MirOS Manual: perllocale(1)


PERLLOCALE(1)   Perl Programmers Reference Guide    PERLLOCALE(1)

NAME

     perllocale - Perl locale handling (internationalization and
     localization)

DESCRIPTION

     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 naieve 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' prefer-
     ences 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 standard-
     ized (ISO C, XPG4, POSIX 1.c) method called "the locale sys-
     tem". The locale system is controlled per application using
     one pragma, one function call, and several environment vari-
     ables.

     NOTE: This feature is new in Perl 5.004, and does not apply
     unless an application specifically requests it--see "Back-
     ward compatibility". The one exception is that write() now
     always uses the current locale - see "NOTES".

PREPARING TO USE LOCALES

     If Perl applications are to understand and present your data
     correctly according a locale of your choice, all of the fol-
     lowing must be true:

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

     +   Definitions for locales that 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 all 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 that are not delivered with
         your operating system.)  Read your system documentation

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         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".

     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 follow-
     ing must be true:

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

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

USING LOCALES

     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:

     +   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".

     +   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

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         "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 informa-
     tion 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 com-
     bination 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 some-
     thing else than LC_ALL, the function returns a string naming
     the current locale for the category.  You can use this value

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     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.  Gen-
     erally, 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 setlo-
     cale(3).

     Finding locales

     For locales available in your system, consult also setlo-
     cale(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

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             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 sys-
     tems are POSIX-conformant), so use "C" when you need expli-
     citly to specify this default locale.

     LOCALE PROBLEMS

     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

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     to work no matter what.  This usually means your locale set-
     tings 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 miss-
     ing).  There are quick and temporary fixes to these prob-
     lems, as well as more thorough and lasting fixes.

     Temporarily fixing locale problems

     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 set-
     ting 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 environ-
     ment 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 dedu-
     cible.  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

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             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

     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".

     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.

     Fixing system locale configuration

     Contact a system administrator (preferably your own) and
     report the exact error message you get, and ask them to read

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     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 com-
     mands and places because these things are not that standard-
     ized.

     The localeconv function

     The POSIX::localeconv() function allows you to get particu-
     lars 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 format-
     ting, 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:

             # 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;

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             # 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";

     I18N::Langinfo

     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 lan-
     ginfo(): 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.

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LOCALE CATEGORIES

     The following subsections describe basic locale categories.
     Beyond these, some combination categories allow manipulation
     of more than one basic category at a time.  See "ENVIRON-
     MENT" for a discussion of these.

     Category LC_COLLATE: Collation

     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 'a' and 'aa'
     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");

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     $equal_in_locale will be true if the collation locale speci-
     fies a dictionary-like ordering that ignores space charac-
     ters 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 "Magic Variables" in
     perlguts) creates the transformed version of a string the
     first time it's needed in a comparison, then keeps this ver-
     sion 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 pro-
     duces to be portable across systems--or even from one revi-
     sion 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.

     Category LC_CTYPE: Character Types

     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

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     expressions.)  Thanks to "LC_CTYPE", depending on your
     locale setting, characters like 'ae', '`', 'ss', and 'o' may
     be understood as "\w" characters.

     The "LC_CTYPE" locale also provides the map used in transli-
     terating 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".

     Category LC_NUMERIC: Numeric Formatting

     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

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             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

     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".

     LC_TIME

     Output produced by POSIX::strftime(), which builds a format-
     ted 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 func-
     tion 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".

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     Other categories

     The remaining locale category, "LC_MESSAGES" (possibly sup-
     plemented 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.

SECURITY

     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 bro-
     ken) locale can make a locale-aware application give unex-
     pected results.  Here are a few possibilities:

     +   Regular expression checks for safe file names or mail
         addresses using "\w" may be spoofed by an "LC_CTYPE"
         locale that 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.

     +   A sneaky "LC_COLLATE" locale could result in the names
         of students with "D" grades appearing ahead of those
         with "A"s.

     +   An application that takes the trouble to use information
         in "LC_MONETARY" may format debits as if they were
         credits and vice versa if that locale has been sub-
         verted.  Or it might 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.")

     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

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     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 conse-
     quence.  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" (whitespace character), or "\S" (non
         whitespace 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()):

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         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(), isdi-
         git(), 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";

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     This third program fails to run because $& is tainted: it is
     the result of a match involving "\w" while "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) in some way--or if
                 you mistyped the name of a locale when you set
                 up your environment.  If this environment vari-
                 able 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      "LC_ALL" is the "override-all" locale environ-
                 ment variable. If set, it overrides all the rest
                 of the locale environment variables.

     LANGUAGE    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, warn-
                 ing, 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_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.

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     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 prior to 5.004 mostly ignored locale infor-
     mation, generally behaving as if something similar to the
     "C" locale were always in force, even if the program
     environment suggested otherwise (see "The setlocale func-
     tion").  By default, Perl still behaves this way for back-
     ward 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 vari-
     ables. 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",

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     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 that unconditionally use
     information from a program's locale; if a program's environ-
     ment 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
     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.

     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 stan-
     dards, 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

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     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 con-
     strued as a bug.

Unicode and UTF-8
     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 "Locales" in perlun-
     icode for examples.

BUGS

     Broken systems

     In certain systems, the operating system's locale support is
     broken and cannot be fixed or used by Perl.  Such deficien-
     cies can and will result in mysterious hangs and/or Perl
     core dumps when the "use locale" is in effect.  When con-
     fronted 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.

SEE ALSO

     I18N::Langinfo, perluniintro, perlunicode, open, "isalnum"
     in POSIX, "isalpha" in POSIX, "isdigit" in POSIX, "isgraph"
     in POSIX, "islower" in POSIX, "isprint" in POSIX, "ispunct"
     in POSIX, "isspace" in POSIX, "isupper" in POSIX, "isxdigit"
     in POSIX, "localeconv" in POSIX, "setlocale" in POSIX,
     "strcoll" in POSIX, "strftime" in POSIX, "strtod" in POSIX,
     "strxfrm" in POSIX.

HISTORY

     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

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