PERLLOCALE(1)    Perl Programmers Reference Guide   PERLLOCALE(1)

NNAAMMEE
       perllocale - Perl locale handling (internationalization
       and localization)

DDEESSCCRRIIPPTTIIOONN
       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
       iinntteerrnnaattiioonnaalliizzaattiioonn (often abbreviated as ii1188nn); telling
       such an application about a particular set of preferences
       is known as llooccaalliizzaattiioonn (ll1100nn).

       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.

       NNOOTTEE: 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 aallwwaayyss uses the current locale - see
       the section on NOTES.

PPRREEPPAARRIINNGG TTOO UUSSEE LLOOCCAALLEESS
       If Perl applications are to understand and present your
       data correctly according a locale of your choice, aallll of
       the following must be true:

       o   YYoouurr ooppeerraattiinngg ssyysstteemm mmuusstt ssuuppppoorrtt tthhee llooccaallee ssyysstteemm.
           If it does, you should find that the setlocale()
           function is a documented part of its C library.

       o   DDeeffiinniittiioonnss ffoorr llooccaalleess tthhaatt yyoouu uussee mmuusstt bbee
           iinnssttaalllleedd.  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   PPeerrll mmuusstt bbeelliieevvee tthhaatt tthhee llooccaallee ssyysstteemm iiss ssuuppppoorrtteedd.
           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 aatt lleeaasstt
       oonnee of the following must be true:

       o   TThhee llooccaallee--ddeetteerrmmiinniinngg eennvviirroonnmmeenntt vvaarriiaabblleess ((sseeee tthhee
           sseeccttiioonn oonn ENVIRONMENT) must be correctly set up at
           the time the application is started, either by
           yourself or by whoever set up your system account.

       o   TThhee aapppplliiccaattiioonn mmuusstt sseett iittss oowwnn llooccaallee using the
           method described in the section on The setlocale
           function.

UUSSIINNGG LLOOCCAALLEESS
       TThhee uussee llooccaallee pprraaggmmaa

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

       o   TThhee ccoommppaarriissoonn ooppeerraattoorrss (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.

           NNoottee:: eq and ne are unaffected by 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   RReegguullaarr eexxpprreessssiioonnss aanndd ccaassee--mmooddiiffiiccaattiioonn ffuunnccttiioonnss
           (uc(), lc(), ucfirst(), and lcfirst()) use LC_CTYPE

       o   TThhee ffoorrmmaattttiinngg ffuunnccttiioonnss (printf(), sprintf() and
           write()) use LC_NUMERIC

       o   TThhee PPOOSSIIXX ddaattee ffoorrmmaattttiinngg ffuunnccttiioonn (strftime()) uses
           LC_TIME.

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

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

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

       TThhee sseettllooccaallee ffuunnccttiioonn

       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 ccaatteeggoorryy, the
       second the llooccaallee.  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 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 locales names (separator also
       implementation-dependent) or a single locale name.  Please
       consult your the setlocale(3) manpage 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 the
       setlocale(3) manpage.

       FFiinnddiinngg llooccaalleess

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

               locale -a

               nlsinfo

               ls /usr/lib/nls/loc

               ls /usr/lib/locale

               ls /usr/lib/nls

               ls /usr/share/locale

       and see whether they list something resembling these

               en_US.ISO8859-1     de_DE.ISO8859-1     ru_RU.ISO8859-5
               en_US.iso88591      de_DE.iso88591      ru_RU.iso88595
               en_US               de_DE               ru_RU
               en                  de                  ru
               english             german              russian
               english.iso88591    german.iso88591     russian.iso88595
               english.roman8                          russian.koi8r

       Sadly, even though the calling interface for setlocale()
       has been standardized, names of locales and the
       directories where the configuration resides have not been.
       The basic form of the name is language_territory..codeset,
       but the latter parts after language are not always
       present.  The language and country are usually from the
       standards IISSOO 33116666 and IISSOO 663399, the two-letter
       abbreviations for the countries and the languages of the
       world, respectively.  The codeset part often mentions some
       IISSOO 88885599 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 ddeeffaauulltt llooccaallee 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.

       NNOOTTEE: 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.

       LLOOCCAALLEE PPRROOBBLLEEMMSS

       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.

       TTeemmppoorraarriillyy ffiixxiinngg llooccaallee pprroobblleemmss

       The two quickest fixes are either to render Perl silent
       about any locale inconsistencies or to run Perl under the
       default locale "C".

       Perl's moaning about locale problems can be silenced by
       setting the environment variable PERL_BADLANG to a zero
       value, for example "0".  This method really just sweeps
       the problem under the carpet: you tell Perl to shut up
       even when Perl sees that something is wrong.  Do not be
       surprised if later something locale-dependent misbehaves.

       Perl can be run under the "C" locale by setting the
       environment variable LC_ALL to "C".  This method is
       perhaps a bit more civilized than the PERL_BADLANG
       approach, but setting LC_ALL (or other locale variables)
       may affect other programs as well, not just Perl.  In
       particular, external programs run from within Perl will
       see these changes.  If you make the new settings permanent
       (read on), all programs you run see the changes.  See the
       ENVIRONMENT manpage for for the full list of relevant
       environment variables and the section on USING LOCALES for
       their effects in Perl.  Effects in other programs are
       easily deducible.  For example, the variable LC_COLLATE
       may well affect your ssoorrtt program (or whatever the program
       that arranges `records' alphabetically in your system is
       called).

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

               LC_ALL=en_US.ISO8859-1
               export LC_ALL

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

               setenv LC_ALL en_US.ISO8859-1

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

       PPeerrmmaanneennttllyy ffiixxiinngg llooccaallee pprroobblleemmss

       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 the section on
       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
       eexxaaccttllyy (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
       the section on Permanently fixing system locale
       configuration.

       PPeerrmmaanneennttllyy ffiixxiinngg yyoouurr llooccaallee ccoonnffiigguurraattiioonn

       This is when you see something like:

               perl: warning: Please check that your locale settings:
                       LC_ALL = "En_US",
                       LANG = (unset)
                   are supported and installed on your system.

       but then cannot see that "En_US" listed by the above-
       mentioned commands.  You may see things like
       "en_US.ISO8859-1", but that isn't the same.  In this case,
       try running under a locale that you can list and which
       somehow matches what you tried.  The rules for matching
       locale names are a bit vague because standardization is
       weak in this area.  See again the the section on Finding
       locales about general rules.

       FFiixxiinngg ssyysstteemm llooccaallee ccoonnffiigguurraattiioonn

       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 the
       section on Finding locales section is unfortunately a bit
       vague about the exact commands and places because these
       things are not that standardized.

       TThhee llooccaalleeccoonnvv ffuunnccttiioonn

       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 aa rreeffeerreennccee
       ttoo 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 the
       localeconv entry in the POSIX (3) manpage 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) {
                   $_ = int;    # Chop non-integer part
                   1 while
                   s/(\d)(\d{$grouping[0]}($|$thousands_sep))/$1$thousands_sep$2/;
                   print "$_";
               }
               print "\n";

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

       CCaatteeggoorryy LLCC_<i>_CCOOLLLLAATTEE:: CCoollllaattiioonn

       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 D 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 alphanumeric
       characters are in the current locale, in that locale's
       order:

               use locale;
               print +(sort grep /\w/, map { chr() } 0..255), "\n";

       Compare this with the characters that you see and their
       order if you state explicitly that the locale should be
       ignored:

               no locale;
               print +(sort grep /\w/, map { chr() } 0..255), "\n";

       This machine-native collation (which is what you get
       unless use locale has appeared earlier in the same block)
       must be used for sorting raw binary data, whereas the
       locale-dependent collation of the first example is useful
       for natural text.

       As noted in 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 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 byte-by-byte comparisons against other
       transformed strings during collation.  "Under the hood",
       locale-affected Perl comparison operators call strxfrm()
       for both 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.  But 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 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.

       CCaatteeggoorryy LLCC_<i>_CCTTYYPPEE:: CChhaarraacctteerr TTyyppeess

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

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

       NNoottee:: 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) letters and digits--for example, in
       command strings--locale-aware applications should use \w
       inside a no locale block.  See the section on SECURITY.

       CCaatteeggoorryy LLCC_<i>_NNUUMMEERRIICC:: NNuummeerriicc FFoorrmmaattttiinngg

       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()
       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.)

       Output produced by print() is nneevveerr 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

       CCaatteeggoorryy LLCC_<i>_MMOONNEETTAARRYY:: FFoorrmmaattttiinngg ooff mmoonneettaarryy aammoouunnttss

       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, voluminous and complex though
       it may be, still does not quite meet your requirements:
       currency formatting is a hard nut to crack.

       LLCC_<i>_TTIIMMEE

       Output produced by POSIX::strftime(), which builds a
       formatted human-readable date/time string, is affected by
       the current LC_TIME locale.  Thus, in a French locale, the
       output produced by the %B format element (full month name)
       for the first month of the year would be "janvier".
       Here's how to get a list of long month names in the
       current locale:

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

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

       OOtthheerr ccaatteeggoorriieess

       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.

SSEECCUURRIITTYY
       Although 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 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   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 that takes the trouble to use
           information in LC_MONETARY may format debits as if
           they were credits and vice versa if that locale has
           been subverted.  Or it might make payments in US
           dollars instead of Hong Kong dollars.

       o   The date and day names in dates formatted by
           strftime() could be manipulated to advantage by a
           malicious user able to subvert the LC_DATE locale.
           ("Look--it says I wasn't in the building on Sunday.")

       Such dangers are not peculiar to the locale system: any
       aspect of an application's environment which may be
       modified maliciously presents similar challenges.
       Similarly, they are not specific to Perl: any programming
       language that allows you to write programs that take
       account of their environment exposes you to these issues.

       Perl cannot protect you from all possibilities shown in
       the examples--there is no substitute for your own
       vigilance--but, when use locale is in effect, Perl uses
       the tainting mechanism (see the perlsec manpage) to mark
       string results that become locale-dependent, and which may
       be untrustworthy in consequence.  Here is a summary of the
       tainting behavior of operators and functions that may be
       affected by the locale:

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

       CCaassee--mmaappppiinngg iinntteerrppoollaattiioonn (with \l, \L, \u or \U)
           Result string containing interpolated material is
           tainted if use locale is in effect.

       MMaattcchhiinngg ooppeerraattoorr (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 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.

       SSuubbssttiittuuttiioonn ooppeerraattoorr (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.

       IInn--mmeemmoorryy ffoorrmmaattttiinngg ffuunnccttiioonn (sprintf()):
           Result is tainted if use locale is in effect.

       OOuuttppuutt ffoorrmmaattttiinngg ffuunnccttiioonnss (printf() and write()):
           Success/failure result is never tainted.

       CCaassee--mmaappppiinngg ffuunnccttiioonnss (lc(), lcfirst(), uc(), ucfirst()):
           Results are tainted if use locale is in effect.

       PPOOSSIIXX llooccaallee--ddeeppeennddeenntt ffuunnccttiioonnss (localeconv(), strcoll(),
           strftime(), strxfrm()):
           Results are never tainted.

       PPOOSSIIXX cchhaarraacctteerr ccllaassss tteessttss (isalnum(), isalpha(),
           isdigit(), isgraph(), islower(), isprint(), ispunct(),
           isspace(), isupper(), isxdigit()):
           True/false results are never tainted.

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

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

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

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

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

               #/usr/local/bin/perl -T

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

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

       Compare this with a similar but locale-aware program:

               #/usr/local/bin/perl -T

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

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

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

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

                   NNOOTTEE: 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 set, it overrides all
                   the rest of the locale environment variables.

       LANGUAGE    NNOOTTEE: 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 the LC_ALL manpage.
                   Moreover, it's not a single value but instead
                   a "path" (":"-separated list) of languages
                   (not locales).  See the GNU gettext library
                   documentation for more information.

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

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

       LC_MONETARY In the absence of LC_ALL, LC_MONETARY chooses
                   the monetary formatting locale.  In the
                   absence of both LC_ALL and LC_MONETARY, LANG
                   chooses the monetary formatting locale.

       LC_NUMERIC  In the absence of LC_ALL, LC_NUMERIC chooses
                   the numeric format locale.  In the absence of
                   both LC_ALL and LC_NUMERIC, LANG chooses the
                   numeric format.

       LC_TIME     In the absence of LC_ALL, LC_TIME chooses the
                   date and time formatting locale.  In the
                   absence of both LC_ALL and LC_TIME, LANG
                   chooses the date and time formatting locale.

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

NNOOTTEESS
       BBaacckkwwaarrdd ccoommppaattiibbiilliittyy

       Versions of Perl prior to 5.004 mmoossttllyy 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 section on The
       setlocale function).  By default, Perl still behaves this
       way for backward compatibility.  If you want a Perl
       application to pay attention to locale information, you
       mmuusstt 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 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.

       II1188NN::CCoollllaattee oobbssoolleettee

       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.

       SSoorrtt ssppeeeedd aanndd mmeemmoorryy uussee iimmppaaccttss

       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 that 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.

       FFrreeeellyy aavvaaiillaabbllee llooccaallee ddeeffiinniittiioonnss

       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 installation of
       arbitrary locales, you may find the definitions useful as
       they are, or as a basis for the development of your own
       locales.

       II1188nn aanndd ll1100nn

       "Internationalization" is often abbreviated as ii1188nn
       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 ll1100nn.

       AAnn iimmppeerrffeecctt ssttaannddaarrdd

       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.

BBUUGGSS
       BBrrookkeenn ssyysstteemmss

       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 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: bug fixes may exist for these problems in
       your operating system.  Sometimes such bug fixes are
       called an operating system upgrade.

SSEEEE AALLSSOO
       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

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

       Last update: Thu Jun 11 08:44:13 MDT 1998

23/Jan/1999            perl 5.005, patch 03                     1