perllocale - Perl locale handling (internationalization and localization)
Perl supports language-specific notions of data such as "is this
a letter", "what is the uppercase equivalent of this letter", and
"which of these letters comes first". These are important issues,
especially for languages other than English--but also for English: it
would be naïve to imagine that A-Za-z defines all the "letters"
needed to write in English. Perl is also aware that some character other
than '.' may be preferred as a decimal point, and that output date
representations may be language-specific. The process of making an
application take account of its users' preferences in such matters is
called internationalization (often abbreviated as i18n); telling
such an application about a particular set of preferences is known as
localization (l10n).
Perl can understand language-specific data via the standardized (ISO C, XPG4, POSIX 1.c) method called "the locale system". The locale system is controlled per application using one pragma, one function call, and several environment variables.
NOTE: This feature is new in Perl 5.004, and does not apply unless an application specifically requests it--see Backward compatibility. The one exception is that write() now always uses the current locale - see "NOTES".
If Perl applications are to understand and present your data correctly according a locale of your choice, all of the following must be true:
perl -V:d_setlocale will say that the value for d_setlocale is
define.
If you want a Perl application to process and present your data
according to a particular locale, the application code should include
the use locale pragma (see The use locale pragma) where
appropriate, and at least one of the following must be true:
By default, Perl ignores the current locale. The use locale
pragma tells Perl to use the current locale for some operations:
The comparison operators (lt, le, cmp, ge, and gt) and
the POSIX string collation functions strcoll() and strxfrm() use
LC_COLLATE. sort() is also affected if used without an
explicit comparison function, because it uses cmp by default.
Note: eq and ne are unaffected by locale: they always
perform a char-by-char comparison of their scalar operands. What's
more, if cmp finds that its operands are equal according to the
collation sequence specified by the current locale, it goes on to
perform a char-by-char comparison, and only returns 0 (equal) if the
operands are char-for-char identical. If you really want to know whether
two strings--which eq and cmp may consider different--are equal
as far as collation in the locale is concerned, see the discussion in
Category LC_COLLATE: Collation.
LC_CTYPE
LC_NUMERIC
LC_TIME.
LC_COLLATE, LC_CTYPE, and so on, are discussed further in
LOCALE CATEGORIES.
The default behavior is restored with the no locale pragma, or
upon reaching the end of block enclosing use locale.
The string result of any operation that uses locale information is tainted, as it is possible for a locale to be untrustworthy. See "SECURITY".
You can switch locales as often as you wish at run time with the POSIX::setlocale() function:
# This functionality not usable prior to Perl 5.004
require 5.004;
# Import locale-handling tool set from POSIX module.
# This example uses: setlocale -- the function call
# LC_CTYPE -- explained below
use POSIX qw(locale_h);
# query and save the old locale
$old_locale = setlocale(LC_CTYPE);
setlocale(LC_CTYPE, "fr_CA.ISO8859-1");
# LC_CTYPE now in locale "French, Canada, codeset ISO 8859-1"
setlocale(LC_CTYPE, "");
# LC_CTYPE now reset to default defined by LC_ALL/LC_CTYPE/LANG
# environment variables. See below for documentation.
# restore the old locale
setlocale(LC_CTYPE, $old_locale);
The first argument of setlocale() gives the category, the second the locale. The category tells in what aspect of data processing you want to apply locale-specific rules. Category names are discussed in LOCALE CATEGORIES and "ENVIRONMENT". The locale is the name of a collection of customization information corresponding to a particular combination of language, country or territory, and codeset. Read on for hints on the naming of locales: not all systems name locales as in the example.
If no second argument is provided and the category is something else than LC_ALL, the function returns a string naming the current locale for the category. You can use this value as the second argument in a subsequent call to setlocale().
If no second argument is provided and the category is LC_ALL, the result is implementation-dependent. It may be a string of concatenated locales names (separator also implementation-dependent) or a single locale name. Please consult your setlocale(3) for details.
If a second argument is given and it corresponds to a valid locale, the locale for the category is set to that value, and the function returns the now-current locale value. You can then use this in yet another call to setlocale(). (In some implementations, the return value may sometimes differ from the value you gave as the second argument--think of it as an alias for the value you gave.)
As the example shows, if the second argument is an empty string, the category's locale is returned to the default specified by the corresponding environment variables. Generally, this results in a return to the default that was in force when Perl started up: changes to the environment made by the application after startup may or may not be noticed, depending on your system's C library.
If the second argument does not correspond to a valid locale, the locale for the category is not changed, and the function returns undef.
For further information about the categories, consult setlocale(3).
For locales available in your system, consult also setlocale(3) to see whether it leads to the list of available locales (search for the SEE ALSO section). If that fails, try the following command lines:
locale -a
nlsinfo
ls /usr/lib/nls/loc
ls /usr/lib/locale
ls /usr/lib/nls
ls /usr/share/locale
and see whether they list something resembling these
en_US.ISO8859-1 de_DE.ISO8859-1 ru_RU.ISO8859-5
en_US.iso88591 de_DE.iso88591 ru_RU.iso88595
en_US de_DE ru_RU
en de ru
english german russian
english.iso88591 german.iso88591 russian.iso88595
english.roman8 russian.koi8r
Sadly, even though the calling interface for setlocale() has been
standardized, names of locales and the directories where the
configuration resides have not been. The basic form of the name is
language_territory.codeset, but the latter parts after
language are not always present. The language and country
are usually from the standards ISO 3166 and ISO 639, the
two-letter abbreviations for the countries and the languages of the
world, respectively. The codeset part often mentions some ISO
8859 character set, the Latin codesets. For example, ISO 8859-1
is the so-called "Western European codeset" that can be used to encode
most Western European languages adequately. Again, there are several
ways to write even the name of that one standard. Lamentably.
Two special locales are worth particular mention: "C" and "POSIX". Currently these are effectively the same locale: the difference is mainly that the first one is defined by the C standard, the second by the POSIX standard. They define the default locale in which every program starts in the absence of locale information in its environment. (The default default locale, if you will.) Its language is (American) English and its character codeset ASCII.
NOTE: Not all systems have the "POSIX" locale (not all systems are POSIX-conformant), so use "C" when you need explicitly to specify this default locale.
You may encounter the following warning message at Perl startup:
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
LC_ALL = "En_US",
LANG = (unset)
are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
This means that your locale settings had LC_ALL set to "En_US" and LANG exists but has no value. Perl tried to believe you but could not. Instead, Perl gave up and fell back to the "C" locale, the default locale that is supposed to work no matter what. This usually means your locale settings were wrong, they mention locales your system has never heard of, or the locale installation in your system has problems (for example, some system files are broken or missing). There are quick and temporary fixes to these problems, as well as more thorough and lasting fixes.
The two quickest fixes are either to render Perl silent about any locale inconsistencies or to run Perl under the default locale "C".
Perl's moaning about locale problems can be silenced by setting the environment variable PERL_BADLANG to a zero value, for example "0". This method really just sweeps the problem under the carpet: you tell Perl to shut up even when Perl sees that something is wrong. Do not be surprised if later something locale-dependent misbehaves.
Perl can be run under the "C" locale by setting the environment variable LC_ALL to "C". This method is perhaps a bit more civilized than the PERL_BADLANG approach, but setting LC_ALL (or other locale variables) may affect other programs as well, not just Perl. In particular, external programs run from within Perl will see these changes. If you make the new settings permanent (read on), all programs you run see the changes. See ENVIRONMENT for the full list of relevant environment variables and USING LOCALES for their effects in Perl. Effects in other programs are easily deducible. For example, the variable LC_COLLATE may well affect your sort program (or whatever the program that arranges `records' alphabetically in your system is called).
You can test out changing these variables temporarily, and if the new settings seem to help, put those settings into your shell startup files. Consult your local documentation for the exact details. For in Bourne-like shells (sh, ksh, bash, zsh):
LC_ALL=en_US.ISO8859-1 export LC_ALL
This assumes that we saw the locale "en_US.ISO8859-1" using the commands discussed above. We decided to try that instead of the above faulty locale "En_US"--and in Cshish shells (csh, tcsh)
setenv LC_ALL en_US.ISO8859-1
or if you have the "env" application you can do in any shell
env LC_ALL=en_US.ISO8859-1 perl ...
If you do not know what shell you have, consult your local helpdesk or the equivalent.
The slower but superior fixes are when you may be able to yourself fix the misconfiguration of your own environment variables. The mis(sing)configuration of the whole system's locales usually requires the help of your friendly system administrator.
First, see earlier in this document about Finding locales. That tells how to find which locales are really supported--and more importantly, installed--on your system. In our example error message, environment variables affecting the locale are listed in the order of decreasing importance (and unset variables do not matter). Therefore, having LC_ALL set to "En_US" must have been the bad choice, as shown by the error message. First try fixing locale settings listed first.
Second, if using the listed commands you see something exactly (prefix matches do not count and case usually counts) like "En_US" without the quotes, then you should be okay because you are using a locale name that should be installed and available in your system. In this case, see Permanently fixing your system's locale configuration.
This is when you see something like:
perl: warning: Please check that your locale settings: LC_ALL = "En_US", LANG = (unset) are supported and installed on your system.
but then cannot see that "En_US" listed by the above-mentioned commands. You may see things like "en_US.ISO8859-1", but that isn't the same. In this case, try running under a locale that you can list and which somehow matches what you tried. The rules for matching locale names are a bit vague because standardization is weak in this area. See again the Finding locales about general rules.
Contact a system administrator (preferably your own) and report the exact error message you get, and ask them to read this same documentation you are now reading. They should be able to check whether there is something wrong with the locale configuration of the system. The Finding locales section is unfortunately a bit vague about the exact commands and places because these things are not that standardized.
The POSIX::localeconv() function allows you to get particulars of the
locale-dependent numeric formatting information specified by the current
LC_NUMERIC and LC_MONETARY locales. (If you just want the name of
the current locale for a particular category, use POSIX::setlocale()
with a single parameter--see The setlocale function.)
use POSIX qw(locale_h);
# Get a reference to a hash of locale-dependent info
$locale_values = localeconv();
# Output sorted list of the values
for (sort keys %$locale_values) {
printf "%-20s = %s\n", $_, $locale_values->{$_}
}
localeconv() takes no arguments, and returns a reference to a hash.
The keys of this hash are variable names for formatting, such as
decimal_point and thousands_sep. The values are the
corresponding, er, values. See POSIX/localeconv for a longer
example listing the categories an implementation might be expected to
provide; some provide more and others fewer. You don't need an
explicit use locale, because localeconv() always observes the
current locale.
Here's a simple-minded example program that rewrites its command-line parameters as integers correctly formatted in the current locale:
# See comments in previous example
require 5.004;
use POSIX qw(locale_h);
# Get some of locale's numeric formatting parameters
my ($thousands_sep, $grouping) =
@{localeconv()}{'thousands_sep', 'grouping'};
# Apply defaults if values are missing
$thousands_sep = ',' unless $thousands_sep;
# grouping and mon_grouping are packed lists
# of small integers (characters) telling the
# grouping (thousand_seps and mon_thousand_seps
# being the group dividers) of numbers and
# monetary quantities. The integers' meanings:
# 255 means no more grouping, 0 means repeat
# the previous grouping, 1-254 means use that
# as the current grouping. Grouping goes from
# right to left (low to high digits). In the
# below we cheat slightly by never using anything
# else than the first grouping (whatever that is).
if ($grouping) {
@grouping = unpack("C*", $grouping);
} else {
@grouping = (3);
}
# Format command line params for current locale
for (@ARGV) {
$_ = int; # Chop non-integer part
1 while
s/(\d)(\d{$grouping[0]}($|$thousands_sep))/$1$thousands_sep$2/;
print "$_";
}
print "\n";
Another interface for querying locale-dependent information is the I18N::Langinfo::langinfo() function, available at least in UNIX-like systems and VMS.
The following example will import the langinfo() function itself and three constants to be used as arguments to langinfo(): a constant for the abbreviated first day of the week (the numbering starts from Sunday = 1) and two more constants for the affirmative and negative answers for a yes/no question in the current locale.
use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
my ($abday_1, $yesstr, $nostr) = map { langinfo } qw(ABDAY_1 YESSTR NOSTR);
print "$abday_1? [$yesstr/$nostr] ";
In other words, in the "C" (or English) locale the above will probably print something like:
Sun? [yes/no]
See I18N::Langinfo for more information.
The following subsections describe basic locale categories. Beyond these, some combination categories allow manipulation of more than one basic category at a time. See "ENVIRONMENT" for a discussion of these.
In the scope of use locale, Perl looks to the LC_COLLATE
environment variable to determine the application's notions on collation
(ordering) of characters. For example, 'b' follows 'a' in Latin
alphabets, but where do 'á' and 'å' belong? And while
'color' follows 'chocolate' in English, what about in Spanish?
The following collations all make sense and you may meet any of them if you "use locale".
A B C D E a b c d e A a B b C c D d E e a A b B c C d D e E a b c d e A B C D E
Here is a code snippet to tell what "word" characters are in the current locale, in that locale's order:
use locale;
print +(sort grep /\w/, map { chr } 0..255), "\n";
Compare this with the characters that you see and their order if you state explicitly that the locale should be ignored:
no locale;
print +(sort grep /\w/, map { chr } 0..255), "\n";
This machine-native collation (which is what you get unless use
locale has appeared earlier in the same block) must be used for
sorting raw binary data, whereas the locale-dependent collation of the
first example is useful for natural text.
As noted in USING LOCALES, cmp compares according to the current
collation locale when use locale is in effect, but falls back to a
char-by-char comparison for strings that the locale says are equal. You
can use POSIX::strcoll() if you don't want this fall-back:
use POSIX qw(strcoll);
$equal_in_locale =
!strcoll("space and case ignored", "SpaceAndCaseIgnored");
$equal_in_locale will be true if the collation locale specifies a dictionary-like ordering that ignores space characters completely and which folds case.
If you have a single string that you want to check for "equality in
locale" against several others, you might think you could gain a little
efficiency by using POSIX::strxfrm() in conjunction with eq:
use POSIX qw(strxfrm);
$xfrm_string = strxfrm("Mixed-case string");
print "locale collation ignores spaces\n"
if $xfrm_string eq strxfrm("Mixed-casestring");
print "locale collation ignores hyphens\n"
if $xfrm_string eq strxfrm("Mixedcase string");
print "locale collation ignores case\n"
if $xfrm_string eq strxfrm("mixed-case string");
strxfrm() takes a string and maps it into a transformed string for use
in char-by-char comparisons against other transformed strings during
collation. "Under the hood", locale-affected Perl comparison operators
call strxfrm() for both operands, then do a char-by-char
comparison of the transformed strings. By calling strxfrm() explicitly
and using a non locale-affected comparison, the example attempts to save
a couple of transformations. But in fact, it doesn't save anything: Perl
magic (see perlguts/Magic Variables) creates the transformed version of a
string the first time it's needed in a comparison, then keeps this version around
in case it's needed again. An example rewritten the easy way with
cmp runs just about as fast. It also copes with null characters
embedded in strings; if you call strxfrm() directly, it treats the first
null it finds as a terminator. don't expect the transformed strings
it produces to be portable across systems--or even from one revision
of your operating system to the next. In short, don't call strxfrm()
directly: let Perl do it for you.
Note: use locale isn't shown in some of these examples because it isn't
needed: strcoll() and strxfrm() exist only to generate locale-dependent
results, and so always obey the current LC_COLLATE locale.
In the scope of use locale, Perl obeys the LC_CTYPE locale
setting. This controls the application's notion of which characters are
alphabetic. This affects Perl's \w regular expression metanotation,
which stands for alphanumeric characters--that is, alphabetic,
numeric, and including other special characters such as the underscore or
hyphen. (Consult perlre for more information about
regular expressions.) Thanks to LC_CTYPE, depending on your locale
setting, characters like 'æ', 'ð', 'ß', and
'ø' may be understood as \w characters.
The LC_CTYPE locale also provides the map used in transliterating
characters between lower and uppercase. This affects the case-mapping
functions--lc(), lcfirst, uc(), and ucfirst(); case-mapping
interpolation with \l, \L, \u, or \U in double-quoted strings
and s/// substitutions; and case-independent regular expression
pattern matching using the i modifier.
Finally, LC_CTYPE affects the POSIX character-class test
functions--isalpha(), islower(), and so on. For example, if you move
from the "C" locale to a 7-bit Scandinavian one, you may find--possibly
to your surprise--that "|" moves from the ispunct() class to isalpha().
Note: A broken or malicious LC_CTYPE locale definition may result
in clearly ineligible characters being considered to be alphanumeric by
your application. For strict matching of (mundane) letters and
digits--for example, in command strings--locale-aware applications
should use \w inside a no locale block. See "SECURITY".
In the scope of use locale, Perl obeys the LC_NUMERIC locale
information, which controls an application's idea of how numbers should
be formatted for human readability by the printf(), sprintf(), and
write() functions. String-to-numeric conversion by the POSIX::strtod()
function is also affected. In most implementations the only effect is to
change the character used for the decimal point--perhaps from '.' to ','.
These functions aren't aware of such niceties as thousands separation and
so on. (See The localeconv function if you care about these things.)
Output produced by print() is also affected by the current locale: it
depends on whether use locale or no locale is in effect, and
corresponds to what you'd get from printf() in the "C" locale. The
same is true for Perl's internal conversions between numeric and
string formats:
use POSIX qw(strtod);
use locale;
$n = 5/2; # Assign numeric 2.5 to $n
$a = " $n"; # Locale-dependent conversion to string
print "half five is $n\n"; # Locale-dependent output
printf "half five is %g\n", $n; # Locale-dependent output
print "DECIMAL POINT IS COMMA\n"
if $n == (strtod("2,5"))[0]; # Locale-dependent conversion
See also I18N::Langinfo and RADIXCHAR.
The C standard defines the LC_MONETARY category, but no function
that is affected by its contents. (Those with experience of standards
committees will recognize that the working group decided to punt on the
issue.) Consequently, Perl takes no notice of it. If you really want
to use LC_MONETARY, you can query its contents--see
The localeconv function--and use the information that it returns in your
application's own formatting of currency amounts. However, you may well
find that the information, voluminous and complex though it may be, still
does not quite meet your requirements: currency formatting is a hard nut
to crack.
See also I18N::Langinfo and CRNCYSTR.
Output produced by POSIX::strftime(), which builds a formatted
human-readable date/time string, is affected by the current LC_TIME
locale. Thus, in a French locale, the output produced by the %B
format element (full month name) for the first month of the year would
be "janvier". Here's how to get a list of long month names in the
current locale:
use POSIX qw(strftime);
for (0..11) {
$long_month_name[$_] =
strftime("%B", 0, 0, 0, 1, $_, 96);
}
Note: use locale isn't needed in this example: as a function that
exists only to generate locale-dependent results, strftime() always
obeys the current LC_TIME locale.
See also I18N::Langinfo and ABDAY_1..ABDAY_7, DAY_1..DAY_7,
ABMON_1..ABMON_12, and ABMON_1..ABMON_12.
The remaining locale category, LC_MESSAGES (possibly supplemented
by others in particular implementations) is not currently used by
Perl--except possibly to affect the behavior of library functions
called by extensions outside the standard Perl distribution and by the
operating system and its utilities. Note especially that the string
value of $! and the error messages given by external utilities may
be changed by LC_MESSAGES. If you want to have portable error
codes, use %!. See Errno.
Although the main discussion of Perl security issues can be found in perlsec, a discussion of Perl's locale handling would be incomplete if it did not draw your attention to locale-dependent security issues. Locales--particularly on systems that allow unprivileged users to build their own locales--are untrustworthy. A malicious (or just plain broken) locale can make a locale-aware application give unexpected results. Here are a few possibilities:
\w may be spoofed by an LC_CTYPE locale that claims that
characters such as ">" and "|" are alphanumeric.
$dest =
"C:\U$name.$ext", may produce dangerous results if a bogus LC_CTYPE
case-mapping table is in effect.
LC_COLLATE locale could result in the names of students with
"D" grades appearing ahead of those with "A"s.
LC_MONETARY may format debits as if they were credits and vice versa
if that locale has been subverted. Or it might make payments in US
dollars instead of Hong Kong dollars.
LC_DATE locale. ("Look--it says I wasn't in the building on
Sunday.")
Such dangers are not peculiar to the locale system: any aspect of an application's environment which may be modified maliciously presents similar challenges. Similarly, they are not specific to Perl: any programming language that allows you to write programs that take account of their environment exposes you to these issues.
Perl cannot protect you from all possibilities shown in the
examples--there is no substitute for your own vigilance--but, when
use locale is in effect, Perl uses the tainting mechanism (see
perlsec) to mark string results that become locale-dependent, and
which may be untrustworthy in consequence. Here is a summary of the
tainting behavior of operators and functions that may be affected by
the locale:
Comparison operators (lt, le, ge, gt and cmp):
Scalar true/false (or less/equal/greater) result is never tainted.
Case-mapping interpolation (with \l, \L, \u or \U)
Result string containing interpolated material is tainted if
use locale is in effect.
Matching operator (m//):
Scalar true/false result never tainted.
Subpatterns, either delivered as a list-context result or as $1 etc.
are tainted if use locale is in effect, and the subpattern regular
expression contains \w (to match an alphanumeric character), \W
(non-alphanumeric character), \s (white-space character), or \S
(non white-space character). The matched-pattern variable, $&, $`
(pre-match), $' (post-match), and $+ (last match) are also tainted if
use locale is in effect and the regular expression contains \w,
\W, \s, or \S.
Substitution operator (s///):
Has the same behavior as the match operator. Also, the left
operand of =~ becomes tainted when use locale in effect
if modified as a result of a substitution based on a regular
expression match involving \w, \W, \s, or \S; or of
case-mapping with \l, \L,\u or \U.
Output formatting functions (printf() and write()):
Results are never tainted because otherwise even output from print,
for example print(1/7), should be tainted if use locale is in
effect.
Case-mapping functions (lc(), lcfirst(), uc(), ucfirst()):
Results are tainted if use locale is in effect.
POSIX locale-dependent functions (localeconv(), strcoll(), strftime(), strxfrm()):
Results are never tainted.
POSIX character class tests (isalnum(), isalpha(), isdigit(), isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(), isxdigit()):
True/false results are never tainted.
Three examples illustrate locale-dependent tainting. The first program, which ignores its locale, won't run: a value taken directly from the command line may not be used to name an output file when taint checks are enabled.
#/usr/local/bin/perl -T
# Run with taint checking
# Command line sanity check omitted...
$tainted_output_file = shift;
open(F, ">$tainted_output_file")
or warn "Open of $untainted_output_file failed: $!\n";
The program can be made to run by "laundering" the tainted value through a regular expression: the second example--which still ignores locale information--runs, creating the file named on its command line if it can.
#/usr/local/bin/perl -T
$tainted_output_file = shift;
$tainted_output_file =~ m%[\w/]+%;
$untainted_output_file = $&;
open(F, ">$untainted_output_file")
or warn "Open of $untainted_output_file failed: $!\n";
Compare this with a similar but locale-aware program:
#/usr/local/bin/perl -T
$tainted_output_file = shift;
use locale;
$tainted_output_file =~ m%[\w/]+%;
$localized_output_file = $&;
open(F, ">$localized_output_file")
or warn "Open of $localized_output_file failed: $!\n";
This third program fails to run because $& is tainted: it is the result
of a match involving \w while use locale is in effect.
A string that can suppress Perl's warning about failed locale settings at startup. Failure can occur if the locale support in the operating system is lacking (broken) in some way--or if you mistyped the name of a locale when you set up your environment. If this environment variable is absent, or has a value that does not evaluate to integer zero--that is, "0" or ""-- Perl will complain about locale setting failures.
NOTE: PERL_BADLANG only gives you a way to hide the warning message. The message tells about some problem in your system's locale support, and you should investigate what the problem is.
The following environment variables are not specific to Perl: They are part of the standardized (ISO C, XPG4, POSIX 1.c) setlocale() method for controlling an application's opinion on data.
LC_ALL is the "override-all" locale environment variable. If
set, it overrides all the rest of the locale environment variables.
NOTE: LANGUAGE is a GNU extension, it affects you only if you
are using the GNU libc. This is the case if you are using e.g. Linux.
If you are using "commercial" UNIXes you are most probably not
using GNU libc and you can ignore LANGUAGE.
However, in the case you are using LANGUAGE: it affects the
language of informational, warning, and error messages output by
commands (in other words, it's like LC_MESSAGES) but it has higher
priority than LC_ALL. Moreover, it's not a single value but
instead a "path" (":"-separated list) of languages (not locales).
See the GNU gettext library documentation for more information.
LC_ALL, LC_CTYPE chooses the character type
locale. In the absence of both LC_ALL and LC_CTYPE, LANG
chooses the character type locale.
LC_ALL, LC_COLLATE chooses the collation
(sorting) locale. In the absence of both LC_ALL and LC_COLLATE,
LANG chooses the collation locale.
LC_ALL, LC_MONETARY chooses the monetary
formatting locale. In the absence of both LC_ALL and LC_MONETARY,
LANG chooses the monetary formatting locale.
LC_ALL, LC_NUMERIC chooses the numeric format
locale. In the absence of both LC_ALL and LC_NUMERIC, LANG
chooses the numeric format.
LC_ALL, LC_TIME chooses the date and time
formatting locale. In the absence of both LC_ALL and LC_TIME,
LANG chooses the date and time formatting locale.
LANG is the "catch-all" locale environment variable. If it is set, it
is used as the last resort after the overall LC_ALL and the
category-specific LC_....
Versions of Perl prior to 5.004 mostly ignored locale information,
generally behaving as if something similar to the "C" locale were
always in force, even if the program environment suggested otherwise
(see The setlocale function). By default, Perl still behaves this
way for backward compatibility. If you want a Perl application to pay
attention to locale information, you must use the use locale
pragma (see The use locale pragma) to instruct it to do so.
Versions of Perl from 5.002 to 5.003 did use the LC_CTYPE
information if available; that is, \w did understand what
were the letters according to the locale environment variables.
The problem was that the user had no control over the feature:
if the C library supported locales, Perl used them.
In versions of Perl prior to 5.004, per-locale collation was possible
using the I18N::Collate library module. This module is now mildly
obsolete and should be avoided in new applications. The LC_COLLATE
functionality is now integrated into the Perl core language: One can
use locale-specific scalar data completely normally with use locale,
so there is no longer any need to juggle with the scalar references of
I18N::Collate.
Comparing and sorting by locale is usually slower than the default sorting; slow-downs of two to four times have been observed. It will also consume more memory: once a Perl scalar variable has participated in any string comparison or sorting operation obeying the locale collation rules, it will take 3-15 times more memory than before. (The exact multiplier depends on the string's contents, the operating system and the locale.) These downsides are dictated more by the operating system's implementation of the locale system than by Perl.
Formats are the only part of Perl that unconditionally use information
from a program's locale; if a program's environment specifies an
LC_NUMERIC locale, it is always used to specify the decimal point
character in formatted output. Formatted output cannot be controlled by
use locale because the pragma is tied to the block structure of the
program, and, for historical reasons, formats exist outside that block
structure.
There is a large collection of locale definitions at ftp://dkuug.dk/i18n/WG15-collection . You should be aware that it is unsupported, and is not claimed to be fit for any purpose. If your system allows installation of arbitrary locales, you may find the definitions useful as they are, or as a basis for the development of your own locales.
"Internationalization" is often abbreviated as i18n because its first and last letters are separated by eighteen others. (You may guess why the internalin ... internaliti ... i18n tends to get abbreviated.) In the same way, "localization" is often abbreviated to l10n.
Internationalization, as defined in the C and POSIX standards, can be criticized as incomplete, ungainly, and having too large a granularity. (Locales apply to a whole process, when it would arguably be more useful to have them apply to a single thread, window group, or whatever.) They also have a tendency, like standards groups, to divide the world into nations, when we all know that the world can equally well be divided into bankers, bikers, gamers, and so on. But, for now, it's the only standard we've got. This may be construed as a bug.
The support of Unicode is new starting from Perl version 5.6, and more fully implemented in the version 5.8. See perluniintro and perlunicode for more details.
Usually locale settings and Unicode do not affect each other, but there are exceptions, see perlunicode/Locales for examples.
In certain systems, the operating system's locale support
is broken and cannot be fixed or used by Perl. Such deficiencies can
and will result in mysterious hangs and/or Perl core dumps when the
use locale is in effect. When confronted with such a system,
please report in excruciating detail to <perlbug@perl.org>, and
complain to your vendor: bug fixes may exist for these problems
in your operating system. Sometimes such bug fixes are called an
operating system upgrade.
I18N::Langinfo, perluniintro, perlunicode, open, POSIX/isalnum, POSIX/isalpha, POSIX/isdigit, POSIX/isgraph, POSIX/islower, POSIX/isprint, POSIX/ispunct, POSIX/isspace, POSIX/isupper, POSIX/isxdigit, POSIX/localeconv, POSIX/setlocale, POSIX/strcoll, POSIX/strftime, POSIX/strtod, POSIX/strxfrm.
Jarkko Hietaniemi's original perli18n.pod heavily hacked by Dominic Dunlop, assisted by the perl5-porters. Prose worked over a bit by Tom Christiansen.
Last update: Thu Jun 11 08:44:13 MDT 1998