perllocale

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



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
       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
       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 understand and present your data correctly
       according a locale of your choice, all of the following must be true:

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

       ·   Definitions for locales that you use must be installed.  You, or
           your system administrator, must make sure that this is the case.
           The available locales, the location in which they are kept, and the
           manner in which they are installed all vary from 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.

       ·   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:

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

       ·   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:

       ·   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
           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.

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

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

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

       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 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.

       Finding locales

       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

       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_country/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 codeset" that can be
       used to encode most Western European languages.  Again, there are
       several ways to write even the name of that one standard.  Lamentably.

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

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

       LOCALE PROBLEMS

       You may encounter the following warning message at Perl startup:

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

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

       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 non-zero value, for example "1".
       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 sort program (or whatever the program that arranges `records'
       alphabetically in your system is called).

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

               LC_ALL=en_US.ISO8859-1
               export LC_ALL

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

               setenv LC_ALL en_US.ISO8859-1

       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 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 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 the section on Fixing system locale configuration.

       Permanently fixing your locale configuration

       This is when you see something like:

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

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

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

       The localeconv function

       The POSIX::localeconv() function allows you to get particulars of the
       locale-dependent numeric formatting information specified by the
       current LC_NUMERIC and LC_MONETARY locales.  (If you just want the name
       of the current locale for a particular category, use POSIX::setlocale()
       with a single parameter--see the 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 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";


LOCALE CATEGORIES
       The following subsections describe basic locale categories.  Beyond
       these, some combination categories allow manipulation of more than one
       basic category at a time.  See the section on 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 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.

       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
       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().

       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) 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

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

       LC_TIME

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

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

       Note: use locale isn't needed in this example: as a function that
       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 outside the standard Perl distribution.

SECURITY
       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:

       ·   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.

       ·   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.

       ·   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.

       ·   A sneaky LC_COLLATE locale could result in the names of students
           with "D" grades appearing ahead of those with "A"s.

       ·   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.

       ·   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:

       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 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.

       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.

       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 similar but locale-aware program:

               #/usr/local/bin/perl -T

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

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

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

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

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

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

       LC_ALL      LC_ALL is the "override-all" locale environment variable.
                   If 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 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 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 available; that is, \w did understand what were the letters
       according to the locale environment variables.  The problem was that
       the user had no control over the feature: if the C library supported
       locales, Perl used them.

       I18N:Collate obsolete

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

       Sort speed and memory use impacts

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

       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.

       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 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 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.

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.  Prose worked over a bit by Tom
       Christiansen.

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







































































3rd Berkeley Distribution    perl 5.005, patch 02                PERLLOCALE(1)