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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
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>>
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
5a964f20
TC
669functions--lc(), lcfirst, uc(), and ucfirst(); case-mapping
670interpolation with C<\l>, C<\L>, C<\u>, or C<\U> in double-quoted strings
671and 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
14280422
DD
681B<Note:> A broken or malicious C<LC_CTYPE> locale definition may result
682in clearly ineligible characters being considered to be alphanumeric by
e199995e 683your application. For strict matching of (mundane) ASCII letters and
5a964f20 684digits--for example, in command strings--locale-aware applications
e199995e 685should use C<\w> with the C</a> regular expression modifier. See L<"SECURITY">.
5f05dabc
PP
686
687=head2 Category LC_NUMERIC: Numeric Formatting
688
2095dafa
RGS
689After a proper POSIX::setlocale() call, Perl obeys the C<LC_NUMERIC>
690locale information, which controls an application's idea of how numbers
691should be formatted for human readability by the printf(), sprintf(), and
692write() functions. String-to-numeric conversion by the POSIX::strtod()
5a964f20 693function is also affected. In most implementations the only effect is to
b4ffc3db 694change the character used for the decimal point--perhaps from "." to ",".
5a964f20 695These functions aren't aware of such niceties as thousands separation and
2095dafa 696so on. (See L<The localeconv function> if you care about these things.)
5a964f20 697
3cf03d68 698Output produced by print() is also affected by the current locale: it
3cf03d68
JH
699corresponds to what you'd get from printf() in the "C" locale. The
700same is true for Perl's internal conversions between numeric and
701string formats:
5f05dabc 702
2095dafa
RGS
703 use POSIX qw(strtod setlocale LC_NUMERIC);
704
705 setlocale LC_NUMERIC, "";
14280422 706
5f05dabc
PP
707 $n = 5/2; # Assign numeric 2.5 to $n
708
35316ca3 709 $a = " $n"; # Locale-dependent conversion to string
5f05dabc 710
35316ca3 711 print "half five is $n\n"; # Locale-dependent output
5f05dabc
PP
712
713 printf "half five is %g\n", $n; # Locale-dependent output
714
14280422
DD
715 print "DECIMAL POINT IS COMMA\n"
716 if $n == (strtod("2,5"))[0]; # Locale-dependent conversion
5f05dabc 717
4bbcc6e8
JH
718See also L<I18N::Langinfo> and C<RADIXCHAR>.
719
5f05dabc
PP
720=head2 Category LC_MONETARY: Formatting of monetary amounts
721
e199995e 722The C standard defines the C<LC_MONETARY> category, but not a function
5a964f20 723that is affected by its contents. (Those with experience of standards
b0c42ed9 724committees will recognize that the working group decided to punt on the
14280422 725issue.) Consequently, Perl takes no notice of it. If you really want
e05ffc7d
KW
726to use C<LC_MONETARY>, you can query its contents--see
727L<The localeconv function>--and use the information that it returns in your
728application's own formatting of currency amounts. However, you may well
729find that the information, voluminous and complex though it may be, still
730does not quite meet your requirements: currency formatting is a hard nut
13a2d996 731to crack.
5f05dabc 732
4bbcc6e8
JH
733See also L<I18N::Langinfo> and C<CRNCYSTR>.
734
5f05dabc
PP
735=head2 LC_TIME
736
5a964f20 737Output produced by POSIX::strftime(), which builds a formatted
5f05dabc
PP
738human-readable date/time string, is affected by the current C<LC_TIME>
739locale. Thus, in a French locale, the output produced by the C<%B>
740format element (full month name) for the first month of the year would
5a964f20 741be "janvier". Here's how to get a list of long month names in the
5f05dabc
PP
742current locale:
743
744 use POSIX qw(strftime);
14280422
DD
745 for (0..11) {
746 $long_month_name[$_] =
747 strftime("%B", 0, 0, 0, 1, $_, 96);
5f05dabc
PP
748 }
749
5a964f20 750Note: C<use locale> isn't needed in this example: as a function that
14280422
DD
751exists only to generate locale-dependent results, strftime() always
752obeys the current C<LC_TIME> locale.
5f05dabc 753
4bbcc6e8 754See also L<I18N::Langinfo> and C<ABDAY_1>..C<ABDAY_7>, C<DAY_1>..C<DAY_7>,
2a2bf5f4 755C<ABMON_1>..C<ABMON_12>, and C<ABMON_1>..C<ABMON_12>.
4bbcc6e8 756
5f05dabc
PP
757=head2 Other categories
758
5a964f20
TC
759The remaining locale category, C<LC_MESSAGES> (possibly supplemented
760by others in particular implementations) is not currently used by
98a6f11e 761Perl--except possibly to affect the behavior of library functions
762called by extensions outside the standard Perl distribution and by the
763operating system and its utilities. Note especially that the string
764value of C<$!> and the error messages given by external utilities may
765be changed by C<LC_MESSAGES>. If you want to have portable error
265f5c4a 766codes, use C<%!>. See L<Errno>.
14280422
DD
767
768=head1 SECURITY
769
5a964f20 770Although the main discussion of Perl security issues can be found in
14280422
DD
771L<perlsec>, a discussion of Perl's locale handling would be incomplete
772if it did not draw your attention to locale-dependent security issues.
5a964f20
TC
773Locales--particularly on systems that allow unprivileged users to
774build their own locales--are untrustworthy. A malicious (or just plain
14280422
DD
775broken) locale can make a locale-aware application give unexpected
776results. Here are a few possibilities:
777
778=over 4
779
780=item *
781
782Regular expression checks for safe file names or mail addresses using
5a964f20 783C<\w> may be spoofed by an C<LC_CTYPE> locale that claims that
14280422
DD
784characters such as "E<gt>" and "|" are alphanumeric.
785
786=item *
787
e38874e2
DD
788String interpolation with case-mapping, as in, say, C<$dest =
789"C:\U$name.$ext">, may produce dangerous results if a bogus LC_CTYPE
790case-mapping table is in effect.
791
792=item *
793
14280422
DD
794A sneaky C<LC_COLLATE> locale could result in the names of students with
795"D" grades appearing ahead of those with "A"s.
796
797=item *
798
5a964f20 799An application that takes the trouble to use information in
14280422 800C<LC_MONETARY> may format debits as if they were credits and vice versa
5a964f20 801if that locale has been subverted. Or it might make payments in US
14280422
DD
802dollars instead of Hong Kong dollars.
803
804=item *
805
806The date and day names in dates formatted by strftime() could be
807manipulated to advantage by a malicious user able to subvert the
5a964f20 808C<LC_DATE> locale. ("Look--it says I wasn't in the building on
14280422
DD
809Sunday.")
810
811=back
812
813Such dangers are not peculiar to the locale system: any aspect of an
5a964f20 814application's environment which may be modified maliciously presents
14280422 815similar challenges. Similarly, they are not specific to Perl: any
5a964f20 816programming language that allows you to write programs that take
14280422
DD
817account of their environment exposes you to these issues.
818
5a964f20
TC
819Perl cannot protect you from all possibilities shown in the
820examples--there is no substitute for your own vigilance--but, when
14280422 821C<use locale> is in effect, Perl uses the tainting mechanism (see
5a964f20 822L<perlsec>) to mark string results that become locale-dependent, and
14280422 823which may be untrustworthy in consequence. Here is a summary of the
5a964f20 824tainting behavior of operators and functions that may be affected by
14280422
DD
825the locale:
826
827=over 4
828
551e1d92
RB
829=item *
830
831B<Comparison operators> (C<lt>, C<le>, C<ge>, C<gt> and C<cmp>):
14280422
DD
832
833Scalar true/false (or less/equal/greater) result is never tainted.
834
551e1d92
RB
835=item *
836
837B<Case-mapping interpolation> (with C<\l>, C<\L>, C<\u> or C<\U>)
e38874e2
DD
838
839Result string containing interpolated material is tainted if
66cbab2c 840C<use locale> (but not S<C<use locale ':not_characters'>>) is in effect.
e38874e2 841
551e1d92
RB
842=item *
843
844B<Matching operator> (C<m//>):
14280422
DD
845
846Scalar true/false result never tainted.
847
5a964f20 848Subpatterns, either delivered as a list-context result or as $1 etc.
66cbab2c
KW
849are tainted if C<use locale> (but not S<C<use locale ':not_characters'>>)
850is in effect, and the subpattern regular
e38874e2 851expression contains C<\w> (to match an alphanumeric character), C<\W>
6b0ac556
OK
852(non-alphanumeric character), C<\s> (whitespace character), or C<\S>
853(non whitespace character). The matched-pattern variable, $&, $`
e38874e2
DD
854(pre-match), $' (post-match), and $+ (last match) are also tainted if
855C<use locale> is in effect and the regular expression contains C<\w>,
856C<\W>, C<\s>, or C<\S>.
14280422 857
551e1d92
RB
858=item *
859
860B<Substitution operator> (C<s///>):
14280422 861
e38874e2 862Has the same behavior as the match operator. Also, the left
66cbab2c
KW
863operand of C<=~> becomes tainted when C<use locale>
864(but not S<C<use locale ':not_characters'>>) is in effect if modified as
865a result of a substitution based on a regular
e38874e2 866expression match involving C<\w>, C<\W>, C<\s>, or C<\S>; or of
7b8d334a 867case-mapping with C<\l>, C<\L>,C<\u> or C<\U>.
14280422 868
551e1d92
RB
869=item *
870
871B<Output formatting functions> (printf() and write()):
14280422 872
3cf03d68
JH
873Results are never tainted because otherwise even output from print,
874for example C<print(1/7)>, should be tainted if C<use locale> is in
875effect.
14280422 876
551e1d92
RB
877=item *
878
879B<Case-mapping functions> (lc(), lcfirst(), uc(), ucfirst()):
14280422 880
66cbab2c
KW
881Results are tainted if C<use locale> (but not
882S<C<use locale ':not_characters'>>) is in effect.
14280422 883
551e1d92
RB
884=item *
885
886B<POSIX locale-dependent functions> (localeconv(), strcoll(),
14280422
DD
887strftime(), strxfrm()):
888
889Results are never tainted.
890
551e1d92
RB
891=item *
892
893B<POSIX character class tests> (isalnum(), isalpha(), isdigit(),
14280422
DD
894isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(),
895isxdigit()):
896
897True/false results are never tainted.
898
899=back
900
901Three examples illustrate locale-dependent tainting.
902The first program, which ignores its locale, won't run: a value taken
54310121 903directly from the command line may not be used to name an output file
14280422
DD
904when taint checks are enabled.
905
906 #/usr/local/bin/perl -T
907 # Run with taint checking
908
54310121 909 # Command line sanity check omitted...
14280422
DD
910 $tainted_output_file = shift;
911
912 open(F, ">$tainted_output_file")
3183d96c 913 or warn "Open of $tainted_output_file failed: $!\n";
14280422
DD
914
915The program can be made to run by "laundering" the tainted value through
5a964f20
TC
916a regular expression: the second example--which still ignores locale
917information--runs, creating the file named on its command line
14280422
DD
918if it can.
919
920 #/usr/local/bin/perl -T
921
922 $tainted_output_file = shift;
923 $tainted_output_file =~ m%[\w/]+%;
924 $untainted_output_file = $&;
925
926 open(F, ">$untainted_output_file")
927 or warn "Open of $untainted_output_file failed: $!\n";
928
5a964f20 929Compare this with a similar but locale-aware program:
14280422
DD
930
931 #/usr/local/bin/perl -T
932
933 $tainted_output_file = shift;
934 use locale;
935 $tainted_output_file =~ m%[\w/]+%;
936 $localized_output_file = $&;
937
938 open(F, ">$localized_output_file")
939 or warn "Open of $localized_output_file failed: $!\n";
940
941This third program fails to run because $& is tainted: it is the result
5a964f20 942of a match involving C<\w> while C<use locale> is in effect.
5f05dabc
PP
943
944=head1 ENVIRONMENT
945
946=over 12
947
948=item PERL_BADLANG
949
14280422 950A string that can suppress Perl's warning about failed locale settings
54310121 951at startup. Failure can occur if the locale support in the operating
5a964f20 952system is lacking (broken) in some way--or if you mistyped the name of
900bd440
JH
953a locale when you set up your environment. If this environment
954variable is absent, or has a value that does not evaluate to integer
955zero--that is, "0" or ""-- Perl will complain about locale setting
956failures.
5f05dabc 957
14280422
DD
958B<NOTE>: PERL_BADLANG only gives you a way to hide the warning message.
959The message tells about some problem in your system's locale support,
960and you should investigate what the problem is.
5f05dabc
PP
961
962=back
963
964The following environment variables are not specific to Perl: They are
14280422
DD
965part of the standardized (ISO C, XPG4, POSIX 1.c) setlocale() method
966for controlling an application's opinion on data.
5f05dabc
PP
967
968=over 12
969
970=item LC_ALL
971
5a964f20 972C<LC_ALL> is the "override-all" locale environment variable. If
5f05dabc
PP
973set, it overrides all the rest of the locale environment variables.
974
528d65ad
JH
975=item LANGUAGE
976
977B<NOTE>: C<LANGUAGE> is a GNU extension, it affects you only if you
978are using the GNU libc. This is the case if you are using e.g. Linux.
e1020413 979If you are using "commercial" Unixes you are most probably I<not>
22b6f60d
JH
980using GNU libc and you can ignore C<LANGUAGE>.
981
982However, in the case you are using C<LANGUAGE>: it affects the
983language of informational, warning, and error messages output by
984commands (in other words, it's like C<LC_MESSAGES>) but it has higher
96090e4f 985priority than C<LC_ALL>. Moreover, it's not a single value but
22b6f60d
JH
986instead a "path" (":"-separated list) of I<languages> (not locales).
987See the GNU C<gettext> library documentation for more information.
528d65ad 988
5f05dabc
PP
989=item LC_CTYPE
990
991In the absence of C<LC_ALL>, C<LC_CTYPE> chooses the character type
992locale. In the absence of both C<LC_ALL> and C<LC_CTYPE>, C<LANG>
993chooses the character type locale.
994
995=item LC_COLLATE
996
14280422
DD
997In the absence of C<LC_ALL>, C<LC_COLLATE> chooses the collation
998(sorting) locale. In the absence of both C<LC_ALL> and C<LC_COLLATE>,
999C<LANG> chooses the collation locale.
5f05dabc
PP
1000
1001=item LC_MONETARY
1002
14280422
DD
1003In the absence of C<LC_ALL>, C<LC_MONETARY> chooses the monetary
1004formatting locale. In the absence of both C<LC_ALL> and C<LC_MONETARY>,
1005C<LANG> chooses the monetary formatting locale.
5f05dabc
PP
1006
1007=item LC_NUMERIC
1008
1009In the absence of C<LC_ALL>, C<LC_NUMERIC> chooses the numeric format
1010locale. In the absence of both C<LC_ALL> and C<LC_NUMERIC>, C<LANG>
1011chooses the numeric format.
1012
1013=item LC_TIME
1014
14280422
DD
1015In the absence of C<LC_ALL>, C<LC_TIME> chooses the date and time
1016formatting locale. In the absence of both C<LC_ALL> and C<LC_TIME>,
1017C<LANG> chooses the date and time formatting locale.
5f05dabc
PP
1018
1019=item LANG
1020
14280422
DD
1021C<LANG> is the "catch-all" locale environment variable. If it is set, it
1022is used as the last resort after the overall C<LC_ALL> and the
5f05dabc
PP
1023category-specific C<LC_...>.
1024
1025=back
1026
7e4353e9
RGS
1027=head2 Examples
1028
1029The LC_NUMERIC controls the numeric output:
1030
ef3087ec
KW
1031 use locale;
1032 use POSIX qw(locale_h); # Imports setlocale() and the LC_ constants.
1033 setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
1034 printf "%g\n", 1.23; # If the "fr_FR" succeeded, probably shows 1,23.
7e4353e9
RGS
1035
1036and also how strings are parsed by POSIX::strtod() as numbers:
1037
ef3087ec
KW
1038 use locale;
1039 use POSIX qw(locale_h strtod);
1040 setlocale(LC_NUMERIC, "de_DE") or die "Entschuldigung";
1041 my $x = strtod("2,34") + 5;
1042 print $x, "\n"; # Probably shows 7,34.
7e4353e9 1043
5f05dabc
PP
1044=head1 NOTES
1045
1046=head2 Backward compatibility
1047
b0c42ed9 1048Versions of Perl prior to 5.004 B<mostly> ignored locale information,
5a964f20
TC
1049generally behaving as if something similar to the C<"C"> locale were
1050always in force, even if the program environment suggested otherwise
1051(see L<The setlocale function>). By default, Perl still behaves this
1052way for backward compatibility. If you want a Perl application to pay
1053attention to locale information, you B<must> use the S<C<use locale>>
062ca197
KW
1054pragma (see L<The use locale pragma>) or, in the unlikely event
1055that you want to do so for just pattern matching, the
70709c68
KW
1056C</l> regular expression modifier (see L<perlre/Character set
1057modifiers>) to instruct it to do so.
b0c42ed9
JH
1058
1059Versions of Perl from 5.002 to 5.003 did use the C<LC_CTYPE>
5a964f20
TC
1060information if available; that is, C<\w> did understand what
1061were the letters according to the locale environment variables.
b0c42ed9
JH
1062The problem was that the user had no control over the feature:
1063if the C library supported locales, Perl used them.
1064
1065=head2 I18N:Collate obsolete
1066
5a964f20 1067In versions of Perl prior to 5.004, per-locale collation was possible
b0c42ed9
JH
1068using the C<I18N::Collate> library module. This module is now mildly
1069obsolete and should be avoided in new applications. The C<LC_COLLATE>
1070functionality is now integrated into the Perl core language: One can
1071use locale-specific scalar data completely normally with C<use locale>,
1072so there is no longer any need to juggle with the scalar references of
1073C<I18N::Collate>.
5f05dabc 1074
14280422 1075=head2 Sort speed and memory use impacts
5f05dabc
PP
1076
1077Comparing and sorting by locale is usually slower than the default
14280422
DD
1078sorting; slow-downs of two to four times have been observed. It will
1079also consume more memory: once a Perl scalar variable has participated
1080in any string comparison or sorting operation obeying the locale
1081collation rules, it will take 3-15 times more memory than before. (The
1082exact multiplier depends on the string's contents, the operating system
1083and the locale.) These downsides are dictated more by the operating
1084system's implementation of the locale system than by Perl.
5f05dabc 1085
e38874e2
DD
1086=head2 write() and LC_NUMERIC
1087
903eb63f
NT
1088If a program's environment specifies an LC_NUMERIC locale and C<use
1089locale> is in effect when the format is declared, the locale is used
1090to specify the decimal point character in formatted output. Formatted
1091output cannot be controlled by C<use locale> at the time when write()
1092is called.
e38874e2 1093
5f05dabc
PP
1094=head2 Freely available locale definitions
1095
66cbab2c
KW
1096The Unicode CLDR project extracts the POSIX portion of many of its
1097locales, available at
1098
1099 http://unicode.org/Public/cldr/latest/
1100
08d7a6b2
LB
1101There is a large collection of locale definitions at:
1102
1103 http://std.dkuug.dk/i18n/WG15-collection/locales/
1104
1105You should be aware that it is
14280422 1106unsupported, and is not claimed to be fit for any purpose. If your
5a964f20 1107system allows installation of arbitrary locales, you may find the
14280422
DD
1108definitions useful as they are, or as a basis for the development of
1109your own locales.
5f05dabc 1110
14280422 1111=head2 I18n and l10n
5f05dabc 1112
b0c42ed9
JH
1113"Internationalization" is often abbreviated as B<i18n> because its first
1114and last letters are separated by eighteen others. (You may guess why
1115the internalin ... internaliti ... i18n tends to get abbreviated.) In
1116the same way, "localization" is often abbreviated to B<l10n>.
14280422
DD
1117
1118=head2 An imperfect standard
1119
1120Internationalization, as defined in the C and POSIX standards, can be
1121criticized as incomplete, ungainly, and having too large a granularity.
1122(Locales apply to a whole process, when it would arguably be more useful
1123to have them apply to a single thread, window group, or whatever.) They
1124also have a tendency, like standards groups, to divide the world into
1125nations, when we all know that the world can equally well be divided
e199995e 1126into bankers, bikers, gamers, and so on.
5f05dabc 1127
b310b053
JH
1128=head1 Unicode and UTF-8
1129
7ee2ae1e
KW
1130The support of Unicode is new starting from Perl version v5.6, and more fully
1131implemented in version v5.8 and later. See L<perluniintro>. It is
66cbab2c 1132strongly recommended that when combining Unicode and locale (starting in
7ee2ae1e 1133v5.16), you use
66cbab2c
KW
1134
1135 use locale ':not_characters';
1136
1137When this form of the pragma is used, only the non-character portions of
1138locales are used by Perl, for example C<LC_NUMERIC>. Perl assumes that
1139you have translated all the characters it is to operate on into Unicode
1140(actually the platform's native character set (ASCII or EBCDIC) plus
1141Unicode). For data in files, this can conveniently be done by also
1142specifying
1143
1144 use open ':locale';
1145
1146This pragma arranges for all inputs from files to be translated into
1147Unicode from the current locale as specified in the environment (see
1148L</ENVIRONMENT>), and all outputs to files to be translated back
1149into the locale. (See L<open>). On a per-filehandle basis, you can
1150instead use the L<PerlIO::locale> module, or the L<Encode::Locale>
1151module, both available from CPAN. The latter module also has methods to
1152ease the handling of C<ARGV> and environment variables, and can be used
1153on individual strings. Also, if you know that all your locales will be
1154UTF-8, as many are these days, you can use the L<B<-C>|perlrun/-C>
1155command line switch.
1156
1157This form of the pragma allows essentially seamless handling of locales
1158with Unicode. The collation order will be Unicode's. It is strongly
1159recommended that when you need to order and sort strings that you use
1160the standard module L<Unicode::Collate> which gives much better results
1161in many instances than you can get with the old-style locale handling.
1162
7ee2ae1e 1163For pre-v5.16 Perls, or if you use the locale pragma without the
66cbab2c
KW
1164C<:not_characters> parameter, Perl tries to work with both Unicode and
1165locales--but there are problems.
1166
1167Perl does not handle multi-byte locales in this case, such as have been
1168used for various
dc4bfc4b
KW
1169Asian languages, such as Big5 or Shift JIS. However, the increasingly
1170common multi-byte UTF-8 locales, if properly implemented, may work
1171reasonably well (depending on your C library implementation) in this
1172form of the locale pragma, simply because both
1173they and Perl store characters that take up multiple bytes the same way.
1174However, some, if not most, C library implementations may not process
1175the characters in the upper half of the Latin-1 range (128 - 255)
1176properly under LC_CTYPE. To see if a character is a particular type
1177under a locale, Perl uses the functions like C<isalnum()>. Your C
1178library may not work for UTF-8 locales with those functions, instead
1179only working under the newer wide library functions like C<iswalnum()>.
e199995e
KW
1180
1181Perl generally takes the tack to use locale rules on code points that can fit
66cbab2c
KW
1182in a single byte, and Unicode rules for those that can't (though this
1183isn't uniformly applied, see the note at the end of this section). This
1184prevents many problems in locales that aren't UTF-8. Suppose the locale
1185is ISO8859-7, Greek. The character at 0xD7 there is a capital Chi. But
1186in the ISO8859-1 locale, Latin1, it is a multiplication sign. The POSIX
1187regular expression character class C<[[:alpha:]]> will magically match
11880xD7 in the Greek locale but not in the Latin one.
e199995e
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1189
1190However, there are places where this breaks down. Certain constructs are
b4ffc3db
TC
1191for Unicode only, such as C<\p{Alpha}>. They assume that 0xD7 always has its
1192Unicode meaning (or the equivalent on EBCDIC platforms). Since Latin1 is a
1193subset of Unicode and 0xD7 is the multiplication sign in both Latin1 and
1194Unicode, C<\p{Alpha}> will never match it, regardless of locale. A similar
1195issue occurs with C<\N{...}>. It is therefore a bad idea to use C<\p{}> or
66cbab2c
KW
1196C<\N{}> under plain C<use locale>--I<unless> you can guarantee that the
1197locale will be a ISO8859-1. Use POSIX character classes instead.
1198
1199Another problem with this approach is that operations that cross the
1200single byte/multiple byte boundary are not well-defined, and so are
1201disallowed. (This boundary is between the codepoints at 255/256.).
1202For example, lower casing LATIN CAPITAL LETTER Y WITH DIAERESIS (U+0178)
1203should return LATIN SMALL LETTER Y WITH DIAERESIS (U+00FF). But in the
1204Greek locale, for example, there is no character at 0xFF, and Perl
1205has no way of knowing what the character at 0xFF is really supposed to
1206represent. Thus it disallows the operation. In this mode, the
1207lowercase of U+0178 is itself.
1208
1209The same problems ensue if you enable automatic UTF-8-ification of your
e199995e 1210standard file handles, default C<open()> layer, and C<@ARGV> on non-ISO8859-1,
b4ffc3db
TC
1211non-UTF-8 locales (by using either the B<-C> command line switch or the
1212C<PERL_UNICODE> environment variable; see L<perlrun>).
1213Things are read in as UTF-8, which would normally imply a Unicode
1214interpretation, but the presence of a locale causes them to be interpreted
1215in that locale instead. For example, a 0xD7 code point in the Unicode
1216input, which should mean the multiplication sign, won't be interpreted by
66cbab2c 1217Perl that way under the Greek locale. This is not a problem
b4ffc3db 1218I<provided> you make certain that all locales will always and only be either
66cbab2c 1219an ISO8859-1, or, if you don't have a deficient C library, a UTF-8 locale.
b4ffc3db
TC
1220
1221Vendor locales are notoriously buggy, and it is difficult for Perl to test
1222its locale-handling code because this interacts with code that Perl has no
1223control over; therefore the locale-handling code in Perl may be buggy as
66cbab2c
KW
1224well. (However, the Unicode-supplied locales should be better, and
1225there is a feed back mechanism to correct any problems. See
1226L</Freely available locale definitions>.)
1227
7ee2ae1e 1228If you have Perl v5.16, the problems mentioned above go away if you use
66cbab2c 1229the C<:not_characters> parameter to the locale pragma (except for vendor
7ee2ae1e 1230bugs in the non-character portions). If you don't have v5.16, and you
66cbab2c
KW
1231I<do> have locales that work, using them may be worthwhile for certain
1232specific purposes, as long as you keep in mind the gotchas already
1233mentioned. For example, if the collation for your locales works, it
1234runs faster under locales than under L<Unicode::Collate>; and you gain
1235access to such things as the local currency symbol and the names of the
7ee2ae1e 1236months and days of the week. (But to hammer home the point, in v5.16,
66cbab2c
KW
1237you get this access without the downsides of locales by using the
1238C<:not_characters> form of the pragma.)
1239
1240Note: The policy of using locale rules for code points that can fit in a
1241byte, and Unicode rules for those that can't is not uniformly applied.
7ee2ae1e 1242Pre-v5.12, it was somewhat haphazard; in v5.12 it was applied fairly
66cbab2c 1243consistently to regular expression matching except for bracketed
7ee2ae1e
KW
1244character classes; in v5.14 it was extended to all regex matches; and in
1245v5.16 to the casing operations such as C<"\L"> and C<uc()>. For
66cbab2c
KW
1246collation, in all releases, the system's C<strxfrm()> function is called,
1247and whatever it does is what you get.
b310b053 1248
5f05dabc
PP
1249=head1 BUGS
1250
1251=head2 Broken systems
1252
5a964f20 1253In certain systems, the operating system's locale support
2bdf8add 1254is broken and cannot be fixed or used by Perl. Such deficiencies can
b4ffc3db 1255and will result in mysterious hangs and/or Perl core dumps when
2bdf8add 1256C<use locale> is in effect. When confronted with such a system,
7f2de2d2 1257please report in excruciating detail to <F<perlbug@perl.org>>, and
b4ffc3db 1258also contact your vendor: bug fixes may exist for these problems
2bdf8add
JH
1259in your operating system. Sometimes such bug fixes are called an
1260operating system upgrade.
5f05dabc
PP
1261
1262=head1 SEE ALSO
1263
b310b053
JH
1264L<I18N::Langinfo>, L<perluniintro>, L<perlunicode>, L<open>,
1265L<POSIX/isalnum>, L<POSIX/isalpha>,
4bbcc6e8
JH
1266L<POSIX/isdigit>, L<POSIX/isgraph>, L<POSIX/islower>,
1267L<POSIX/isprint>, L<POSIX/ispunct>, L<POSIX/isspace>,
1268L<POSIX/isupper>, L<POSIX/isxdigit>, L<POSIX/localeconv>,
1269L<POSIX/setlocale>, L<POSIX/strcoll>, L<POSIX/strftime>,
1270L<POSIX/strtod>, L<POSIX/strxfrm>.
5f05dabc
PP
1271
1272=head1 HISTORY
1273
b0c42ed9 1274Jarkko Hietaniemi's original F<perli18n.pod> heavily hacked by Dominic
5a964f20 1275Dunlop, assisted by the perl5-porters. Prose worked over a bit by
c052850d 1276Tom Christiansen, and updated by Perl 5 porters.