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

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

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

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

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

       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

       If you want a Perl application to process and present your data

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

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

       The operations that are affected by locale are:

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

           Note: "eq" and "ne" are unaffected by locale: they always perform a
           char-by-char comparison of their scalar operands.  What's more, if
           "cmp" finds that its operands are equal according to the collation
           sequence specified by the current locale, it goes on to perform a
           char-by-char comparison, and only returns 0 (equal) if the operands
           are char-for-char identical.  If you really want to know whether
           two strings--which "eq" and "cmp" may consider different--are equal
           as far as collation in the locale is concerned, see the discussion
           in "Category LC_COLLATE: Collation".

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

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

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

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

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

       The string result of any operation that uses locale information is
       tainted, as it is possible for a locale to be untrustworthy.  See

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

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

       The first argument of setlocale() gives the category, the second the
       locale.  The category tells in what aspect of data processing you want
       to apply locale-specific rules.  Category names are discussed in
       "LOCALE CATEGORIES" and "ENVIRONMENT".  The locale is the name of a
       collection of customization information corresponding to a particular
       combination of language, country or territory, and codeset.  Read on
       for hints on the naming of locales: not all systems name locales as in
       the example.

       If no second argument is provided and the category is something else
       than LC_ALL, the function returns a string naming the current locale
       for the category.  You can use this value as the second argument in a
       subsequent call to setlocale().

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

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

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

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

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

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

               locale -a


               en_US               de_DE               ru_RU
               en                  de                  ru
               english             german              russian
               english.iso88591    german.iso88591     russian.iso88595
               english.roman8                          russian.koi8r

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

       Two special locales are worth particular mention: "C" and "POSIX".
       Currently these are effectively the same locale: the difference is
       mainly that the first one is defined by the C standard, the second by
       the POSIX standard.  They define the default locale in which every
       program starts in the absence of locale information in its environment.
       (The default default locale, if you will.)  Its language is (American)
       English and its character codeset ASCII.  Warning. The C locale
       delivered by some vendors may not actually exactly match what the C
       standard calls for.  So beware.

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

       You may encounter the following warning message at Perl startup:

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

       This means that your locale settings had LC_ALL set to "En_US" and LANG
       exists but has no value.  Perl tried to believe you but could not.
       Instead, Perl gave up and fell back to the "C" locale, the default
       locale that is supposed to work no matter what.  This usually means
       your locale settings were wrong, they mention locales your system has
       never heard of, or the locale installation in your system has problems
       (for example, some system files are broken or missing).  There are
       quick and temporary fixes to these problems, as well as more thorough
       and lasting fixes.

   Temporarily fixing locale problems
       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

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

               export LC_ALL

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

               setenv LC_ALL en_US.ISO8859-1

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

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

       If you do not know what shell you have, consult your local helpdesk or
       the equivalent.

   Permanently fixing locale problems
       The slower but superior fixes are when you may be able to yourself fix
       the misconfiguration of your own environment variables.  The
       mis(sing)configuration of the whole system's locales usually requires
       the help of your friendly system administrator.

       First, see earlier in this document about "Finding locales".  That
       tells how to find which locales are really supported--and more
       importantly, installed--on your system.  In our example error message,
       environment variables affecting the locale are listed in the order of
       decreasing importance (and unset variables do not matter).  Therefore,
       having LC_ALL set to "En_US" must have been the bad choice, as shown by
       the error message.  First try fixing locale settings listed first.

       Second, if using the listed commands you see something exactly (prefix
       matches do not count and case usually counts) like "En_US" without the
       quotes, then you should be okay because you are using a locale name
       that should be installed and available in your system.  In this case,
       see "Permanently fixing your system's locale configuration".

   Permanently fixing your system's locale configuration
       This is when you see something like:

   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

   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

               use POSIX qw(locale_h);

               # Get a reference to a hash of locale-dependent info
               $locale_values = localeconv();

               # Output sorted list of the values
               for (sort keys %$locale_values) {
                   printf "%-20s = %s\n", $_, $locale_values->{$_}

       localeconv() takes no arguments, and returns a reference to a hash.
       The keys of this hash are variable names for formatting, such as
       "decimal_point" and "thousands_sep".  The values are the corresponding,
       er, values.  See "localeconv" in POSIX for a longer example listing the
       categories an implementation might be expected to provide; some provide
       more and others fewer.  You don't need an explicit "use locale",
       because localeconv() always observes the current locale.

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

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

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

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

               # grouping and mon_grouping are packed lists
               # of small integers (characters) telling the
               # grouping (thousand_seps and mon_thousand_seps
               # being the group dividers) of numbers and
               # monetary quantities.  The integers' meanings:
               # Format command line params for current locale
               for (@ARGV) {
                   $_ = int;    # Chop non-integer part
                   1 while
                   print "$_";
               print "\n";

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

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

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

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

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

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

           Sun? [yes/no]

       See I18N::Langinfo for more information.

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

   Category LC_COLLATE: Collation
       In the scope of "use locale", Perl looks to the "LC_COLLATE"
       environment variable to determine the application's notions on
       collation (ordering) of characters.  For example, "b" follows "a" in
       Latin alphabets, but where do "a" and "aa" belong?  And while "color"
       follows "chocolate" in English, what about in Spanish?

       The following collations all make sense and you may meet any of them if
       you "use locale".

               A B C D E a b c d e
               A a B b C c D d E e
               a A b B c C d D e E
               a b c d e A B C D E

       Here is a code snippet to tell what "word" characters are in the
       "use locale" has appeared earlier in the same block) must be used for
       sorting raw binary data, whereas the locale-dependent collation of the
       first example is useful for natural text.

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

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

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

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

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

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

       Note: "use locale" isn't shown in some of these examples because it
       isn't needed: strcoll() and strxfrm() exist only to generate locale-
       dependent results, and so always obey the current "LC_COLLATE" locale.

   Category LC_CTYPE: Character Types
       In the scope of "use locale", Perl obeys the "LC_CTYPE" locale setting.
       This controls the application's notion of which characters are
       and "s///" substitutions; and case-independent regular expression
       pattern matching using the "i" modifier.

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

       Note: A broken or malicious "LC_CTYPE" locale definition may result in
       clearly ineligible characters being considered to be alphanumeric by
       your application.  For strict matching of (mundane) ASCII letters and
       digits--for example, in command strings--locale-aware applications
       should use "\w" with the "/a" regular expression modifier.  See

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

       Output produced by print() is also affected by the current locale: it
       corresponds to what you'd get from printf() in the "C" locale.  The
       same is true for Perl's internal conversions between numeric and string

               use POSIX qw(strtod setlocale LC_NUMERIC);

               setlocale LC_NUMERIC, "";

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

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

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

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

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

       See also I18N::Langinfo and "RADIXCHAR".

   Category LC_MONETARY: Formatting of monetary amounts
       The C standard defines the "LC_MONETARY" category, but not a function
       that is affected by its contents.  (Those with experience of standards
       committees will recognize that the working group decided to punt on the
       issue.)  Consequently, Perl takes no notice of it.  If you really want
       to use "LC_MONETARY", you can query its contents--see "The localeconv
       (full month name) for the first month of the year would be "janvier".
       Here's how to get a list of long month names in the current locale:

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

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

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

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

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

       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" or "\U")

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

       o   Matching operator ("m//"):

           Scalar true/false result never tainted.

           Subpatterns, either delivered as a list-context result or as $1
           etc.  are tainted if "use locale" is in effect, and the subpattern
           regular expression contains "\w" (to match an alphanumeric
           character), "\W" (non-alphanumeric character), "\s" (whitespace
           character), or "\S" (non whitespace character).  The matched-
           pattern variable, $&, $` (pre-match), $' (post-match), and $+ (last
           match) are also tainted if "use locale" is in effect and the
           regular expression contains "\w", "\W", "\s", or "\S".

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

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

       o   Output formatting functions (printf() and write()):

           Results are never tainted because otherwise even output from print,
           for example "print(1/7)", should be tainted if "use locale" is in

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

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

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

           Results are never tainted.

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

           True/false results are never tainted.

                   or warn "Open of $untainted_output_file failed: $!\n";

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

               #/usr/local/bin/perl -T

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

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

       Compare this with a similar but locale-aware program:

               #/usr/local/bin/perl -T

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

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

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

                   A string that can suppress Perl's warning about failed
                   locale settings at startup.  Failure can occur if the
                   locale support in the operating system is lacking (broken)
                   in some way--or if you mistyped the name of a locale when
                   you set up your environment.  If this environment variable
                   is absent, or has a value that does not evaluate to integer
                   zero--that is, "0" or ""-- Perl will complain about locale
                   setting failures.

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

                   On Debian systems, if the DPKG_RUNNING_VERSION environment
                   variable is set (to any value), the locale failure warnings
                   will be suppressed just like with a zero PERL_BADLANG
                   setting. This is done to avoid floods of spurious warnings
                   during system upgrades.  See
                   are most probably not using GNU libc and you can ignore

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

       LC_CTYPE    In the absence of "LC_ALL", "LC_CTYPE" chooses the
                   character type locale.  In the absence of both "LC_ALL" and
                   "LC_CTYPE", "LANG" chooses the character type locale.

       LC_COLLATE  In the absence of "LC_ALL", "LC_COLLATE" chooses the
                   collation (sorting) locale.  In the absence of both
                   "LC_ALL" and "LC_COLLATE", "LANG" chooses the collation

       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

       LANG        "LANG" is the "catch-all" locale environment variable. If
                   it is set, it is used as the last resort after the overall
                   "LC_ALL" and the category-specific "LC_...".

       The LC_NUMERIC controls the numeric output:

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

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

       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

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

   write() and LC_NUMERIC
       If a program's environment specifies an LC_NUMERIC locale and "use
       locale" is in effect when the format is declared, the locale is used to
       specify the decimal point character in formatted output.  Formatted
       output cannot be controlled by "use locale" at the time when write() is

   Freely available locale definitions
       There is a large collection of locale definitions at:

       You should be aware that it is unsupported, and is not claimed to be
       fit for any purpose.  If your system allows installation of arbitrary
       locales, you may find the definitions useful as they are, or as a basis
       for the development of your own locales.

   I18n and l10n
       "Internationalization" is often abbreviated as i18n because its first
       and last letters are separated by eighteen others.  (You may guess why
       the internalin ... internaliti ... i18n tends to get abbreviated.)  In
       the same way, "localization" is often abbreviated to l10n.

   An imperfect standard
       Internationalization, as defined in the C and POSIX standards, can be
       criticized as incomplete, ungainly, and having too large a granularity.
       (Locales apply to a whole process, when it would arguably be more
       useful to have them apply to a single thread, window group, or
       whatever.)  They also have a tendency, like standards groups, to divide
       tend to work reasonably well in Perl, simply because both they and Perl
       store characters that take up multiple bytes the same way.

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

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

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

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

   Broken systems
       In certain systems, the operating system's locale support is broken and
       cannot be fixed or used by Perl.  Such deficiencies can and will result
       in mysterious hangs and/or Perl core dumps when "use locale" is in
       effect.  When confronted with such a system, please report in
       excruciating detail to <>, and also contact your
       vendor: bug fixes may exist for these problems in your operating
       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 v5.14.2                      2016-03-01                     PERLLOCALE(1)
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