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.
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:
Note: eq and ne are unaffected by the 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.
LC_COLLATE, LC_CTYPE, and so on, are discussed further in the section on LOCALE CATEGORIES.
The default behavior returns with no locale or on reaching the end of the enclosing block.
Note that 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.
# 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, 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 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 use this in a subsequent 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 that 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 which 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 the implementation of 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. For the locales available in your system, also consult the setlocale(3) manpage and see whether it leads you to the list of the 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/nlsand see whether they list something resembling these
en_US.ISO8859-1 de_DE.ISO8859-1 ru_RU.ISO8859-5
en_US de_DE ru_RU
en de ru
english german russian
english.iso88591 german.iso88591 russian.iso88595
Sadly, even though the calling interface for setlocale() has been
standardized, the names of the locales and the directories where
the configuration is, have not. The basic form of the name is
language_country/territory.codeset, but the
latter parts are not always present.
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 and the second by the POSIX standard. What they define is 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.
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 formatting variable names such as
decimal_point and thousands_sep; the values are the corresponding
values. See the localeconv entry in the POSIX (3) manpage for a longer example, which lists
all the categories an implementation might be expected to provide; some
provide more and others fewer, however. Note that you don't need use
locale: as a function with the job of querying the locale, localeconv()
always observes the current locale.
Here's a simple-minded example program which rewrites its command line parameters as integers formatted correctly 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 = 3 unless $grouping;
# Format command line params for current locale
for (@ARGV) {
$_ = int; # Chop non-integer part
1 while
s/(\d)(\d{$grouping}($|$thousands_sep))/$1$thousands_sep$2/;
print "$_";
}
print "\n";
Here is a code snippet that will tell you what are the alphanumeric characters in the current locale, in the locale 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 which 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 which ignores space characters completely, and
which folds case.
If you have a single string which 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 their 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. 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 it 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. And 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, as it isn't needed: strcoll() and strxfrm() exist only to generate locale-dependent results, and so always obey the current LC_COLLATE locale.
The LC_CTYPE locale also provides the map used in translating 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 in 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 (unaccented) letters and digits - for example, in command strings - locale-aware applications should use \w inside a no locale block. See the section on SECURITY.
Note that 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
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 which
exists only to generate locale-dependent results, strftime() always
obeys the current LC_TIME locale.
Such dangers are not peculiar to the locale system: any aspect of an application's environment which may maliciously be modified presents similar challenges. Similarly, they are not specific to Perl: any programming language which allows you to write programs which take account of their environment exposes you to these issues.
Perl cannot protect you from all of the 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 which become locale-dependent, and
which may be untrustworthy in consequence. Here is a summary of the
tainting behavior of operators and functions which may be affected by
the locale:
Subpatterns, either delivered as an array-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.
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 very similar program which is locale-aware:
#/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 when use locale is in effect.
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.
Versions of Perl from 5.002 to 5.003 did use the LC_CTYPE information if that was available, that is, \w did understand what are 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.
Last update: Wed Jan 22 11:04:58 EST 1997