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1=head1 NAME
2
b0c42ed9 3perllocale - Perl locale handling (internationalization and localization)
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4
5=head1 DESCRIPTION
6
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7Perl supports language-specific notions of data such as "is this
8a letter", "what is the uppercase equivalent of this letter", and
9"which of these letters comes first". These are important issues,
10especially for languages other than English--but also for English: it
11would be naE<iuml>ve to imagine that C<A-Za-z> defines all the "letters"
12needed to write in English. Perl is also aware that some character other
13than '.' may be preferred as a decimal point, and that output date
14representations may be language-specific. The process of making an
15application take account of its users' preferences in such matters is
16called B<internationalization> (often abbreviated as B<i18n>); telling
17such an application about a particular set of preferences is known as
18B<localization> (B<l10n>).
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19
20Perl can understand language-specific data via the standardized (ISO C,
21XPG4, POSIX 1.c) method called "the locale system". The locale system is
b0c42ed9 22controlled per application using one pragma, one function call, and
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23several environment variables.
24
25B<NOTE>: This feature is new in Perl 5.004, and does not apply unless an
5a964f20 26application specifically requests it--see L<Backward compatibility>.
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27The one exception is that write() now B<always> uses the current locale
28- see L<"NOTES">.
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29
30=head1 PREPARING TO USE LOCALES
31
5a964f20 32If Perl applications are to understand and present your data
14280422 33correctly according a locale of your choice, B<all> of the following
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34must be true:
35
36=over 4
37
38=item *
39
40B<Your operating system must support the locale system>. If it does,
14280422 41you should find that the setlocale() function is a documented part of
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42its C library.
43
44=item *
45
5a964f20 46B<Definitions for locales that you use must be installed>. You, or
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47your system administrator, must make sure that this is the case. The
48available locales, the location in which they are kept, and the manner
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49in which they are installed all vary from system to system. Some systems
50provide only a few, hard-wired locales and do not allow more to be
51added. Others allow you to add "canned" locales provided by the system
52supplier. Still others allow you or the system administrator to define
14280422 53and add arbitrary locales. (You may have to ask your supplier to
5a964f20 54provide canned locales that are not delivered with your operating
14280422 55system.) Read your system documentation for further illumination.
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56
57=item *
58
59B<Perl must believe that the locale system is supported>. If it does,
60C<perl -V:d_setlocale> will say that the value for C<d_setlocale> is
61C<define>.
62
63=back
64
65If you want a Perl application to process and present your data
66according to a particular locale, the application code should include
2ae324a7 67the S<C<use locale>> pragma (see L<The use locale pragma>) where
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68appropriate, and B<at least one> of the following must be true:
69
70=over 4
71
72=item *
73
14280422 74B<The locale-determining environment variables (see L<"ENVIRONMENT">)
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75must be correctly set up> at the time the application is started, either
76by yourself or by whoever set up your system account.
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77
78=item *
79
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80B<The application must set its own locale> using the method described in
81L<The setlocale function>.
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82
83=back
84
85=head1 USING LOCALES
86
87=head2 The use locale pragma
88
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89By default, Perl ignores the current locale. The S<C<use locale>>
90pragma tells Perl to use the current locale for some operations:
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91
92=over 4
93
94=item *
95
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96B<The comparison operators> (C<lt>, C<le>, C<cmp>, C<ge>, and C<gt>) and
97the POSIX string collation functions strcoll() and strxfrm() use
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98C<LC_COLLATE>. sort() is also affected if used without an
99explicit comparison function, because it uses C<cmp> by default.
14280422 100
5a964f20 101B<Note:> C<eq> and C<ne> are unaffected by locale: they always
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102perform a byte-by-byte comparison of their scalar operands. What's
103more, if C<cmp> finds that its operands are equal according to the
104collation sequence specified by the current locale, it goes on to
105perform a byte-by-byte comparison, and only returns I<0> (equal) if the
106operands are bit-for-bit identical. If you really want to know whether
5a964f20 107two strings--which C<eq> and C<cmp> may consider different--are equal
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108as far as collation in the locale is concerned, see the discussion in
109L<Category LC_COLLATE: Collation>.
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110
111=item *
112
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113B<Regular expressions and case-modification functions> (uc(), lc(),
114ucfirst(), and lcfirst()) use C<LC_CTYPE>
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115
116=item *
117
14280422 118B<The formatting functions> (printf(), sprintf() and write()) use
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119C<LC_NUMERIC>
120
121=item *
122
14280422 123B<The POSIX date formatting function> (strftime()) uses C<LC_TIME>.
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124
125=back
126
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127C<LC_COLLATE>, C<LC_CTYPE>, and so on, are discussed further in
128L<LOCALE CATEGORIES>.
5f05dabc 129
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130The default behavior is restored with the S<C<no locale>> pragma, or
131upon reaching the end of block enclosing C<use locale>.
5f05dabc 132
5a964f20 133The string result of any operation that uses locale
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134information is tainted, as it is possible for a locale to be
135untrustworthy. See L<"SECURITY">.
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136
137=head2 The setlocale function
138
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139You can switch locales as often as you wish at run time with the
140POSIX::setlocale() function:
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141
142 # This functionality not usable prior to Perl 5.004
143 require 5.004;
144
145 # Import locale-handling tool set from POSIX module.
146 # This example uses: setlocale -- the function call
147 # LC_CTYPE -- explained below
148 use POSIX qw(locale_h);
149
14280422 150 # query and save the old locale
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151 $old_locale = setlocale(LC_CTYPE);
152
153 setlocale(LC_CTYPE, "fr_CA.ISO8859-1");
154 # LC_CTYPE now in locale "French, Canada, codeset ISO 8859-1"
155
156 setlocale(LC_CTYPE, "");
157 # LC_CTYPE now reset to default defined by LC_ALL/LC_CTYPE/LANG
158 # environment variables. See below for documentation.
159
160 # restore the old locale
161 setlocale(LC_CTYPE, $old_locale);
162
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163The first argument of setlocale() gives the B<category>, the second the
164B<locale>. The category tells in what aspect of data processing you
165want to apply locale-specific rules. Category names are discussed in
166L<LOCALE CATEGORIES> and L<"ENVIRONMENT">. The locale is the name of a
167collection of customization information corresponding to a particular
168combination of language, country or territory, and codeset. Read on for
169hints on the naming of locales: not all systems name locales as in the
170example.
171
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172If no second argument is provided and the category is something else
173than LC_ALL, the function returns a string naming the current locale
174for the category. You can use this value as the second argument in a
175subsequent call to setlocale().
176
177If no second argument is provided and the category is LC_ALL, the
178result is implementation-dependent. It may be a string of
179concatenated locales names (separator also implementation-dependent)
180or a single locale name. Please consult your L<setlocale(3)> for
181details.
182
183If a second argument is given and it corresponds to a valid locale,
184the locale for the category is set to that value, and the function
185returns the now-current locale value. You can then use this in yet
186another call to setlocale(). (In some implementations, the return
187value may sometimes differ from the value you gave as the second
188argument--think of it as an alias for the value you gave.)
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189
190As the example shows, if the second argument is an empty string, the
191category's locale is returned to the default specified by the
192corresponding environment variables. Generally, this results in a
5a964f20 193return to the default that was in force when Perl started up: changes
54310121 194to the environment made by the application after startup may or may not
5a964f20 195be noticed, depending on your system's C library.
5f05dabc 196
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197If the second argument does not correspond to a valid locale, the locale
198for the category is not changed, and the function returns I<undef>.
5f05dabc 199
14280422 200For further information about the categories, consult L<setlocale(3)>.
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201
202=head2 Finding locales
203
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204For locales available in your system, consult also L<setlocale(3)> to
205see whether it leads to the list of available locales (search for the
206I<SEE ALSO> section). If that fails, try the following command lines:
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207
208 locale -a
209
210 nlsinfo
211
212 ls /usr/lib/nls/loc
213
214 ls /usr/lib/locale
215
216 ls /usr/lib/nls
217
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218 ls /usr/share/locale
219
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220and see whether they list something resembling these
221
2bdf8add 222 en_US.ISO8859-1 de_DE.ISO8859-1 ru_RU.ISO8859-5
502a173a 223 en_US.iso88591 de_DE.iso88591 ru_RU.iso88595
2bdf8add 224 en_US de_DE ru_RU
14280422 225 en de ru
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226 english german russian
227 english.iso88591 german.iso88591 russian.iso88595
502a173a 228 english.roman8 russian.koi8r
5f05dabc 229
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230Sadly, even though the calling interface for setlocale() has been
231standardized, names of locales and the directories where the
5a964f20 232configuration resides have not been. The basic form of the name is
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233I<language_territory>B<.>I<codeset>, but the latter parts after
234I<language> are not always present. The I<language> and I<country>
235are usually from the standards B<ISO 3166> and B<ISO 639>, the
236two-letter abbreviations for the countries and the languages of the
237world, respectively. The I<codeset> part often mentions some B<ISO
2388859> character set, the Latin codesets. For example, C<ISO 8859-1>
239is the so-called "Western European codeset" that can be used to encode
240most Western European languages adequately. Again, there are several
241ways to write even the name of that one standard. Lamentably.
5f05dabc 242
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243Two special locales are worth particular mention: "C" and "POSIX".
244Currently these are effectively the same locale: the difference is
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245mainly that the first one is defined by the C standard, the second by
246the POSIX standard. They define the B<default locale> in which
14280422 247every program starts in the absence of locale information in its
5a964f20 248environment. (The I<default> default locale, if you will.) Its language
14280422 249is (American) English and its character codeset ASCII.
5f05dabc 250
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251B<NOTE>: Not all systems have the "POSIX" locale (not all systems are
252POSIX-conformant), so use "C" when you need explicitly to specify this
253default locale.
5f05dabc 254
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255=head2 LOCALE PROBLEMS
256
5a964f20 257You may encounter the following warning message at Perl startup:
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258
259 perl: warning: Setting locale failed.
260 perl: warning: Please check that your locale settings:
261 LC_ALL = "En_US",
262 LANG = (unset)
263 are supported and installed on your system.
264 perl: warning: Falling back to the standard locale ("C").
265
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266This means that your locale settings had LC_ALL set to "En_US" and
267LANG exists but has no value. Perl tried to believe you but could not.
268Instead, Perl gave up and fell back to the "C" locale, the default locale
269that is supposed to work no matter what. This usually means your locale
270settings were wrong, they mention locales your system has never heard
271of, or the locale installation in your system has problems (for example,
272some system files are broken or missing). There are quick and temporary
273fixes to these problems, as well as more thorough and lasting fixes.
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274
275=head2 Temporarily fixing locale problems
276
5a964f20 277The two quickest fixes are either to render Perl silent about any
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278locale inconsistencies or to run Perl under the default locale "C".
279
280Perl's moaning about locale problems can be silenced by setting the
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281environment variable PERL_BADLANG to a zero value, for example "0".
282This method really just sweeps the problem under the carpet: you tell
283Perl to shut up even when Perl sees that something is wrong. Do not
284be surprised if later something locale-dependent misbehaves.
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285
286Perl can be run under the "C" locale by setting the environment
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287variable LC_ALL to "C". This method is perhaps a bit more civilized
288than the PERL_BADLANG approach, but setting LC_ALL (or
289other locale variables) may affect other programs as well, not just
290Perl. In particular, external programs run from within Perl will see
3e6e419a 291these changes. If you make the new settings permanent (read on), all
106325ad 292programs you run see the changes. See L<ENVIRONMENT> for
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293the full list of relevant environment variables and L<USING LOCALES>
294for their effects in Perl. Effects in other programs are
295easily deducible. For example, the variable LC_COLLATE may well affect
296your B<sort> program (or whatever the program that arranges `records'
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297alphabetically in your system is called).
298
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299You can test out changing these variables temporarily, and if the
300new settings seem to help, put those settings into your shell startup
301files. Consult your local documentation for the exact details. For in
302Bourne-like shells (B<sh>, B<ksh>, B<bash>, B<zsh>):
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303
304 LC_ALL=en_US.ISO8859-1
305 export LC_ALL
306
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307This assumes that we saw the locale "en_US.ISO8859-1" using the commands
308discussed above. We decided to try that instead of the above faulty
309locale "En_US"--and in Cshish shells (B<csh>, B<tcsh>)
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310
311 setenv LC_ALL en_US.ISO8859-1
c47ff5f1 312
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313or if you have the "env" application you can do in any shell
314
315 env LC_ALL=en_US.ISO8859-1 perl ...
316
5a964f20 317If you do not know what shell you have, consult your local
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318helpdesk or the equivalent.
319
320=head2 Permanently fixing locale problems
321
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322The slower but superior fixes are when you may be able to yourself
323fix the misconfiguration of your own environment variables. The
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324mis(sing)configuration of the whole system's locales usually requires
325the help of your friendly system administrator.
326
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327First, see earlier in this document about L<Finding locales>. That tells
328how to find which locales are really supported--and more importantly,
329installed--on your system. In our example error message, environment
330variables affecting the locale are listed in the order of decreasing
331importance (and unset variables do not matter). Therefore, having
332LC_ALL set to "En_US" must have been the bad choice, as shown by the
333error message. First try fixing locale settings listed first.
3e6e419a 334
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335Second, if using the listed commands you see something B<exactly>
336(prefix matches do not count and case usually counts) like "En_US"
337without the quotes, then you should be okay because you are using a
338locale name that should be installed and available in your system.
4a4eefd0 339In this case, see L<Permanently fixing your system's locale configuration>.
3e6e419a 340
4a4eefd0 341=head2 Permanently fixing your system's locale configuration
3e6e419a 342
5a964f20 343This is when you see something like:
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344
345 perl: warning: Please check that your locale settings:
346 LC_ALL = "En_US",
347 LANG = (unset)
348 are supported and installed on your system.
349
350but then cannot see that "En_US" listed by the above-mentioned
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351commands. You may see things like "en_US.ISO8859-1", but that isn't
352the same. In this case, try running under a locale
353that you can list and which somehow matches what you tried. The
3e6e419a 354rules for matching locale names are a bit vague because
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355standardization is weak in this area. See again the
356L<Finding locales> about general rules.
3e6e419a 357
b687b08b 358=head2 Fixing system locale configuration
3e6e419a 359
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360Contact a system administrator (preferably your own) and report the exact
361error message you get, and ask them to read this same documentation you
362are now reading. They should be able to check whether there is something
363wrong with the locale configuration of the system. The L<Finding locales>
364section is unfortunately a bit vague about the exact commands and places
365because these things are not that standardized.
3e6e419a 366
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367=head2 The localeconv function
368
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369The POSIX::localeconv() function allows you to get particulars of the
370locale-dependent numeric formatting information specified by the current
371C<LC_NUMERIC> and C<LC_MONETARY> locales. (If you just want the name of
372the current locale for a particular category, use POSIX::setlocale()
5a964f20 373with a single parameter--see L<The setlocale function>.)
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374
375 use POSIX qw(locale_h);
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376
377 # Get a reference to a hash of locale-dependent info
378 $locale_values = localeconv();
379
380 # Output sorted list of the values
381 for (sort keys %$locale_values) {
14280422 382 printf "%-20s = %s\n", $_, $locale_values->{$_}
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383 }
384
14280422 385localeconv() takes no arguments, and returns B<a reference to> a hash.
5a964f20 386The keys of this hash are variable names for formatting, such as
502a173a 387C<decimal_point> and C<thousands_sep>. The values are the
cea6626f 388corresponding, er, values. See L<POSIX/localeconv> for a longer
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389example listing the categories an implementation might be expected to
390provide; some provide more and others fewer. You don't need an
391explicit C<use locale>, because localeconv() always observes the
392current locale.
5f05dabc 393
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394Here's a simple-minded example program that rewrites its command-line
395parameters as integers correctly formatted in the current locale:
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396
397 # See comments in previous example
398 require 5.004;
399 use POSIX qw(locale_h);
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400
401 # Get some of locale's numeric formatting parameters
402 my ($thousands_sep, $grouping) =
14280422 403 @{localeconv()}{'thousands_sep', 'grouping'};
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404
405 # Apply defaults if values are missing
406 $thousands_sep = ',' unless $thousands_sep;
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407
408 # grouping and mon_grouping are packed lists
409 # of small integers (characters) telling the
410 # grouping (thousand_seps and mon_thousand_seps
411 # being the group dividers) of numbers and
412 # monetary quantities. The integers' meanings:
413 # 255 means no more grouping, 0 means repeat
414 # the previous grouping, 1-254 means use that
415 # as the current grouping. Grouping goes from
416 # right to left (low to high digits). In the
417 # below we cheat slightly by never using anything
418 # else than the first grouping (whatever that is).
419 if ($grouping) {
420 @grouping = unpack("C*", $grouping);
421 } else {
422 @grouping = (3);
423 }
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424
425 # Format command line params for current locale
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426 for (@ARGV) {
427 $_ = int; # Chop non-integer part
5f05dabc 428 1 while
502a173a 429 s/(\d)(\d{$grouping[0]}($|$thousands_sep))/$1$thousands_sep$2/;
14280422 430 print "$_";
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431 }
432 print "\n";
433
74c76037 434=head2 I18N::Langinfo
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435
436Another interface for querying locale-dependent information is the
437I18N::Langinfo::langinfo() function, available at least in UNIX-like
438systems and VMS.
439
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440The following example will import the langinfo() function itself and
441three constants to be used as arguments to langinfo(): a constant for
442the abbreviated first day of the week (the numbering starts from
443Sunday = 1) and two more constants for the affirmative and negative
444answers for a yes/no question in the current locale.
4bbcc6e8 445
74c76037 446 use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
4bbcc6e8 447
74c76037 448 my ($abday_1, $yesstr, $nostr) = map { langinfo } qw(ABDAY_1 YESSTR NOSTR);
4bbcc6e8 449
74c76037 450 print "$abday_1? [$yesstr/$nostr] ";
4bbcc6e8 451
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452In other words, in the "C" (or English) locale the above will probably
453print something like:
454
455 Sun? [yes/no]
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456
457See L<I18N::Langinfo> for more information.
458
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459=head1 LOCALE CATEGORIES
460
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461The following subsections describe basic locale categories. Beyond these,
462some combination categories allow manipulation of more than one
463basic category at a time. See L<"ENVIRONMENT"> for a discussion of these.
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464
465=head2 Category LC_COLLATE: Collation
466
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467In the scope of S<C<use locale>>, Perl looks to the C<LC_COLLATE>
468environment variable to determine the application's notions on collation
469(ordering) of characters. For example, 'b' follows 'a' in Latin
470alphabets, but where do 'E<aacute>' and 'E<aring>' belong? And while
471'color' follows 'chocolate' in English, what about in Spanish?
5f05dabc 472
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473The following collations all make sense and you may meet any of them
474if you "use locale".
475
476 A B C D E a b c d e
35316ca3 477 A a B b C c D d E e
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478 a A b B c C d D e E
479 a b c d e A B C D E
480
f1cbbd6e 481Here is a code snippet to tell what "word"
5a964f20 482characters are in the current locale, in that locale's order:
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483
484 use locale;
35316ca3 485 print +(sort grep /\w/, map { chr } 0..255), "\n";
5f05dabc 486
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487Compare this with the characters that you see and their order if you
488state explicitly that the locale should be ignored:
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489
490 no locale;
35316ca3 491 print +(sort grep /\w/, map { chr } 0..255), "\n";
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492
493This machine-native collation (which is what you get unless S<C<use
494locale>> has appeared earlier in the same block) must be used for
495sorting raw binary data, whereas the locale-dependent collation of the
b0c42ed9 496first example is useful for natural text.
5f05dabc 497
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498As noted in L<USING LOCALES>, C<cmp> compares according to the current
499collation locale when C<use locale> is in effect, but falls back to a
5a964f20 500byte-by-byte comparison for strings that the locale says are equal. You
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501can use POSIX::strcoll() if you don't want this fall-back:
502
503 use POSIX qw(strcoll);
504 $equal_in_locale =
505 !strcoll("space and case ignored", "SpaceAndCaseIgnored");
506
507$equal_in_locale will be true if the collation locale specifies a
5a964f20 508dictionary-like ordering that ignores space characters completely and
9e3a2af8 509which folds case.
14280422 510
5a964f20 511If you have a single string that you want to check for "equality in
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512locale" against several others, you might think you could gain a little
513efficiency by using POSIX::strxfrm() in conjunction with C<eq>:
514
515 use POSIX qw(strxfrm);
516 $xfrm_string = strxfrm("Mixed-case string");
517 print "locale collation ignores spaces\n"
518 if $xfrm_string eq strxfrm("Mixed-casestring");
519 print "locale collation ignores hyphens\n"
520 if $xfrm_string eq strxfrm("Mixedcase string");
521 print "locale collation ignores case\n"
522 if $xfrm_string eq strxfrm("mixed-case string");
523
524strxfrm() takes a string and maps it into a transformed string for use
525in byte-by-byte comparisons against other transformed strings during
526collation. "Under the hood", locale-affected Perl comparison operators
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527call strxfrm() for both operands, then do a byte-by-byte
528comparison of the transformed strings. By calling strxfrm() explicitly
14280422 529and using a non locale-affected comparison, the example attempts to save
5a964f20 530a couple of transformations. But in fact, it doesn't save anything: Perl
2ae324a7 531magic (see L<perlguts/Magic Variables>) creates the transformed version of a
5a964f20 532string the first time it's needed in a comparison, then keeps this version around
14280422 533in case it's needed again. An example rewritten the easy way with
e38874e2 534C<cmp> runs just about as fast. It also copes with null characters
14280422 535embedded in strings; if you call strxfrm() directly, it treats the first
5a964f20
TC
536null it finds as a terminator. don't expect the transformed strings
537it produces to be portable across systems--or even from one revision
e38874e2
DD
538of your operating system to the next. In short, don't call strxfrm()
539directly: let Perl do it for you.
14280422 540
5a964f20 541Note: C<use locale> isn't shown in some of these examples because it isn't
14280422
DD
542needed: strcoll() and strxfrm() exist only to generate locale-dependent
543results, and so always obey the current C<LC_COLLATE> locale.
5f05dabc
PP
544
545=head2 Category LC_CTYPE: Character Types
546
5a964f20 547In the scope of S<C<use locale>>, Perl obeys the C<LC_CTYPE> locale
14280422
DD
548setting. This controls the application's notion of which characters are
549alphabetic. This affects Perl's C<\w> regular expression metanotation,
f1cbbd6e
GS
550which stands for alphanumeric characters--that is, alphabetic,
551numeric, and including other special characters such as the underscore or
552hyphen. (Consult L<perlre> for more information about
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DD
553regular expressions.) Thanks to C<LC_CTYPE>, depending on your locale
554setting, characters like 'E<aelig>', 'E<eth>', 'E<szlig>', and
555'E<oslash>' may be understood as C<\w> characters.
5f05dabc 556
2c268ad5 557The C<LC_CTYPE> locale also provides the map used in transliterating
68dc0745 558characters between lower and uppercase. This affects the case-mapping
5a964f20
TC
559functions--lc(), lcfirst, uc(), and ucfirst(); case-mapping
560interpolation with C<\l>, C<\L>, C<\u>, or C<\U> in double-quoted strings
561and C<s///> substitutions; and case-independent regular expression
e38874e2
DD
562pattern matching using the C<i> modifier.
563
5a964f20
TC
564Finally, C<LC_CTYPE> affects the POSIX character-class test
565functions--isalpha(), islower(), and so on. For example, if you move
566from the "C" locale to a 7-bit Scandinavian one, you may find--possibly
567to your surprise--that "|" moves from the ispunct() class to isalpha().
5f05dabc 568
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DD
569B<Note:> A broken or malicious C<LC_CTYPE> locale definition may result
570in clearly ineligible characters being considered to be alphanumeric by
5a964f20
TC
571your application. For strict matching of (mundane) letters and
572digits--for example, in command strings--locale-aware applications
14280422 573should use C<\w> inside a C<no locale> block. See L<"SECURITY">.
5f05dabc
PP
574
575=head2 Category LC_NUMERIC: Numeric Formatting
576
5a964f20
TC
577In the scope of S<C<use locale>>, Perl obeys the C<LC_NUMERIC> locale
578information, which controls an application's idea of how numbers should
579be formatted for human readability by the printf(), sprintf(), and
580write() functions. String-to-numeric conversion by the POSIX::strtod()
581function is also affected. In most implementations the only effect is to
582change the character used for the decimal point--perhaps from '.' to ','.
583These functions aren't aware of such niceties as thousands separation and
584so on. (See L<The localeconv function> if you care about these things.)
585
3cf03d68
JH
586Output produced by print() is also affected by the current locale: it
587depends on whether C<use locale> or C<no locale> is in effect, and
588corresponds to what you'd get from printf() in the "C" locale. The
589same is true for Perl's internal conversions between numeric and
590string formats:
5f05dabc
PP
591
592 use POSIX qw(strtod);
593 use locale;
14280422 594
5f05dabc
PP
595 $n = 5/2; # Assign numeric 2.5 to $n
596
35316ca3 597 $a = " $n"; # Locale-dependent conversion to string
5f05dabc 598
35316ca3 599 print "half five is $n\n"; # Locale-dependent output
5f05dabc
PP
600
601 printf "half five is %g\n", $n; # Locale-dependent output
602
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DD
603 print "DECIMAL POINT IS COMMA\n"
604 if $n == (strtod("2,5"))[0]; # Locale-dependent conversion
5f05dabc 605
4bbcc6e8
JH
606See also L<I18N::Langinfo> and C<RADIXCHAR>.
607
5f05dabc
PP
608=head2 Category LC_MONETARY: Formatting of monetary amounts
609
5a964f20
TC
610The C standard defines the C<LC_MONETARY> category, but no function
611that is affected by its contents. (Those with experience of standards
b0c42ed9 612committees will recognize that the working group decided to punt on the
14280422 613issue.) Consequently, Perl takes no notice of it. If you really want
13a2d996
SP
614to use C<LC_MONETARY>, you can query its contents--see
615L<The localeconv function>--and use the information that it returns in your
616application's own formatting of currency amounts. However, you may well
617find that the information, voluminous and complex though it may be, still
618does not quite meet your requirements: currency formatting is a hard nut
619to crack.
5f05dabc 620
4bbcc6e8
JH
621See also L<I18N::Langinfo> and C<CRNCYSTR>.
622
5f05dabc
PP
623=head2 LC_TIME
624
5a964f20 625Output produced by POSIX::strftime(), which builds a formatted
5f05dabc
PP
626human-readable date/time string, is affected by the current C<LC_TIME>
627locale. Thus, in a French locale, the output produced by the C<%B>
628format element (full month name) for the first month of the year would
5a964f20 629be "janvier". Here's how to get a list of long month names in the
5f05dabc
PP
630current locale:
631
632 use POSIX qw(strftime);
14280422
DD
633 for (0..11) {
634 $long_month_name[$_] =
635 strftime("%B", 0, 0, 0, 1, $_, 96);
5f05dabc
PP
636 }
637
5a964f20 638Note: C<use locale> isn't needed in this example: as a function that
14280422
DD
639exists only to generate locale-dependent results, strftime() always
640obeys the current C<LC_TIME> locale.
5f05dabc 641
4bbcc6e8 642See also L<I18N::Langinfo> and C<ABDAY_1>..C<ABDAY_7>, C<DAY_1>..C<DAY_7>,
2a2bf5f4 643C<ABMON_1>..C<ABMON_12>, and C<ABMON_1>..C<ABMON_12>.
4bbcc6e8 644
5f05dabc
PP
645=head2 Other categories
646
5a964f20
TC
647The remaining locale category, C<LC_MESSAGES> (possibly supplemented
648by others in particular implementations) is not currently used by
98a6f11e 649Perl--except possibly to affect the behavior of library functions
650called by extensions outside the standard Perl distribution and by the
651operating system and its utilities. Note especially that the string
652value of C<$!> and the error messages given by external utilities may
653be changed by C<LC_MESSAGES>. If you want to have portable error
265f5c4a 654codes, use C<%!>. See L<Errno>.
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DD
655
656=head1 SECURITY
657
5a964f20 658Although the main discussion of Perl security issues can be found in
14280422
DD
659L<perlsec>, a discussion of Perl's locale handling would be incomplete
660if it did not draw your attention to locale-dependent security issues.
5a964f20
TC
661Locales--particularly on systems that allow unprivileged users to
662build their own locales--are untrustworthy. A malicious (or just plain
14280422
DD
663broken) locale can make a locale-aware application give unexpected
664results. Here are a few possibilities:
665
666=over 4
667
668=item *
669
670Regular expression checks for safe file names or mail addresses using
5a964f20 671C<\w> may be spoofed by an C<LC_CTYPE> locale that claims that
14280422
DD
672characters such as "E<gt>" and "|" are alphanumeric.
673
674=item *
675
e38874e2
DD
676String interpolation with case-mapping, as in, say, C<$dest =
677"C:\U$name.$ext">, may produce dangerous results if a bogus LC_CTYPE
678case-mapping table is in effect.
679
680=item *
681
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DD
682A sneaky C<LC_COLLATE> locale could result in the names of students with
683"D" grades appearing ahead of those with "A"s.
684
685=item *
686
5a964f20 687An application that takes the trouble to use information in
14280422 688C<LC_MONETARY> may format debits as if they were credits and vice versa
5a964f20 689if that locale has been subverted. Or it might make payments in US
14280422
DD
690dollars instead of Hong Kong dollars.
691
692=item *
693
694The date and day names in dates formatted by strftime() could be
695manipulated to advantage by a malicious user able to subvert the
5a964f20 696C<LC_DATE> locale. ("Look--it says I wasn't in the building on
14280422
DD
697Sunday.")
698
699=back
700
701Such dangers are not peculiar to the locale system: any aspect of an
5a964f20 702application's environment which may be modified maliciously presents
14280422 703similar challenges. Similarly, they are not specific to Perl: any
5a964f20 704programming language that allows you to write programs that take
14280422
DD
705account of their environment exposes you to these issues.
706
5a964f20
TC
707Perl cannot protect you from all possibilities shown in the
708examples--there is no substitute for your own vigilance--but, when
14280422 709C<use locale> is in effect, Perl uses the tainting mechanism (see
5a964f20 710L<perlsec>) to mark string results that become locale-dependent, and
14280422 711which may be untrustworthy in consequence. Here is a summary of the
5a964f20 712tainting behavior of operators and functions that may be affected by
14280422
DD
713the locale:
714
715=over 4
716
551e1d92
RB
717=item *
718
719B<Comparison operators> (C<lt>, C<le>, C<ge>, C<gt> and C<cmp>):
14280422
DD
720
721Scalar true/false (or less/equal/greater) result is never tainted.
722
551e1d92
RB
723=item *
724
725B<Case-mapping interpolation> (with C<\l>, C<\L>, C<\u> or C<\U>)
e38874e2
DD
726
727Result string containing interpolated material is tainted if
728C<use locale> is in effect.
729
551e1d92
RB
730=item *
731
732B<Matching operator> (C<m//>):
14280422
DD
733
734Scalar true/false result never tainted.
735
5a964f20 736Subpatterns, either delivered as a list-context result or as $1 etc.
14280422 737are tainted if C<use locale> is in effect, and the subpattern regular
e38874e2
DD
738expression contains C<\w> (to match an alphanumeric character), C<\W>
739(non-alphanumeric character), C<\s> (white-space character), or C<\S>
5a964f20 740(non white-space character). The matched-pattern variable, $&, $`
e38874e2
DD
741(pre-match), $' (post-match), and $+ (last match) are also tainted if
742C<use locale> is in effect and the regular expression contains C<\w>,
743C<\W>, C<\s>, or C<\S>.
14280422 744
551e1d92
RB
745=item *
746
747B<Substitution operator> (C<s///>):
14280422 748
e38874e2 749Has the same behavior as the match operator. Also, the left
5a964f20
TC
750operand of C<=~> becomes tainted when C<use locale> in effect
751if modified as a result of a substitution based on a regular
e38874e2 752expression match involving C<\w>, C<\W>, C<\s>, or C<\S>; or of
7b8d334a 753case-mapping with C<\l>, C<\L>,C<\u> or C<\U>.
14280422 754
551e1d92
RB
755=item *
756
757B<Output formatting functions> (printf() and write()):
14280422 758
3cf03d68
JH
759Results are never tainted because otherwise even output from print,
760for example C<print(1/7)>, should be tainted if C<use locale> is in
761effect.
14280422 762
551e1d92
RB
763=item *
764
765B<Case-mapping functions> (lc(), lcfirst(), uc(), ucfirst()):
14280422
DD
766
767Results are tainted if C<use locale> is in effect.
768
551e1d92
RB
769=item *
770
771B<POSIX locale-dependent functions> (localeconv(), strcoll(),
14280422
DD
772strftime(), strxfrm()):
773
774Results are never tainted.
775
551e1d92
RB
776=item *
777
778B<POSIX character class tests> (isalnum(), isalpha(), isdigit(),
14280422
DD
779isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(),
780isxdigit()):
781
782True/false results are never tainted.
783
784=back
785
786Three examples illustrate locale-dependent tainting.
787The first program, which ignores its locale, won't run: a value taken
54310121 788directly from the command line may not be used to name an output file
14280422
DD
789when taint checks are enabled.
790
791 #/usr/local/bin/perl -T
792 # Run with taint checking
793
54310121 794 # Command line sanity check omitted...
14280422
DD
795 $tainted_output_file = shift;
796
797 open(F, ">$tainted_output_file")
798 or warn "Open of $untainted_output_file failed: $!\n";
799
800The program can be made to run by "laundering" the tainted value through
5a964f20
TC
801a regular expression: the second example--which still ignores locale
802information--runs, creating the file named on its command line
14280422
DD
803if it can.
804
805 #/usr/local/bin/perl -T
806
807 $tainted_output_file = shift;
808 $tainted_output_file =~ m%[\w/]+%;
809 $untainted_output_file = $&;
810
811 open(F, ">$untainted_output_file")
812 or warn "Open of $untainted_output_file failed: $!\n";
813
5a964f20 814Compare this with a similar but locale-aware program:
14280422
DD
815
816 #/usr/local/bin/perl -T
817
818 $tainted_output_file = shift;
819 use locale;
820 $tainted_output_file =~ m%[\w/]+%;
821 $localized_output_file = $&;
822
823 open(F, ">$localized_output_file")
824 or warn "Open of $localized_output_file failed: $!\n";
825
826This third program fails to run because $& is tainted: it is the result
5a964f20 827of a match involving C<\w> while C<use locale> is in effect.
5f05dabc
PP
828
829=head1 ENVIRONMENT
830
831=over 12
832
833=item PERL_BADLANG
834
14280422 835A string that can suppress Perl's warning about failed locale settings
54310121 836at startup. Failure can occur if the locale support in the operating
5a964f20 837system is lacking (broken) in some way--or if you mistyped the name of
900bd440
JH
838a locale when you set up your environment. If this environment
839variable is absent, or has a value that does not evaluate to integer
840zero--that is, "0" or ""-- Perl will complain about locale setting
841failures.
5f05dabc 842
14280422
DD
843B<NOTE>: PERL_BADLANG only gives you a way to hide the warning message.
844The message tells about some problem in your system's locale support,
845and you should investigate what the problem is.
5f05dabc
PP
846
847=back
848
849The following environment variables are not specific to Perl: They are
14280422
DD
850part of the standardized (ISO C, XPG4, POSIX 1.c) setlocale() method
851for controlling an application's opinion on data.
5f05dabc
PP
852
853=over 12
854
855=item LC_ALL
856
5a964f20 857C<LC_ALL> is the "override-all" locale environment variable. If
5f05dabc
PP
858set, it overrides all the rest of the locale environment variables.
859
528d65ad
JH
860=item LANGUAGE
861
862B<NOTE>: C<LANGUAGE> is a GNU extension, it affects you only if you
863are using the GNU libc. This is the case if you are using e.g. Linux.
864If you are using "commercial" UNIXes you are most probably I<not>
22b6f60d
JH
865using GNU libc and you can ignore C<LANGUAGE>.
866
867However, in the case you are using C<LANGUAGE>: it affects the
868language of informational, warning, and error messages output by
869commands (in other words, it's like C<LC_MESSAGES>) but it has higher
870priority than L<LC_ALL>. Moreover, it's not a single value but
871instead a "path" (":"-separated list) of I<languages> (not locales).
872See the GNU C<gettext> library documentation for more information.
528d65ad 873
5f05dabc
PP
874=item LC_CTYPE
875
876In the absence of C<LC_ALL>, C<LC_CTYPE> chooses the character type
877locale. In the absence of both C<LC_ALL> and C<LC_CTYPE>, C<LANG>
878chooses the character type locale.
879
880=item LC_COLLATE
881
14280422
DD
882In the absence of C<LC_ALL>, C<LC_COLLATE> chooses the collation
883(sorting) locale. In the absence of both C<LC_ALL> and C<LC_COLLATE>,
884C<LANG> chooses the collation locale.
5f05dabc
PP
885
886=item LC_MONETARY
887
14280422
DD
888In the absence of C<LC_ALL>, C<LC_MONETARY> chooses the monetary
889formatting locale. In the absence of both C<LC_ALL> and C<LC_MONETARY>,
890C<LANG> chooses the monetary formatting locale.
5f05dabc
PP
891
892=item LC_NUMERIC
893
894In the absence of C<LC_ALL>, C<LC_NUMERIC> chooses the numeric format
895locale. In the absence of both C<LC_ALL> and C<LC_NUMERIC>, C<LANG>
896chooses the numeric format.
897
898=item LC_TIME
899
14280422
DD
900In the absence of C<LC_ALL>, C<LC_TIME> chooses the date and time
901formatting locale. In the absence of both C<LC_ALL> and C<LC_TIME>,
902C<LANG> chooses the date and time formatting locale.
5f05dabc
PP
903
904=item LANG
905
14280422
DD
906C<LANG> is the "catch-all" locale environment variable. If it is set, it
907is used as the last resort after the overall C<LC_ALL> and the
5f05dabc
PP
908category-specific C<LC_...>.
909
910=back
911
912=head1 NOTES
913
914=head2 Backward compatibility
915
b0c42ed9 916Versions of Perl prior to 5.004 B<mostly> ignored locale information,
5a964f20
TC
917generally behaving as if something similar to the C<"C"> locale were
918always in force, even if the program environment suggested otherwise
919(see L<The setlocale function>). By default, Perl still behaves this
920way for backward compatibility. If you want a Perl application to pay
921attention to locale information, you B<must> use the S<C<use locale>>
b687b08b 922pragma (see L<The use locale pragma>) to instruct it to do so.
b0c42ed9
JH
923
924Versions of Perl from 5.002 to 5.003 did use the C<LC_CTYPE>
5a964f20
TC
925information if available; that is, C<\w> did understand what
926were the letters according to the locale environment variables.
b0c42ed9
JH
927The problem was that the user had no control over the feature:
928if the C library supported locales, Perl used them.
929
930=head2 I18N:Collate obsolete
931
5a964f20 932In versions of Perl prior to 5.004, per-locale collation was possible
b0c42ed9
JH
933using the C<I18N::Collate> library module. This module is now mildly
934obsolete and should be avoided in new applications. The C<LC_COLLATE>
935functionality is now integrated into the Perl core language: One can
936use locale-specific scalar data completely normally with C<use locale>,
937so there is no longer any need to juggle with the scalar references of
938C<I18N::Collate>.
5f05dabc 939
14280422 940=head2 Sort speed and memory use impacts
5f05dabc
PP
941
942Comparing and sorting by locale is usually slower than the default
14280422
DD
943sorting; slow-downs of two to four times have been observed. It will
944also consume more memory: once a Perl scalar variable has participated
945in any string comparison or sorting operation obeying the locale
946collation rules, it will take 3-15 times more memory than before. (The
947exact multiplier depends on the string's contents, the operating system
948and the locale.) These downsides are dictated more by the operating
949system's implementation of the locale system than by Perl.
5f05dabc 950
e38874e2
DD
951=head2 write() and LC_NUMERIC
952
5a964f20 953Formats are the only part of Perl that unconditionally use information
e38874e2
DD
954from a program's locale; if a program's environment specifies an
955LC_NUMERIC locale, it is always used to specify the decimal point
956character in formatted output. Formatted output cannot be controlled by
957C<use locale> because the pragma is tied to the block structure of the
958program, and, for historical reasons, formats exist outside that block
959structure.
960
5f05dabc
PP
961=head2 Freely available locale definitions
962
963There is a large collection of locale definitions at
14280422
DD
964C<ftp://dkuug.dk/i18n/WG15-collection>. You should be aware that it is
965unsupported, and is not claimed to be fit for any purpose. If your
5a964f20 966system allows installation of arbitrary locales, you may find the
14280422
DD
967definitions useful as they are, or as a basis for the development of
968your own locales.
5f05dabc 969
14280422 970=head2 I18n and l10n
5f05dabc 971
b0c42ed9
JH
972"Internationalization" is often abbreviated as B<i18n> because its first
973and last letters are separated by eighteen others. (You may guess why
974the internalin ... internaliti ... i18n tends to get abbreviated.) In
975the same way, "localization" is often abbreviated to B<l10n>.
14280422
DD
976
977=head2 An imperfect standard
978
979Internationalization, as defined in the C and POSIX standards, can be
980criticized as incomplete, ungainly, and having too large a granularity.
981(Locales apply to a whole process, when it would arguably be more useful
982to have them apply to a single thread, window group, or whatever.) They
983also have a tendency, like standards groups, to divide the world into
984nations, when we all know that the world can equally well be divided
985into bankers, bikers, gamers, and so on. But, for now, it's the only
986standard we've got. This may be construed as a bug.
5f05dabc
PP
987
988=head1 BUGS
989
990=head2 Broken systems
991
5a964f20 992In certain systems, the operating system's locale support
2bdf8add
JH
993is broken and cannot be fixed or used by Perl. Such deficiencies can
994and will result in mysterious hangs and/or Perl core dumps when the
995C<use locale> is in effect. When confronted with such a system,
7f2de2d2 996please report in excruciating detail to <F<perlbug@perl.org>>, and
5a964f20 997complain to your vendor: bug fixes may exist for these problems
2bdf8add
JH
998in your operating system. Sometimes such bug fixes are called an
999operating system upgrade.
5f05dabc
PP
1000
1001=head1 SEE ALSO
1002
4bbcc6e8
JH
1003L<I18N::Langinfo>, L<POSIX/isalnum>, L<POSIX/isalpha>,
1004L<POSIX/isdigit>, L<POSIX/isgraph>, L<POSIX/islower>,
1005L<POSIX/isprint>, L<POSIX/ispunct>, L<POSIX/isspace>,
1006L<POSIX/isupper>, L<POSIX/isxdigit>, L<POSIX/localeconv>,
1007L<POSIX/setlocale>, L<POSIX/strcoll>, L<POSIX/strftime>,
1008L<POSIX/strtod>, L<POSIX/strxfrm>.
5f05dabc
PP
1009
1010=head1 HISTORY
1011
b0c42ed9 1012Jarkko Hietaniemi's original F<perli18n.pod> heavily hacked by Dominic
5a964f20
TC
1013Dunlop, assisted by the perl5-porters. Prose worked over a bit by
1014Tom Christiansen.
5f05dabc 1015
5a964f20 1016Last update: Thu Jun 11 08:44:13 MDT 1998