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perllocale - Perl locale handling (internationalization and localization)
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 Backward compatibility.
The one exception is that write() now always uses the current locale
- see NOTES.
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 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.
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.
You can switch locales as often as you wish at run time with the
POSIX::setlocale() function:
require 5.004;
use POSIX qw(locale_h);
$old_locale = setlocale(LC_CTYPE);
setlocale(LC_CTYPE, "fr_CA.ISO8859-1");
setlocale(LC_CTYPE, "");
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) man page 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 setlocale(3).
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
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.
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.
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 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 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
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.
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 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 Permanently fixing your system's 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
Finding locales about general rules.
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 Finding locales
section is unfortunately a bit vague about the exact commands and places
because these things are not that standardized.
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 setlocale function.)
use POSIX qw(locale_h);
$locale_values = localeconv();
for (sort keys %$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 localeconv in the POSIX 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:
require 5.004;
use POSIX qw(locale_h);
my ($thousands_sep, $grouping) =
@{localeconv()}{'thousands_sep', 'grouping'};
$thousands_sep = ',' unless $thousands_sep;
if ($grouping) {
@grouping = unpack("C*", $grouping);
} else {
@grouping = (3);
}
for (@ARGV) {
$_ = int;
1 while
s/(\d)(\d{$grouping[0]}($|$thousands_sep))/$1$thousands_sep$2/;
print "$_";
}
print "\n";
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 the I18N::Langinfo manpage for more information.
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.
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 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 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 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
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 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 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.
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,
numeric, and including other special characters such as the underscore or
hyphen. (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 SECURITY.
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 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
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;
$a = " $n"; | 
