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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
589e2f52 25Perl was 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
75This for the most part is beyond the scope of Perl
76
77=item Category LC_COLLATE: Collation
78
76073c88 79This indicates the ordering of letters for comparison and sorting.
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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>>
66cbab2c 154pragma tells Perl to use the current locale for some operations.
7ee2ae1e 155Starting in v5.16, there is an optional parameter to this pragma:
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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:
5f05dabc 248
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249 # Import locale-handling tool set from POSIX module.
250 # This example uses: setlocale -- the function call
251 # LC_CTYPE -- explained below
252 use POSIX qw(locale_h);
253
14280422 254 # query and save the old locale
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255 $old_locale = setlocale(LC_CTYPE);
256
257 setlocale(LC_CTYPE, "fr_CA.ISO8859-1");
258 # LC_CTYPE now in locale "French, Canada, codeset ISO 8859-1"
259
260 setlocale(LC_CTYPE, "");
261 # LC_CTYPE now reset to default defined by LC_ALL/LC_CTYPE/LANG
262 # environment variables. See below for documentation.
263
264 # restore the old locale
265 setlocale(LC_CTYPE, $old_locale);
266
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267The first argument of setlocale() gives the B<category>, the second the
268B<locale>. The category tells in what aspect of data processing you
269want to apply locale-specific rules. Category names are discussed in
66cbab2c 270L</LOCALE CATEGORIES> and L</"ENVIRONMENT">. The locale is the name of a
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271collection of customization information corresponding to a particular
272combination of language, country or territory, and codeset. Read on for
273hints on the naming of locales: not all systems name locales as in the
274example.
275
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276If no second argument is provided and the category is something else
277than LC_ALL, the function returns a string naming the current locale
278for the category. You can use this value as the second argument in a
279subsequent call to setlocale().
280
281If no second argument is provided and the category is LC_ALL, the
282result is implementation-dependent. It may be a string of
c052850d 283concatenated locale names (separator also implementation-dependent)
f979aebc 284or a single locale name. Please consult your setlocale(3) man page for
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285details.
286
287If a second argument is given and it corresponds to a valid locale,
288the locale for the category is set to that value, and the function
289returns the now-current locale value. You can then use this in yet
290another call to setlocale(). (In some implementations, the return
291value may sometimes differ from the value you gave as the second
292argument--think of it as an alias for the value you gave.)
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293
294As the example shows, if the second argument is an empty string, the
295category's locale is returned to the default specified by the
296corresponding environment variables. Generally, this results in a
5a964f20 297return to the default that was in force when Perl started up: changes
54310121 298to the environment made by the application after startup may or may not
5a964f20 299be noticed, depending on your system's C library.
5f05dabc 300
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301If the second argument does not correspond to a valid locale, the locale
302for the category is not changed, and the function returns I<undef>.
5f05dabc 303
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304Note that Perl ignores the current C<LC_CTYPE> and C<LC_COLLATE> locales
305within the scope of a C<use locale ':not_characters'>.
306
f979aebc 307For further information about the categories, consult setlocale(3).
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308
309=head2 Finding locales
310
f979aebc 311For locales available in your system, consult also setlocale(3) to
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312see whether it leads to the list of available locales (search for the
313I<SEE ALSO> section). If that fails, try the following command lines:
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314
315 locale -a
316
317 nlsinfo
318
319 ls /usr/lib/nls/loc
320
321 ls /usr/lib/locale
322
323 ls /usr/lib/nls
324
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325 ls /usr/share/locale
326
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327and see whether they list something resembling these
328
2bdf8add 329 en_US.ISO8859-1 de_DE.ISO8859-1 ru_RU.ISO8859-5
502a173a 330 en_US.iso88591 de_DE.iso88591 ru_RU.iso88595
2bdf8add 331 en_US de_DE ru_RU
14280422 332 en de ru
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333 english german russian
334 english.iso88591 german.iso88591 russian.iso88595
502a173a 335 english.roman8 russian.koi8r
5f05dabc 336
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337Sadly, even though the calling interface for setlocale() has been
338standardized, names of locales and the directories where the
5a964f20 339configuration resides have not been. The basic form of the name is
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340I<language_territory>B<.>I<codeset>, but the latter parts after
341I<language> are not always present. The I<language> and I<country>
342are usually from the standards B<ISO 3166> and B<ISO 639>, the
343two-letter abbreviations for the countries and the languages of the
344world, respectively. The I<codeset> part often mentions some B<ISO
3458859> character set, the Latin codesets. For example, C<ISO 8859-1>
346is the so-called "Western European codeset" that can be used to encode
347most Western European languages adequately. Again, there are several
348ways to write even the name of that one standard. Lamentably.
5f05dabc 349
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350Two special locales are worth particular mention: "C" and "POSIX".
351Currently these are effectively the same locale: the difference is
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352mainly that the first one is defined by the C standard, the second by
353the POSIX standard. They define the B<default locale> in which
14280422 354every program starts in the absence of locale information in its
5a964f20 355environment. (The I<default> default locale, if you will.) Its language
14280422 356is (American) English and its character codeset ASCII.
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357B<Warning>. The C locale delivered by some vendors may not
358actually exactly match what the C standard calls for. So beware.
5f05dabc 359
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360B<NOTE>: Not all systems have the "POSIX" locale (not all systems are
361POSIX-conformant), so use "C" when you need explicitly to specify this
362default locale.
5f05dabc 363
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364=head2 LOCALE PROBLEMS
365
5a964f20 366You may encounter the following warning message at Perl startup:
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367
368 perl: warning: Setting locale failed.
369 perl: warning: Please check that your locale settings:
370 LC_ALL = "En_US",
371 LANG = (unset)
372 are supported and installed on your system.
373 perl: warning: Falling back to the standard locale ("C").
374
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375This means that your locale settings had LC_ALL set to "En_US" and
376LANG exists but has no value. Perl tried to believe you but could not.
377Instead, Perl gave up and fell back to the "C" locale, the default locale
378that is supposed to work no matter what. This usually means your locale
379settings were wrong, they mention locales your system has never heard
380of, or the locale installation in your system has problems (for example,
381some system files are broken or missing). There are quick and temporary
382fixes to these problems, as well as more thorough and lasting fixes.
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383
384=head2 Temporarily fixing locale problems
385
5a964f20 386The two quickest fixes are either to render Perl silent about any
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387locale inconsistencies or to run Perl under the default locale "C".
388
389Perl's moaning about locale problems can be silenced by setting the
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390environment variable PERL_BADLANG to a zero value, for example "0".
391This method really just sweeps the problem under the carpet: you tell
392Perl to shut up even when Perl sees that something is wrong. Do not
393be surprised if later something locale-dependent misbehaves.
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394
395Perl can be run under the "C" locale by setting the environment
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396variable LC_ALL to "C". This method is perhaps a bit more civilized
397than the PERL_BADLANG approach, but setting LC_ALL (or
398other locale variables) may affect other programs as well, not just
399Perl. In particular, external programs run from within Perl will see
3e6e419a 400these changes. If you make the new settings permanent (read on), all
f979aebc 401programs you run see the changes. See L<"ENVIRONMENT"> for
5a964f20 402the full list of relevant environment variables and L<USING LOCALES>
e05ffc7d 403for their effects in Perl. Effects in other programs are
5a964f20 404easily deducible. For example, the variable LC_COLLATE may well affect
b432a672 405your B<sort> program (or whatever the program that arranges "records"
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406alphabetically in your system is called).
407
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408You can test out changing these variables temporarily, and if the
409new settings seem to help, put those settings into your shell startup
410files. Consult your local documentation for the exact details. For in
411Bourne-like shells (B<sh>, B<ksh>, B<bash>, B<zsh>):
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412
413 LC_ALL=en_US.ISO8859-1
414 export LC_ALL
415
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416This assumes that we saw the locale "en_US.ISO8859-1" using the commands
417discussed above. We decided to try that instead of the above faulty
418locale "En_US"--and in Cshish shells (B<csh>, B<tcsh>)
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419
420 setenv LC_ALL en_US.ISO8859-1
c47ff5f1 421
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422or if you have the "env" application you can do in any shell
423
424 env LC_ALL=en_US.ISO8859-1 perl ...
425
5a964f20 426If you do not know what shell you have, consult your local
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427helpdesk or the equivalent.
428
429=head2 Permanently fixing locale problems
430
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431The slower but superior fixes are when you may be able to yourself
432fix the misconfiguration of your own environment variables. The
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433mis(sing)configuration of the whole system's locales usually requires
434the help of your friendly system administrator.
435
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436First, see earlier in this document about L<Finding locales>. That tells
437how to find which locales are really supported--and more importantly,
438installed--on your system. In our example error message, environment
439variables affecting the locale are listed in the order of decreasing
440importance (and unset variables do not matter). Therefore, having
441LC_ALL set to "En_US" must have been the bad choice, as shown by the
442error message. First try fixing locale settings listed first.
3e6e419a 443
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444Second, if using the listed commands you see something B<exactly>
445(prefix matches do not count and case usually counts) like "En_US"
446without the quotes, then you should be okay because you are using a
447locale name that should be installed and available in your system.
4a4eefd0 448In this case, see L<Permanently fixing your system's locale configuration>.
3e6e419a 449
4a4eefd0 450=head2 Permanently fixing your system's locale configuration
3e6e419a 451
5a964f20 452This is when you see something like:
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453
454 perl: warning: Please check that your locale settings:
455 LC_ALL = "En_US",
456 LANG = (unset)
457 are supported and installed on your system.
458
459but then cannot see that "En_US" listed by the above-mentioned
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460commands. You may see things like "en_US.ISO8859-1", but that isn't
461the same. In this case, try running under a locale
462that you can list and which somehow matches what you tried. The
3e6e419a 463rules for matching locale names are a bit vague because
e05ffc7d 464standardization is weak in this area. See again the
13a2d996 465L<Finding locales> about general rules.
3e6e419a 466
b687b08b 467=head2 Fixing system locale configuration
3e6e419a 468
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469Contact a system administrator (preferably your own) and report the exact
470error message you get, and ask them to read this same documentation you
471are now reading. They should be able to check whether there is something
472wrong with the locale configuration of the system. The L<Finding locales>
473section is unfortunately a bit vague about the exact commands and places
474because these things are not that standardized.
3e6e419a 475
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476=head2 The localeconv function
477
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478The POSIX::localeconv() function allows you to get particulars of the
479locale-dependent numeric formatting information specified by the current
480C<LC_NUMERIC> and C<LC_MONETARY> locales. (If you just want the name of
481the current locale for a particular category, use POSIX::setlocale()
5a964f20 482with a single parameter--see L<The setlocale function>.)
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483
484 use POSIX qw(locale_h);
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485
486 # Get a reference to a hash of locale-dependent info
487 $locale_values = localeconv();
488
489 # Output sorted list of the values
490 for (sort keys %$locale_values) {
14280422 491 printf "%-20s = %s\n", $_, $locale_values->{$_}
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492 }
493
14280422 494localeconv() takes no arguments, and returns B<a reference to> a hash.
5a964f20 495The keys of this hash are variable names for formatting, such as
502a173a 496C<decimal_point> and C<thousands_sep>. The values are the
cea6626f 497corresponding, er, values. See L<POSIX/localeconv> for a longer
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498example listing the categories an implementation might be expected to
499provide; some provide more and others fewer. You don't need an
500explicit C<use locale>, because localeconv() always observes the
501current locale.
5f05dabc 502
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503Here's a simple-minded example program that rewrites its command-line
504parameters as integers correctly formatted in the current locale:
5f05dabc 505
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506 use POSIX qw(locale_h);
507
508 # Get some of locale's numeric formatting parameters
509 my ($thousands_sep, $grouping) =
510 @{localeconv()}{'thousands_sep', 'grouping'};
511
512 # Apply defaults if values are missing
513 $thousands_sep = ',' unless $thousands_sep;
514
515 # grouping and mon_grouping are packed lists
516 # of small integers (characters) telling the
517 # grouping (thousand_seps and mon_thousand_seps
518 # being the group dividers) of numbers and
519 # monetary quantities. The integers' meanings:
520 # 255 means no more grouping, 0 means repeat
521 # the previous grouping, 1-254 means use that
522 # as the current grouping. Grouping goes from
523 # right to left (low to high digits). In the
524 # below we cheat slightly by never using anything
525 # else than the first grouping (whatever that is).
526 if ($grouping) {
527 @grouping = unpack("C*", $grouping);
528 } else {
529 @grouping = (3);
530 }
531
532 # Format command line params for current locale
533 for (@ARGV) {
534 $_ = int; # Chop non-integer part
535 1 while
536 s/(\d)(\d{$grouping[0]}($|$thousands_sep))/$1$thousands_sep$2/;
537 print "$_";
538 }
539 print "\n";
5f05dabc 540
74c76037 541=head2 I18N::Langinfo
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542
543Another interface for querying locale-dependent information is the
e1020413 544I18N::Langinfo::langinfo() function, available at least in Unix-like
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545systems and VMS.
546
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547The following example will import the langinfo() function itself and
548three constants to be used as arguments to langinfo(): a constant for
549the abbreviated first day of the week (the numbering starts from
550Sunday = 1) and two more constants for the affirmative and negative
551answers for a yes/no question in the current locale.
4bbcc6e8 552
74c76037 553 use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
4bbcc6e8 554
ef3087ec
KW
555 my ($abday_1, $yesstr, $nostr)
556 = map { langinfo } qw(ABDAY_1 YESSTR NOSTR);
4bbcc6e8 557
74c76037 558 print "$abday_1? [$yesstr/$nostr] ";
4bbcc6e8 559
74c76037
JH
560In other words, in the "C" (or English) locale the above will probably
561print something like:
562
e05ffc7d 563 Sun? [yes/no]
4bbcc6e8
JH
564
565See L<I18N::Langinfo> for more information.
566
5f05dabc
PP
567=head1 LOCALE CATEGORIES
568
5a964f20
TC
569The following subsections describe basic locale categories. Beyond these,
570some combination categories allow manipulation of more than one
571basic category at a time. See L<"ENVIRONMENT"> for a discussion of these.
5f05dabc
PP
572
573=head2 Category LC_COLLATE: Collation
574
66cbab2c
KW
575In the scope of S<C<use locale>> (but not a
576C<use locale ':not_characters'>), Perl looks to the C<LC_COLLATE>
5a964f20 577environment variable to determine the application's notions on collation
b4ffc3db
TC
578(ordering) of characters. For example, "b" follows "a" in Latin
579alphabets, but where do "E<aacute>" and "E<aring>" belong? And while
f87fa335 580"color" follows "chocolate" in English, what about in traditional Spanish?
5f05dabc 581
60f0fa02
JH
582The following collations all make sense and you may meet any of them
583if you "use locale".
584
585 A B C D E a b c d e
35316ca3 586 A a B b C c D d E e
60f0fa02
JH
587 a A b B c C d D e E
588 a b c d e A B C D E
589
f1cbbd6e 590Here is a code snippet to tell what "word"
5a964f20 591characters are in the current locale, in that locale's order:
5f05dabc
PP
592
593 use locale;
35316ca3 594 print +(sort grep /\w/, map { chr } 0..255), "\n";
5f05dabc 595
14280422
DD
596Compare this with the characters that you see and their order if you
597state explicitly that the locale should be ignored:
5f05dabc
PP
598
599 no locale;
35316ca3 600 print +(sort grep /\w/, map { chr } 0..255), "\n";
5f05dabc
PP
601
602This machine-native collation (which is what you get unless S<C<use
603locale>> has appeared earlier in the same block) must be used for
604sorting raw binary data, whereas the locale-dependent collation of the
b0c42ed9 605first example is useful for natural text.
5f05dabc 606
14280422
DD
607As noted in L<USING LOCALES>, C<cmp> compares according to the current
608collation locale when C<use locale> is in effect, but falls back to a
de108802 609char-by-char comparison for strings that the locale says are equal. You
14280422
DD
610can use POSIX::strcoll() if you don't want this fall-back:
611
612 use POSIX qw(strcoll);
613 $equal_in_locale =
614 !strcoll("space and case ignored", "SpaceAndCaseIgnored");
615
616$equal_in_locale will be true if the collation locale specifies a
5a964f20 617dictionary-like ordering that ignores space characters completely and
9e3a2af8 618which folds case.
14280422 619
5a964f20 620If you have a single string that you want to check for "equality in
14280422
DD
621locale" against several others, you might think you could gain a little
622efficiency by using POSIX::strxfrm() in conjunction with C<eq>:
623
624 use POSIX qw(strxfrm);
625 $xfrm_string = strxfrm("Mixed-case string");
626 print "locale collation ignores spaces\n"
627 if $xfrm_string eq strxfrm("Mixed-casestring");
628 print "locale collation ignores hyphens\n"
629 if $xfrm_string eq strxfrm("Mixedcase string");
630 print "locale collation ignores case\n"
631 if $xfrm_string eq strxfrm("mixed-case string");
632
633strxfrm() takes a string and maps it into a transformed string for use
de108802 634in char-by-char comparisons against other transformed strings during
14280422 635collation. "Under the hood", locale-affected Perl comparison operators
de108802 636call strxfrm() for both operands, then do a char-by-char
5a964f20 637comparison of the transformed strings. By calling strxfrm() explicitly
14280422 638and using a non locale-affected comparison, the example attempts to save
5a964f20 639a couple of transformations. But in fact, it doesn't save anything: Perl
2ae324a7 640magic (see L<perlguts/Magic Variables>) creates the transformed version of a
5a964f20 641string the first time it's needed in a comparison, then keeps this version around
14280422 642in case it's needed again. An example rewritten the easy way with
e38874e2 643C<cmp> runs just about as fast. It also copes with null characters
14280422 644embedded in strings; if you call strxfrm() directly, it treats the first
5a964f20
TC
645null it finds as a terminator. don't expect the transformed strings
646it produces to be portable across systems--or even from one revision
e38874e2
DD
647of your operating system to the next. In short, don't call strxfrm()
648directly: let Perl do it for you.
14280422 649
5a964f20 650Note: C<use locale> isn't shown in some of these examples because it isn't
14280422
DD
651needed: strcoll() and strxfrm() exist only to generate locale-dependent
652results, and so always obey the current C<LC_COLLATE> locale.
5f05dabc
PP
653
654=head2 Category LC_CTYPE: Character Types
655
66cbab2c
KW
656In the scope of S<C<use locale>> (but not a
657C<use locale ':not_characters'>), Perl obeys the C<LC_CTYPE> locale
14280422
DD
658setting. This controls the application's notion of which characters are
659alphabetic. This affects Perl's C<\w> regular expression metanotation,
f1cbbd6e
GS
660which stands for alphanumeric characters--that is, alphabetic,
661numeric, and including other special characters such as the underscore or
662hyphen. (Consult L<perlre> for more information about
14280422 663regular expressions.) Thanks to C<LC_CTYPE>, depending on your locale
b4ffc3db
TC
664setting, characters like "E<aelig>", "E<eth>", "E<szlig>", and
665"E<oslash>" may be understood as C<\w> characters.
5f05dabc 666
2c268ad5 667The C<LC_CTYPE> locale also provides the map used in transliterating
68dc0745 668characters between lower and uppercase. This affects the case-mapping
b9cc4f69
KW
669functions--fc(), lc(), lcfirst(), uc(), and ucfirst(); case-mapping
670interpolation with C<\F>, C<\l>, C<\L>, C<\u>, or C<\U> in double-quoted
671strings and C<s///> substitutions; and case-independent regular expression
e38874e2
DD
672pattern matching using the C<i> modifier.
673
5a964f20
TC
674Finally, C<LC_CTYPE> affects the POSIX character-class test
675functions--isalpha(), islower(), and so on. For example, if you move
676from the "C" locale to a 7-bit Scandinavian one, you may find--possibly
677to your surprise--that "|" moves from the ispunct() class to isalpha().
ef3087ec
KW
678Unfortunately, this creates big problems for regular expressions. "|" still
679means alternation even though it matches C<\w>.
5f05dabc 680
5d63e270
KW
681Note that there are quite a few things that are unaffected by the
682current locale. All the escape sequences for particular characters,
683C<\n> for example, always mean the platform's native one. This means,
684for example, that C<\N> in regular expressions (every character
685but new-line) work on the platform character set.
686
14280422
DD
687B<Note:> A broken or malicious C<LC_CTYPE> locale definition may result
688in clearly ineligible characters being considered to be alphanumeric by
e199995e 689your application. For strict matching of (mundane) ASCII letters and
5a964f20 690digits--for example, in command strings--locale-aware applications
e199995e 691should use C<\w> with the C</a> regular expression modifier. See L<"SECURITY">.
5f05dabc
PP
692
693=head2 Category LC_NUMERIC: Numeric Formatting
694
2095dafa
RGS
695After a proper POSIX::setlocale() call, Perl obeys the C<LC_NUMERIC>
696locale information, which controls an application's idea of how numbers
697should be formatted for human readability by the printf(), sprintf(), and
698write() functions. String-to-numeric conversion by the POSIX::strtod()
5a964f20 699function is also affected. In most implementations the only effect is to
b4ffc3db 700change the character used for the decimal point--perhaps from "." to ",".
5a964f20 701These functions aren't aware of such niceties as thousands separation and
2095dafa 702so on. (See L<The localeconv function> if you care about these things.)
5a964f20 703
3cf03d68 704Output produced by print() is also affected by the current locale: it
3cf03d68
JH
705corresponds to what you'd get from printf() in the "C" locale. The
706same is true for Perl's internal conversions between numeric and
707string formats:
5f05dabc 708
2095dafa
RGS
709 use POSIX qw(strtod setlocale LC_NUMERIC);
710
711 setlocale LC_NUMERIC, "";
14280422 712
5f05dabc
PP
713 $n = 5/2; # Assign numeric 2.5 to $n
714
35316ca3 715 $a = " $n"; # Locale-dependent conversion to string
5f05dabc 716
35316ca3 717 print "half five is $n\n"; # Locale-dependent output
5f05dabc
PP
718
719 printf "half five is %g\n", $n; # Locale-dependent output
720
14280422
DD
721 print "DECIMAL POINT IS COMMA\n"
722 if $n == (strtod("2,5"))[0]; # Locale-dependent conversion
5f05dabc 723
4bbcc6e8
JH
724See also L<I18N::Langinfo> and C<RADIXCHAR>.
725
5f05dabc
PP
726=head2 Category LC_MONETARY: Formatting of monetary amounts
727
e199995e 728The C standard defines the C<LC_MONETARY> category, but not a function
5a964f20 729that is affected by its contents. (Those with experience of standards
b0c42ed9 730committees will recognize that the working group decided to punt on the
14280422 731issue.) Consequently, Perl takes no notice of it. If you really want
e05ffc7d
KW
732to use C<LC_MONETARY>, you can query its contents--see
733L<The localeconv function>--and use the information that it returns in your
734application's own formatting of currency amounts. However, you may well
735find that the information, voluminous and complex though it may be, still
736does not quite meet your requirements: currency formatting is a hard nut
13a2d996 737to crack.
5f05dabc 738
4bbcc6e8
JH
739See also L<I18N::Langinfo> and C<CRNCYSTR>.
740
5f05dabc
PP
741=head2 LC_TIME
742
5a964f20 743Output produced by POSIX::strftime(), which builds a formatted
5f05dabc
PP
744human-readable date/time string, is affected by the current C<LC_TIME>
745locale. Thus, in a French locale, the output produced by the C<%B>
746format element (full month name) for the first month of the year would
5a964f20 747be "janvier". Here's how to get a list of long month names in the
5f05dabc
PP
748current locale:
749
750 use POSIX qw(strftime);
14280422
DD
751 for (0..11) {
752 $long_month_name[$_] =
753 strftime("%B", 0, 0, 0, 1, $_, 96);
5f05dabc
PP
754 }
755
5a964f20 756Note: C<use locale> isn't needed in this example: as a function that
14280422
DD
757exists only to generate locale-dependent results, strftime() always
758obeys the current C<LC_TIME> locale.
5f05dabc 759
4bbcc6e8 760See also L<I18N::Langinfo> and C<ABDAY_1>..C<ABDAY_7>, C<DAY_1>..C<DAY_7>,
2a2bf5f4 761C<ABMON_1>..C<ABMON_12>, and C<ABMON_1>..C<ABMON_12>.
4bbcc6e8 762
5f05dabc
PP
763=head2 Other categories
764
5a964f20
TC
765The remaining locale category, C<LC_MESSAGES> (possibly supplemented
766by others in particular implementations) is not currently used by
98a6f11e 767Perl--except possibly to affect the behavior of library functions
768called by extensions outside the standard Perl distribution and by the
769operating system and its utilities. Note especially that the string
770value of C<$!> and the error messages given by external utilities may
771be changed by C<LC_MESSAGES>. If you want to have portable error
265f5c4a 772codes, use C<%!>. See L<Errno>.
14280422
DD
773
774=head1 SECURITY
775
5a964f20 776Although the main discussion of Perl security issues can be found in
14280422
DD
777L<perlsec>, a discussion of Perl's locale handling would be incomplete
778if it did not draw your attention to locale-dependent security issues.
5a964f20
TC
779Locales--particularly on systems that allow unprivileged users to
780build their own locales--are untrustworthy. A malicious (or just plain
14280422
DD
781broken) locale can make a locale-aware application give unexpected
782results. Here are a few possibilities:
783
784=over 4
785
786=item *
787
788Regular expression checks for safe file names or mail addresses using
5a964f20 789C<\w> may be spoofed by an C<LC_CTYPE> locale that claims that
14280422
DD
790characters such as "E<gt>" and "|" are alphanumeric.
791
792=item *
793
e38874e2
DD
794String interpolation with case-mapping, as in, say, C<$dest =
795"C:\U$name.$ext">, may produce dangerous results if a bogus LC_CTYPE
796case-mapping table is in effect.
797
798=item *
799
14280422
DD
800A sneaky C<LC_COLLATE> locale could result in the names of students with
801"D" grades appearing ahead of those with "A"s.
802
803=item *
804
5a964f20 805An application that takes the trouble to use information in
14280422 806C<LC_MONETARY> may format debits as if they were credits and vice versa
5a964f20 807if that locale has been subverted. Or it might make payments in US
14280422
DD
808dollars instead of Hong Kong dollars.
809
810=item *
811
812The date and day names in dates formatted by strftime() could be
813manipulated to advantage by a malicious user able to subvert the
5a964f20 814C<LC_DATE> locale. ("Look--it says I wasn't in the building on
14280422
DD
815Sunday.")
816
817=back
818
819Such dangers are not peculiar to the locale system: any aspect of an
5a964f20 820application's environment which may be modified maliciously presents
14280422 821similar challenges. Similarly, they are not specific to Perl: any
5a964f20 822programming language that allows you to write programs that take
14280422
DD
823account of their environment exposes you to these issues.
824
5a964f20
TC
825Perl cannot protect you from all possibilities shown in the
826examples--there is no substitute for your own vigilance--but, when
14280422 827C<use locale> is in effect, Perl uses the tainting mechanism (see
5a964f20 828L<perlsec>) to mark string results that become locale-dependent, and
14280422 829which may be untrustworthy in consequence. Here is a summary of the
5a964f20 830tainting behavior of operators and functions that may be affected by
14280422
DD
831the locale:
832
833=over 4
834
551e1d92
RB
835=item *
836
837B<Comparison operators> (C<lt>, C<le>, C<ge>, C<gt> and C<cmp>):
14280422
DD
838
839Scalar true/false (or less/equal/greater) result is never tainted.
840
551e1d92
RB
841=item *
842
843B<Case-mapping interpolation> (with C<\l>, C<\L>, C<\u> or C<\U>)
e38874e2
DD
844
845Result string containing interpolated material is tainted if
66cbab2c 846C<use locale> (but not S<C<use locale ':not_characters'>>) is in effect.
e38874e2 847
551e1d92
RB
848=item *
849
850B<Matching operator> (C<m//>):
14280422
DD
851
852Scalar true/false result never tainted.
853
5a964f20 854Subpatterns, either delivered as a list-context result or as $1 etc.
66cbab2c
KW
855are tainted if C<use locale> (but not S<C<use locale ':not_characters'>>)
856is in effect, and the subpattern regular
e38874e2 857expression contains C<\w> (to match an alphanumeric character), C<\W>
6b0ac556
OK
858(non-alphanumeric character), C<\s> (whitespace character), or C<\S>
859(non whitespace character). The matched-pattern variable, $&, $`
e38874e2
DD
860(pre-match), $' (post-match), and $+ (last match) are also tainted if
861C<use locale> is in effect and the regular expression contains C<\w>,
862C<\W>, C<\s>, or C<\S>.
14280422 863
551e1d92
RB
864=item *
865
866B<Substitution operator> (C<s///>):
14280422 867
e38874e2 868Has the same behavior as the match operator. Also, the left
66cbab2c
KW
869operand of C<=~> becomes tainted when C<use locale>
870(but not S<C<use locale ':not_characters'>>) is in effect if modified as
871a result of a substitution based on a regular
e38874e2 872expression match involving C<\w>, C<\W>, C<\s>, or C<\S>; or of
7b8d334a 873case-mapping with C<\l>, C<\L>,C<\u> or C<\U>.
14280422 874
551e1d92
RB
875=item *
876
877B<Output formatting functions> (printf() and write()):
14280422 878
3cf03d68
JH
879Results are never tainted because otherwise even output from print,
880for example C<print(1/7)>, should be tainted if C<use locale> is in
881effect.
14280422 882
551e1d92
RB
883=item *
884
885B<Case-mapping functions> (lc(), lcfirst(), uc(), ucfirst()):
14280422 886
66cbab2c
KW
887Results are tainted if C<use locale> (but not
888S<C<use locale ':not_characters'>>) is in effect.
14280422 889
551e1d92
RB
890=item *
891
892B<POSIX locale-dependent functions> (localeconv(), strcoll(),
14280422
DD
893strftime(), strxfrm()):
894
895Results are never tainted.
896
551e1d92
RB
897=item *
898
899B<POSIX character class tests> (isalnum(), isalpha(), isdigit(),
14280422
DD
900isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(),
901isxdigit()):
902
903True/false results are never tainted.
904
905=back
906
907Three examples illustrate locale-dependent tainting.
908The first program, which ignores its locale, won't run: a value taken
54310121 909directly from the command line may not be used to name an output file
14280422
DD
910when taint checks are enabled.
911
912 #/usr/local/bin/perl -T
913 # Run with taint checking
914
54310121 915 # Command line sanity check omitted...
14280422
DD
916 $tainted_output_file = shift;
917
918 open(F, ">$tainted_output_file")
3183d96c 919 or warn "Open of $tainted_output_file failed: $!\n";
14280422
DD
920
921The program can be made to run by "laundering" the tainted value through
5a964f20
TC
922a regular expression: the second example--which still ignores locale
923information--runs, creating the file named on its command line
14280422
DD
924if it can.
925
926 #/usr/local/bin/perl -T
927
928 $tainted_output_file = shift;
929 $tainted_output_file =~ m%[\w/]+%;
930 $untainted_output_file = $&;
931
932 open(F, ">$untainted_output_file")
933 or warn "Open of $untainted_output_file failed: $!\n";
934
5a964f20 935Compare this with a similar but locale-aware program:
14280422
DD
936
937 #/usr/local/bin/perl -T
938
939 $tainted_output_file = shift;
940 use locale;
941 $tainted_output_file =~ m%[\w/]+%;
942 $localized_output_file = $&;
943
944 open(F, ">$localized_output_file")
945 or warn "Open of $localized_output_file failed: $!\n";
946
947This third program fails to run because $& is tainted: it is the result
5a964f20 948of a match involving C<\w> while C<use locale> is in effect.
5f05dabc
PP
949
950=head1 ENVIRONMENT
951
952=over 12
953
954=item PERL_BADLANG
955
14280422 956A string that can suppress Perl's warning about failed locale settings
54310121 957at startup. Failure can occur if the locale support in the operating
5a964f20 958system is lacking (broken) in some way--or if you mistyped the name of
900bd440
JH
959a locale when you set up your environment. If this environment
960variable is absent, or has a value that does not evaluate to integer
961zero--that is, "0" or ""-- Perl will complain about locale setting
962failures.
5f05dabc 963
14280422
DD
964B<NOTE>: PERL_BADLANG only gives you a way to hide the warning message.
965The message tells about some problem in your system's locale support,
966and you should investigate what the problem is.
5f05dabc
PP
967
968=back
969
970The following environment variables are not specific to Perl: They are
14280422
DD
971part of the standardized (ISO C, XPG4, POSIX 1.c) setlocale() method
972for controlling an application's opinion on data.
5f05dabc
PP
973
974=over 12
975
976=item LC_ALL
977
5a964f20 978C<LC_ALL> is the "override-all" locale environment variable. If
5f05dabc
PP
979set, it overrides all the rest of the locale environment variables.
980
528d65ad
JH
981=item LANGUAGE
982
983B<NOTE>: C<LANGUAGE> is a GNU extension, it affects you only if you
984are using the GNU libc. This is the case if you are using e.g. Linux.
e1020413 985If you are using "commercial" Unixes you are most probably I<not>
22b6f60d
JH
986using GNU libc and you can ignore C<LANGUAGE>.
987
988However, in the case you are using C<LANGUAGE>: it affects the
989language of informational, warning, and error messages output by
990commands (in other words, it's like C<LC_MESSAGES>) but it has higher
96090e4f 991priority than C<LC_ALL>. Moreover, it's not a single value but
22b6f60d
JH
992instead a "path" (":"-separated list) of I<languages> (not locales).
993See the GNU C<gettext> library documentation for more information.
528d65ad 994
5f05dabc
PP
995=item LC_CTYPE
996
997In the absence of C<LC_ALL>, C<LC_CTYPE> chooses the character type
998locale. In the absence of both C<LC_ALL> and C<LC_CTYPE>, C<LANG>
999chooses the character type locale.
1000
1001=item LC_COLLATE
1002
14280422
DD
1003In the absence of C<LC_ALL>, C<LC_COLLATE> chooses the collation
1004(sorting) locale. In the absence of both C<LC_ALL> and C<LC_COLLATE>,
1005C<LANG> chooses the collation locale.
5f05dabc
PP
1006
1007=item LC_MONETARY
1008
14280422
DD
1009In the absence of C<LC_ALL>, C<LC_MONETARY> chooses the monetary
1010formatting locale. In the absence of both C<LC_ALL> and C<LC_MONETARY>,
1011C<LANG> chooses the monetary formatting locale.
5f05dabc
PP
1012
1013=item LC_NUMERIC
1014
1015In the absence of C<LC_ALL>, C<LC_NUMERIC> chooses the numeric format
1016locale. In the absence of both C<LC_ALL> and C<LC_NUMERIC>, C<LANG>
1017chooses the numeric format.
1018
1019=item LC_TIME
1020
14280422
DD
1021In the absence of C<LC_ALL>, C<LC_TIME> chooses the date and time
1022formatting locale. In the absence of both C<LC_ALL> and C<LC_TIME>,
1023C<LANG> chooses the date and time formatting locale.
5f05dabc
PP
1024
1025=item LANG
1026
14280422
DD
1027C<LANG> is the "catch-all" locale environment variable. If it is set, it
1028is used as the last resort after the overall C<LC_ALL> and the
5f05dabc
PP
1029category-specific C<LC_...>.
1030
1031=back
1032
7e4353e9
RGS
1033=head2 Examples
1034
1035The LC_NUMERIC controls the numeric output:
1036
ef3087ec
KW
1037 use locale;
1038 use POSIX qw(locale_h); # Imports setlocale() and the LC_ constants.
1039 setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
1040 printf "%g\n", 1.23; # If the "fr_FR" succeeded, probably shows 1,23.
7e4353e9
RGS
1041
1042and also how strings are parsed by POSIX::strtod() as numbers:
1043
ef3087ec
KW
1044 use locale;
1045 use POSIX qw(locale_h strtod);
1046 setlocale(LC_NUMERIC, "de_DE") or die "Entschuldigung";
1047 my $x = strtod("2,34") + 5;
1048 print $x, "\n"; # Probably shows 7,34.
7e4353e9 1049
5f05dabc
PP
1050=head1 NOTES
1051
1052=head2 Backward compatibility
1053
b0c42ed9 1054Versions of Perl prior to 5.004 B<mostly> ignored locale information,
5a964f20
TC
1055generally behaving as if something similar to the C<"C"> locale were
1056always in force, even if the program environment suggested otherwise
1057(see L<The setlocale function>). By default, Perl still behaves this
1058way for backward compatibility. If you want a Perl application to pay
1059attention to locale information, you B<must> use the S<C<use locale>>
062ca197
KW
1060pragma (see L<The use locale pragma>) or, in the unlikely event
1061that you want to do so for just pattern matching, the
70709c68
KW
1062C</l> regular expression modifier (see L<perlre/Character set
1063modifiers>) to instruct it to do so.
b0c42ed9
JH
1064
1065Versions of Perl from 5.002 to 5.003 did use the C<LC_CTYPE>
5a964f20
TC
1066information if available; that is, C<\w> did understand what
1067were the letters according to the locale environment variables.
b0c42ed9
JH
1068The problem was that the user had no control over the feature:
1069if the C library supported locales, Perl used them.
1070
1071=head2 I18N:Collate obsolete
1072
5a964f20 1073In versions of Perl prior to 5.004, per-locale collation was possible
b0c42ed9
JH
1074using the C<I18N::Collate> library module. This module is now mildly
1075obsolete and should be avoided in new applications. The C<LC_COLLATE>
1076functionality is now integrated into the Perl core language: One can
1077use locale-specific scalar data completely normally with C<use locale>,
1078so there is no longer any need to juggle with the scalar references of
1079C<I18N::Collate>.
5f05dabc 1080
14280422 1081=head2 Sort speed and memory use impacts
5f05dabc
PP
1082
1083Comparing and sorting by locale is usually slower than the default
14280422
DD
1084sorting; slow-downs of two to four times have been observed. It will
1085also consume more memory: once a Perl scalar variable has participated
1086in any string comparison or sorting operation obeying the locale
1087collation rules, it will take 3-15 times more memory than before. (The
1088exact multiplier depends on the string's contents, the operating system
1089and the locale.) These downsides are dictated more by the operating
1090system's implementation of the locale system than by Perl.
5f05dabc 1091
e38874e2
DD
1092=head2 write() and LC_NUMERIC
1093
903eb63f
NT
1094If a program's environment specifies an LC_NUMERIC locale and C<use
1095locale> is in effect when the format is declared, the locale is used
1096to specify the decimal point character in formatted output. Formatted
1097output cannot be controlled by C<use locale> at the time when write()
1098is called.
e38874e2 1099
5f05dabc
PP
1100=head2 Freely available locale definitions
1101
66cbab2c
KW
1102The Unicode CLDR project extracts the POSIX portion of many of its
1103locales, available at
1104
1105 http://unicode.org/Public/cldr/latest/
1106
08d7a6b2
LB
1107There is a large collection of locale definitions at:
1108
1109 http://std.dkuug.dk/i18n/WG15-collection/locales/
1110
1111You should be aware that it is
14280422 1112unsupported, and is not claimed to be fit for any purpose. If your
5a964f20 1113system allows installation of arbitrary locales, you may find the
14280422
DD
1114definitions useful as they are, or as a basis for the development of
1115your own locales.
5f05dabc 1116
14280422 1117=head2 I18n and l10n
5f05dabc 1118
b0c42ed9
JH
1119"Internationalization" is often abbreviated as B<i18n> because its first
1120and last letters are separated by eighteen others. (You may guess why
1121the internalin ... internaliti ... i18n tends to get abbreviated.) In
1122the same way, "localization" is often abbreviated to B<l10n>.
14280422
DD
1123
1124=head2 An imperfect standard
1125
1126Internationalization, as defined in the C and POSIX standards, can be
1127criticized as incomplete, ungainly, and having too large a granularity.
1128(Locales apply to a whole process, when it would arguably be more useful
1129to have them apply to a single thread, window group, or whatever.) They
1130also have a tendency, like standards groups, to divide the world into
1131nations, when we all know that the world can equally well be divided
e199995e 1132into bankers, bikers, gamers, and so on.
5f05dabc 1133
b310b053
JH
1134=head1 Unicode and UTF-8
1135
7ee2ae1e
KW
1136The support of Unicode is new starting from Perl version v5.6, and more fully
1137implemented in version v5.8 and later. See L<perluniintro>. It is
66cbab2c 1138strongly recommended that when combining Unicode and locale (starting in
7ee2ae1e 1139v5.16), you use
66cbab2c
KW
1140
1141 use locale ':not_characters';
1142
1143When this form of the pragma is used, only the non-character portions of
1144locales are used by Perl, for example C<LC_NUMERIC>. Perl assumes that
1145you have translated all the characters it is to operate on into Unicode
1146(actually the platform's native character set (ASCII or EBCDIC) plus
1147Unicode). For data in files, this can conveniently be done by also
1148specifying
1149
1150 use open ':locale';
1151
1152This pragma arranges for all inputs from files to be translated into
1153Unicode from the current locale as specified in the environment (see
1154L</ENVIRONMENT>), and all outputs to files to be translated back
1155into the locale. (See L<open>). On a per-filehandle basis, you can
1156instead use the L<PerlIO::locale> module, or the L<Encode::Locale>
1157module, both available from CPAN. The latter module also has methods to
1158ease the handling of C<ARGV> and environment variables, and can be used
1159on individual strings. Also, if you know that all your locales will be
1160UTF-8, as many are these days, you can use the L<B<-C>|perlrun/-C>
1161command line switch.
1162
1163This form of the pragma allows essentially seamless handling of locales
1164with Unicode. The collation order will be Unicode's. It is strongly
1165recommended that when you need to order and sort strings that you use
1166the standard module L<Unicode::Collate> which gives much better results
1167in many instances than you can get with the old-style locale handling.
1168
7ee2ae1e 1169For pre-v5.16 Perls, or if you use the locale pragma without the
66cbab2c
KW
1170C<:not_characters> parameter, Perl tries to work with both Unicode and
1171locales--but there are problems.
1172
1173Perl does not handle multi-byte locales in this case, such as have been
1174used for various
dc4bfc4b
KW
1175Asian languages, such as Big5 or Shift JIS. However, the increasingly
1176common multi-byte UTF-8 locales, if properly implemented, may work
1177reasonably well (depending on your C library implementation) in this
1178form of the locale pragma, simply because both
1179they and Perl store characters that take up multiple bytes the same way.
1180However, some, if not most, C library implementations may not process
1181the characters in the upper half of the Latin-1 range (128 - 255)
1182properly under LC_CTYPE. To see if a character is a particular type
1183under a locale, Perl uses the functions like C<isalnum()>. Your C
1184library may not work for UTF-8 locales with those functions, instead
1185only working under the newer wide library functions like C<iswalnum()>.
e199995e
KW
1186
1187Perl generally takes the tack to use locale rules on code points that can fit
66cbab2c
KW
1188in a single byte, and Unicode rules for those that can't (though this
1189isn't uniformly applied, see the note at the end of this section). This
1190prevents many problems in locales that aren't UTF-8. Suppose the locale
1191is ISO8859-7, Greek. The character at 0xD7 there is a capital Chi. But
1192in the ISO8859-1 locale, Latin1, it is a multiplication sign. The POSIX
1193regular expression character class C<[[:alpha:]]> will magically match
11940xD7 in the Greek locale but not in the Latin one.
e199995e
KW
1195
1196However, there are places where this breaks down. Certain constructs are
b4ffc3db
TC
1197for Unicode only, such as C<\p{Alpha}>. They assume that 0xD7 always has its
1198Unicode meaning (or the equivalent on EBCDIC platforms). Since Latin1 is a
1199subset of Unicode and 0xD7 is the multiplication sign in both Latin1 and
1200Unicode, C<\p{Alpha}> will never match it, regardless of locale. A similar
1201issue occurs with C<\N{...}>. It is therefore a bad idea to use C<\p{}> or
66cbab2c
KW
1202C<\N{}> under plain C<use locale>--I<unless> you can guarantee that the
1203locale will be a ISO8859-1. Use POSIX character classes instead.
1204
1205Another problem with this approach is that operations that cross the
1206single byte/multiple byte boundary are not well-defined, and so are
1207disallowed. (This boundary is between the codepoints at 255/256.).
1208For example, lower casing LATIN CAPITAL LETTER Y WITH DIAERESIS (U+0178)
1209should return LATIN SMALL LETTER Y WITH DIAERESIS (U+00FF). But in the
1210Greek locale, for example, there is no character at 0xFF, and Perl
1211has no way of knowing what the character at 0xFF is really supposed to
1212represent. Thus it disallows the operation. In this mode, the
1213lowercase of U+0178 is itself.
1214
1215The same problems ensue if you enable automatic UTF-8-ification of your
e199995e 1216standard file handles, default C<open()> layer, and C<@ARGV> on non-ISO8859-1,
b4ffc3db
TC
1217non-UTF-8 locales (by using either the B<-C> command line switch or the
1218C<PERL_UNICODE> environment variable; see L<perlrun>).
1219Things are read in as UTF-8, which would normally imply a Unicode
1220interpretation, but the presence of a locale causes them to be interpreted
1221in that locale instead. For example, a 0xD7 code point in the Unicode
1222input, which should mean the multiplication sign, won't be interpreted by
66cbab2c 1223Perl that way under the Greek locale. This is not a problem
b4ffc3db 1224I<provided> you make certain that all locales will always and only be either
66cbab2c 1225an ISO8859-1, or, if you don't have a deficient C library, a UTF-8 locale.
b4ffc3db
TC
1226
1227Vendor locales are notoriously buggy, and it is difficult for Perl to test
1228its locale-handling code because this interacts with code that Perl has no
1229control over; therefore the locale-handling code in Perl may be buggy as
66cbab2c
KW
1230well. (However, the Unicode-supplied locales should be better, and
1231there is a feed back mechanism to correct any problems. See
1232L</Freely available locale definitions>.)
1233
7ee2ae1e 1234If you have Perl v5.16, the problems mentioned above go away if you use
66cbab2c 1235the C<:not_characters> parameter to the locale pragma (except for vendor
7ee2ae1e 1236bugs in the non-character portions). If you don't have v5.16, and you
66cbab2c
KW
1237I<do> have locales that work, using them may be worthwhile for certain
1238specific purposes, as long as you keep in mind the gotchas already
1239mentioned. For example, if the collation for your locales works, it
1240runs faster under locales than under L<Unicode::Collate>; and you gain
1241access to such things as the local currency symbol and the names of the
7ee2ae1e 1242months and days of the week. (But to hammer home the point, in v5.16,
66cbab2c
KW
1243you get this access without the downsides of locales by using the
1244C<:not_characters> form of the pragma.)
1245
1246Note: The policy of using locale rules for code points that can fit in a
1247byte, and Unicode rules for those that can't is not uniformly applied.
7ee2ae1e 1248Pre-v5.12, it was somewhat haphazard; in v5.12 it was applied fairly
66cbab2c 1249consistently to regular expression matching except for bracketed
7ee2ae1e
KW
1250character classes; in v5.14 it was extended to all regex matches; and in
1251v5.16 to the casing operations such as C<"\L"> and C<uc()>. For
66cbab2c
KW
1252collation, in all releases, the system's C<strxfrm()> function is called,
1253and whatever it does is what you get.
b310b053 1254
5f05dabc
PP
1255=head1 BUGS
1256
1257=head2 Broken systems
1258
5a964f20 1259In certain systems, the operating system's locale support
2bdf8add 1260is broken and cannot be fixed or used by Perl. Such deficiencies can
b4ffc3db 1261and will result in mysterious hangs and/or Perl core dumps when
2bdf8add 1262C<use locale> is in effect. When confronted with such a system,
7f2de2d2 1263please report in excruciating detail to <F<perlbug@perl.org>>, and
b4ffc3db 1264also contact your vendor: bug fixes may exist for these problems
2bdf8add
JH
1265in your operating system. Sometimes such bug fixes are called an
1266operating system upgrade.
5f05dabc
PP
1267
1268=head1 SEE ALSO
1269
b310b053
JH
1270L<I18N::Langinfo>, L<perluniintro>, L<perlunicode>, L<open>,
1271L<POSIX/isalnum>, L<POSIX/isalpha>,
4bbcc6e8
JH
1272L<POSIX/isdigit>, L<POSIX/isgraph>, L<POSIX/islower>,
1273L<POSIX/isprint>, L<POSIX/ispunct>, L<POSIX/isspace>,
1274L<POSIX/isupper>, L<POSIX/isxdigit>, L<POSIX/localeconv>,
1275L<POSIX/setlocale>, L<POSIX/strcoll>, L<POSIX/strftime>,
1276L<POSIX/strtod>, L<POSIX/strxfrm>.
5f05dabc
PP
1277
1278=head1 HISTORY
1279
b0c42ed9 1280Jarkko Hietaniemi's original F<perli18n.pod> heavily hacked by Dominic
5a964f20 1281Dunlop, assisted by the perl5-porters. Prose worked over a bit by
c052850d 1282Tom Christiansen, and updated by Perl 5 porters.