perllocale - Perl locale handling (internationalization and localization)


Perl supports language-specific notions of data such as ``is this a letter'', ``what is the upper-case 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 very naïve to think that A-Za-z defines all the ``letters''. 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 be able to understand and present your data correctly according a locale of your choice, all of the following must be true:

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:


The use locale pragma

By default, Perl ignores the current locale. The use locale pragma tells Perl to use the current locale for some operations:

LC_COLLATE, LC_CTYPE, and so on, are discussed further in LOCALE CATEGORIES.

The default behavior returns with no locale or on reaching the end of the enclosing block.

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

The setlocale function

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, 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 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 use this in a subsequent 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 that 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 which was in force when Perl started up: changes to the environment made by the application after start-up may or may not be noticed, depending on the implementation of 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 the locales available in your system, also consult setlocale(3) and see whether it leads you to the list of the available locales (search for the SEE ALSO section). If that fails, try the following command lines:

        locale -a


        ls /usr/lib/nls/loc

        ls /usr/lib/locale

        ls /usr/lib/nls

and see whether they list something resembling these

        en_US.ISO8859-1     de_DE.ISO8859-1     ru_RU.ISO8859-5
        en_US               de_DE               ru_RU
        en                  de                  ru
        english             german              russian
        english.iso88591    german.iso88591     russian.iso88595

Sadly, even though the calling interface for setlocale has been standardized, the names of the locales and the directories where the configuration is, have not. The basic form of the name is language_country/territory.codeset, but the latter parts are not always present.

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 and the second by the POSIX standard. What they define is 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.

The localeconv function

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 formatting variable names such as decimal_point and thousands_sep; the values are the corresponding values. See POSIX (3) for a longer example, which lists all the categories an implementation might be expected to provide; some provide more and others fewer, however. Note that you don't need use locale: as a function with the job of querying the locale, localeconv always observes the current locale.

Here's a simple-minded example program which rewrites its command line parameters as integers formatted correctly 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 = 3 unless $grouping;

        # Format command line params for current locale
        for (@ARGV) {
            $_ = int;    # Chop non-integer part
            1 while
            print "$_";
        print "\n";


The subsections which follow describe basic locale categories. As well as these, there are some combination categories which allow the manipulation of more than one basic category at a time. See ENVIRONMENT for a discussion of these.

Category LC_COLLATE: Collation

When in the scope of use locale, Perl looks to the LC_COLLATE environment variable to determine the application's notions on the collation (ordering) of characters. ('b' follows 'a' in Latin alphabets, but where do 'á' and 'å' belong?)

Here is a code snippet that will tell you what are the alphanumeric characters in the current locale, in the locale 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 byte-by-byte comparison for strings which 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 which ignores space characters completely, and which folds case.

If you have a single string which 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 byte-by-byte comparisons against other transformed strings during collation. ``Under the hood'', locale-affected Perl comparison operators call strxfrm for both their operands, then do a byte-by-byte 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. In fact, it doesn't save anything: Perl magic (see Magic Variables) creates the transformed version of a string the first time it's needed in a comparison, then keeps it 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. And 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, as it isn't needed: strcoll and strxfrm exist only to generate locale-dependent results, and so always obey the current LC_COLLATE locale.

Category LC_CTYPE: Character Types

When 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 and numeric characters. (Consult the perlre manpage 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 translating characters between lower- and upper-case. 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 in 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 (unaccented) letters and digits - for example, in command strings - locale-aware applications should use \w inside a no locale block. See SECURITY.

Category LC_NUMERIC: Numeric Formatting

When in the scope of use locale, Perl obeys the LC_NUMERIC locale information, which controls 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.)

Note that output produced by print is never affected by the current locale: it is independent of 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-independent conversion to string

        print "half five is $n\n";       # Locale-independent 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

Category LC_MONETARY: Formatting of monetary amounts

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, though voluminous and complex, does not quite meet your requirements: currency formatting is a hard nut to crack.


The 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 the 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 which exists only to generate locale-dependent results, strftime always obeys the current LC_TIME locale.

Other categories

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 which are not part of the standard Perl distribution.


While the main discussion of Perl security issues can be found in the perlsec manpage, 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 which 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:

Such dangers are not peculiar to the locale system: any aspect of an application's environment which may maliciously be modified presents similar challenges. Similarly, they are not specific to Perl: any programming language which allows you to write programs which take account of their environment exposes you to these issues.

Perl cannot protect you from all of the 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 the perlsec manpage) to mark string results which become locale-dependent, and which may be untrustworthy in consequence. Here is a summary of the tainting behavior of operators and functions which 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 an array-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 it is 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>.

In-memory formatting function (sprintf()):
Result is tainted if ``use locale'' is in effect.

Output formatting functions (printf() and write()):
Success/failure result is never tainted.

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 very similar program which is locale-aware:

        #/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 when use locale is in effect.


A string that can suppress Perl's warning about failed locale settings at start-up. Failure can occur if the locale support in the operating system is lacking (broken) is 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 which 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 it is set, it overrides all the rest of the locale environment variables.

In the absence of 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.

In the absence of LC_ALL, LC_COLLATE chooses the collation (sorting) locale. In the absence of both LC_ALL and LC_COLLATE, LANG chooses the collation locale.

In the absence of 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.

In the absence of LC_ALL, LC_NUMERIC chooses the numeric format locale. In the absence of both LC_ALL and LC_NUMERIC, LANG chooses the numeric format.

In the absence of 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_....


Backward compatibility

Versions of Perl prior to 5.004 mostly ignored locale information, generally behaving as if something similar to the "C" locale (see The setlocale function) was always in force, even if the program environment suggested otherwise. By default, Perl still behaves this way so as to maintain 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 that was available, that is, \w did understand what are 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

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.

Sort speed and memory use impacts

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.

write() and LC_NUMERIC

Formats are the only part of Perl which 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.

Freely available locale definitions

There is a large collection of locale definitions at You should be aware that it is unsupported, and is not claimed to be fit for any purpose. If your system allows the 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

``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.

An imperfect standard

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.


Broken systems

In certain system environments 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 <>, and complain to your vendor: maybe some bug fixes exist for these problems in your operating system. Sometimes such bug fixes are called an operating system upgrade.


POSIX (3), POSIX (3), POSIX (3), POSIX (3), POSIX (3), POSIX (3), POSIX (3), POSIX (3), POSIX (3), POSIX (3), POSIX (3), POSIX (3), POSIX (3), POSIX (3), POSIX (3), POSIX (3)


Jarkko Hietaniemi's original perli18n.pod heavily hacked by Dominic Dunlop, assisted by the perl5-porters.

Last update: Wed Jan 22 11:04:58 EST 1997