perllocale



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




NAME

       perllocale - Perl locale handling (internationalization and localiza-
       tion)


DESCRIPTION

       Perl supports language-specific notions of data such as "is this a let-
       ter", "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 interna-
       tionalization (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".


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 documenta-
           tion 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 accord-
       ing to a particular locale, the application code should include the
       "use locale" pragma (see "The use locale pragma") where appropriate,
       and at least one of the following must be true:

       ·   The locale-determining environment variables (see "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 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
           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".

       ·   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 "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
       "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
       "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
       locales names (separator also implementation-dependent) or a single
       locale name.  Please consult your setlocale(3) for details.

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

               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 stan-
       dardized, names of locales and the directories where the configuration
       resides have not been.  The basic form of the name is language_terri-
       tory.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 men-
       tions 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 pro-
       gram 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 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 vari-
       able LC_ALL to "C".  This method is perhaps a bit more civilized than
       the PERL_BADLANG approach, but setting LC_ALL (or other locale vari-
       ables) may affect other programs as well, not just Perl.  In particu-
       lar, 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 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 com-
       mands 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 impor-
       tantly, installed--on your system.  In our example error message, envi-
       ronment 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 systems 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 com-
       mands.  You may see things like "en_US.ISO8859-1", but that isn’t the
       same.  In this case, try running under a locale that you can list and
       which somehow matches what you tried.  The rules for matching locale
       names are a bit vague because standardization is weak in this area.
       See again the "Finding locales" about general rules.

       Fixing system locale configuration

       Contact a system administrator (preferably your own) and report the
       exact error message you get, and ask them to read this same documenta-
       tion you are now reading.  They should be able to check whether there
       is something wrong with the locale configuration of the system.  The
       "Finding locales" section is unfortunately a bit vague about the exact
       commands and places because these things are not that standardized.

       The localeconv function

       The POSIX::localeconv() function allows you to get particulars of the
       locale-dependent numeric formatting information specified by the cur-
       rent "LC_NUMERIC" and "LC_MONETARY" locales.  (If you just want the
       name of the current locale for a particular category, use POSIX::setlo-
       cale() with a single parameter--see "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 "deci-
       mal_point" and "thousands_sep".  The values are the corresponding, er,
       values.  See "localeconv" in POSIX for a longer example listing the
       categories an implementation might be expected to provide; some provide
       more and others fewer.  You don’t need an explicit "use locale",
       because localeconv() always observes the current locale.

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

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

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

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

               # grouping and mon_grouping are packed lists
               # of small integers (characters) telling the
               # grouping (thousand_seps and mon_thousand_seps
               # being the group dividers) of numbers and
               # monetary quantities.  The integers’ meanings:
               # 255 means no more grouping, 0 means repeat
               # the previous grouping, 1-254 means use that
               # as the current grouping.  Grouping goes from
               # right to left (low to high digits).  In the
               # below we cheat slightly by never using anything
               # else than the first grouping (whatever that is).
               if ($grouping) {
                   @grouping = unpack("C*", $grouping);
               } else {
                   @grouping = (3);
               }

               # Format command line params for current locale
               for (@ARGV) {
                   $_ = int;    # Chop non-integer part
                   1 while
                   s/(\d)(\d{$grouping[0]}($│$thousands_sep))/$1$thousands_sep$2/;
                   print "$_";
               }
               print "\n";

       I18N::Langinfo

       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.


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 "ENVIRONMENT" for a discussion of these.

       Category LC_COLLATE: Collation

       In the scope of "use locale", Perl looks to the "LC_COLLATE" environ-
       ment variable to determine the application’s notions on collation
       (ordering) of characters.  For example, ’b’ follows ’a’ in Latin alpha-
       bets, 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 cur-
       rent 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 "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 dic-
       tionary-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 alpha-
       betic.  This affects Perl’s "\w" regular expression metanotation, which
       stands for alphanumeric characters--that is, alphabetic, numeric, and
       including other special characters such as the underscore or hyphen.
       (Consult perlre 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 interpola-
       tion 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 func-
       tions--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 dig-
       its--for example, in command strings--locale-aware applications should
       use "\w" inside a "no locale" block.  See "SECURITY".

       Category LC_NUMERIC: Numeric Formatting

       In the scope of "use locale", Perl obeys the "LC_NUMERIC" locale infor-
       mation, which controls an application’s idea of how numbers should be
       formatted for human readability by the printf(), sprintf(), and write()
       functions.  String-to-numeric conversion by the POSIX::strtod() func-
       tion is also affected.  In most implementations the only effect is to
       change the character used for the decimal point--perhaps from ’.’  to
       ’,’.  These functions aren’t aware of such niceties as thousands sepa-
       ration 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
       depends on whether "use locale" or "no locale" is in effect, and corre-
       sponds to what you’d get from printf() in the "C" locale.  The same is
       true for Perl’s internal conversions between numeric and string for-
       mats:

               use POSIX qw(strtod);
               use locale;

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

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

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

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

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

       See also I18N::Langinfo and "RADIXCHAR".

       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 com-
       mittees 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
       function"--and use the information that it returns in your applica-
       tion’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.

       See also I18N::Langinfo and "CRNCYSTR".

       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.

       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.


SECURITY

       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 bro-
       ken) 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.

       ·   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 Sun-
           day.")

       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 pro-
       gramming 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 exam-
       ples--there is no substitute for your own vigilance--but, when "use
       locale" is in effect, Perl uses the tainting mechanism (see perlsec) to
       mark string results that become locale-dependent, and which may be
       untrustworthy in consequence.  Here is a summary of the tainting behav-
       ior 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 charac-
           ter), "\W" (non-alphanumeric character), "\s" (white-space charac-
           ter), 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 mod-
           ified 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".

       ·   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
           effect.

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

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

       ·   POSIX locale-dependent functions (localeconv(), strcoll(), strf-
           time(), 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 pro-
       gram, 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 sys-
                   tem’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    NOTE: "LANGUAGE" is a GNU extension, it affects you only if
                   you are using the GNU libc.  This is the case if you are
                   using e.g. Linux.  If you are using "commercial" UNIXes you
                   are most probably not using GNU libc and you can ignore
                   "LANGUAGE".

                   However, in the case you are using "LANGUAGE": it affects
                   the language of informational, warning, and error messages
                   output by commands (in other words, it’s like "LC_MES-
                   SAGES") 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 charac-
                   ter 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 colla-
                   tion (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 mone-
                   tary 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, gen-
       erally behaving as if something similar to the "C" locale were always
       in force, even if the program environment suggested otherwise (see "The
       setlocale function").  By default, Perl still behaves this way for
       backward compatibility.  If you want a Perl application to pay atten-
       tion to locale information, you must use the "use locale" pragma (see
       "The use locale pragma") to instruct it to do so.

       Versions of Perl from 5.002 to 5.003 did use the "LC_CTYPE" information
       if available; that is, "\w" did understand what were the letters
       according to the locale environment variables.  The problem was that
       the user had no control over the feature: if the C library supported
       locales, Perl used them.

       I18N:Collate obsolete

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

       Sort speed and memory use impacts

       Comparing and sorting by locale is usually slower than the default
       sorting; slow-downs of two to four times have been observed.  It will
       also consume more memory: once a Perl scalar variable has participated
       in any string comparison or sorting operation obeying the locale colla-
       tion 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 char-
       acter 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 defi-
       nitions 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 use-
       ful to have them apply to a single thread, window group, or whatever.)
       They also have a tendency, like standards groups, to divide the world
       into nations, when we all know that the world can equally well be
       divided into bankers, bikers, gamers, and so on.  But, for now, it’s
       the only standard we’ve got.  This may be construed as a bug.


Unicode and UTF-8

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

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


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 excruci-
       ating detail to <perlbug@perl.org>, and complain to your vendor: bug
       fixes may exist for these problems in your operating system.  Sometimes
       such bug fixes are called an operating system upgrade.


SEE ALSO

       I18N::Langinfo, perluniintro, perlunicode, open, "isalnum" in POSIX,
       "isalpha" in POSIX, "isdigit" in POSIX, "isgraph" in POSIX, "islower"
       in POSIX, "isprint" in POSIX, "ispunct" in POSIX, "isspace" in POSIX,
       "isupper" in POSIX, "isxdigit" in POSIX, "localeconv" in POSIX, "setlo-
       cale" in POSIX, "strcoll" in POSIX, "strftime" in POSIX, "strtod" in
       POSIX, "strxfrm" in POSIX.


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



perl v5.8.6                       2004-11-05                     PERLLOCALE(1)

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