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       Perl supports language-specific notions of data such as
       "is this a letter", "what is the uppercase equivalent of
       this letter", and "which of these letters comes first".
       These are important issues, especially for languages other
       than English--but also for English: it would be naieve to
       imagine that "A-Za-z" defines all the "letters" needed to
       write in English. Perl is also aware that some character
       other than '.' may be preferred as a decimal point, and
       that output date representations may be language-specific.
       The process of making an application take account of its
       users' preferences in such matters is called internation­
       alization (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 stan­
       dardized (ISO C, XPG4, POSIX 1.c) method called "the
       locale system". The locale system is controlled per appli­
       cation 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() func­
           tion is a documented part of its C library.

       ·   Definitions for locales that you use must be
           installed.  You, or your system administrator, must
           make sure that this is the case. The available
           locales, the location in which they are kept, and the
           manner in which they are installed all vary from sys­
           tem to system.  Some systems provide only a few, hard-
           wired locales and do not allow more to be added.  Oth­
           ers 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

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


       The use locale pragma

       By default, Perl ignores the current locale.  The
       "use locale" pragma tells Perl to use the current locale
       for some operations:

       ·   The comparison operators ("lt", "le", "cmp", "ge", and
           "gt") and the POSIX string collation functions str­
           coll() and strxfrm() use "LC_COLLATE".  sort() is also
           affected if used without an explicit comparison func­
           tion, 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 discus­
           sion in "Category LC_COLLATE: Collation".

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

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

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

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

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

       The string result of any operation that uses locale infor­
       mation 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

               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 code­
       set.  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

       If no second argument is provided and the category is
       LC_ALL, the result is implementation-dependent.  It may be
       a string of concatenated locales names (separator also
       implementation-dependent) or a single locale name.  Please
       consult your setlocale(3) for details.

       If a second argument is given and it corresponds to a
       valid locale, the locale for the category is set to that
       value, and the function returns the now-current locale
       value.  You can then use this in yet another call to set­
       locale().  (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 environ­
       ment 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.

               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 directo­
       ries where the configuration resides have not been.  The
       basic form of the name is language_territory.codeset, but
       the latter parts after language are not always present.
       The language and country are usually from the standards
       ISO 3166 and ISO 639, the two-letter abbreviations for the
       countries and the languages of the world, respectively.
       The codeset part often mentions some ISO 8859 character
       set, the Latin codesets.  For example, "ISO 8859-1" is the
       so-called "Western European codeset" that can be used to
       encode most Western European languages adequately.  Again,
       there are several ways to write even the name of that one
       standard.  Lamentably.

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

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

       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 sup­
       posed to work no matter what.  This usually means your
       locale settings were wrong, they mention locales your sys­
       tem 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

       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 envi­
       ronment 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 ENVIRON­
       MENT 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' alphabeti­
       cally 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 documenta­
       tion 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
       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 sys­
       tem'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 sys­
       tem.  In our example error message, environment variables
       affecting the locale are listed in the order of decreasing
       importance (and unset variables do not matter).  There­
       fore, 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-men­
       tioned 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.

               # 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

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

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

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

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

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

           Sun? [yes/no]

       See I18N::Langinfo for more information.


       The following subsections describe basic locale cate­
       gories.  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_COL­
       LATE" environment variable to determine the application's
       notions on collation (ordering) of characters.  For exam­
       ple, '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
       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 sys­
       tems--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

       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 consid­
       ered to be alphanumeric by your application.  For strict
       matching of (mundane) letters and digits--for example, in
       command strings--locale-aware applications should use "\w"
       inside a "no locale" block.  See "SECURITY".

       Category LC_NUMERIC: Numeric Formatting

       In the scope of "use locale", Perl obeys the "LC_NUMERIC"
       locale information, which controls an application's idea
       of how numbers should be formatted for human readability
       by the printf(), sprintf(), and write() functions.
       String-to-numeric conversion by the POSIX::strtod() func­
       tion 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

       Output produced by print() is also affected by the current
       locale: it depends on whether "use locale" or "no locale"
       is in effect, and corresponds to what you'd get from
       printf() in the "C" locale.  The same is true for Perl's
       internal conversions between numeric and string formats:

               use POSIX qw(strtod);
               use locale;

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

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

               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

       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 for­
       matted 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 cur­
       rent locale:

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

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

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

       Other categories

       The remaining locale category, "LC_MESSAGES" (possibly
       supplemented by others in particular implementations) is
       not currently used by Perl--except possibly to affect the
       behavior of library functions called by extensions outside
       the standard Perl distribution and by the operating system
       and its utilities.  Note especially that the string value
       of $! and the error messages given by external utilities
       may be changed by "LC_MESSAGES".  If you want to have
       portable error codes, use "%!".  See Errno.


       Although the main discussion of Perl security issues can
       be found in perlsec, a discussion of Perl's locale han­
       dling would be incomplete if it did not draw your atten­
       tion to locale-dependent security issues.  Locales--par­
       ticularly 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 pos­

       ·   An application that takes the trouble to use informa­
           tion 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 strf­
           time() could be manipulated to advantage by a mali­
           cious 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 modi­
       fied 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 vigi­
       lance--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 untrustwor­
       thy 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

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

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

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

       ·   Matching operator ("m//"):

           Scalar true/false result never tainted.

           Subpatterns, either delivered as a list-context result
           or as $1 etc.  are tainted if "use locale" is in
           effect, and the subpattern regular expression contains
           "\w" (to match an alphanumeric character), "\W"
           (non-alphanumeric character), "\s" (white-space char­
           acter), or "\S" (non white-space character).  The
           matched-pattern variable, $&, $` (pre-match), $'
           (post-match), and $+ (last match) are also tainted if
           Results are never tainted because otherwise even out­
           put from print, for example "print(1/7)", should be
           tainted if "use locale" is in effect.

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

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

       ·   POSIX locale-dependent functions (localeconv(), str­
           coll(), 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 exam­
       ple--which still ignores locale information--runs, creat­
       ing 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

                   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 applica­
       tion's opinion on data.

       LC_ALL      "LC_ALL" is the "override-all" locale environ­
                   ment variable. If set, it overrides all the
                   rest of the locale environment variables.

       LANGUAGE    NOTE: "LANGUAGE" is a GNU extension, it
                   affects you only if you are using the GNU
                   libc.  This is the case if you are using e.g.
                   Linux.  If you are using "commercial" UNIXes
                   you are most probably not using GNU libc and
                   you can ignore "LANGUAGE".

                   However, in the case you are using "LANGUAGE":
                   it affects the language of informational,
                   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 docu­
                   mentation 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.
                   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 cat­
                   egory-specific "LC_...".


       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 func­
       tion").  By default, Perl still behaves this way for back­
       ward compatibility.  If you want a Perl application to pay
       attention to locale information, you must use the
       "use locale" pragma (see "The use locale pragma") to
       instruct it to do so.

       Versions of Perl from 5.002 to 5.003 did use the
       "LC_CTYPE" information if available; that is, "\w" did
       understand what were the letters according to the locale
       environment 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 dic­
       tated more by the operating system's implementation of the
       locale system than by Perl.

       ftp://dkuug.dk/i18n/WG15-collection .  You should be aware
       that it is unsupported, and is not claimed to be fit for
       any purpose.  If your system allows installation of arbi­
       trary locales, you may find the definitions useful as they
       are, or as a basis for the development of your own

       I18n and l10n

       "Internationalization" is often abbreviated as i18n
       because its first and last letters are separated by eigh­
       teen others.  (You may guess why the internalin ... inter­
       naliti ... i18n tends to get abbreviated.)  In the same
       way, "localization" is often abbreviated to l10n.

       An imperfect standard

       Internationalization, as defined in the C and POSIX stan­
       dards, can be criticized as incomplete, ungainly, and hav­
       ing too large a granularity.  (Locales apply to a whole
       process, when it would arguably be more useful to have
       them apply to a single thread, window group, or whatever.)
       They also have a tendency, like standards groups, to
       divide the world into nations, when we all know that the
       world can equally well be divided into bankers, bikers,
       gamers, and so on.  But, for now, it's the only standard
       we've got.  This may be construed as a bug.

Unicode and UTF-8

       The support of Unicode is new starting from Perl version
       5.6, and more fully implemented in the version 5.8.  See
       perluniintro and perlunicode for more details.

       Usually locale settings and Unicode do not affect each
       other, but there are exceptions, see "Locales" in perluni­
       code for examples.


       Broken systems

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


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

perl v5.8.1                 2003-09-02              PERLLOCALE(1)

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