations all make sense and you may meet any of them
588if you "use locale".
589
590 A B C D E a b c d e
35316ca3 591 A a B b C c D d E e
60f0fa02
JH
592 a A b B c C d D e E
593 a b c d e A B C D E
594
f1cbbd6e 595Here is a code snippet to tell what "word"
5a964f20 596characters are in the current locale, in that locale's order:
5f05dabc
PP
597
598 use locale;
35316ca3 599 print +(sort grep /\w/, map { chr } 0..255), "\n";
5f05dabc 600
14280422
DD
601Compare this with the characters that you see and their order if you
602state explicitly that the locale should be ignored:
5f05dabc
PP
603
604 no locale;
35316ca3 605 print +(sort grep /\w/, map { chr } 0..255), "\n";
5f05dabc
PP
606
607This machine-native collation (which is what you get unless S<C<use
608locale>> has appeared earlier in the same block) must be used for
609sorting raw binary data, whereas the locale-dependent collation of the
b0c42ed9 610first example is useful for natural text.
5f05dabc 611
14280422
DD
612As noted in L<USING LOCALES>, C<cmp> compares according to the current
613collation locale when C<use locale> is in effect, but falls back to a
de108802 614char-by-char comparison for strings that the locale says are equal. You
14280422
DD
615can use POSIX::strcoll() if you don't want this fall-back:
616
617 use POSIX qw(strcoll);
618 $equal_in_locale =
619 !strcoll("space and case ignored", "SpaceAndCaseIgnored");
620
621$equal_in_locale will be true if the collation locale specifies a
5a964f20 622dictionary-like ordering that ignores space characters completely and
9e3a2af8 623which folds case.
14280422 624
5a964f20 625If you have a single string that you want to check for "equality in
14280422
DD
626locale" against several others, you might think you could gain a little
627efficiency by using POSIX::strxfrm() in conjunction with C<eq>:
628
629 use POSIX qw(strxfrm);
630 $xfrm_string = strxfrm("Mixed-case string");
631 print "locale collation ignores spaces\n"
632 if $xfrm_string eq strxfrm("Mixed-casestring");
633 print "locale collation ignores hyphens\n"
634 if $xfrm_string eq strxfrm("Mixedcase string");
635 print "locale collation ignores case\n"
636 if $xfrm_string eq strxfrm("mixed-case string");
637
638strxfrm() takes a string and maps it into a transformed string for use
de108802 639in char-by-char comparisons against other transformed strings during
14280422 640collation. "Under the hood", locale-affected Perl comparison operators
de108802 641call strxfrm() for both operands, then do a char-by-char
5a964f20 642comparison of the transformed strings. By calling strxfrm() explicitly
14280422 643and using a non locale-affected comparison, the example attempts to save
5a964f20 644a couple of transformations. But in fact, it doesn't save anything: Perl
2ae324a7 645magic (see L<perlguts/Magic Variables>) creates the transformed version of a
5a964f20 646string the first time it's needed in a comparison, then keeps this version around
14280422 647in case it's needed again. An example rewritten the easy way with
e38874e2 648C<cmp> runs just about as fast. It also copes with null characters
14280422 649embedded in strings; if you call strxfrm() directly, it treats the first
5a964f20
TC
650null it finds as a terminator. don't expect the transformed strings
651it produces to be portable across systems--or even from one revision
e38874e2
DD
652of your operating system to the next. In short, don't call strxfrm()
653directly: let Perl do it for you.
14280422 654
5a964f20 655Note: C<use locale> isn't shown in some of these examples because it isn't
14280422
DD
656needed: strcoll() and strxfrm() exist only to generate locale-dependent
657results, and so always obey the current C<LC_COLLATE> locale.
5f05dabc
PP
658
659=head2 Category LC_CTYPE: Character Types
660
66cbab2c
KW
661In the scope of S<C<use locale>> (but not a
662C<use locale ':not_characters'>), Perl obeys the C<LC_CTYPE> locale
14280422
DD
663setting. This controls the application's notion of which characters are
664alphabetic. This affects Perl's C<\w> regular expression metanotation,
f1cbbd6e
GS
665which stands for alphanumeric characters--that is, alphabetic,
666numeric, and including other special characters such as the underscore or
667hyphen. (Consult L<perlre> for more information about
14280422 668regular expressions.) Thanks to C<LC_CTYPE>, depending on your locale
b4ffc3db
TC
669setting, characters like "E<aelig>", "E<eth>", "E<szlig>", and
670"E<oslash>" may be understood as C<\w> characters.
5f05dabc 671
2c268ad5 672The C<LC_CTYPE> locale also provides the map used in transliterating
68dc0745 673characters between lower and uppercase. This affects the case-mapping
5a964f20
TC
674functions--lc(), lcfirst, uc(), and ucfirst(); case-mapping
675interpolation with C<\l>, C<\L>, C<\u>, or C<\U> in double-quoted strings
676and C<s///> substitutions; and case-independent regular expression
e38874e2
DD
677pattern matching using the C<i> modifier.
678
5a964f20
TC
679Finally, C<LC_CTYPE> affects the POSIX character-class test
680functions--isalpha(), islower(), and so on. For example, if you move
681from the "C" locale to a 7-bit Scandinavian one, you may find--possibly
682to your surprise--that "|" moves from the ispunct() class to isalpha().
ef3087ec
KW
683Unfortunately, this creates big problems for regular expressions. "|" still
684means alternation even though it matches C<\w>.
5f05dabc 685
14280422
DD
686B<Note:> A broken or malicious C<LC_CTYPE> locale definition may result
687in clearly ineligible characters being considered to be alphanumeric by
e199995e 688your application. For strict matching of (mundane) ASCII letters and
5a964f20 689digits--for example, in command strings--locale-aware applications
e199995e 690should use C<\w> with the C</a> regular expression modifier. See L<"SECURITY">.
5f05dabc
PP
691
692=head2 Category LC_NUMERIC: Numeric Formatting
693
2095dafa
RGS
694After a proper POSIX::setlocale() call, Perl obeys the C<LC_NUMERIC>
695locale information, which controls an application's idea of how numbers
696should be formatted for human readability by the printf(), sprintf(), and
697write() functions. String-to-numeric conversion by the POSIX::strtod()
5a964f20 698function is also affected. In most implementations the only effect is to
b4ffc3db 699change the character used for the decimal point--perhaps from "." to ",".
5a964f20 700These functions aren't aware of such niceties as thousands separation and
2095dafa 701so on. (See L<The localeconv function> if you care about these things.)
5a964f20 702
3cf03d68 703Output produced by print() is also affected by the current locale: it
3cf03d68
JH
704corresponds to what you'd get from printf() in the "C" locale. The
705same is true for Perl's internal conversions between numeric and
706string formats:
5f05dabc 707
2095dafa
RGS
708 use POSIX qw(strtod setlocale LC_NUMERIC);
709
710 setlocale LC_NUMERIC, "";
14280422 711
5f05dabc
PP
712 $n = 5/2; # Assign numeric 2.5 to $n
713
35316ca3 714 $a = " $n"; # Locale-dependent conversion to string
5f05dabc 715
35316ca3 716 print "half five is $n\n"; # Locale-dependent output
5f05dabc
PP
717
718 printf "half five is %g\n", $n; # Locale-dependent output
719
14280422
DD
720 print "DECIMAL POINT IS COMMA\n"
721 if $n == (strtod("2,5"))[0]; # Locale-dependent conversion
5f05dabc 722
4bbcc6e8
JH
723See also L<I18N::Langinfo> and C<RADIXCHAR>.
724
5f05dabc
PP
725=head2 Category LC_MONETARY: Formatting of monetary amounts
726
e199995e 727The C standard defines the C<LC_MONETARY> category, but not a function
5a964f20 728that is affected by its contents. (Those with experience of standards
b0c42ed9 729committees will recognize that the working group decided to punt on the
14280422 730issue.) Consequently, Perl takes no notice of it. If you really want
e05ffc7d
KW
731to use C<LC_MONETARY>, you can query its contents--see
732L<The localeconv function>--and use the information that it returns in your
733application's own formatting of currency amounts. However, you may well
734find that the information, voluminous and complex though it may be, still
735does not quite meet your requirements: currency formatting is a hard nut
13a2d996 736to crack.
5f05dabc 737
4bbcc6e8
JH
738See also L<I18N::Langinfo> and C<CRNCYSTR>.
739
5f05dabc
PP
740=head2 LC_TIME
741
5a964f20 742Output produced by POSIX::strftime(), which builds a formatted
5f05dabc
PP
743human-readable date/time string, is affected by the current C<LC_TIME>
744locale. Thus, in a French locale, the output produced by the C<%B>
745format element (full month name) for the first month of the year would
5a964f20 746be "janvier". Here's how to get a list of long month names in the
5f05dabc
PP
747current locale:
748
749 use POSIX qw(strftime);
14280422
DD
750 for (0..11) {
751 $long_month_name[$_] =
752 strftime("%B", 0, 0, 0, 1, $_, 96);
5f05dabc
PP
753 }
754
5a964f20 755Note: C<use locale> isn't needed in this example: as a function that
14280422
DD
756exists only to generate locale-dependent results, strftime() always
757obeys the current C<LC_TIME> locale.
5f05dabc 758
4bbcc6e8 759See also L<I18N::Langinfo> and C<ABDAY_1>..C<ABDAY_7>, C<DAY_1>..C<DAY_7>,
2a2bf5f4 760C<ABMON_1>..C<ABMON_12>, and C<ABMON_1>..C<ABMON_12>.
4bbcc6e8 761
5f05dabc
PP
762=head2 Other categories
763
5a964f20
TC
764The remaining locale category, C<LC_MESSAGES> (possibly supplemented
765by others in particular implementations) is not currently used by
98a6f11e 766Perl--except possibly to affect the behavior of library functions
767called by extensions outside the standard Perl distribution and by the
768operating system and its utilities. Note especially that the string
769value of C<$!> and the error messages given by external utilities may
770be changed by C<LC_MESSAGES>. If you want to have portable error
265f5c4a 771codes, use C<%!>. See L<Errno>.
14280422
DD
772
773=head1 SECURITY
774
5a964f20 775Although the main discussion of Perl security issues can be found in
14280422
DD
776L<perlsec>, a discussion of Perl's locale handling would be incomplete
777if it did not draw your attention to locale-dependent security issues.
5a964f20
TC
778Locales--particularly on systems that allow unprivileged users to
779build their own locales--are untrustworthy. A malicious (or just plain
14280422
DD
780broken) locale can make a locale-aware application give unexpected
781results. Here are a few possibilities:
782
783=over 4
784
785=item *
786
787Regular expression checks for safe file names or mail addresses using
5a964f20 788C<\w> may be spoofed by an C<LC_CTYPE> locale that claims that
14280422
DD
789characters such as "E<gt>" and "|" are alphanumeric.
790
791=item *
792
e38874e2
DD
793String interpolation with case-mapping, as in, say, C<$dest =
794"C:\U$name.$ext">, may produce dangerous results if a bogus LC_CTYPE
795case-mapping table is in effect.
796
797=item *
798
14280422
DD
799A sneaky C<LC_COLLATE> locale could result in the names of students with
800"D" grades appearing ahead of those with "A"s.
801
802=item *
803
5a964f20 804An application that takes the trouble to use information in
14280422 805C<LC_MONETARY> may format debits as if they were credits and vice versa
5a964f20 806if that locale has been subverted. Or it might make payments in US
14280422
DD
807dollars instead of Hong Kong dollars.
808
809=item *
810
811The date and day names in dates formatted by strftime() could be
812manipulated to advantage by a malicious user able to subvert the
5a964f20 813C<LC_DATE> locale. ("Look--it says I wasn't in the building on
14280422
DD
814Sunday.")
815
816=back
817
818Such dangers are not peculiar to the locale system: any aspect of an
5a964f20 819application's environment which may be modified maliciously presents
14280422 820similar challenges. Similarly, they are not specific to Perl: any
5a964f20 821programming language that allows you to write programs that take
14280422
DD
822account of their environment exposes you to these issues.
823
5a964f20
TC
824Perl cannot protect you from all possibilities shown in the
825examples--there is no substitute for your own vigilance--but, when
14280422 826C<use locale> is in effect, Perl uses the tainting mechanism (see
5a964f20 827L<perlsec>) to mark string results that become locale-dependent, and
14280422 828which may be untrustworthy in consequence. Here is a summary of the
5a964f20 829tainting behavior of operators and functions that may be affected by
14280422
DD
830the locale:
831
832=over 4
833
551e1d92
RB
834=item *
835
836B<Comparison operators> (C<lt>, C<le>, C<ge>, C<gt> and C<cmp>):
14280422
DD
837
838Scalar true/false (or less/equal/greater) result is never tainted.
839
551e1d92
RB
840=item *
841
842B<Case-mapping interpolation> (with C<\l>, C<\L>, C<\u> or C<\U>)
e38874e2
DD
843
844Result string containing interpolated material is tainted if
66cbab2c 845C<use locale> (but not S<C<use locale ':not_characters'>>) is in effect.
e38874e2 846
551e1d92
RB
847=item *
848
849B<Matching operator> (C<m//>):
14280422
DD
850
851Scalar true/false result never tainted.
852
5a964f20 853Subpatterns, either delivered as a list-context result or as $1 etc.
66cbab2c
KW
854are tainted if C<use locale> (but not S<C<use locale ':not_characters'>>)
855is in effect, and the subpattern regular
e38874e2 856expression contains C<\w> (to match an alphanumeric character), C<\W>
6b0ac556
OK
857(non-alphanumeric character), C<\s> (whitespace character), or C<\S>
858(non whitespace character). The matched-pattern variable, $&, $`
e38874e2
DD
859(pre-match), $' (post-match), and $+ (last match) are also tainted if
860C<use locale> is in effect and the regular expression contains C<\w>,
861C<\W>, C<\s>, or C<\S>.
14280422 862
551e1d92
RB
863=item *
864
865B<Substitution operator> (C<s///>):
14280422 866
e38874e2 867Has the same behavior as the match operator. Also, the left
66cbab2c
KW
868operand of C<=~> becomes tainted when C<use locale>
869(but not S<C<use locale ':not_characters'>>) is in effect if modified as
870a result of a substitution based on a regular
e38874e2 871expression match involving C<\w>, C<\W>, C<\s>, or C<\S>; or of
7b8d334a 872case-mapping with C<\l>, C<\L>,C<\u> or C<\U>.
14280422 873
551e1d92
RB
874=item *
875
876B<Output formatting functions> (printf() and write()):
14280422 877
3cf03d68
JH
878Results are never tainted because otherwise even output from print,
879for example C<print(1/7)>, should be tainted if C<use locale> is in
880effect.
14280422 881
551e1d92
RB
882=item *
883
884B<Case-mapping functions> (lc(), lcfirst(), uc(), ucfirst()):
14280422 885
66cbab2c
KW
886Results are tainted if C<use locale> (but not
887S<C<use locale ':not_characters'>>) is in effect.
14280422 888
551e1d92
RB
889=item *
890
891B<POSIX locale-dependent functions> (localeconv(), strcoll(),
14280422
DD
892strftime(), strxfrm()):
893
894Results are never tainted.
895
551e1d92
RB
896=item *
897
898B<POSIX character class tests> (isalnum(), isalpha(), isdigit(),
14280422
DD
899isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(),
900isxdigit()):
901
902True/false results are never tainted.
903
904=back
905
906Three examples illustrate locale-dependent tainting.
907The first program, which ignores its locale, won't run: a value taken
54310121 908directly from the command line may not be used to name an output file
14280422
DD
909when taint checks are enabled.
910
911 #/usr/local/bin/perl -T
912 # Run with taint checking
913
54310121 914 # Command line sanity check omitted...
14280422
DD
915 $tainted_output_file = shift;
916
917 open(F, ">$tainted_output_file")
918 or warn "Open of $untainted_output_file failed: $!\n";
919
920The program can be made to run by "laundering" the tainted value through
5a964f20
TC
921a regular expression: the second example--which still ignores locale
922information--runs, creating the file named on its command line
14280422
DD
923if it can.
924
925 #/usr/local/bin/perl -T
926
927 $tainted_output_file = shift;
928 $tainted_output_file =~ m%[\w/]+%;
929 $untainted_output_file = $&;
930
931 open(F, ">$untainted_output_file")
932 or warn "Open of $untainted_output_file failed: $!\n";
933
5a964f20 934Compare this with a similar but locale-aware program:
14280422
DD
935
936 #/usr/local/bin/perl -T
937
938 $tainted_output_file = shift;
939 use locale;
940 $tainted_output_file =~ m%[\w/]+%;
941 $localized_output_file = $&;
942
943 open(F, ">$localized_output_file")
944 or warn "Open of $localized_output_file failed: $!\n";
945
946This third program fails to run because $& is tainted: it is the result
5a964f20 947of a match involving C<\w> while C<use locale> is in effect.
5f05dabc
PP
948
949=head1 ENVIRONMENT
950
951=over 12
952
953=item PERL_BADLANG
954
14280422 955A string that can suppress Perl's warning about failed locale settings
54310121 956at startup. Failure can occur if the locale support in the operating
5a964f20 957system is lacking (broken) in some way--or if you mistyped the name of
900bd440
JH
958a locale when you set up your environment. If this environment
959variable is absent, or has a value that does not evaluate to integer
960zero--that is, "0" or ""-- Perl will complain about locale setting
961failures.
5f05dabc 962
14280422
DD
963B<NOTE>: PERL_BADLANG only gives you a way to hide the warning message.
964The message tells about some problem in your system's locale support,
965and you should investigate what the problem is.
5f05dabc
PP
966
967=back
968
969The following environment variables are not specific to Perl: They are
14280422
DD
970part of the standardized (ISO C, XPG4, POSIX 1.c) setlocale() method
971for controlling an application's opinion on data.
5f05dabc
PP
972
973=over 12
974
975=item LC_ALL
976
5a964f20 977C<LC_ALL> is the "override-all" locale environment variable. If
5f05dabc
PP
978set, it overrides all the rest of the locale environment variables.
979
528d65ad
JH
980=item LANGUAGE
981
982B<NOTE>: C<LANGUAGE> is a GNU extension, it affects you only if you
983are using the GNU libc. This is the case if you are using e.g. Linux.
e1020413 984If you are using "commercial" Unixes you are most probably I<not>
22b6f60d
JH
985using GNU libc and you can ignore C<LANGUAGE>.
986
987However, in the case you are using C<LANGUAGE>: it affects the
988language of informational, warning, and error messages output by
989commands (in other words, it's like C<LC_MESSAGES>) but it has higher
96090e4f 990priority than C<LC_ALL>. Moreover, it's not a single value but
22b6f60d
JH
991instead a "path" (":"-separated list) of I<languages> (not locales).
992See the GNU C<gettext> library documentation for more information.
528d65ad 993
5f05dabc
PP
994=item LC_CTYPE
995
996In the absence of C<LC_ALL>, C<LC_CTYPE> chooses the character type
997locale. In the absence of both C<LC_ALL> and C<LC_CTYPE>, C<LANG>
998chooses the character type locale.
999
1000=item LC_COLLATE
1001
14280422
DD
1002In the absence of C<LC_ALL>, C<LC_COLLATE> chooses the collation
1003(sorting) locale. In the absence of both C<LC_ALL> and C<LC_COLLATE>,
1004C<LANG> chooses the collation locale.
5f05dabc
PP
1005
1006=item LC_MONETARY
1007
14280422
DD
1008In the absence of C<LC_ALL>, C<LC_MONETARY> chooses the monetary
1009formatting locale. In the absence of both C<LC_ALL> and C<LC_MONETARY>,
1010C<LANG> chooses the monetary formatting locale.
5f05dabc
PP
1011
1012=item LC_NUMERIC
1013
1014In the absence of C<LC_ALL>, C<LC_NUMERIC> chooses the numeric format
1015locale. In the absence of both C<LC_ALL> and C<LC_NUMERIC>, C<LANG>
1016chooses the numeric format.
1017
1018=item LC_TIME
1019
14280422
DD
1020In the absence of C<LC_ALL>, C<LC_TIME> chooses the date and time
1021formatting locale. In the absence of both C<LC_ALL> and C<LC_TIME>,
1022C<LANG> chooses the date and time formatting locale.
5f05dabc
PP
1023
1024=item LANG
1025
14280422
DD
1026C<LANG> is the "catch-all" locale environment variable. If it is set, it
1027is used as the last resort after the overall C<LC_ALL> and the
5f05dabc
PP
1028category-specific C<LC_...>.
1029
1030=back
1031
7e4353e9
RGS
1032=head2 Examples
1033
1034The LC_NUMERIC controls the numeric output:
1035
ef3087ec
KW
1036 use locale;
1037 use POSIX qw(locale_h); # Imports setlocale() and the LC_ constants.
1038 setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
1039 printf "%g\n", 1.23; # If the "fr_FR" succeeded, probably shows 1,23.
7e4353e9
RGS
1040
1041and also how strings are parsed by POSIX::strtod() as numbers:
1042
ef3087ec
KW
1043 use locale;
1044 use POSIX qw(locale_h strtod);
1045 setlocale(LC_NUMERIC, "de_DE") or die "Entschuldigung";
1046 my $x = strtod("2,34") + 5;
1047 print $x, "\n"; # Probably shows 7,34.
7e4353e9 1048
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PP
1049=head1 NOTES
1050
1051=head2 Backward compatibility
1052
b0c42ed9 1053Versions of Perl prior to 5.004 B<mostly> ignored locale information,
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1054generally behaving as if something similar to the C<"C"> locale were
1055always in force, even if the program environment suggested otherwise
1056(see L<The setlocale function>). By default, Perl still behaves this
1057way for backward compatibility. If you want a Perl application to pay
1058attention to locale information, you B<must> use the S<C<use locale>>
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1059pragma (see L<The use locale pragma>) or, in the unlikely event
1060that you want to do so for just pattern matching, the
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1061C</l> regular expression modifier (see L<perlre/Character set
1062modifiers>) to instruct it to do so.
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1063
1064Versions of Perl from 5.002 to 5.003 did use the C<LC_CTYPE>
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1065information if available; that is, C<\w> did understand what
1066were the letters according to the locale environment variables.
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1067The problem was that the user had no control over the feature:
1068if the C library supported locales, Perl used them.
1069
1070=head2 I18N:Collate obsolete
1071
5a964f20 1072In versions of Perl prior to 5.004, per-locale collation was possible
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1073using the C<I18N::Collate> library module. This module is now mildly
1074obsolete and should be avoided in new applications. The C<LC_COLLATE>
1075functionality is now integrated into the Perl core language: One can
1076use locale-specific scalar data completely normally with C<use locale>,
1077so there is no longer any need to juggle with the scalar references of
1078C<I18N::Collate>.
5f05dabc 1079
14280422 1080=head2 Sort speed and memory use impacts
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1081
1082Comparing and sorting by locale is usually slower than the default
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1083sorting; slow-downs of two to four times have been observed. It will
1084also consume more memory: once a Perl scalar variable has participated
1085in any string comparison or sorting operation obeying the locale
1086collation rules, it will take 3-15 times more memory than before. (The
1087exact multiplier depends on the string's contents, the operating system
1088and the locale.) These downsides are dictated more by the operating
1089system's implementation of the locale system than by Perl.
5f05dabc 1090
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1091=head2 write() and LC_NUMERIC
1092
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1093If a program's environment specifies an LC_NUMERIC locale and C<use
1094locale> is in effect when the format is declared, the locale is used
1095to specify the decimal point character in formatted output. Formatted
1096output cannot be controlled by C<use locale> at the time when write()
1097is called.
e38874e2 1098
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1099=head2 Freely available locale definitions
1100
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1101The Unicode CLDR project extracts the POSIX portion of many of its
1102locales, available at
1103
1104 http://unicode.org/Public/cldr/latest/
1105
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1106There is a large collection of locale definitions at:
1107
1108 http://std.dkuug.dk/i18n/WG15-collection/locales/
1109
1110You should be aware that it is
14280422 1111unsupported, and is not claimed to be fit for any purpose. If your
5a964f20 1112system allows installation of arbitrary locales, you may find the
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1113definitions useful as they are, or as a basis for the development of
1114your own locales.
5f05dabc 1115
14280422 1116=head2 I18n and l10n
5f05dabc 1117
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1118"Internationalization" is often abbreviated as B<i18n> because its first
1119and last letters are separated by eighteen others. (You may guess why
1120the internalin ... internaliti ... i18n tends to get abbreviated.) In
1121the same way, "localization" is often abbreviated to B<l10n>.
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1122
1123=head2 An imperfect standard
1124
1125Internationalization, as defined in the C and POSIX standards, can be
1126criticized as incomplete, ungainly, and having too large a granularity.
1127(Locales apply to a whole process, when it would arguably be more useful
1128to have them apply to a single thread, window group, or whatever.) They
1129also have a tendency, like standards groups, to divide the world into
1130nations, when we all know that the world can equally well be divided
e199995e 1131into bankers, bikers, gamers, and so on.
5f05dabc 1132
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1133=head1 Unicode and UTF-8
1134
e199995e 1135The support of Unicode is new starting from Perl version 5.6, and more fully
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1136implemented in version 5.8 and later. See L<perluniintro>. It is
1137strongly recommended that when combining Unicode and locale (starting in
11385.16), you use
1139
1140 use locale ':not_characters';
1141
1142When this form of the pragma is used, only the non-character portions of
1143locales are used by Perl, for example C<LC_NUMERIC>. Perl assumes that
1144you have translated all the characters it is to operate on into Unicode
1145(actually the platform's native character set (ASCII or EBCDIC) plus
1146Unicode). For data in files, this can conveniently be done by also
1147specifying
1148
1149 use open ':locale';
1150
1151This pragma arranges for all inputs from files to be translated into
1152Unicode from the current locale as specified in the environment (see
1153L</ENVIRONMENT>), and all outputs to files to be translated back
1154into the locale. (See L<open>). On a per-filehandle basis, you can
1155instead use the L<PerlIO::locale> module, or the L<Encode::Locale>
1156module, both available from CPAN. The latter module also has methods to
1157ease the handling of C<ARGV> and environment variables, and can be used
1158on individual strings. Also, if you know that all your locales will be
1159UTF-8, as many are these days, you can use the L<B<-C>|perlrun/-C>
1160command line switch.
1161
1162This form of the pragma allows essentially seamless handling of locales
1163with Unicode. The collation order will be Unicode's. It is strongly
1164recommended that when you need to order and sort strings that you use
1165the standard module L<Unicode::Collate> which gives much better results
1166in many instances than you can get with the old-style locale handling.
1167
1168For pre-5.16 Perls, or if you use the locale pragma without the
1169C<:not_characters> parameter, Perl tries to work with both Unicode and
1170locales--but there are problems.
1171
1172Perl does not handle multi-byte locales in this case, such as have been
1173used for various
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1174Asian languages, such as Big5 or Shift JIS. However, the increasingly
1175common multi-byte UTF-8 locales, if properly implemented, may work
1176reasonably well (depending on your C library implementation) in this
1177form of the locale pragma, simply because both
1178they and Perl store characters that take up multiple bytes the same way.
1179However, some, if not most, C library implementations may not process
1180the characters in the upper half of the Latin-1 range (128 - 255)
1181properly under LC_CTYPE. To see if a character is a particular type
1182under a locale, Perl uses the functions like C<isalnum()>. Your C
1183library may not work for UTF-8 locales with those functions, instead
1184only working under the newer wide library functions like C<iswalnum()>.
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1185
1186Perl generally takes the tack to use locale rules on code points that can fit
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1187in a single byte, and Unicode rules for those that can't (though this
1188isn't uniformly applied, see the note at the end of this section). This
1189prevents many problems in locales that aren't UTF-8. Suppose the locale
1190is ISO8859-7, Greek. The character at 0xD7 there is a capital Chi. But
1191in the ISO8859-1 locale, Latin1, it is a multiplication sign. The POSIX
1192regular expression character class C<[[:alpha:]]> will magically match
11930xD7 in the Greek locale but not in the Latin one.
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1194
1195However, there are places where this breaks down. Certain constructs are
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1196for Unicode only, such as C<\p{Alpha}>. They assume that 0xD7 always has its
1197Unicode meaning (or the equivalent on EBCDIC platforms). Since Latin1 is a
1198subset of Unicode and 0xD7 is the multiplication sign in both Latin1 and
1199Unicode, C<\p{Alpha}> will never match it, regardless of locale. A similar
1200issue occurs with C<\N{...}>. It is therefore a bad idea to use C<\p{}> or
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1201C<\N{}> under plain C<use locale>--I<unless> you can guarantee that the
1202locale will be a ISO8859-1. Use POSIX character classes instead.
1203
1204Another problem with this approach is that operations that cross the
1205single byte/multiple byte boundary are not well-defined, and so are
1206disallowed. (This boundary is between the codepoints at 255/256.).
1207For example, lower casing LATIN CAPITAL LETTER Y WITH DIAERESIS (U+0178)
1208should return LATIN SMALL LETTER Y WITH DIAERESIS (U+00FF). But in the
1209Greek locale, for example, there is no character at 0xFF, and Perl
1210has no way of knowing what the character at 0xFF is really supposed to
1211represent. Thus it disallows the operation. In this mode, the
1212lowercase of U+0178 is itself.
1213
1214The same problems ensue if you enable automatic UTF-8-ification of your
e199995e 1215standard file handles, default C<open()> layer, and C<@ARGV> on non-ISO8859-1,
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1216non-UTF-8 locales (by using either the B<-C> command line switch or the
1217C<PERL_UNICODE> environment variable; see L<perlrun>).
1218Things are read in as UTF-8, which would normally imply a Unicode
1219interpretation, but the presence of a locale causes them to be interpreted
1220in that locale instead. For example, a 0xD7 code point in the Unicode
1221input, which should mean the multiplication sign, won't be interpreted by
66cbab2c 1222Perl that way under the Greek locale. This is not a problem
b4ffc3db 1223I<provided> you make certain that all locales will always and only be either
66cbab2c 1224an ISO8859-1, or, if you don't have a deficient C library, a UTF-8 locale.
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1225
1226Vendor locales are notoriously buggy, and it is difficult for Perl to test
1227its locale-handling code because this interacts with code that Perl has no
1228control over; therefore the locale-handling code in Perl may be buggy as
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1229well. (However, the Unicode-supplied locales should be better, and
1230there is a feed back mechanism to correct any problems. See
1231L</Freely available locale definitions>.)
1232
1233If you have Perl 5.16, the problems mentioned above go away if you use
1234the C<:not_characters> parameter to the locale pragma (except for vendor
1235bugs in the non-character portions). If you don't have 5.16, and you
1236I<do> have locales that work, using them may be worthwhile for certain
1237specific purposes, as long as you keep in mind the gotchas already
1238mentioned. For example, if the collation for your locales works, it
1239runs faster under locales than under L<Unicode::Collate>; and you gain
1240access to such things as the local currency symbol and the names of the
1241months and days of the week. (But to hammer home the point, in 5.16,
1242you get this access without the downsides of locales by using the
1243C<:not_characters> form of the pragma.)
1244
1245Note: The policy of using locale rules for code points that can fit in a
1246byte, and Unicode rules for those that can't is not uniformly applied.
1247Pre-5.12, it was somewhat haphazard; in 5.12 it was applied fairly
1248consistently to regular expression matching except for bracketed
1249character classes; in 5.14 it was extended to all regex matches; and in
12505.16 to the casing operations such as C<"\L"> and C<uc()>. For
1251collation, in all releases, the system's C<strxfrm()> function is called,
1252and whatever it does is what you get.
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1254=head1 BUGS
1255
1256=head2 Broken systems
1257
5a964f20 1258In certain systems, the operating system's locale support
2bdf8add 1259is broken and cannot be fixed or used by Perl. Such deficiencies can
b4ffc3db 1260and will result in mysterious hangs and/or Perl core dumps when
2bdf8add 1261C<use locale> is in effect. When confronted with such a system,
7f2de2d2 1262please report in excruciating detail to <F<perlbug@perl.org>>, and
b4ffc3db 1263also contact your vendor: bug fixes may exist for these problems
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1264in your operating system. Sometimes such bug fixes are called an
1265operating system upgrade.
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1266
1267=head1 SEE ALSO
1268
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1269L<I18N::Langinfo>, L<perluniintro>, L<perlunicode>, L<open>,
1270L<POSIX/isalnum>, L<POSIX/isalpha>,
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1271L<POSIX/isdigit>, L<POSIX/isgraph>, L<POSIX/islower>,
1272L<POSIX/isprint>, L<POSIX/ispunct>, L<POSIX/isspace>,
1273L<POSIX/isupper>, L<POSIX/isxdigit>, L<POSIX/localeconv>,
1274L<POSIX/setlocale>, L<POSIX/strcoll>, L<POSIX/strftime>,
1275L<POSIX/strtod>, L<POSIX/strxfrm>.
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1276
1277=head1 HISTORY
1278
b0c42ed9 1279Jarkko Hietaniemi's original F<perli18n.pod> heavily hacked by Dominic
5a964f20 1280Dunlop, assisted by the perl5-porters. Prose worked over a bit by
c052850d 1281Tom Christiansen, and updated by Perl 5 porters.