• NAME
• DESCRIPTION
• PREPARING TO USE LOCALES
• USING LOCALES
  • The use locale pragma
  • The setlocale function
  • The localeconv function
• LOCALE CATEGORIES
  • Category LC_COLLATE: Collation
  • Category LC_CTYPE: Character Types
  • Category LC_NUMERIC: Numeric Formatting
  • Category LC_MONETARY: Formatting of monetary amounts
  • LC_TIME
  • Other categories
• SECURITY
• ENVIRONMENT
• NOTES
  • Backward compatibility
  • I18N:Collate obsolete
  • Sort speed and memory use impacts
  • write() and LC_NUMERIC
  • Freely available locale definitions
  • I18n and l10n
  • An imperfect standard
• BUGS
  • Broken systems
• SEE ALSO
• HISTORY

NAME

DESCRIPTION

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.

PREPARING TO USE LOCALES

• Your operating system must support the locale system. If it does, you should find that the setlocale() function is a documented part of its C library.

• Definitions for the locales which you use must be installed. You, or your system administrator, must make sure that this is the case. The available locales, the location in which they are kept, and the manner in which they are installed, vary from system to system. Some systems provide only a few, hard-wired, locales, and do not allow more to be added; others allow you to add ``canned'' locales provided by the system supplier; still others allow you or the system administrator to define and add arbitrary locales. (You may have to ask your supplier to provide canned locales which are not delivered with your operating system.) Read your system documentation for further illumination.

• Perl must believe that the locale system is supported. If it does, perl -V:d_setlocale will say that the value for d_setlocale is define.

• The locale-determining environment variables (see ENVIRONMENT) must be correctly set up, either by yourself, or by the person who set up your system account, at the time the application is started.

• The application must set its own locale using the method described in The setlocale function.

USING LOCALES

The use locale pragma

• 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 it is used without an explicit comparison function because it uses cmp by default.

  Note: eq and ne are unaffected by the locale: they always perform a byte-by-byte 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 byte-by-byte comparison, and only returns (equal) if the operands are bit-for-bit 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.

• Regular expressions and case-modification functions (uc(), lc(), ucfirst(), and lcfirst()) use LC_CTYPE

• The formatting functions (printf(), sprintf() and write()) use LC_NUMERIC

• The POSIX date formatting function (strftime()) uses LC_TIME.

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

        # 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 startup 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

        nlsinfo

        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

        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) {
            $_ = int;    # Chop non-integer part
            1 while
            s/(\d)(\d{$grouping}($|$thousands_sep))/$1$thousands_sep$2/;
            print "$_";
        }
        print "\n";

LOCALE CATEGORIES

Category LC_COLLATE: Collation

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

The LC_CTYPE locale also provides the map used in translating 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 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

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

LC_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: as a function which exists only to generate locale-dependent results, strftime() always obeys the current LC_TIME locale.

Other categories

SECURITY

• Regular expression checks for safe file names or mail addresses using \w may be spoofed by an LC_CTYPE locale which claims that characters such as ``>'' and ``|'' are alphanumeric.

• String interpolation with case-mapping, as in, say, $dest = "C:\U$name.$ext", may produce dangerous results if a bogus LC_CTYPE case-mapping table is in effect.

• If the decimal point character in the LC_NUMERIC locale is surreptitiously changed from a dot to a comma, sprintf("%g", 0.123456e3) produces a string result of ``123,456''. Many people would interpret this as one hundred and twenty-three thousand, four hundred and fifty-six.

• A sneaky LC_COLLATE locale could result in the names of students with ``D'' grades appearing ahead of those with ``A''s.

• An application which takes the trouble to use the information in LC_MONETARY may format debits as if they were credits and vice versa if that locale has been subverted. Or it make may make payments in US dollars instead of Hong Kong dollars.

• The date and day names in dates formatted by strftime() could be manipulated to advantage by a malicious user able to subvert the LC_DATE locale. (``Look - it says I wasn't in the building on Sunday.'')

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.

        #/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.

ENVIRONMENT

PERL_BADLANG

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) 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.

LC_ALL

LC_ALL is the ``override-all'' locale environment variable. If it is set, it overrides all the rest of the locale environment variables.

LC_CTYPE

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.

LC_COLLATE

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.

LC_MONETARY

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.

LC_NUMERIC

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.

LC_TIME

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

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_....

NOTES

Backward compatibility

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

Sort speed and memory use impacts

write() and LC_NUMERIC

Freely available locale definitions

I18n and l10n

An imperfect standard

BUGS

Broken systems

SEE ALSO

HISTORY

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