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perllocale (1)


perllocale - Perl locale handling (internationalization and localization)


Please see following description for synopsis


Perl Programmers Reference Guide                    PERLLOCALE(1)

     perllocale - Perl locale handling (internationalization and

     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'
     preferences in such matters is called internationalization
     (often abbreviated as i18n); telling such an application
     about a particular set of preferences is known as
     localization (l10n).

     Perl can understand language-specific data via the
     standardized (ISO C, XPG4, POSIX 1.c) method called "the
     locale system". The locale system is controlled per
     application using one pragma, one function call, and several
     environment variables.

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

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

     o   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.

     o   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.

     o   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
     following must be true:

     o   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.

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

  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:

     o   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".

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

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

     o   The POSIX date formatting function (strftime()) uses

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     "LC_COLLATE", "LC_CTYPE", and so on, are discussed further

     The default behavior is restored with the "no locale"
     pragma, or upon reaching the end of block enclosing "use

     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 and the category is
     something else than LC_ALL, the function returns a string
     naming the current locale for the category.  You can use
     this value as the second argument in a subsequent call to

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     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) man page for details.

     If a second argument is given and it corresponds to a valid
     locale, the locale for the category is set to that value,
     and the function returns the now-current locale value.  You
     can then use this in yet another call to setlocale().  (In
     some implementations, the return value may sometimes differ
     from the value you gave as the second argument--think of it
     as an alias for the value you gave.)

     As the example shows, if the second argument is an empty
     string, the category's locale is returned to the default
     specified by the corresponding environment variables.
     Generally, this results in a return to the default that was
     in force when Perl started up: changes to the environment
     made by the application after startup may or may not be
     noticed, depending on your system's C library.

     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

  Finding locales
     For locales available in your system, consult also
     setlocale(3) to see whether it leads to the list of
     available locales (search for the SEE ALSO section).  If
     that fails, try the following command lines:

             locale -a


             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.

     Two special locales are worth particular mention: "C" and
     "POSIX".  Currently these are effectively the same locale:
     the difference is mainly that the first one is defined by
     the C standard, the second by the POSIX standard.  They
     define the default locale in which every program starts in
     the absence of locale information in its environment.  (The
     default default locale, if you will.)  Its language is
     (American) English and its character codeset ASCII.

     NOTE: Not all systems have the "POSIX" locale (not all
     systems are POSIX-conformant), so use "C" when you need
     explicitly to specify this default locale.

     You may encounter the following warning message at Perl

             perl: warning: Setting locale failed.
             perl: warning: Please check that your locale settings:
                     LC_ALL = "En_US",
                     LANG = (unset)
                 are supported and installed on your system.
             perl: warning: Falling back to the standard locale ("C").

     This means that your locale settings had LC_ALL set to
     "En_US" and LANG exists but has no value.  Perl tried to
     believe you but could not.  Instead, Perl gave up and fell
     back to the "C" locale, the default locale that is supposed
     to work no matter what.  This usually means your locale

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     settings were wrong, they mention locales your system has
     never heard of, or the locale installation in your system
     has problems (for example, some system files are broken or
     missing).  There are quick and temporary fixes to these
     problems, as well as more thorough and lasting fixes.

  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
     setting the environment variable PERL_BADLANG to a zero
     value, for example "0".  This method really just sweeps the
     problem under the carpet: you tell Perl to shut up even when
     Perl sees that something is wrong.  Do not be surprised if
     later something locale-dependent misbehaves.

     Perl can be run under the "C" locale by setting the
     environment variable LC_ALL to "C".  This method is perhaps
     a bit more civilized than the PERL_BADLANG approach, but
     setting LC_ALL (or other locale variables) may affect other
     programs as well, not just Perl.  In particular, external
     programs run from within Perl will see these changes.  If
     you make the new settings permanent (read on), all programs
     you run see the changes.  See "ENVIRONMENT" for the full
     list of relevant environment variables and "USING LOCALES"
     for their effects in Perl.  Effects in other programs are
     easily deducible.  For example, the variable LC_COLLATE may
     well affect your sort program (or whatever the program that
     arranges "records" alphabetically in your system is called).

     You can test out changing these variables temporarily, and
     if the new settings seem to help, put those settings into
     your shell startup files.  Consult your local documentation
     for the exact details.  For in Bourne-like shells (sh, ksh,
     bash, zsh):

             export LC_ALL

     This assumes that we saw the locale "en_US.ISO8859-1" using
     the commands discussed above.  We decided to try that
     instead of the above faulty locale "En_US"--and in Cshish
     shells (csh, tcsh)

             setenv LC_ALL en_US.ISO8859-1

     or if you have the "env" application you can do in any shell

             env LC_ALL=en_US.ISO8859-1 perl ...

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     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

     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

  Fixing system locale configuration
     Contact a system administrator (preferably your own) and
     report the exact error message you get, and ask them to read
     this same documentation you are now reading.  They should be
     able to check whether there is something wrong with the
     locale configuration of the system.  The "Finding locales"
     section is unfortunately a bit vague about the exact
     commands and places because these things are not that

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  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 variable names for
     formatting, such as "decimal_point" and "thousands_sep".
     The values are the corresponding, er, values.  See
     "localeconv" in POSIX for a longer example listing the
     categories an implementation might be expected to provide;
     some provide more and others fewer.  You don't need an
     explicit "use locale", because localeconv() always observes
     the current locale.

     Here's a simple-minded example program that rewrites its
     command-line parameters as integers correctly formatted in
     the current locale:

             # See comments in previous example
             require 5.004;
             use POSIX qw(locale_h);

             # Get some of locale's numeric formatting parameters
             my ($thousands_sep, $grouping) =
                  @{localeconv()}{'thousands_sep', 'grouping'};

             # Apply defaults if values are missing
             $thousands_sep = ',' unless $thousands_sep;

             # grouping and mon_grouping are packed lists
             # of small integers (characters) telling the
             # grouping (thousand_seps and mon_thousand_seps
             # being the group dividers) of numbers and
             # monetary quantities.  The integers' meanings:
             # 255 means no more grouping, 0 means repeat

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             # 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) {
                 $_ = int;    # Chop non-integer part
                 1 while
                 print "$_";
             print "\n";

     Another interface for querying locale-dependent information
     is the I18N::Langinfo::langinfo() function, available at
     least in Unix-like systems and VMS.

     The following example will import the langinfo() function
     itself and three constants to be used as arguments to
     langinfo(): a constant for the abbreviated first day of the
     week (the numbering starts from Sunday = 1) and two more
     constants for the affirmative and negative answers for a
     yes/no question in the current locale.

         use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);

         my ($abday_1, $yesstr, $nostr) = map { langinfo } qw(ABDAY_1 YESSTR NOSTR);

         print "$abday_1? [$yesstr/$nostr] ";

     In other words, in the "C" (or English) locale the above
     will probably print something like:

         Sun? [yes/no]

     See I18N::Langinfo for more information.

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

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  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

             no locale;
             print +(sort grep /\w/, map { chr } 0..255), "\n";

     This machine-native collation (which is what you get unless
     "use locale" has appeared earlier in the same block) must be
     used for sorting raw binary data, whereas the locale-
     dependent collation of the first example is useful for
     natural text.

     As noted in "USING LOCALES", "cmp" compares according to the
     current collation locale when "use locale" is in effect, but
     falls back to a char-by-char comparison for strings that the
     locale says are equal. You can use POSIX::strcoll() if you
     don't want this fall-back:

             use POSIX qw(strcoll);
             $equal_in_locale =
                 !strcoll("space and case ignored", "SpaceAndCaseIgnored");

     $equal_in_locale will be true if the collation locale
     specifies a dictionary-like ordering that ignores space
     characters completely and which folds case.

     If you have a single string that you want to check for
     "equality in locale" against several others, you might think
     you could gain a little efficiency by using POSIX::strxfrm()

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     in conjunction with "eq":

             use POSIX qw(strxfrm);
             $xfrm_string = strxfrm("Mixed-case string");
             print "locale collation ignores spaces\n"
                 if $xfrm_string eq strxfrm("Mixed-casestring");
             print "locale collation ignores hyphens\n"
                 if $xfrm_string eq strxfrm("Mixedcase string");
             print "locale collation ignores case\n"
                 if $xfrm_string eq strxfrm("mixed-case string");

     strxfrm() takes a string and maps it into a transformed
     string for use in char-by-char comparisons against other
     transformed strings during collation.  "Under the hood",
     locale-affected Perl comparison operators call strxfrm() for
     both operands, then do a char-by-char comparison of the
     transformed strings.  By calling strxfrm() explicitly and
     using a non locale-affected comparison, the example attempts
     to save a couple of transformations.  But in fact, it
     doesn't save anything: Perl magic (see "Magic Variables" in
     perlguts) creates the transformed version of a string the
     first time it's needed in a comparison, then keeps this
     version around in case it's needed again.  An example
     rewritten the easy way with "cmp" runs just about as fast.
     It also copes with null characters embedded in strings; if
     you call strxfrm() directly, it treats the first null it
     finds as a terminator.  don't expect the transformed strings
     it produces to be portable across systems--or even from one
     revision of your operating system to the next.  In short,
     don't call strxfrm() directly: let Perl do it for you.

     Note: "use locale" isn't shown in some of these examples
     because it isn't needed: strcoll() and strxfrm() 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
     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
     transliterating characters between lower and uppercase.
     This affects the case-mapping functions--lc(), lcfirst,
     uc(), and ucfirst(); case-mapping interpolation with "\l",

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     "\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
     After a proper POSIX::setlocale() call, 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 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 setlocale LC_NUMERIC);

             setlocale LC_NUMERIC, "";

             $n = 5/2;   # Assign numeric 2.5 to $n

             $a = " $n"; # Locale-dependent conversion to string

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

             printf "half five is %g\n", $n;  # Locale-dependent output

             print "DECIMAL POINT IS COMMA\n"
                 if $n == (strtod("2,5"))[0]; # Locale-dependent conversion

     See also I18N::Langinfo and "RADIXCHAR".

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  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".

     Output produced by POSIX::strftime(), which builds a
     formatted human-readable date/time string, is affected by
     the current "LC_TIME" locale.  Thus, in a French locale, the
     output produced by the %B format element (full month name)
     for the first month of the year would be "janvier".  Here's
     how to get a list of long month names in the current locale:

             use POSIX qw(strftime);
             for (0..11) {
                 $long_month_name[$_] =
                     strftime("%B", 0, 0, 0, 1, $_, 96);

     Note: "use locale" isn't needed in this example: as a
     function that exists only to generate locale-dependent
     results, strftime() always obeys the current "LC_TIME"

     See also I18N::Langinfo and "ABDAY_1".."ABDAY_7",
     "DAY_1".."DAY_7", "ABMON_1".."ABMON_12", and

  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 outside
     the standard Perl distribution and by the operating system
     and its utilities.  Note especially that the string value of
     $! and the error messages given by external utilities may be
     changed by "LC_MESSAGES".  If you want to have portable
     error codes, use "%!".  See Errno.

     Although the main discussion of Perl security issues can be

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     found in perlsec, a discussion of Perl's locale handling
     would be incomplete if it did not draw your attention to
     locale-dependent security issues.  Locales--particularly on
     systems that allow unprivileged users to build their own
     locales--are untrustworthy.  A malicious (or just plain
     broken) locale can make a locale-aware application give
     unexpected results.  Here are a few possibilities:

     o   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.

     o   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

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

     o   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
         subverted.  Or it might make payments in US dollars
         instead of Hong Kong dollars.

     o   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
     environment exposes you to these issues.

     Perl cannot protect you from all possibilities shown in the
     examples--there is no substitute for your own
     vigilance--but, when "use locale" is in effect, Perl uses
     the tainting mechanism (see perlsec) to mark string results
     that become locale-dependent, and which may be untrustworthy
     in consequence.  Here is a summary of the tainting behavior
     of operators and functions that may be affected by the

     o   Comparison operators ("lt", "le", "ge", "gt" and "cmp"):

         Scalar true/false (or less/equal/greater) result is

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         never tainted.

     o   Case-mapping interpolation (with "\l", "\L", "\u" or

         Result string containing interpolated material is
         tainted if "use locale" is in effect.

     o   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".

     o   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".

     o   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.

     o   Case-mapping functions (lc(), lcfirst(), uc(),

         Results are tainted if "use locale" is in effect.

     o   POSIX locale-dependent functions (localeconv(),
         strcoll(), strftime(), strxfrm()):

         Results are never tainted.

     o   POSIX character class tests (isalnum(), isalpha(),
         isdigit(), isgraph(), islower(), isprint(), ispunct(),
         isspace(), isupper(), isxdigit()):

         True/false results are never tainted.

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     Three examples illustrate locale-dependent tainting.  The
     first program, which ignores its locale, won't run: a value
     taken directly from the command line may not be used to name
     an output file when taint checks are enabled.

             #/usr/local/bin/perl -T
             # Run with taint checking

             # Command line sanity check omitted...
             $tainted_output_file = shift;

             open(F, ">$tainted_output_file")
                 or warn "Open of $untainted_output_file failed: $!\n";

     The program can be made to run by "laundering" the tainted
     value through a regular expression: the second
     example--which still ignores locale information--runs,
     creating the file named on its command line if it can.

             #/usr/local/bin/perl -T

             $tainted_output_file = shift;
             $tainted_output_file =~ m%[\w/]+%;
             $untainted_output_file = $&;

             open(F, ">$untainted_output_file")
                 or warn "Open of $untainted_output_file failed: $!\n";

     Compare this with a similar but locale-aware program:

             #/usr/local/bin/perl -T

             $tainted_output_file = shift;
             use locale;
             $tainted_output_file =~ m%[\w/]+%;
             $localized_output_file = $&;

             open(F, ">$localized_output_file")
                 or warn "Open of $localized_output_file failed: $!\n";

     This third program fails to run because $& is tainted: it is
     the result of a match involving "\w" while "use locale" is
     in effect.

                 A string that can suppress Perl's warning about
                 failed locale settings at startup.  Failure can
                 occur if the locale support in the operating
                 system is lacking (broken) in some way--or if
                 you mistyped the name of a locale when you set
                 up your environment.  If this environment

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                 variable is absent, or has a value that does not
                 evaluate to integer zero--that is, "0" or ""--
                 Perl will complain about locale setting

                 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
                 environment 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

                 However, in the case you are using "LANGUAGE":
                 it affects the language of informational,
                 warning, and error messages output by commands
                 (in other words, it's like "LC_MESSAGES") but it
                 has higher priority than LC_ALL.  Moreover, it's
                 not a single value but instead a "path"
                 (":"-separated list) of languages (not locales).
                 See the GNU "gettext" library documentation for
                 more information.

     LC_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

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                 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_...".

     The LC_NUMERIC controls the numeric output:

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

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

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

     See attributes(5) for descriptions of the following

     |Availability   | runtime/perl-512 |
     |Stability      | Uncommitted      |
  Backward compatibility
     Versions of Perl prior to 5.004 mostly ignored locale
     information, generally behaving as if something similar to
     the "C" locale were always in force, even if the program
     environment suggested otherwise (see "The setlocale
     function").  By default, Perl still behaves this way for
     backward compatibility.  If you want a Perl application to
     pay attention to locale information, you must use the

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     "use locale" pragma (see "The use locale pragma") to
     instruct it to do so.

     Versions of Perl from 5.002 to 5.003 did use the "LC_CTYPE"
     information if available; that is, "\w" did understand what
     were the letters according to the locale environment
     variables.  The problem was that the user had no control
     over the feature: if the C library supported locales, Perl
     used them.

  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 that unconditionally use
     information from a program's locale; if a program's
     environment specifies an LC_NUMERIC locale, it is always
     used to specify the decimal point character in formatted
     output.  Formatted output cannot be controlled by "use
     locale" because the pragma is tied to the block structure of
     the program, and, for historical reasons, formats exist
     outside that block structure.

  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
     installation of arbitrary locales, you may find the
     definitions useful as they are, or as a basis for the
     development of your own locales.

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  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.

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
     perlunicode for examples.

  Broken systems
     In certain systems, the operating system's locale support is
     broken and cannot be fixed or used by Perl.  Such
     deficiencies can and will result in mysterious hangs and/or
     Perl core dumps when the "use locale" is in effect.  When
     confronted with such a system, please report in excruciating
     detail to <>, and complain to your vendor:
     bug fixes may exist for these problems in your operating
     system.  Sometimes such bug fixes are called an operating
     system upgrade.

     I18N::Langinfo, perluniintro, perlunicode, open, "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.

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

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     over a bit by Tom Christiansen.

     Last update: Thu Jun 11 08:44:13 MDT 1998

     This software was built from source available at  The original
     community source was downloaded from

     Further information about this software can be found on the
     open source community website at

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