perllocale

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NAME

       perllocale - Perl locale handling (internationalization
       and localization)


DESCRIPTION

       Perl supports language-specific notions of data such as
       "is this a letter", "what is the uppercase equivalent of
       this letter", and "which of these letters comes first".
       These are important issues, especially for languages other
       than English - but also for English: it would be very
       naieve to think that A-Za-z defines all the "letters".
       Perl is also aware that some character other than '.' may
       be preferred as a decimal point, and that output date
       representations may be language-specific.  The process of
       making an application take account of its users'
       preferences in such matters is called internationalization
       (often abbreviated as i18n); telling such an application
       about a particular set of preferences is known as
       localization (l10n).

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

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


PREPARING TO USE LOCALES

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

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

       o   Definitions for the locales which 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, 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 which 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 section
       on The use locale pragma) where appropriate, and at least
       one of the following must be true:

       o   The locale-determining environment variables (see the
           section on ENVIRONMENT) must be correctly set up,
           either by yourself, or by the person who set up your
           system account, at the time the application is
           started.

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


USING LOCALES

       The use locale pragma

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

       o   The comparison operators (lt, le, cmp, ge, and gt) and
           the POSIX string collation functions strcoll() and
           strxfrm() use LC_COLLATE.  sort() is also affected if
           it is used without an explicit comparison function
           because it uses cmp by default.

           Note: eq and ne are unaffected by the locale: they
           always perform a byte-by-byte 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 byte-by-byte comparison, and only returns 0 (equal)
           if the operands are bit-for-bit 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 the section on Category LC_COLLATE:
           Collation.

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

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

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

       LC_COLLATE, LC_CTYPE, and so on, are discussed further in
       the section on LOCALE CATEGORIES.

       The default behavior returns with no locale or on reaching
       the end of the enclosing block.

       Note that the string result of any operation that uses
       locale information is tainted, as it is possible for a
       locale to be untrustworthy.  See the section on SECURITY.

       The setlocale function

       You can switch locales as often as you wish at run time
       with the POSIX::setlocale() function:

               # This functionality not usable prior to Perl 5.004
               require 5.004;

               # Import locale-handling tool set from POSIX module.
               # This example uses: setlocale -- the function call
               #                    LC_CTYPE -- explained below
               use POSIX qw(locale_h);

               # query and save the old locale
               $old_locale = setlocale(LC_CTYPE);

               setlocale(LC_CTYPE, "fr_CA.ISO8859-1");
               # LC_CTYPE now in locale "French, Canada, codeset ISO 8859-1"

               setlocale(LC_CTYPE, "");
               # LC_CTYPE now reset to default defined by LC_ALL/LC_CTYPE/LANG
               # environment variables.  See below for documentation.

               # restore the old locale
               setlocale(LC_CTYPE, $old_locale);

       The first argument of setlocale() gives the category, the
       second the locale.  The category tells in what aspect of
       data processing you want to apply locale-specific rules.
       Category names are discussed in the section on LOCALE
       CATEGORIES and the section on 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, the function returns a
       string naming the current locale for the category.  You
       can use this value as the second argument in a subsequent
       call to setlocale().  If 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 use this in a subsequent
       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
       that 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 which
       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 the implementation of
       your system's C library.

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

       For further information about the categories, consult the
       setlocale(3) manpage.  For the locales available in your
       system, also consult the setlocale(3) manpage and see
       whether it leads you to the list of the 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

       and see whether they list something resembling these

               en_US.ISO8859-1     de_DE.ISO8859-1     ru_RU.ISO8859-5
               en_US               de_DE               ru_RU
               en                  de                  ru
               english             german              russian
               english.iso88591    german.iso88591     russian.iso88595

       Sadly, even though the calling interface for setlocale()
       has been standardized, the names of the locales and the
       directories where the configuration is, have not.  The
       basic form of the name is
       language_country/territory.codeset, but the latter parts
       are not always present.

       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 and the second by the POSIX standard.  What
       they define is 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.

       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
       section on 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 formatting variable
       names such as decimal_point and thousands_sep; the values
       are the corresponding values.  See the localeconv entry in
       the POSIX (3) manpage for a longer example, which lists
       all the categories an implementation might be expected to
       provide; some provide more and others fewer, however.
       Note that you don't need use locale: as a function with
       the job of querying the locale, localeconv() always
       observes the current locale.

       Here's a simple-minded example program which rewrites its
       command line parameters as integers formatted correctly 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 = 3 unless $grouping;

               # Format command line params for current locale
               for (@ARGV) {
                   $_ = int;    # Chop non-integer part
                   1 while
                   s/(\d)(\d{$grouping}($|$thousands_sep))/$1$thousands_sep$2/;
                   print "$_";
               }
               print "\n";



LOCALE CATEGORIES

       The subsections which follow describe basic locale
       categories.  As well as these, there are some combination
       categories which allow the manipulation of more than one
       basic category at a time.  See the section on ENVIRONMENT
       for a discussion of these.

       Category LC_COLLATE: Collation

       When in the scope of use locale, Perl looks to the
       LC_COLLATE environment variable to determine the
       application's notions on the collation (ordering) of
       characters.  ('b' follows 'a' in Latin alphabets, but
       where do 'a' and 'aa' belong?)

       Here is a code snippet that will tell you what are the
       alphanumeric characters in the current locale, in the
       locale 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 the section on USING LOCALES, cmp compares
       according to the current collation locale when use locale
       is in effect, but falls back to a byte-by-byte comparison
       for strings which 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 which ignores space
       characters completely, and which folds case.

       If you have a single string which 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 byte-by-byte comparisons against other
       transformed strings during collation.  "Under the hood",
       locale-affected Perl comparison operators call strxfrm()
       for both their operands, then do a byte-by-byte 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.
       In fact, it doesn't save anything: Perl magic (see the
       section on Magic Variables in the perlguts manpage)
       creates the transformed version of a string the first time
       it's needed in a comparison, then keeps it 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.  And 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, as
       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

       When in the scope of use locale, Perl obeys the LC_CTYPE
       locale setting.  This controls the application's notion of
       which characters are alphabetic.  This affects Perl's \w
       regular expression metanotation, which stands for
       alphanumeric characters - that is, alphabetic and numeric
       characters.  (Consult the perlre manpage for more
       information about regular expressions.)  Thanks to
       LC_CTYPE, depending on your locale setting, characters
       like 'ae', '`', 'ss', and 'o' may be understood as \w
       characters.

       The LC_CTYPE locale also provides the map used in
       translating characters between lower and uppercase.  This
       affects the case-mapping functions - lc(), lcfirst, uc()
       and ucfirst(); case-mapping interpolation with \l, \L, \u
       or <\U> in double-quoted strings and in s///
       substitutions; and case-independent regular expression
       pattern matching using the i modifier.

       Finally, LC_CTYPE affects the POSIX character-class test
       functions - isalpha(), islower() and so on.  For example,
       if you move from the "C" locale to a 7-bit Scandinavian
       one, you may find - possibly to your surprise - that "|"
       moves from the ispunct() class to isalpha().

       Note: A broken or malicious LC_CTYPE locale definition may
       result in clearly ineligible characters being considered
       to be alphanumeric by your application.  For strict
       matching of (unaccented) letters and digits - for example,
       in command strings - locale-aware applications should use
       \w inside a no locale block.  See the section on SECURITY.

       Category LC_NUMERIC: Numeric Formatting

       When in the scope of use locale, Perl obeys the LC_NUMERIC
       locale information, which controls application's idea of
       how numbers should be formatted for human readability by
       the printf(), sprintf(), and write() functions.  String to
       numeric conversion by the POSIX::strtod() function is also
       affected.  In most implementations the only effect is to
       change the character used for the decimal point - perhaps
       from '.'  to ',': these functions aren't aware of such
       niceties as thousands separation and so on.  (See the
       section on The localeconv function if you care about these
       things.)

       Note that output produced by print() is never affected by
       the current locale: it is independent of 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-independent conversion to string

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


       Category LC_MONETARY: Formatting of monetary amounts

       The C standard defines the LC_MONETARY category, but no
       function that is affected by its contents.  (Those with
       experience of standards committees will recognize that the
       working group decided to punt on the issue.)
       Consequently, Perl takes no notice of it.  If you really
       want to use LC_MONETARY, you can query its contents - see
       the section on 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, though voluminous and complex,
       does not quite meet your requirements: currency formatting
       is a hard nut to crack.

       LC_TIME

       The 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 the long month names in the
       current locale:

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

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




       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 which
       are not part of the standard Perl distribution.


SECURITY

       While the main discussion of Perl security issues can be
       found in the perlsec manpage, 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 which 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 which 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   If the decimal point character in the LC_NUMERIC
           locale is surreptitiously changed from a dot to a
           comma, sprintf("%g", 0.123456e3) produces a string
           result of "123,456". Many people would interpret this
           as one hundred and twenty-three thousand, four hundred
           and fifty-six.

       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 which takes the trouble to use the
           information in LC_MONETARY may format debits as if
           they were credits and vice versa if that locale has
           been subverted.  Or it make may 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
       maliciously be modified presents similar challenges.
       Similarly, they are not specific to Perl: any programming
       language which allows you to write programs which take
       account of their environment exposes you to these issues.

       Perl cannot protect you from all of the 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 the perlsec manpage) to
       mark string results which become locale-dependent, and
       which may be untrustworthy in consequence.  Here is a
       summary of the tainting behavior of operators and
       functions which may be affected by the locale:

       Comparison operators (lt, le, ge, gt and cmp):
           Scalar true/false (or less/equal/greater) result is
           never tainted.

       Case-mapping interpolation (with \l, \L, \u or <\U>)
           Result string containing interpolated material is
           tainted if use locale is in effect.

       Matching operator (m//):
           Scalar true/false result never tainted.

           Subpatterns, either delivered as an array-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 character),
           or \S (non white-space character).  The matched
           pattern variable, $&, $` (pre-match), $' (post-match),
           and $+ (last match) are also tainted if use locale is
           in effect and the regular expression contains \w, \W,
           \s, or \S.

       Substitution operator (s///):
           Has the same behavior as the match operator.  Also,
           the left operand of =~ becomes tainted when use locale
           in effect, if it is modified as a result of a
           substitution based on a regular expression match
           involving \w, \W, \s, or \S; or of case-mapping with
           \l, \L,\u or <\U>.

       In-memory formatting function (sprintf()):
           Result is tainted if "use locale" is in effect.

       Output formatting functions (printf() and write()):
           Success/failure result is never tainted.

       Case-mapping functions (lc(), lcfirst(), uc(), ucfirst()):
           Results are tainted if use locale is in effect.

       POSIX locale-dependent functions (localeconv(), strcoll(),
           strftime(), strxfrm()):
           Results are never tainted.

       POSIX character class tests (isalnum(), isalpha(),
           isdigit(), isgraph(), islower(), isprint(), ispunct(),
           isspace(), isupper(), isxdigit()):
           True/false results are never tainted.

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

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

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

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

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

               #/usr/local/bin/perl -T

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

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

       Compare this with a very similar program which is locale-
       aware:

               #/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 when use locale is
       in effect.


ENVIRONMENT


       PERL_BADLANG
                   A string that can suppress Perl's warning
                   about failed locale settings at startup.
                   Failure can occur if the locale support in the
                   operating system is lacking (broken) is 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
                   which does not evaluate to integer zero - that
                   is "0" or "" - Perl will complain about locale
                   setting failures.

                   NOTE: PERL_BADLANG only gives you a way to
                   hide the warning message.  The message tells
                   about some problem in your system's locale
                   support, and you should investigate what the
                   problem is.

       The following environment variables are not specific to
       Perl: They are part of the standardized (ISO C, XPG4,
       POSIX 1.c) setlocale() method for controlling an
       application's opinion on data.

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

       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_....


NOTES

       Backward compatibility

       Versions of Perl prior to 5.004 mostly ignored locale
       information, generally behaving as if something similar to
       the "C" locale (see the section on The setlocale function)
       was always in force, even if the program environment
       suggested otherwise.  By default, Perl still behaves this
       way so as to maintain backward compatibility.  If you want
       a Perl application to pay attention to locale information,
       you must use the use locale pragma (see the section on 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 that was available, that is, \w did
       understand what are the letters according to the locale
       environment variables.  The problem was that the user had
       no control over the feature: if the C library supported
       locales, Perl used them.

       I18N:Collate obsolete

       In versions of Perl prior to 5.004 per-locale collation
       was possible using the I18N::Collate library module.  This
       module is now mildly obsolete and should be avoided in new
       applications.  The LC_COLLATE functionality is now
       integrated into the Perl core language: One can use
       locale-specific scalar data completely normally with use
       locale, so there is no longer any need to juggle with the
       scalar references of I18N::Collate.

       Sort speed and memory use impacts

       Comparing and sorting by locale is usually slower than the
       default sorting; slow-downs of two to four times have been
       observed.  It will also consume more memory: once a Perl
       scalar variable has participated in any string comparison
       or sorting operation obeying the locale collation rules,
       it will take 3-15 times more memory than before.  (The
       exact multiplier depends on the string's contents, the
       operating system and the locale.) These downsides are
       dictated more by the operating system's implementation of
       the locale system than by Perl.

       write() and LC_NUMERIC

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

       Freely available locale definitions

       There is a large collection of locale definitions at
       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 the 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.  But, for now, it's the only standard
       we've got.  This may be construed as a bug.


BUGS

       Broken systems

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


SEE ALSO

       the isalnum entry in the POSIX (3) manpage, the isalpha
       entry in the POSIX (3) manpage, the isdigit entry in the
       POSIX (3) manpage, the isgraph entry in the POSIX (3)
       manpage, the islower entry in the POSIX (3) manpage, the
       isprint entry in the POSIX (3) manpage, the ispunct entry
       in the POSIX (3) manpage, the isspace entry in the POSIX
       (3) manpage, the isupper entry in the POSIX (3) manpage,
       the isxdigit entry in the POSIX (3) manpage, the
       localeconv entry in the POSIX (3) manpage, the setlocale
       entry in the POSIX (3) manpage, the strcoll entry in the
       POSIX (3) manpage, the strftime entry in the POSIX (3)
       manpage, the strtod entry in the POSIX (3) manpage, the
       strxfrm entry in the POSIX (3) manpage


HISTORY

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

       Last update: Wed Jan 22 11:04:58 EST 1997
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