Acorn User 10/AU_CD10.iso/Updates/Perl/Non-RPC/Docs/perllocale

Text File | 1999-04-17 | 43KB | 992 lines

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 naïve 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 Backward
    compatibility manpage. 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 The use locale pragma
    manpage) 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 The setlocale function manpage.


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 Category LC_COLLATE: Collation manpage.

    *   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 LOCALE CATEGORIES manpage.

    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 LOCALE CATEGORIES manpage 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

        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 ISO 3166 and ISO 639,
    the two-letter abbreviations for the countries and the languages
    of the world, respectively. The *codeset* part often mentions
    some ISO 8859 character set, the Latin codesets. For example,
    `ISO 8859-1' is the so-called "Western European codeset" that
    can be used to encode most Western European languages
    adequately. Again, there are several ways to write even the name
    of that one standard. Lamentably.

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

    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
    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 USING LOCALES manpage 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 Finding locales
    manpage. 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 Permanently fixing system
    locale configuration manpage.

  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 Finding
    locales manpage 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
    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 Finding locales manpage 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 The setlocale function manpage.)

            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 'á' and 'å' 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 USING LOCALES manpage, `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 "Magic
    Variables" entry 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 'æ', 'ð', 'ß', and 'ø' 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 The localeconv function manpage 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 The localeconv function
    manpage--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.

    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_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_...'.


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 The setlocale function
    manpage). 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 The use locale pragma manpage) 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
    <[e-mail]>, 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