The "use locale" pragma

By default, Perl itself (outside the POSIX module) ignores the current locale. The "use locale" pragma tells Perl to use the current locale for some operations. Starting in v5.16, there are optional parameters to this pragma, described below, which restrict which operations are affected by it.

The current locale is set at execution time by setlocale() described below. If that function hasn't yet been called in the course of the program's execution, the current locale is that which was determined by the "ENVIRONMENT" in effect at the start of the program. If there is no valid environment, the current locale is whatever the system default has been set to. On POSIX systems, it is likely, but not necessarily, the "C" locale. On Windows, the default is set via the computer's "Control Panel->Regional and Language Options" (or its current equivalent).

The operations that are affected by locale are:

Not within the scope of "use locale"

Only certain operations (all originating outside Perl) should be affected, as follows:

Lingering effects of "use locale"

Certain Perl operations that are set-up within the scope of a "use locale" retain that effect even outside the scope. These include:

Under ""use locale";"

The default behavior is restored with the "no locale" pragma, or upon reaching the end of the block enclosing "use locale". Note that "use locale" calls may be nested, and that what is in effect within an inner scope will revert to the outer scope's rules at the end of the inner scope.

The string result of any operation that uses locale information is tainted, as it is possible for a locale to be untrustworthy. See "SECURITY".

Starting in Perl v5.16 in a very limited way, and more generally in v5.22, you can restrict which category or categories are enabled by this particular instance of the pragma by adding parameters to it. For example,

 use locale qw(:ctype :numeric);

enables locale awareness within its scope of only those operations (listed above) that are affected by "LC_CTYPE" and "LC_NUMERIC".

The possible categories are: ":collate", ":ctype", ":messages", ":monetary", ":numeric", ":time", and the pseudo category ":characters" (described below).

Thus you can say

 use locale ':messages';

and only $! and $^E will be locale aware. Everything else is unaffected.

Since Perl doesn't currently do anything with the "LC_MONETARY" category, specifying ":monetary" does effectively nothing. Some systems have other categories, such as "LC_PAPER", but Perl also doesn't do anything with them, and there is no way to specify them in this pragma's arguments.

You can also easily say to use all categories but one, by either, for example,

 use locale ':!ctype';
 use locale ':not_ctype';

both of which mean to enable locale awareness of all categories but "LC_CTYPE". Only one category argument may be specified in a "use locale" if it is of the negated form.

Prior to v5.22 only one form of the pragma with arguments is available:

 use locale ':not_characters';

(and you have to say "not_"; you can't use the bang "!" form). This pseudo category is a shorthand for specifying both ":collate" and ":ctype". Hence, in the negated form, it is nearly the same thing as saying

 use locale qw(:messages :monetary :numeric :time);

We use the term "nearly", because ":not_characters" also turns on "use feature 'unicode_strings'" within its scope. This form is less useful in v5.20 and later, and is described fully in "Unicode and UTF-8", but briefly, it tells Perl to not use the character portions of the locale definition, that is the "LC_CTYPE" and "LC_COLLATE" categories. Instead it will use the native character set (extended by Unicode). When using this parameter, you are responsible for getting the external character set translated into the native/Unicode one (which it already will be if it is one of the increasingly popular UTF-8 locales). There are convenient ways of doing this, as described in "Unicode and UTF-8".

The setlocale function

You can switch locales as often as you wish at run time with the "POSIX::setlocale()" function:

        # Import locale-handling tool set from POSIX module.
        # This example uses: setlocale -- the function call
        #                    LC_CTYPE -- explained below
        # (Showing the testing for success/failure of operations is
        # omitted in these examples to avoid distracting from the main
        # point)

        use POSIX qw(locale_h);
        use locale;
        my $old_locale;

        # 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 the default defined by the
        # LC_ALL/LC_CTYPE/LANG environment variables, or to the system
        # default.  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 other 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()", but on some platforms the string is opaque, not something that most people would be able to decipher as to what locale it means.

If no second argument is provided and the category is "LC_ALL", the result is implementation-dependent. It may be a string of concatenated locale names (separator also implementation-dependent) or a single locale name. Please consult your setlocale(3) man page 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.

Note that when a form of "use locale" that doesn't include all categories is specified, Perl ignores the excluded categories.

If "setlocale()" fails for some reason (for example, an attempt to set to a locale unknown to the system), the locale for the category is not changed, and the function returns "undef".

Starting in Perl 5.28, on multi-threaded perls compiled on systems that implement POSIX 2008 thread-safe locale operations, this function doesn't actually call the system "setlocale". Instead those thread-safe operations are used to emulate the "setlocale" function, but in a thread-safe manner.

You can force the thread-safe locale operations to always be used (if available) by recompiling perl with

 -Accflags='-DUSE_THREAD_SAFE_LOCALE'

added to your call to Configure.

For further information about the categories, consult setlocale(3).

Multi-threaded operation

You can tell if using locales is safe on your system by looking at the read-only boolean variable "${^SAFE_LOCALES}". The value is 1 if the perl is not threaded, or if it is using thread-safe locale operations.

Thread-safe operations are supported in Windows starting in Visual Studio 2005, and in systems compatible with POSIX 2008. Some platforms claim to support POSIX 2008, but have buggy implementations, so that the hints files for compiling to run on them turn off attempting to use thread-safety. "${^SAFE_LOCALES}" will be 0 on them.

Be aware that writing a multi-threaded application will not be portable to a platform which lacks the native thread-safe locale support. On systems that do have it, you automatically get this behavior for threaded perls, without having to do anything. If for some reason, you don't want to use this capability (perhaps the POSIX 2008 support is buggy on your system), you can manually compile Perl to use the old non-thread-safe implementation by passing the argument "-Accflags='-DNO_THREAD_SAFE_LOCALE'" to Configure. Except on Windows, this will continue to use certain of the POSIX 2008 functions in some situations. If these are buggy, you can pass the following to Configure instead or additionally: "-Accflags='-DNO_POSIX_2008_LOCALE'". This will also keep the code from using thread-safe locales. "${^SAFE_LOCALES}" will be 0 on systems that turn off the thread-safe operations.

Normally on unthreaded builds, the traditional "setlocale()" is used and not the thread-safe locale functions. You can force the use of these on systems that have them by adding the "-Accflags='-DUSE_THREAD_SAFE_LOCALE'" to Configure.

The initial program is started up using the locale specified from the environment, as currently, described in "ENVIRONMENT". All newly created threads start with "LC_ALL" set to "C". Each thread may use "POSIX::setlocale()" to query or switch its locale at any time, without affecting any other thread. All locale-dependent operations automatically use their thread's locale.

This should be completely transparent to any applications written entirely in Perl (minus a few rarely encountered caveats given in the "Multi-threaded" section). Information for XS module writers is given in "Locale-aware XS code" in perlxs.

Finding locales

        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 or, rarely, a superset thereof (such as the "DEC Multinational Character Set (DEC-MCS)"). Warning. The C locale delivered by some vendors may not actually exactly match what the C standard calls for. So beware.

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.

LOCALE PROBLEMS

        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. (On Windows, it first tries falling back to the system default locale.) 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.

Testing for broken locales

 PERL_DEBUG_FULL_TEST=1 ./perl -T -Ilib lib/locale.t > locale.log 2>&1

Besides many other tests, it will test every locale it finds on your system to see if they conform to the POSIX standard. If any have errors, it will include a summary near the end of the output of which locales passed all its tests, and which failed, and why.

Temporarily fixing locale problems

Perl's moaning about locale problems can be silenced by setting the environment variable "PERL_BADLANG" to "0" or "". 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 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.

Permanently fixing locale problems

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".

Permanently fixing your system's locale configuration

        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.

Fixing system locale configuration

The localeconv 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 "localeconv" in POSIX 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:

    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";

Note that if the platform doesn't have "LC_NUMERIC" and/or "LC_MONETARY" available or enabled, the corresponding elements of the hash will be missing.

I18N::Langinfo

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.

Category "LC_COLLATE": Collation: Text Comparisons and Sorting

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.

Perl uses the platform's C library collation functions "strcoll()" and "strxfrm()". That means you get whatever they give. On some platforms, these functions work well on UTF-8 locales, giving a reasonable default collation for the code points that are important in that locale. (And if they aren't working well, the problem may only be that the locale definition is deficient, so can be fixed by using a better definition file. Unicode's definitions (see "Freely available locale definitions") provide reasonable UTF-8 locale collation definitions.) Starting in Perl v5.26, Perl's use of these functions has been made more seamless. This may be sufficient for your needs. For more control, and to make sure strings containing any code point (not just the ones important in the locale) collate properly, the Unicode::Collate module is suggested.

In non-UTF-8 locales (hence single byte), code points above 0xFF are technically invalid. But if present, again starting in v5.26, they will collate to the same position as the highest valid code point does. This generally gives good results, but the collation order may be skewed if the valid code point gets special treatment when it forms particular sequences with other characters as defined by the locale. When two strings collate identically, the code point order is used as a tie breaker.

If Perl detects that there are problems with the locale collation order, it reverts to using non-locale collation rules for that locale.

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 "Magic Variables" in perlguts) 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()" are POSIX functions which use the standard system-supplied "libc" functions that always obey the current "LC_COLLATE" locale.

Category "LC_CTYPE": Character Types

The "LC_CTYPE" locale also provides the map used in transliterating characters between lower and uppercase. This affects the case-mapping functions--"fc()", "lc()", "lcfirst()", "uc()", and "ucfirst()"; case-mapping interpolation with "\F", "\l", "\L", "\u", or "\U" in double-quoted strings and "s///" substitutions; and case-insensitive regular expression pattern matching using the "i" modifier.

Starting in v5.20, Perl supports UTF-8 locales for "LC_CTYPE", but otherwise Perl only supports single-byte locales, such as the ISO 8859 series. This means that wide character locales, for example for Asian languages, are not well-supported. Use of these locales may cause core dumps. If the platform has the capability for Perl to detect such a locale, starting in Perl v5.22, Perl will warn, default enabled, using the "locale" warning category, whenever such a locale is switched into. The UTF-8 locale support is actually a superset of POSIX locales, because it is really full Unicode behavior as if no "LC_CTYPE" locale were in effect at all (except for tainting; see "SECURITY"). POSIX locales, even UTF-8 ones, are lacking certain concepts in Unicode, such as the idea that changing the case of a character could expand to be more than one character. Perl in a UTF-8 locale, will give you that expansion. Prior to v5.20, Perl treated a UTF-8 locale on some platforms like an ISO 8859-1 one, with some restrictions, and on other platforms more like the "C" locale. For releases v5.16 and v5.18, "use locale 'not_characters" could be used as a workaround for this (see "Unicode and UTF-8").

Note that there are quite a few things that are unaffected by the current locale. Any literal character is the native character for the given platform. Hence 'A' means the character at code point 65 on ASCII platforms, and 193 on EBCDIC. That may or may not be an 'A' in the current locale, if that locale even has an 'A'. Similarly, all the escape sequences for particular characters, "\n" for example, always mean the platform's native one. This means, for example, that "\N" in regular expressions (every character but new-line) works on the platform character set.

Starting in v5.22, Perl will by default warn when switching into a locale that redefines any ASCII printable character (plus "\t" and "\n") into a different class than expected. This is likely to happen on modern locales only on EBCDIC platforms, where, for example, a CCSID 0037 locale on a CCSID 1047 machine moves "[", but it can happen on ASCII platforms with the ISO 646 and other 7-bit locales that are essentially obsolete. Things may still work, depending on what features of Perl are used by the program. For example, in the example from above where "|" becomes a "\w", and there are no regular expressions where this matters, the program may still work properly. The warning lists all the characters that it can determine could be adversely affected.

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) ASCII letters and digits--for example, in command strings--locale-aware applications should use "\w" with the "/a" regular expression modifier. See "SECURITY".

Category "LC_NUMERIC": Numeric Formatting

 use POSIX qw(strtod setlocale LC_NUMERIC);
 use locale;

 setlocale LC_NUMERIC, "";

 $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".

Category "LC_MONETARY": Formatting of monetary amounts

See also I18N::Langinfo and "CRNCYSTR".

Category "LC_TIME": Respresentation of time

        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: "strftime()" is a POSIX function which uses the standard system-supplied "libc" function that 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".

Other categories

Examples

   use locale;
   use POSIX qw(locale_h); # Imports setlocale() and the LC_ constants.
   setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
   printf "%g\n", 1.23; # If the "fr_FR" succeeded, probably shows 1,23.

and also how strings are parsed by "POSIX::strtod()" as numbers:

   use locale;
   use POSIX qw(locale_h strtod);
   setlocale(LC_NUMERIC, "de_DE") or die "Entschuldigung";
   my $x = strtod("2,34") + 5;
   print $x, "\n"; # Probably shows 7,34.

String "eval" and "LC_NUMERIC"

 use locale;
 use POSIX qw(locale_h);
 setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
 my $a = 1.2;
 print eval "$a + 1.5";
 print "\n";

prints "13,5". This is because in that locale, the comma is the decimal point character. The "eval" thus expands to:

 eval "1,2 + 1.5"

and the result is not what you likely expected. No warnings are generated. If you do string "eval"'s within the scope of "use locale", you should instead change the "eval" line to do something like:

 print eval "no locale; $a + 1.5";

This prints 2.7.

You could also exclude "LC_NUMERIC", if you don't need it, by

 use locale ':!numeric';

Backward compatibility

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.

I18N:Collate obsolete

Sort speed and memory use impacts

Freely available locale definitions

  https://unicode.org/Public/cldr/2.0.1/

(Newer versions of CLDR require you to compute the POSIX data yourself. See <http://unicode.org/Public/cldr/latest/>.)

There is a large collection of locale definitions at:

  http://std.dkuug.dk/i18n/WG15-collection/locales/

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.

I18n and l10n

An imperfect standard

Collation of strings containing embedded "NUL" characters

Multi-threaded

An XS module that is locale-dependent could have been written under the assumption that it will never be called in a multi-threaded environment, and so uses other non-locale constructs that aren't multi-thread-safe. See "Thread-aware system interfaces" in perlxs.

POSIX does not define a way to get the name of the current per-thread locale. Some systems, such as Darwin and NetBSD do implement a function, querylocale(3) to do this. On non-Windows systems without it, such as Linux, there are some additional caveats:

• An embedded perl needs to be started up while the global locale is in effect. See "Using embedded Perl with POSIX locales" in perlembed.
• It becomes more important for perl to know about all the possible locale categories on the platform, even if they aren't apparently used in your program. Perl knows all of the Linux ones. If your platform has others, you can submit an issue at <https://github.com/Perl/perl5/issues> for inclusion of it in the next release. In the meantime, it is possible to edit the Perl source to teach it about the category, and then recompile. Search for instances of, say, "LC_PAPER" in the source, and use that as a template to add the omitted one.
• It is possible, though hard to do, to call "POSIX::setlocale" with a locale that it doesn't recognize as syntactically legal, but actually is legal on that system. This should happen only with embedded perls, or if you hand-craft a locale name yourself.

Broken systems