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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 L<LOCALE
128CATEGORIES>.
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
172If no second argument is provided, the function returns a string naming
173the current locale for the category. You can use this value as the
174second argument in a subsequent call to setlocale(). If a second
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175argument is given and it corresponds to a valid locale, the locale for
176the category is set to that value, and the function returns the
5a964f20 177now-current locale value. You can then use this in yet another call to
14280422 178setlocale(). (In some implementations, the return value may sometimes
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179differ from the value you gave as the second argument--think of it as
180an alias for the value you gave.)
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181
182As the example shows, if the second argument is an empty string, the
183category's locale is returned to the default specified by the
184corresponding environment variables. Generally, this results in a
5a964f20 185return to the default that was in force when Perl started up: changes
54310121 186to the environment made by the application after startup may or may not
5a964f20 187be noticed, depending on your system's C library.
5f05dabc 188
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189If the second argument does not correspond to a valid locale, the locale
190for the category is not changed, and the function returns I<undef>.
5f05dabc 191
14280422 192For further information about the categories, consult L<setlocale(3)>.
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193
194=head2 Finding locales
195
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196For locales available in your system, consult also L<setlocale(3)> to
197see whether it leads to the list of available locales (search for the
198I<SEE ALSO> section). If that fails, try the following command lines:
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199
200 locale -a
201
202 nlsinfo
203
204 ls /usr/lib/nls/loc
205
206 ls /usr/lib/locale
207
208 ls /usr/lib/nls
209
210and see whether they list something resembling these
211
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212 en_US.ISO8859-1 de_DE.ISO8859-1 ru_RU.ISO8859-5
213 en_US de_DE ru_RU
14280422 214 en de ru
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215 english german russian
216 english.iso88591 german.iso88591 russian.iso88595
5f05dabc 217
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218Sadly, even though the calling interface for setlocale() has
219been standardized, names of locales and the directories where the
220configuration resides have not been. The basic form of the name is
221I<language_country/territory>B<.>I<codeset>, but the latter parts after
222I<language> are not always present. The I<language> and I<country> are
223usually from the standards B<ISO 3166> and B<ISO 639>, the two-letter
224abbreviations for the countries and the languages of the world,
225respectively. The I<codeset> part often mentions some B<ISO 8859>
226character set, the Latin codesets. For example, C<ISO 8859-1> is the
227so-called "Western codeset" that can be used to encode most Western
228European languages. Again, there are several ways to write even the
229name of that one standard. Lamentably.
5f05dabc 230
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231Two special locales are worth particular mention: "C" and "POSIX".
232Currently these are effectively the same locale: the difference is
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233mainly that the first one is defined by the C standard, the second by
234the POSIX standard. They define the B<default locale> in which
14280422 235every program starts in the absence of locale information in its
5a964f20 236environment. (The I<default> default locale, if you will.) Its language
14280422 237is (American) English and its character codeset ASCII.
5f05dabc 238
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239B<NOTE>: Not all systems have the "POSIX" locale (not all systems are
240POSIX-conformant), so use "C" when you need explicitly to specify this
241default locale.
5f05dabc 242
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243=head2 LOCALE PROBLEMS
244
5a964f20 245You may encounter the following warning message at Perl startup:
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246
247 perl: warning: Setting locale failed.
248 perl: warning: Please check that your locale settings:
249 LC_ALL = "En_US",
250 LANG = (unset)
251 are supported and installed on your system.
252 perl: warning: Falling back to the standard locale ("C").
253
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254This means that your locale settings had LC_ALL set to "En_US" and
255LANG exists but has no value. Perl tried to believe you but could not.
256Instead, Perl gave up and fell back to the "C" locale, the default locale
257that is supposed to work no matter what. This usually means your locale
258settings were wrong, they mention locales your system has never heard
259of, or the locale installation in your system has problems (for example,
260some system files are broken or missing). There are quick and temporary
261fixes to these problems, as well as more thorough and lasting fixes.
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262
263=head2 Temporarily fixing locale problems
264
5a964f20 265The two quickest fixes are either to render Perl silent about any
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266locale inconsistencies or to run Perl under the default locale "C".
267
268Perl's moaning about locale problems can be silenced by setting the
269environment variable PERL_BADLANG to a non-zero value, for example
270"1". This method really just sweeps the problem under the carpet: you
271tell Perl to shut up even when Perl sees that something is wrong. Do
5a964f20 272not be surprised if later something locale-dependent misbehaves.
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273
274Perl can be run under the "C" locale by setting the environment
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275variable LC_ALL to "C". This method is perhaps a bit more civilized
276than the PERL_BADLANG approach, but setting LC_ALL (or
277other locale variables) may affect other programs as well, not just
278Perl. In particular, external programs run from within Perl will see
3e6e419a 279these changes. If you make the new settings permanent (read on), all
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280programs you run see the changes. See L<ENVIRONMENT> for for
281the full list of relevant environment variables and L<USING LOCALES>
282for their effects in Perl. Effects in other programs are
283easily deducible. For example, the variable LC_COLLATE may well affect
284your B<sort> program (or whatever the program that arranges `records'
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285alphabetically in your system is called).
286
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287You can test out changing these variables temporarily, and if the
288new settings seem to help, put those settings into your shell startup
289files. Consult your local documentation for the exact details. For in
290Bourne-like shells (B<sh>, B<ksh>, B<bash>, B<zsh>):
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291
292 LC_ALL=en_US.ISO8859-1
293 export LC_ALL
294
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295This assumes that we saw the locale "en_US.ISO8859-1" using the commands
296discussed above. We decided to try that instead of the above faulty
297locale "En_US"--and in Cshish shells (B<csh>, B<tcsh>)
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298
299 setenv LC_ALL en_US.ISO8859-1
300
5a964f20 301If you do not know what shell you have, consult your local
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302helpdesk or the equivalent.
303
304=head2 Permanently fixing locale problems
305
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306The slower but superior fixes are when you may be able to yourself
307fix the misconfiguration of your own environment variables. The
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308mis(sing)configuration of the whole system's locales usually requires
309the help of your friendly system administrator.
310
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311First, see earlier in this document about L<Finding locales>. That tells
312how to find which locales are really supported--and more importantly,
313installed--on your system. In our example error message, environment
314variables affecting the locale are listed in the order of decreasing
315importance (and unset variables do not matter). Therefore, having
316LC_ALL set to "En_US" must have been the bad choice, as shown by the
317error message. First try fixing locale settings listed first.
3e6e419a 318
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319Second, if using the listed commands you see something B<exactly>
320(prefix matches do not count and case usually counts) like "En_US"
321without the quotes, then you should be okay because you are using a
322locale name that should be installed and available in your system.
323In this case, see L<Fixing system locale configuration>.
3e6e419a 324
5a964f20 325=head2 Permanently fixing your locale configuration
3e6e419a 326
5a964f20 327This is when you see something like:
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328
329 perl: warning: Please check that your locale settings:
330 LC_ALL = "En_US",
331 LANG = (unset)
332 are supported and installed on your system.
333
334but then cannot see that "En_US" listed by the above-mentioned
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335commands. You may see things like "en_US.ISO8859-1", but that isn't
336the same. In this case, try running under a locale
337that you can list and which somehow matches what you tried. The
3e6e419a 338rules for matching locale names are a bit vague because
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339standardization is weak in this area. See again the L<Finding
340locales> about general rules.
3e6e419a 341
5a964f20 342=head2 Permanently fixing system locale configuration
3e6e419a 343
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344Contact a system administrator (preferably your own) and report the exact
345error message you get, and ask them to read this same documentation you
346are now reading. They should be able to check whether there is something
347wrong with the locale configuration of the system. The L<Finding locales>
348section is unfortunately a bit vague about the exact commands and places
349because these things are not that standardized.
3e6e419a 350
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351=head2 The localeconv function
352
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353The POSIX::localeconv() function allows you to get particulars of the
354locale-dependent numeric formatting information specified by the current
355C<LC_NUMERIC> and C<LC_MONETARY> locales. (If you just want the name of
356the current locale for a particular category, use POSIX::setlocale()
5a964f20 357with a single parameter--see L<The setlocale function>.)
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358
359 use POSIX qw(locale_h);
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360
361 # Get a reference to a hash of locale-dependent info
362 $locale_values = localeconv();
363
364 # Output sorted list of the values
365 for (sort keys %$locale_values) {
14280422 366 printf "%-20s = %s\n", $_, $locale_values->{$_}
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367 }
368
14280422 369localeconv() takes no arguments, and returns B<a reference to> a hash.
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370The keys of this hash are variable names for formatting, such as
371C<decimal_point> and C<thousands_sep>. The values are the corresponding,
372er, values. See L<POSIX (3)/localeconv> for a longer example listing
373the categories an implementation might be expected to provide; some
374provide more and others fewer, however. You don't need an explicit C<use
375locale>, because localeconv() always observes the current locale.
5f05dabc 376
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377Here's a simple-minded example program that rewrites its command-line
378parameters as integers correctly formatted in the current locale:
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379
380 # See comments in previous example
381 require 5.004;
382 use POSIX qw(locale_h);
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383
384 # Get some of locale's numeric formatting parameters
385 my ($thousands_sep, $grouping) =
14280422 386 @{localeconv()}{'thousands_sep', 'grouping'};
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387
388 # Apply defaults if values are missing
389 $thousands_sep = ',' unless $thousands_sep;
390 $grouping = 3 unless $grouping;
391
392 # Format command line params for current locale
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393 for (@ARGV) {
394 $_ = int; # Chop non-integer part
5f05dabc 395 1 while
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396 s/(\d)(\d{$grouping}($|$thousands_sep))/$1$thousands_sep$2/;
397 print "$_";
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398 }
399 print "\n";
400
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401=head1 LOCALE CATEGORIES
402
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403The following subsections describe basic locale categories. Beyond these,
404some combination categories allow manipulation of more than one
405basic category at a time. See L<"ENVIRONMENT"> for a discussion of these.
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406
407=head2 Category LC_COLLATE: Collation
408
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409In the scope of S<C<use locale>>, Perl looks to the C<LC_COLLATE>
410environment variable to determine the application's notions on collation
411(ordering) of characters. For example, 'b' follows 'a' in Latin
412alphabets, but where do 'E<aacute>' and 'E<aring>' belong? And while
413'color' follows 'chocolate' in English, what about in Spanish?
5f05dabc 414
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415Here is a code snippet to tell what alphanumeric
416characters are in the current locale, in that locale's order:
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417
418 use locale;
419 print +(sort grep /\w/, map { chr() } 0..255), "\n";
420
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421Compare this with the characters that you see and their order if you
422state explicitly that the locale should be ignored:
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423
424 no locale;
425 print +(sort grep /\w/, map { chr() } 0..255), "\n";
426
427This machine-native collation (which is what you get unless S<C<use
428locale>> has appeared earlier in the same block) must be used for
429sorting raw binary data, whereas the locale-dependent collation of the
b0c42ed9 430first example is useful for natural text.
5f05dabc 431
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432As noted in L<USING LOCALES>, C<cmp> compares according to the current
433collation locale when C<use locale> is in effect, but falls back to a
5a964f20 434byte-by-byte comparison for strings that the locale says are equal. You
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435can use POSIX::strcoll() if you don't want this fall-back:
436
437 use POSIX qw(strcoll);
438 $equal_in_locale =
439 !strcoll("space and case ignored", "SpaceAndCaseIgnored");
440
441$equal_in_locale will be true if the collation locale specifies a
5a964f20 442dictionary-like ordering that ignores space characters completely and
9e3a2af8 443which folds case.
14280422 444
5a964f20 445If you have a single string that you want to check for "equality in
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446locale" against several others, you might think you could gain a little
447efficiency by using POSIX::strxfrm() in conjunction with C<eq>:
448
449 use POSIX qw(strxfrm);
450 $xfrm_string = strxfrm("Mixed-case string");
451 print "locale collation ignores spaces\n"
452 if $xfrm_string eq strxfrm("Mixed-casestring");
453 print "locale collation ignores hyphens\n"
454 if $xfrm_string eq strxfrm("Mixedcase string");
455 print "locale collation ignores case\n"
456 if $xfrm_string eq strxfrm("mixed-case string");
457
458strxfrm() takes a string and maps it into a transformed string for use
459in byte-by-byte comparisons against other transformed strings during
460collation. "Under the hood", locale-affected Perl comparison operators
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461call strxfrm() for both operands, then do a byte-by-byte
462comparison of the transformed strings. By calling strxfrm() explicitly
14280422 463and using a non locale-affected comparison, the example attempts to save
5a964f20 464a couple of transformations. But in fact, it doesn't save anything: Perl
2ae324a7 465magic (see L<perlguts/Magic Variables>) creates the transformed version of a
5a964f20 466string the first time it's needed in a comparison, then keeps this version around
14280422 467in case it's needed again. An example rewritten the easy way with
e38874e2 468C<cmp> runs just about as fast. It also copes with null characters
14280422 469embedded in strings; if you call strxfrm() directly, it treats the first
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470null it finds as a terminator. don't expect the transformed strings
471it produces to be portable across systems--or even from one revision
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472of your operating system to the next. In short, don't call strxfrm()
473directly: let Perl do it for you.
14280422 474
5a964f20 475Note: C<use locale> isn't shown in some of these examples because it isn't
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476needed: strcoll() and strxfrm() exist only to generate locale-dependent
477results, and so always obey the current C<LC_COLLATE> locale.
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478
479=head2 Category LC_CTYPE: Character Types
480
5a964f20 481In the scope of S<C<use locale>>, Perl obeys the C<LC_CTYPE> locale
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482setting. This controls the application's notion of which characters are
483alphabetic. This affects Perl's C<\w> regular expression metanotation,
5a964f20 484which stands for alphanumeric characters--that is, alphabetic and
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485numeric characters. (Consult L<perlre> for more information about
486regular expressions.) Thanks to C<LC_CTYPE>, depending on your locale
487setting, characters like 'E<aelig>', 'E<eth>', 'E<szlig>', and
488'E<oslash>' may be understood as C<\w> characters.
5f05dabc 489
2c268ad5 490The C<LC_CTYPE> locale also provides the map used in transliterating
68dc0745 491characters between lower and uppercase. This affects the case-mapping
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492functions--lc(), lcfirst, uc(), and ucfirst(); case-mapping
493interpolation with C<\l>, C<\L>, C<\u>, or C<\U> in double-quoted strings
494and C<s///> substitutions; and case-independent regular expression
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495pattern matching using the C<i> modifier.
496
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497Finally, C<LC_CTYPE> affects the POSIX character-class test
498functions--isalpha(), islower(), and so on. For example, if you move
499from the "C" locale to a 7-bit Scandinavian one, you may find--possibly
500to your surprise--that "|" moves from the ispunct() class to isalpha().
5f05dabc 501
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502B<Note:> A broken or malicious C<LC_CTYPE> locale definition may result
503in clearly ineligible characters being considered to be alphanumeric by
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504your application. For strict matching of (mundane) letters and
505digits--for example, in command strings--locale-aware applications
14280422 506should use C<\w> inside a C<no locale> block. See L<"SECURITY">.
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507
508=head2 Category LC_NUMERIC: Numeric Formatting
509
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510In the scope of S<C<use locale>>, Perl obeys the C<LC_NUMERIC> locale
511information, which controls an application's idea of how numbers should
512be formatted for human readability by the printf(), sprintf(), and
513write() functions. String-to-numeric conversion by the POSIX::strtod()
514function is also affected. In most implementations the only effect is to
515change the character used for the decimal point--perhaps from '.' to ','.
516These functions aren't aware of such niceties as thousands separation and
517so on. (See L<The localeconv function> if you care about these things.)
518
519Output produced by print() is B<never> affected by the
5f05dabc 520current locale: it is independent of whether C<use locale> or C<no
14280422 521locale> is in effect, and corresponds to what you'd get from printf()
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522in the "C" locale. The same is true for Perl's internal conversions
523between numeric and string formats:
524
525 use POSIX qw(strtod);
526 use locale;
14280422 527
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528 $n = 5/2; # Assign numeric 2.5 to $n
529
530 $a = " $n"; # Locale-independent conversion to string
531
532 print "half five is $n\n"; # Locale-independent output
533
534 printf "half five is %g\n", $n; # Locale-dependent output
535
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536 print "DECIMAL POINT IS COMMA\n"
537 if $n == (strtod("2,5"))[0]; # Locale-dependent conversion
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538
539=head2 Category LC_MONETARY: Formatting of monetary amounts
540
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541The C standard defines the C<LC_MONETARY> category, but no function
542that is affected by its contents. (Those with experience of standards
b0c42ed9 543committees will recognize that the working group decided to punt on the
14280422 544issue.) Consequently, Perl takes no notice of it. If you really want
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545to use C<LC_MONETARY>, you can query its contents--see L<The localeconv
546function>--and use the information that it returns in your application's
547own formatting of currency amounts. However, you may well find that
548the information, voluminous and complex though it may be, still does not
549quite meet your requirements: currency formatting is a hard nut to crack.
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550
551=head2 LC_TIME
552
5a964f20 553Output produced by POSIX::strftime(), which builds a formatted
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554human-readable date/time string, is affected by the current C<LC_TIME>
555locale. Thus, in a French locale, the output produced by the C<%B>
556format element (full month name) for the first month of the year would
5a964f20 557be "janvier". Here's how to get a list of long month names in the
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558current locale:
559
560 use POSIX qw(strftime);
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561 for (0..11) {
562 $long_month_name[$_] =
563 strftime("%B", 0, 0, 0, 1, $_, 96);
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564 }
565
5a964f20 566Note: C<use locale> isn't needed in this example: as a function that
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567exists only to generate locale-dependent results, strftime() always
568obeys the current C<LC_TIME> locale.
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569
570=head2 Other categories
571
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572The remaining locale category, C<LC_MESSAGES> (possibly supplemented
573by others in particular implementations) is not currently used by
574Perl--except possibly to affect the behavior of library functions called
575by extensions outside the standard Perl distribution.
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576
577=head1 SECURITY
578
5a964f20 579Although the main discussion of Perl security issues can be found in
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580L<perlsec>, a discussion of Perl's locale handling would be incomplete
581if it did not draw your attention to locale-dependent security issues.
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582Locales--particularly on systems that allow unprivileged users to
583build their own locales--are untrustworthy. A malicious (or just plain
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584broken) locale can make a locale-aware application give unexpected
585results. Here are a few possibilities:
586
587=over 4
588
589=item *
590
591Regular expression checks for safe file names or mail addresses using
5a964f20 592C<\w> may be spoofed by an C<LC_CTYPE> locale that claims that
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593characters such as "E<gt>" and "|" are alphanumeric.
594
595=item *
596
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597String interpolation with case-mapping, as in, say, C<$dest =
598"C:\U$name.$ext">, may produce dangerous results if a bogus LC_CTYPE
599case-mapping table is in effect.
600
601=item *
602
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603If the decimal point character in the C<LC_NUMERIC> locale is
604surreptitiously changed from a dot to a comma, C<sprintf("%g",
6050.123456e3)> produces a string result of "123,456". Many people would
606interpret this as one hundred and twenty-three thousand, four hundred
607and fifty-six.
608
609=item *
610
611A sneaky C<LC_COLLATE> locale could result in the names of students with
612"D" grades appearing ahead of those with "A"s.
613
614=item *
615
5a964f20 616An application that takes the trouble to use information in
14280422 617C<LC_MONETARY> may format debits as if they were credits and vice versa
5a964f20 618if that locale has been subverted. Or it might make payments in US
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619dollars instead of Hong Kong dollars.
620
621=item *
622
623The date and day names in dates formatted by strftime() could be
624manipulated to advantage by a malicious user able to subvert the
5a964f20 625C<LC_DATE> locale. ("Look--it says I wasn't in the building on
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626Sunday.")
627
628=back
629
630Such dangers are not peculiar to the locale system: any aspect of an
5a964f20 631application's environment which may be modified maliciously presents
14280422 632similar challenges. Similarly, they are not specific to Perl: any
5a964f20 633programming language that allows you to write programs that take
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634account of their environment exposes you to these issues.
635
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636Perl cannot protect you from all possibilities shown in the
637examples--there is no substitute for your own vigilance--but, when
14280422 638C<use locale> is in effect, Perl uses the tainting mechanism (see
5a964f20 639L<perlsec>) to mark string results that become locale-dependent, and
14280422 640which may be untrustworthy in consequence. Here is a summary of the
5a964f20 641tainting behavior of operators and functions that may be affected by
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642the locale:
643
644=over 4
645
646=item B<Comparison operators> (C<lt>, C<le>, C<ge>, C<gt> and C<cmp>):
647
648Scalar true/false (or less/equal/greater) result is never tainted.
649
7b8d334a 650=item B<Case-mapping interpolation> (with C<\l>, C<\L>, C<\u> or C<\U>)
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651
652Result string containing interpolated material is tainted if
653C<use locale> is in effect.
654
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655=item B<Matching operator> (C<m//>):
656
657Scalar true/false result never tainted.
658
5a964f20 659Subpatterns, either delivered as a list-context result or as $1 etc.
14280422 660are tainted if C<use locale> is in effect, and the subpattern regular
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661expression contains C<\w> (to match an alphanumeric character), C<\W>
662(non-alphanumeric character), C<\s> (white-space character), or C<\S>
5a964f20 663(non white-space character). The matched-pattern variable, $&, $`
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664(pre-match), $' (post-match), and $+ (last match) are also tainted if
665C<use locale> is in effect and the regular expression contains C<\w>,
666C<\W>, C<\s>, or C<\S>.
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667
668=item B<Substitution operator> (C<s///>):
669
e38874e2 670Has the same behavior as the match operator. Also, the left
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671operand of C<=~> becomes tainted when C<use locale> in effect
672if modified as a result of a substitution based on a regular
e38874e2 673expression match involving C<\w>, C<\W>, C<\s>, or C<\S>; or of
7b8d334a 674case-mapping with C<\l>, C<\L>,C<\u> or C<\U>.
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675
676=item B<In-memory formatting function> (sprintf()):
677
678Result is tainted if "use locale" is in effect.
679
680=item B<Output formatting functions> (printf() and write()):
681
682Success/failure result is never tainted.
683
684=item B<Case-mapping functions> (lc(), lcfirst(), uc(), ucfirst()):
685
686Results are tainted if C<use locale> is in effect.
687
688=item B<POSIX locale-dependent functions> (localeconv(), strcoll(),
689strftime(), strxfrm()):
690
691Results are never tainted.
692
693=item B<POSIX character class tests> (isalnum(), isalpha(), isdigit(),
694isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(),
695isxdigit()):
696
697True/false results are never tainted.
698
699=back
700
701Three examples illustrate locale-dependent tainting.
702The first program, which ignores its locale, won't run: a value taken
54310121 703directly from the command line may not be used to name an output file
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704when taint checks are enabled.
705
706 #/usr/local/bin/perl -T
707 # Run with taint checking
708
54310121 709 # Command line sanity check omitted...
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710 $tainted_output_file = shift;
711
712 open(F, ">$tainted_output_file")
713 or warn "Open of $untainted_output_file failed: $!\n";
714
715The program can be made to run by "laundering" the tainted value through
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716a regular expression: the second example--which still ignores locale
717information--runs, creating the file named on its command line
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718if it can.
719
720 #/usr/local/bin/perl -T
721
722 $tainted_output_file = shift;
723 $tainted_output_file =~ m%[\w/]+%;
724 $untainted_output_file = $&;
725
726 open(F, ">$untainted_output_file")
727 or warn "Open of $untainted_output_file failed: $!\n";
728
5a964f20 729Compare this with a similar but locale-aware program:
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730
731 #/usr/local/bin/perl -T
732
733 $tainted_output_file = shift;
734 use locale;
735 $tainted_output_file =~ m%[\w/]+%;
736 $localized_output_file = $&;
737
738 open(F, ">$localized_output_file")
739 or warn "Open of $localized_output_file failed: $!\n";
740
741This third program fails to run because $& is tainted: it is the result
5a964f20 742of a match involving C<\w> while C<use locale> is in effect.
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743
744=head1 ENVIRONMENT
745
746=over 12
747
748=item PERL_BADLANG
749
14280422 750A string that can suppress Perl's warning about failed locale settings
54310121 751at startup. Failure can occur if the locale support in the operating
5a964f20 752system is lacking (broken) in some way--or if you mistyped the name of
14280422 753a locale when you set up your environment. If this environment variable
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754is absent, or has a value that does not evaluate to integer zero--that
755is, "0" or ""--Perl will complain about locale setting failures.
5f05dabc 756
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757B<NOTE>: PERL_BADLANG only gives you a way to hide the warning message.
758The message tells about some problem in your system's locale support,
759and you should investigate what the problem is.
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760
761=back
762
763The following environment variables are not specific to Perl: They are
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764part of the standardized (ISO C, XPG4, POSIX 1.c) setlocale() method
765for controlling an application's opinion on data.
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766
767=over 12
768
769=item LC_ALL
770
5a964f20 771C<LC_ALL> is the "override-all" locale environment variable. If
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772set, it overrides all the rest of the locale environment variables.
773
774=item LC_CTYPE
775
776In the absence of C<LC_ALL>, C<LC_CTYPE> chooses the character type
777locale. In the absence of both C<LC_ALL> and C<LC_CTYPE>, C<LANG>
778chooses the character type locale.
779
780=item LC_COLLATE
781
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782In the absence of C<LC_ALL>, C<LC_COLLATE> chooses the collation
783(sorting) locale. In the absence of both C<LC_ALL> and C<LC_COLLATE>,
784C<LANG> chooses the collation locale.
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785
786=item LC_MONETARY
787
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788In the absence of C<LC_ALL>, C<LC_MONETARY> chooses the monetary
789formatting locale. In the absence of both C<LC_ALL> and C<LC_MONETARY>,
790C<LANG> chooses the monetary formatting locale.
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791
792=item LC_NUMERIC
793
794In the absence of C<LC_ALL>, C<LC_NUMERIC> chooses the numeric format
795locale. In the absence of both C<LC_ALL> and C<LC_NUMERIC>, C<LANG>
796chooses the numeric format.
797
798=item LC_TIME
799
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800In the absence of C<LC_ALL>, C<LC_TIME> chooses the date and time
801formatting locale. In the absence of both C<LC_ALL> and C<LC_TIME>,
802C<LANG> chooses the date and time formatting locale.
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803
804=item LANG
805
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806C<LANG> is the "catch-all" locale environment variable. If it is set, it
807is used as the last resort after the overall C<LC_ALL> and the
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808category-specific C<LC_...>.
809
810=back
811
812=head1 NOTES
813
814=head2 Backward compatibility
815
b0c42ed9 816Versions of Perl prior to 5.004 B<mostly> ignored locale information,
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817generally behaving as if something similar to the C<"C"> locale were
818always in force, even if the program environment suggested otherwise
819(see L<The setlocale function>). By default, Perl still behaves this
820way for backward compatibility. If you want a Perl application to pay
821attention to locale information, you B<must> use the S<C<use locale>>
822pragma (see L<The use locale Pragma>) to instruct it to do so.
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823
824Versions of Perl from 5.002 to 5.003 did use the C<LC_CTYPE>
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825information if available; that is, C<\w> did understand what
826were the letters according to the locale environment variables.
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827The problem was that the user had no control over the feature:
828if the C library supported locales, Perl used them.
829
830=head2 I18N:Collate obsolete
831
5a964f20 832In versions of Perl prior to 5.004, per-locale collation was possible
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833using the C<I18N::Collate> library module. This module is now mildly
834obsolete and should be avoided in new applications. The C<LC_COLLATE>
835functionality is now integrated into the Perl core language: One can
836use locale-specific scalar data completely normally with C<use locale>,
837so there is no longer any need to juggle with the scalar references of
838C<I18N::Collate>.
5f05dabc 839
14280422 840=head2 Sort speed and memory use impacts
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841
842Comparing and sorting by locale is usually slower than the default
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843sorting; slow-downs of two to four times have been observed. It will
844also consume more memory: once a Perl scalar variable has participated
845in any string comparison or sorting operation obeying the locale
846collation rules, it will take 3-15 times more memory than before. (The
847exact multiplier depends on the string's contents, the operating system
848and the locale.) These downsides are dictated more by the operating
849system's implementation of the locale system than by Perl.
5f05dabc 850
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851=head2 write() and LC_NUMERIC
852
5a964f20 853Formats are the only part of Perl that unconditionally use information
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854from a program's locale; if a program's environment specifies an
855LC_NUMERIC locale, it is always used to specify the decimal point
856character in formatted output. Formatted output cannot be controlled by
857C<use locale> because the pragma is tied to the block structure of the
858program, and, for historical reasons, formats exist outside that block
859structure.
860
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861=head2 Freely available locale definitions
862
863There is a large collection of locale definitions at
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864C<ftp://dkuug.dk/i18n/WG15-collection>. You should be aware that it is
865unsupported, and is not claimed to be fit for any purpose. If your
5a964f20 866system allows installation of arbitrary locales, you may find the
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867definitions useful as they are, or as a basis for the development of
868your own locales.
5f05dabc 869
14280422 870=head2 I18n and l10n
5f05dabc 871
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872"Internationalization" is often abbreviated as B<i18n> because its first
873and last letters are separated by eighteen others. (You may guess why
874the internalin ... internaliti ... i18n tends to get abbreviated.) In
875the same way, "localization" is often abbreviated to B<l10n>.
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876
877=head2 An imperfect standard
878
879Internationalization, as defined in the C and POSIX standards, can be
880criticized as incomplete, ungainly, and having too large a granularity.
881(Locales apply to a whole process, when it would arguably be more useful
882to have them apply to a single thread, window group, or whatever.) They
883also have a tendency, like standards groups, to divide the world into
884nations, when we all know that the world can equally well be divided
885into bankers, bikers, gamers, and so on. But, for now, it's the only
886standard we've got. This may be construed as a bug.
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887
888=head1 BUGS
889
890=head2 Broken systems
891
5a964f20 892In certain systems, the operating system's locale support
2bdf8add
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893is broken and cannot be fixed or used by Perl. Such deficiencies can
894and will result in mysterious hangs and/or Perl core dumps when the
895C<use locale> is in effect. When confronted with such a system,
9607fc9c 896please report in excruciating detail to <F<perlbug@perl.com>>, and
5a964f20 897complain to your vendor: bug fixes may exist for these problems
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898in your operating system. Sometimes such bug fixes are called an
899operating system upgrade.
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900
901=head1 SEE ALSO
902
7b8d334a
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903L<POSIX (3)/isalnum>
904
905L<POSIX (3)/isalpha>
906
907L<POSIX (3)/isdigit>
908
909L<POSIX (3)/isgraph>
910
911L<POSIX (3)/islower>
912
913L<POSIX (3)/isprint>,
914
915L<POSIX (3)/ispunct>
916
917L<POSIX (3)/isspace>
918
919L<POSIX (3)/isupper>,
920
921L<POSIX (3)/isxdigit>
922
923L<POSIX (3)/localeconv>
924
925L<POSIX (3)/setlocale>,
926
927L<POSIX (3)/strcoll>
928
929L<POSIX (3)/strftime>
930
931L<POSIX (3)/strtod>,
932
14280422 933L<POSIX (3)/strxfrm>
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934
935=head1 HISTORY
936
b0c42ed9 937Jarkko Hietaniemi's original F<perli18n.pod> heavily hacked by Dominic
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938Dunlop, assisted by the perl5-porters. Prose worked over a bit by
939Tom Christiansen.
5f05dabc 940
5a964f20 941Last update: Thu Jun 11 08:44:13 MDT 1998