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       perllocale - Perl locale handling (internationalization and localization)


       Locales these days have been mostly been supplanted by Unicode, but Perl continues to
       support them.  See "Unicode and UTF-8" below.

       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 correct
       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:

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

       ·   Definitions for 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 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 following must be true:

       1.  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; or

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


   The use locale pragma
       By default, Perl ignores the current locale.  The "use locale" pragma and the "/l" regular
       expression modifier tell Perl to use the current locale for some operations ("/l" for just
       pattern matching).

       The current locale is set at execution time by setlocale() described below.  If that
       function hasn't yet been called in the course of the program's execution, the current
       locale is that which was determined by the "ENVIRONMENT" in effect at the start of the
       program, except that "LC_NUMERIC" is always initialized to the C locale (mentioned under
       "Finding locales").  If there is no valid environment, the current locale is undefined.
       It is likely, but not necessarily, the "C" locale.

       The operations that are affected by locale are:

       ·   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"

       ·   Format declarations (format()) use "LC_NUMERIC"

       ·   The POSIX date formatting function (strftime()) uses "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 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()

               # 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 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 locale names (separator also
       implementation-dependent) or a single locale name.  Please consult your setlocale(3) man
       page for details.

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

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

       If the second argument does not correspond to a valid locale, the locale for the category
       is not changed, and the function returns undef.

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

   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

               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.  Warning. The C locale delivered by some vendors may not actually
       exactly match what the C standard calls for.  So beware.

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

       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 to work no matter what.  This usually
       means your locale settings were wrong, they mention locales your system has never heard
       of, or the locale installation in your system has problems (for example, some system files
       are broken or missing).  There are quick and temporary fixes to these problems, as well as
       more thorough and lasting fixes.

   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 ...

       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 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 standardized.

   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
               # 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

           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.

   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");

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

   Category LC_NUMERIC: Numeric Formatting
       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".

   Category LC_MONETARY: Formatting of monetary amounts
       The C standard defines the "LC_MONETARY" category, but not a 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" locale.

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

   Other categories
       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 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

       ·   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

       ·   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 subverted.  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 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 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

       ·   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()):

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

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

           Results are never tainted.

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

           True/false results are never tainted.

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

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

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

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

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

               #/usr/local/bin/perl -T

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

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

       Compare this with a 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 variable 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.

                   On Debian systems, if the DPKG_RUNNING_VERSION environment variable is set (to
                   any value), the locale failure warnings will be suppressed just like with a
                   zero PERL_BADLANG setting. This is done to avoid floods of spurious warnings
                   during system upgrades.  See <>.

       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 "LANGUAGE".

                   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

       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

       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

       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

       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 numbers:

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


   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 "use locale" pragma (see "The use locale
       pragma") or for just pattern matching, the "/l" regular expression modifier (see
       "Character set modifiers" in perlre) 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
       If a program's environment specifies an LC_NUMERIC locale and "use locale" is in effect
       when the format is declared, the locale is used to specify the decimal point character in
       formatted output.  Formatted output cannot be controlled by "use locale" at the time when
       write() is called.

   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.

   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.

Unicode and UTF-8

       The support of Unicode is new starting from Perl version 5.6, and more fully implemented
       in version 5.8 and later.  See perluniintro.  Perl tries to work with both Unicode and
       locales--but of course, there are problems.

       Perl does not handle multi-byte locales, such as have been used for various Asian
       languages, such as Big5 or Shift JIS.  However, the increasingly common multi-byte UTF-8
       locales, if properly implemented, tend to work reasonably well in Perl, simply because
       both they and Perl store characters that take up multiple bytes the same way.

       Perl generally takes the tack to use locale rules on code points that can fit in a single
       byte, and Unicode rules for those that can't (though this wasn't uniformly applied prior
       to Perl 5.14).  This prevents many problems in locales that aren't UTF-8.  Suppose the
       locale is ISO8859-7, Greek.  The character at 0xD7 there is a capital Chi. But in the
       ISO8859-1 locale, Latin1, it is a multiplication sign.  The POSIX regular expression
       character class "[[:alpha:]]" will magically match 0xD7 in the Greek locale but not in the
       Latin one, even if the string is encoded in UTF-8, which would normally imply Unicode
       semantics.  (The "U" in UTF-8 stands for Unicode.)

       However, there are places where this breaks down.  Certain constructs are for Unicode
       only, such as "\p{Alpha}".  They assume that 0xD7 always has its Unicode meaning (or the
       equivalent on EBCDIC platforms).  Since Latin1 is a subset of Unicode and 0xD7 is the
       multiplication sign in both Latin1 and Unicode, "\p{Alpha}" will never match it,
       regardless of locale.  A similar issue occurs with "\N{...}".  It is therefore a bad idea
       to use "\p{}" or "\N{}" under "use locale"--unless you can guarantee that the locale will
       be a ISO8859-1 or UTF-8 one.  Use POSIX character classes instead.

       The same problem ensues if you enable automatic UTF-8-ification of your standard file
       handles, default "open()" layer, and @ARGV on non-ISO8859-1, non-UTF-8 locales (by using
       either the -C command line switch or the "PERL_UNICODE" environment variable; see
       perlrun).  Things are read in as UTF-8, which would normally imply a Unicode
       interpretation, but the presence of a locale causes them to be interpreted in that locale
       instead.  For example, a 0xD7 code point in the Unicode input, which should mean the
       multiplication sign, won't be interpreted by Perl that way under the Greek locale.  Again,
       this is not a problem provided you make certain that all locales will always and only be
       either an ISO8859-1 or a UTF-8 locale.

       Vendor locales are notoriously buggy, and it is difficult for Perl to test its locale-
       handling code because this interacts with code that Perl has no control over; therefore
       the locale-handling code in Perl may be buggy as well.  But if you do have locales that
       work, using them may be worthwhile for certain specific purposes, as long as you keep in
       mind the gotchas already mentioned.  For example, collation runs faster under locales than
       under Unicode::Collate (albeit with less flexibility), and you gain access to such things
       as the local currency symbol and the names of the months and days of the week.


   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 "use locale" is in effect.  When confronted with such a system, please report
       in excruciating detail to <>, and also contact 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 over a bit by Tom Christiansen, and updated by Perl 5