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perllocale(1)          Perl Programmers Reference Guide          perllocale(1)




NAME

       perllocale - Perl locale handling (internationalization and
       localization)


DESCRIPTION

       In the beginning there was ASCII, the "American Standard Code for
       Information Interchange", which works quite well for Americans with
       their English alphabet and dollar-denominated currency.  But it doesn't
       work so well even for other English speakers, who may use different
       currencies, such as the pound sterling (as the symbol for that currency
       is not in ASCII); and it's hopelessly inadequate for many of the
       thousands of the world's other languages.

       To address these deficiencies, the concept of locales was invented
       (formally the ISO C, XPG4, POSIX 1.c "locale system").  And
       applications were and are being written that use the locale mechanism.
       The process of making such an application take account of its users'
       preferences in these kinds of matters is called internationalization
       (often abbreviated as i18n); telling such an application about a
       particular set of preferences is known as localization (l10n).

       Perl has been extended to support the locale system.  This is
       controlled per application by using one pragma, one function call, and
       several environment variables.

       Unfortunately, there are quite a few deficiencies with the design (and
       often, the implementations) of locales.  Unicode was invented (see
       perlunitut for an introduction to that) in part to address these design
       deficiencies, and nowadays, there is a series of "UTF-8 locales", based
       on Unicode.  These are locales whose character set is Unicode, encoded
       in UTF-8.  Starting in v5.20, Perl fully supports UTF-8 locales, except
       for sorting and string comparisions.  (Use Unicode::Collate for these.)
       Perl continues to support the old non UTF-8 locales as well.

       (Unicode is also creating "CLDR", the "Common Locale Data Repository",
       <http://cldr.unicode.org/> which includes more types of information
       than are available in the POSIX locale system.  At the time of this
       writing, there was no CPAN module that provides access to this XML-
       encoded data.  However, many of its locales have the POSIX-only data
       extracted, and are available as UTF-8 locales at
       <http://unicode.org/Public/cldr/latest/>.)


WHAT IS A LOCALE

       A locale is a set of data that describes various aspects of how various
       communities in the world categorize their world.  These categories are
       broken down into the following types (some of which include a brief
       note here):

       Category LC_NUMERIC: Numeric formatting
           This indicates how numbers should be formatted for human
           readability, for example the character used as the decimal point.

       Category LC_MONETARY: Formatting of monetary amounts


       Category LC_TIME: Date/Time formatting


       Category LC_MESSAGES: Error and other messages
           This is used by Perl itself only for accessing operating system
           error messages via $! and $^E.

       Category LC_COLLATE: Collation
           This indicates the ordering of letters for comparison and sorting.
           In Latin alphabets, for example, "b", generally follows "a".

       Category LC_CTYPE: Character Types
           This indicates, for example if a character is an uppercase letter.

       Other categories
           Some platforms have other categories, dealing with such things as
           measurement units and paper sizes.  None of these are used directly
           by Perl, but outside operations that Perl interacts with may use
           these.  See "Not within the scope of any "use locale" variant"
           below.

       More details on the categories used by Perl are given below in "LOCALE
       CATEGORIES".

       Together, these categories go a long way towards being able to
       customize a single program to run in many different locations.  But
       there are deficiencies, so keep reading.


PREPARING TO USE LOCALES

       Perl itself will not use locales unless specifically requested to (but
       again note that Perl may interact with code that does use them).  Even
       if there is such a request, all of the following must be true for it to
       work properly:

       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 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:

       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 whomever set up your system account; or

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


USING LOCALES

   The use locale pragma
       By default, Perl itself ignores the current locale.  The "use locale"
       pragma tells Perl to use the current locale for some operations.
       Starting in v5.16, there is an optional parameter to this pragma:

           use locale ':not_characters';

       This parameter allows better mixing of locales and Unicode (less useful
       in v5.20 and later), and is described fully in "Unicode and UTF-8", but
       briefly, it tells Perl to not use the character portions of the locale
       definition, that is the "LC_CTYPE" and "LC_COLLATE" categories.
       Instead it will use the native character set (extended by Unicode).
       When using this parameter, you are responsible for getting the external
       character set translated into the native/Unicode one (which it already
       will be if it is one of the increasingly popular UTF-8 locales).  There
       are convenient ways of doing this, as described in "Unicode and UTF-8".

       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.  If there is
       no valid environment, the current locale is whatever the system default
       has been set to.   On POSIX systems, it is likely, but not necessarily,
       the "C" locale.  On Windows, the default is set via the computer's
       "Control Panel->Regional and Language Options" (or its current
       equivalent).

       The operations that are affected by locale are:

       Not within the scope of any "use locale" variant
           Only operations originating outside Perl should be affected, as
           follows:

           o   The variables $! (and its synonyms $ERRNO and $OS_ERROR) and
               $^E (and its synonym $EXTENDED_OS_ERROR) when used as strings
               always are in terms of the current locale and as if within the
               scope of "use bytes".  This is likely to change in Perl v5.22.

           o   The current locale is also used when going outside of Perl with
               operations like system() or qx//, if those operations are
               locale-sensitive.

           o   Also Perl gives access to various C library functions through
               the POSIX module.  Some of those functions are always affected
               by the current locale.  For example, "POSIX::strftime()" uses
               "LC_TIME"; "POSIX::strtod()" uses "LC_NUMERIC";
               "POSIX::strcoll()" and "POSIX::strxfrm()" use "LC_COLLATE"; and
               character classification functions like "POSIX::isalnum()" use
               "LC_CTYPE".  All such functions will behave according to the
               current underlying locale, even if that locale isn't exposed to
               Perl space.

           o   XS modules for all categories but "LC_NUMERIC" get the
               underlying locale, and hence any C library functions they call
               will use that underlying locale.  Perl always initializes
               "LC_NUMERIC" to "C" because too many modules are unable to cope
               with the decimal point in a floating point number not being a
               dot (it's a comma in many locales).  But note that these
               modules are vulnerable because "LC_NUMERIC" currently can be
               changed at any time by a call to the C "set_locale()" by XS
               code or by something XS code calls, or by "POSIX::setlocale()"
               by Perl code.  This is true also for the Perl-provided lite
               wrappers for XS modules to use some C library "printf"
               functions: "Gconvert", my_sprintf, my_snprintf, and
               my_vsnprintf.



       Lingering effects of "use locale"
           Certain Perl operations that are set-up within the scope of a "use
           locale" variant retain that effect even outside the scope.  These
           include:

           o   The output format of a write() is determined by an earlier
               format declaration ("format" in perlfunc), so whether or not
               the output is affected by locale is determined by if the
               "format()" is within the scope of a "use locale" variant, not
               whether the "write()" is.

           o   Regular expression patterns can be compiled using qr// with
               actual matching deferred to later.  Again, it is whether or not
               the compilation was done within the scope of "use locale" that
               determines the match behavior, not if the matches are done
               within such a scope or not.



       Under "use locale ':not_characters';"
           o   All the non-Perl operations.

           o   Format declarations ("format" in perlfunc) and hence any
               subsequent "write()"s use "LC_NUMERIC".

           o   stringification and output use "LC_NUMERIC".  These include the
               results of "print()", "printf()", "say()", and "sprintf()".



       Under just plain ""use locale";"
           o   All the above operations

           o   The comparison operators ("lt", "le", "cmp", "ge", and "gt")
               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"

       The default behavior is restored with the "no locale" pragma, or upon
       reaching the end of the block enclosing "use locale".  Note that "use
       locale" and "use locale ':not_characters'" may be nested, and that what
       is in effect within an inner scope will revert to the outer scope's
       rules at the end of the inner scope.

       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:

               # Import locale-handling tool set from POSIX module.
               # This example uses: setlocale -- the function call
               #                    LC_CTYPE -- explained below
               # (Showing the testing for success/failure of operations is
               # omitted in these examples to avoid distracting from the main
               # point)

               use POSIX qw(locale_h);
               use locale;
               my $old_locale;

               # 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 the default defined by the
               # LC_ALL/LC_CTYPE/LANG environment variables, or to the system
               # default.  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 other
       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()", but on some platforms the string is
       opaque, not something that most people would be able to decipher as to
       what locale it means.

       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.

       Note that Perl ignores the current "LC_CTYPE" and "LC_COLLATE" locales
       within the scope of a "use locale ':not_characters'".

       If "set_locale()" fails for some reason (for example, an attempt to set
       to a locale unknown to the system), 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

               nlsinfo

               ls /usr/lib/nls/loc

               ls /usr/lib/locale

               ls /usr/lib/nls

               ls /usr/share/locale

       and see whether they list something resembling these

               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 or, rarely, a superset thereof
       (such as the "DEC Multinational Character Set (DEC-MCS)").  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.

   LOCALE PROBLEMS
       You may encounter the following warning message at Perl startup:

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

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

   Testing for broken locales
       If you are building Perl from source, the Perl test suite file
       lib/locale.t can be used to test the locales on your system.  Setting
       the environment variable "PERL_DEBUG_FULL_TEST" to 1 will cause it to
       output detailed results.  For example, on Linux, you could say

        PERL_DEBUG_FULL_TEST=1 ./perl -T -Ilib lib/locale.t > locale.log 2>&1

       Besides many other tests, it will test every locale it finds on your
       system to see if they conform to the POSIX standard.  If any have
       errors, it will include a summary near the end of the output of which
       locales passed all its tests, and which failed, and why.

   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):

               LC_ALL=en_US.ISO8859-1
               export LC_ALL

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

               setenv LC_ALL en_US.ISO8859-1

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

               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:

           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) {
               $_ = int;    # Chop non-integer part
               1 while
               s/(\d)(\d{$grouping[0]}($|$thousands_sep))/$1$thousands_sep$2/;
               print "$_";
           }
           print "\n";

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

       The following example will import the "langinfo()" function itself and
       three constants to be used as arguments to "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.


LOCALE CATEGORIES

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

   Category LC_COLLATE: Collation
       In the scope of "use locale" (but not a "use locale
       ':not_characters'"), 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 traditional 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.

       Perl only supports single-byte locales for "LC_COLLATE".  This means
       that a UTF-8 locale likely will just give you machine-native ordering.
       Use Unicode::Collate for the full implementation of the Unicode
       Collation Algorithm.

       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()" are POSIX functions which use
       the standard system-supplied "libc" functions that always obey the
       current "LC_COLLATE" locale.

   Category LC_CTYPE: Character Types
       In the scope of "use locale" (but not a "use locale
       ':not_characters'"), Perl obeys the "LC_CTYPE" locale setting.  This
       controls the application's notion of which characters are alphabetic,
       numeric, punctuation, etc.  This affects Perl's "\w" regular expression
       metanotation, which stands for alphanumeric characters--that is,
       alphabetic, numeric, and the platform's native underscore.  (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.  It also
       affects things like "\s", "\D", and the POSIX character classes, like
       "[[:graph:]]".  (See perlrecharclass for more information on all
       these.)

       The "LC_CTYPE" locale also provides the map used in transliterating
       characters between lower and uppercase.  This affects the case-mapping
       functions--"fc()", "lc()", "lcfirst()", "uc()", and "ucfirst()"; case-
       mapping interpolation with "\F", "\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 (deprecated) POSIX character-class test
       functions--"POSIX::isalpha()", "POSIX::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
       "POSIX::ispunct()" class to "POSIX::isalpha()".  Unfortunately, this
       creates big problems for regular expressions. "|" still means
       alternation even though it matches "\w".

       Starting in v5.20, Perl supports UTF-8 locales for "LC_CTYPE", but
       otherwise Perl only supports single-byte locales, such as the ISO 8859
       series.  This means that wide character locales, for example for Asian
       languages, are not supported.  The UTF-8 locale support is actually a
       superset of POSIX locales, because it is really full Unicode behavior
       as if no locale were in effect at all (except for tainting; see
       "SECURITY").  POSIX locales, even UTF-8 ones, are lacking certain
       concepts in Unicode, such as the idea that changing the case of a
       character could expand to be more than one character.  Perl in a UTF-8
       locale, will give you that expansion.  Prior to v5.20, Perl treated a
       UTF-8 locale on some platforms like an ISO 8859-1 one, with some
       restrictions, and on other platforms more like the "C" locale.  For
       releases v5.16 and v5.18, "use locale 'not_characters" could be used as
       a workaround for this (see "Unicode and UTF-8").

       Note that there are quite a few things that are unaffected by the
       current locale.  All the escape sequences for particular characters,
       "\n" for example, always mean the platform's native one.  This means,
       for example, that "\N" in regular expressions (every character but new-
       line) works on the platform character set.

       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, and within the scope of one
       of the "use locale" variants, Perl obeys the "LC_NUMERIC" locale
       information, which controls an application's idea of how numbers should
       be formatted for human readability.  In most implementations the only
       effect is to change the character used for the decimal point--perhaps
       from "."  to ",".  The functions aren't aware of such niceties as
       thousands separation and so on. (See "The localeconv function" if you
       care about these things.)

        use POSIX qw(strtod setlocale LC_NUMERIC);
        use locale;

        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 essentially takes no notice of it.  If you
       really want to use "LC_MONETARY", you can query its contents--see "The
       localeconv function"--and use the information that it returns in your
       application's own formatting of currency amounts.  However, you may
       well find that the information, voluminous and complex though it may
       be, still does not quite meet your requirements: currency formatting is
       a hard nut to crack.

       See also I18N::Langinfo and "CRNCYSTR".

   LC_TIME
       Output produced by "POSIX::strftime()", which builds a 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: "strftime()" is a
       POSIX function which uses the standard system-supplied "libc" function
       that 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 categories are not currently used by Perl itself.
       But again note that things Perl interacts with may use these, including
       extensions outside the standard Perl distribution, and by the operating
       system and its utilities.  Note especially that the string value of $!
       and the error messages given by external utilities may be changed by
       "LC_MESSAGES".  If you want to have portable error codes, use "%!".
       See Errno.


SECURITY

       Although the main discussion of Perl security issues can be found in
       perlsec, a discussion of Perl's locale handling would be incomplete if
       it did not draw your attention to locale-dependent security issues.
       Locales--particularly on systems that allow unprivileged users to build
       their own locales--are untrustworthy.  A malicious (or just plain
       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 effect.

       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 locale:

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

           Scalar true/false (or less/equal/greater) result is never tainted.

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

           Result string containing interpolated material is tainted if "use
           locale" (but not "use locale ':not_characters'") is in effect.

       o   Matching operator ("m//"):

           Scalar true/false result never tainted.

           All subpatterns, either delivered as a list-context result or as $1
           etc., are tainted if "use locale" (but not
           "use locale ':not_characters'") is in effect, and the subpattern
           regular expression contains a locale-dependent construct.  These
           constructs include "\w" (to match an alphanumeric character), "\W"
           (non-alphanumeric character), "\b" and "\B" (word-boundary and non-
           boundardy, which depend on what "\w" and "\W" match), "\s"
           (whitespace character), "\S" (non whitespace character), "\d" and
           "\D" (digits and non-digits), and the POSIX character classes, such
           as "[:alpha:]" (see "POSIX Character Classes" in perlrecharclass).

           Tainting is also likely if the pattern is to be matched case-
           insensitively (via "/i").  The exception is if all the code points
           to be matched this way are above 255 and do not have folds under
           Unicode rules to below 256.  Tainting is not done for these because
           Perl only uses Unicode rules for such code points, and those rules
           are the same no matter what the current locale.

           The matched-pattern variables, $&, "$`" (pre-match), "$'" (post-
           match), and $+ (last match) also are tainted.

       o   Substitution operator ("s///"):

           Has the same behavior as the match operator.  Also, the left
           operand of "=~" becomes tainted when "use locale" (but not
           "use locale ':not_characters'") is in effect if modified as a
           result of a substitution based on a regular expression match
           involving any of the things mentioned in the previous item, or of
           case-mapping, such as "\l", "\L","\u", "\U", or "\F".

       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()", "ucfirst()"):

           Results are tainted if "use locale" (but not
           "use locale ':not_characters'") is in effect.

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

           Results are never tainted.

       o   POSIX character class tests ("POSIX::isalnum()",
           "POSIX::isalpha()", "POSIX::isdigit()", "POSIX::isgraph()",
           "POSIX::islower()", "POSIX::isprint()", "POSIX::ispunct()",
           "POSIX::isspace()", "POSIX::isupper()", "POSIX::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 $tainted_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.


ENVIRONMENT

       PERL_SKIP_LOCALE_INIT
                   This environment variable, available starting in Perl
                   v5.20, and if it evaluates to a TRUE value, tells Perl to
                   not use the rest of the environment variables to initialize
                   with.  Instead, Perl uses whatever the current locale
                   settings are.  This is particularly useful in embedded
                   environments, see "Using embedded Perl with POSIX locales"
                   in perlembed.

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

       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.  Windows is non-
       POSIX, but Perl arranges for the following to work as described anyway.
       If the locale given by an environment variable is not valid, Perl tries
       the next lower one in priority.  If none are valid, on Windows, the
       system default locale is then tried.  If all else fails, the "C" locale
       is used.  If even that doesn't work, something is badly broken, but
       Perl tries to forge ahead with whatever the locale settinga might be.

       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 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 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_...".

   Examples
       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.


NOTES

   String "eval" and "LC_NUMERIC"
       A string eval parses its expression as standard Perl.  It is therefore
       expecting the decimal point to be a dot.  If "LC_NUMERIC" is set to
       have this be a comma instead, the parsing will be confused, perhaps
       silently.

        use locale;
        use POSIX qw(locale_h);
        setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
        my $a = 1.2;
        print eval "$a + 1.5";
        print "\n";

       prints "13,5".  This is because in that locale, the comma is the
       decimal point character.  The "eval" thus expands to:

        eval "1,2 + 1.5"

       and the result is not what you likely expected.  No warnings are
       generated.  If you do string "eval"'s within the scope of "use locale",
       you should instead change the "eval" line to do something like:

        print eval "no locale; $a + 1.5";

       This prints 2.7.

   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, in the unlikely event that you want
       to do so 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.

   Freely available locale definitions
       The Unicode CLDR project extracts the POSIX portion of many of its
       locales, available at

         http://unicode.org/Public/cldr/latest/

       There is a large collection of locale definitions at:

         http://std.dkuug.dk/i18n/WG15-collection/locales/

       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 v5.6, and more
       fully implemented in versions v5.8 and later.  See perluniintro.

       Starting in Perl v5.20, UTF-8 locales are supported in Perl, except for
       "LC_COLLATE" (use Unicode::Collate instead).  If you have Perl v5.16 or
       v5.18 and can't upgrade, you can use

           use locale ':not_characters';

       When this form of the pragma is used, only the non-character portions
       of locales are used by Perl, for example "LC_NUMERIC".  Perl assumes
       that you have translated all the characters it is to operate on into
       Unicode (actually the platform's native character set (ASCII or EBCDIC)
       plus Unicode).  For data in files, this can conveniently be done by
       also specifying

           use open ':locale';

       This pragma arranges for all inputs from files to be translated into
       Unicode from the current locale as specified in the environment (see
       "ENVIRONMENT"), and all outputs to files to be translated back into the
       locale.  (See open).  On a per-filehandle basis, you can instead use
       the PerlIO::locale module, or the Encode::Locale module, both available
       from CPAN.  The latter module also has methods to ease the handling of
       "ARGV" and environment variables, and can be used on individual
       strings.  If you know that all your locales will be UTF-8, as many are
       these days, you can use the -C command line switch.

       This form of the pragma allows essentially seamless handling of locales
       with Unicode.  The collation order will be by Unicode code point order.
       It is strongly recommended that when you need to order and sort strings
       that you use the standard module Unicode::Collate which gives much
       better results in many instances than you can get with the old-style
       locale handling.

       All the modules and switches just described can be used in v5.20 with
       just plain "use locale", and, should the input locales not be UTF-8,
       you'll get the less than ideal behavior, described below, that you get
       with pre-v5.16 Perls, or when you use the locale pragma without the
       ":not_characters" parameter in v5.16 and v5.18.  If you are using
       exclusively UTF-8 locales in v5.20 and higher, the rest of this section
       does not apply to you.

       There are two cases, multi-byte and single-byte locales.  First multi-
       byte:

       The only multi-byte (or wide character) locale that Perl is ever likely
       to support is UTF-8.  This is due to the difficulty of implementation,
       the fact that high quality UTF-8 locales are now published for every
       area of the world (<http://unicode.org/Public/cldr/latest/>), and that
       failing all that you can use the Encode module to translate to/from
       your locale.  So, you'll have to do one of those things if you're using
       one of these locales, such as Big5 or Shift JIS.  For UTF-8 locales, in
       Perls (pre v5.20) that don't have full UTF-8 locale support, they may
       work reasonably well (depending on your C library implementation)
       simply because both they and Perl store characters that take up
       multiple bytes the same way.  However, some, if not most, C library
       implementations may not process the characters in the upper half of the
       Latin-1 range (128 - 255) properly under LC_CTYPE.  To see if a
       character is a particular type under a locale, Perl uses the functions
       like "isalnum()".  Your C library may not work for UTF-8 locales with
       those functions, instead only working under the newer wide library
       functions like "iswalnum()".  However, they are treated like single-
       byte locales, and will have the restrictions described below.

       For single-byte locales, 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 isn't uniformly applied, see the note
       at the end of this section).  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.

       However, there are places where this breaks down.  Certain Perl
       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{...}".
       Prior to v5.20, It is therefore a bad idea to use "\p{}" or "\N{}"
       under plain "use locale"--unless you can guarantee that the locale will
       be a ISO8859-1.  Use POSIX character classes instead.

       Another problem with this approach is that operations that cross the
       single byte/multiple byte boundary are not well-defined, and so are
       disallowed.  (This boundary is between the codepoints at 255/256.)  For
       example, lower casing LATIN CAPITAL LETTER Y WITH DIAERESIS (U+0178)
       should return LATIN SMALL LETTER Y WITH DIAERESIS (U+00FF).  But in the
       Greek locale, for example, there is no character at 0xFF, and Perl has
       no way of knowing what the character at 0xFF is really supposed to
       represent.  Thus it disallows the operation.  In this mode, the
       lowercase of U+0178 is itself.

       The same problems ensue 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.  This is not a
       problem provided you make certain that all locales will always and only
       be either an ISO8859-1, or, if you don't have a deficient C library, a
       UTF-8 locale.

       Still another problem is that this approach can lead to two code points
       meaning the same character.  Thus in a Greek locale, both U+03A7 and
       U+00D7 are GREEK CAPITAL LETTER CHI.

       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.  (However, the Unicode-supplied locales should be
       better, and there is a feed back mechanism to correct any problems.
       See "Freely available locale definitions".)

       If you have Perl v5.16, the problems mentioned above go away if you use
       the ":not_characters" parameter to the locale pragma (except for vendor
       bugs in the non-character portions).  If you don't have v5.16, and 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, if the collation for your locales works, it
       runs faster under locales than under Unicode::Collate; and you gain
       access to such things as the local currency symbol and the names of the
       months and days of the week.  (But to hammer home the point, in v5.16,
       you get this access without the downsides of locales by using the
       ":not_characters" form of the pragma.)

       Note: The policy of using locale rules for code points that can fit in
       a byte, and Unicode rules for those that can't is not uniformly
       applied.  Pre-v5.12, it was somewhat haphazard; in v5.12 it was applied
       fairly consistently to regular expression matching except for bracketed
       character classes; in v5.14 it was extended to all regex matches; and
       in v5.16 to the casing operations such as "\L" and "uc()".  For
       collation, in all releases, the system's "strxfrm()" function is
       called, and whatever it does is what you get.


BUGS

   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 <perlbug@perl.org>, 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.  If you have the source for Perl, include in the perlbug email
       the output of the test described above in "Testing for broken locales".


SEE ALSO

       I18N::Langinfo(3), perluniintro(1), perlunicode(1), open(3), "isalnum(3)"
       in POSIX, "isalpha(3)" in POSIX, "isdigit(3)" in POSIX, "isgraph(3)" in
       POSIX, "islower(3)" in POSIX, "isprint(3)" in POSIX, "ispunct(3)"
       in POSIX, "isspace(3)" in POSIX, "isupper(3)" in POSIX, "isxdigit(3)" in
       POSIX, "localeconv(3)" in POSIX, "setlocale(3)" in POSIX, "strcoll(3)" in
       POSIX, "strftime(3)" in POSIX, "strtod(3)" in POSIX, "strxfrm(3)" in POSIX.

       For special considerations when Perl is embedded in a C program, see
       "Using embedded Perl with POSIX locales" in perlembed(1).


HISTORY

       Jarkko Hietaniemi's original perli18n.pod heavily hacked by Dominic
       Dunlop, assisted by the perl5-porters.  Prose worked over a bit by Tom
       Christiansen, and updated by Perl 5 porters.



perl v5.20.0                      2014-05-26                     perllocale(1)

perl 5.20.0 - Generated Sat May 31 07:42:35 CDT 2014