PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
NAME
perllocale - Perl locale handling (internationalization and localization)
DESCRIPTION
In the beginning there was ASCII, the "American Standard Code for Information Interchange", which works quite
well for Americans with their English alphabet and dollar-denominated currency. But it doesn't work so well
even for other English speakers, who may use different currencies, such as the pound sterling (as the symbol
for that currency is not in ASCII); and it's hopelessly inadequate for many of the thousands of the world's
other languages.
To address these deficiencies, the concept of locales was invented (formally the ISO C, XPG4, POSIX 1.c
"locale system"). And applications were and are being written that use the locale mechanism. The process of
making such an application take account of its users' preferences in these kinds of matters is called
internationalization (often abbreviated as i18n); telling such an application about a particular set of
preferences is known as localization (l10n).
Perl was extended, starting in 5.004, to support the locale system. This is controlled per application by
using one pragma, one function call, and several environment variables.
Unfortunately, there are quite a few deficiencies with the design (and often, the implementations) of locales,
and their use for character sets has mostly been supplanted by Unicode (see perlunitut for an introduction to
that, and keep on reading here for how Unicode interacts with locales in Perl).
Perl continues to support the old locale system, and starting in v5.16, provides a hybrid way to use the
Unicode character set, along with the other portions of locales that may not be so problematic. (Unicode is
also creating "CLDR", the "Common Locale Data Repository", <http://cldr.unicode.org/> which includes more
types of information than are available in the POSIX locale system. At the time of this writing, there was no
CPAN module that provides access to this XML-encoded data. However, many of its locales have the POSIX-only
data extracted, and are available at <http://unicode.org/Public/cldr/latest/>.)
WHAT IS A LOCALE
A locale is a set of data that describes various aspects of how various communities in the world categorize
their world. These categories are broken down into the following types (some of which include a brief note
here):
Category LC_NUMERIC: Numeric formatting
This indicates how numbers should be formatted for human readability, for example the character used as
the decimal point.
Category LC_MONETARY: Formatting of monetary amounts
Category LC_TIME: Date/Time formatting
Category LC_MESSAGES: Error and other messages
This for the most part is beyond the scope of Perl
Category LC_COLLATE: Collation
This indicates the ordering of letters for comparision and sorting. In Latin alphabets, for example, "b",
generally follows "a".
Category LC_CTYPE: Character Types
This indicates, for example if a character is an uppercase letter.
More details on the categories are given below in "LOCALE CATEGORIES".
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:
1. The locale-determining environment variables (see "ENVIRONMENT") must be correctly set up at the time the
application is started, either by yourself or by whomever set up your system account; or
2. 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. Starting in v5.16, there is an optional parameter to this pragma:
use locale ':not_characters';
This parameter allows better mixing of locales and Unicode, and is described fully in "Unicode and UTF-8", but
briefly, it tells Perl to not use the character portions of the locale definition, that is the "LC_CTYPE" and
"LC_COLLATE" categories. Instead it will use the native (extended by Unicode) character set. When using this
parameter, you are responsible for getting the external character set translated into the native/Unicode one
(which it already will be if it is one of the increasingly popular UTF-8 locales). There are convenient ways
of doing this, as described in "Unicode and UTF-8".
The current locale is set at execution time by setlocale() described below. If that function hasn't yet been
called in the course of the program's execution, the current locale is that which was determined by the
"ENVIRONMENT" in effect at the start of the program, except that "LC_NUMERIC" is always initialized to the C
locale (mentioned under "Finding locales"). If there is no valid environment, the current locale is
undefined. It is likely, but not necessarily, the "C" locale.
The operations that are affected by locale are:
Under "use locale ':not_characters';"
· Format declarations (format()) use "LC_NUMERIC"
· The POSIX date formatting function (strftime()) uses "LC_TIME".
Under just plain "use locale;"
The above operations are affected, as well as the following:
· 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.
"use locale". Note that "use locale" and "use locale ':not_characters'" may be nested, and that what is in
effect within an inner scope will revert to the outer scope's rules at the end of the inner scope.
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 locale 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.
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. Warning. The C locale delivered by some vendors may not actually exactly match what
the C standard calls for. So beware.
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
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.
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 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".
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
setlocale function".)
use POSIX qw(locale_h);
# Get a reference to a hash of locale-dependent info
$locale_values = localeconv();
# Output sorted list of the values
for (sort keys %$locale_values) {
printf "%-20s = %s\n", $_, $locale_values->{$_}
}
localeconv() takes no arguments, and returns a reference to a hash. The keys of this hash are variable names
for formatting, such as "decimal_point" and "thousands_sep". The values are the corresponding, er, values.
See "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$2/;
use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
my ($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" (but not a "use locale ':not_characters'"), Perl looks to the "LC_COLLATE"
environment variable to determine the application's notions on collation (ordering) of characters. For
example, "b" follows "a" in Latin alphabets, but where do "a" and "aa" belong? And while "color" follows
"chocolate" in English, what about in Spanish?
The following collations all make sense and you may meet any of them if you "use locale".
A B C D E a b c d e
A a B b C c D d 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
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" (but not a "use locale ':not_characters'"), 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 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 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(). Unfortunately, this creates big problems for
regular expressions. "|" still means alternation even though it matches "\w".
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) ASCII letters and
digits--for example, in command strings--locale-aware applications should use "\w" with the "/a" regular
expression modifier. See "SECURITY".
Category LC_NUMERIC: Numeric Formatting
After a proper POSIX::setlocale() call, 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 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 setlocale LC_NUMERIC);
See also I18N::Langinfo and "RADIXCHAR".
Category LC_MONETARY: Formatting of monetary amounts
The C standard defines the "LC_MONETARY" category, but not a 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 localeconv function"--and use the information that it returns in your application's own
formatting of currency amounts. However, you may well find that the information, voluminous and complex
though it may be, still does not quite meet your requirements: currency formatting is a hard nut to crack.
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 $! and the error messages given by external utilities may be changed by
"LC_MESSAGES". If you want to have portable error codes, use "%!". See Errno.
SECURITY
Although the main discussion of Perl security issues can be found in perlsec, a discussion of Perl's locale
handling would be incomplete if it did not draw your attention to locale-dependent security issues.
Locales--particularly on systems that allow unprivileged users to build their own locales--are untrustworthy.
A malicious (or just plain broken) locale can make a locale-aware application give unexpected results. Here
are a few possibilities:
· Regular expression checks for safe file names or mail addresses using "\w" may be spoofed by an "LC_CTYPE"
locale that claims that characters such as ">" and "|" are alphanumeric.
· String interpolation with case-mapping, as in, say, "$dest = "C:\U$name.$ext"", may produce dangerous
results if a bogus LC_CTYPE case-mapping table is in effect.
· A sneaky "LC_COLLATE" locale could result in the names of students with "D" grades appearing ahead of
those with "A"s.
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 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" (but not
"use locale ':not_characters'") 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" (but not
"use locale ':not_characters'") is in effect, and the subpattern regular expression contains "\w" (to
match an alphanumeric character), "\W" (non-alphanumeric character), "\s" (whitespace character), or "\S"
(non whitespace 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" (but not "use locale ':not_characters'") is 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".
· 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" (but not "use locale ':not_characters'") 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
$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 "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 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
after the overall "LC_ALL" and the category-specific "LC_...".
Examples
The LC_NUMERIC controls the numeric output:
use locale;
use POSIX qw(locale_h); # Imports setlocale() and the LC_ constants.
setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
printf "%g\n", 1.23; # If the "fr_FR" succeeded, probably shows 1,23.
and also how strings are parsed by POSIX::strtod() as numbers:
use locale;
use POSIX qw(locale_h strtod);
setlocale(LC_NUMERIC, "de_DE") or die "Entschuldigung";
my $x = strtod("2,34") + 5;
print $x, "\n"; # Probably shows 7,34.
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
setlocale function"). By default, Perl still behaves this way for backward compatibility. If you want a Perl
application to pay attention to locale information, you must use the "use locale" pragma (see "The use locale
pragma") or, in the unlikely event that you want to do so for just pattern matching, the "/l" regular
expression modifier (see "Character set modifiers" in perlre) 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
If a program's environment specifies an LC_NUMERIC locale and "use locale" is in effect when the format is
declared, the locale is used to specify the decimal point character in formatted output. Formatted output
cannot be controlled by "use locale" at the time when write() is called.
Freely available locale definitions
The Unicode CLDR project extracts the POSIX portion of many of its locales, available at
http://unicode.org/Public/cldr/latest/
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.
Unicode and UTF-8
The support of Unicode is new starting from Perl version v5.6, and more fully implemented in version v5.8 and
later. See perluniintro. It is strongly recommended that when combining Unicode and locale (starting in
v5.16), you use
use locale ':not_characters';
When this form of the pragma is used, only the non-character portions of locales are used by Perl, for example
"LC_NUMERIC". Perl assumes that you have translated all the characters it is to operate on into Unicode
(actually the platform's native character set (ASCII or EBCDIC) plus Unicode). For data in files, this can
conveniently be done by also specifying
use open ':locale';
This pragma arranges for all inputs from files to be translated into Unicode from the current locale as
specified in the environment (see "ENVIRONMENT"), and all outputs to files to be translated back into the
locale. (See open). On a per-filehandle basis, you can instead use the PerlIO::locale module, or the
Encode::Locale module, both available from CPAN. The latter module also has methods to ease the handling of
"ARGV" and environment variables, and can be used on individual strings. Also, if you know that all your
locales will be UTF-8, as many are these days, you can use the -C command line switch.
This form of the pragma allows essentially seamless handling of locales with Unicode. The collation order
will be Unicode's. It is strongly recommended that when you need to order and sort strings that you use the
standard module Unicode::Collate which gives much better results in many instances than you can get with the
old-style locale handling.
For pre-v5.16 Perls, or if you use the locale pragma without the ":not_characters" parameter, Perl tries to
work with both Unicode and locales--but there are problems.
Perl does not handle multi-byte locales in this case, such as have been used for various Asian languages, such
as Big5 or Shift JIS. However, the increasingly common multi-byte UTF-8 locales, if properly implemented, may
work reasonably well (depending on your C library implementation) in this form of the locale pragma, simply
because both they and Perl store characters that take up multiple bytes the same way. However, some, if not
most, C library implementations may not process the characters in the upper half of the Latin-1 range (128 -
255) properly under LC_CTYPE. To see if a character is a particular type under a locale, Perl uses the
functions like "isalnum()". Your C library may not work for UTF-8 locales with those functions, instead only
working under the newer wide library functions like "iswalnum()".
Perl generally takes the tack to use locale rules on code points that can fit in a single byte, and Unicode
rules for those that can't (though this isn't uniformly applied, see the note at the end of this section).
This prevents many problems in locales that aren't UTF-8. Suppose the locale is ISO8859-7, Greek. The
character at 0xD7 there is a capital Chi. But in the ISO8859-1 locale, Latin1, it is a multiplication sign.
The POSIX regular expression character class "[[:alpha:]]" will magically match 0xD7 in the Greek locale but
not in the Latin one.
the lowercase of U+0178 is itself.
The same problems ensue if you enable automatic UTF-8-ification of your standard file handles, default
"open()" layer, and @ARGV on non-ISO8859-1, non-UTF-8 locales (by using either the -C command line switch or
the "PERL_UNICODE" environment variable; see perlrun). Things are read in as UTF-8, which would normally
imply a Unicode interpretation, but the presence of a locale causes them to be interpreted in that locale
instead. For example, a 0xD7 code point in the Unicode input, which should mean the multiplication sign,
won't be interpreted by Perl that way under the Greek locale. This is not a problem provided you make certain
that all locales will always and only be either an ISO8859-1, or, if you don't have a deficient C library, a
UTF-8 locale.
Vendor locales are notoriously buggy, and it is difficult for Perl to test its locale-handling code because
this interacts with code that Perl has no control over; therefore the locale-handling code in Perl may be
buggy as well. (However, the Unicode-supplied locales should be better, and there is a feed back mechanism to
correct any problems. See "Freely available locale definitions".)
If you have Perl v5.16, the problems mentioned above go away if you use the ":not_characters" parameter to the
locale pragma (except for vendor bugs in the non-character portions). If you don't have v5.16, and you do
have locales that work, using them may be worthwhile for certain specific purposes, as long as you keep in
mind the gotchas already mentioned. For example, if the collation for your locales works, it runs faster
under locales than under Unicode::Collate; and you gain access to such things as the local currency symbol and
the names of the months and days of the week. (But to hammer home the point, in v5.16, you get this access
without the downsides of locales by using the ":not_characters" form of the pragma.)
Note: The policy of using locale rules for code points that can fit in a byte, and Unicode rules for those
that can't is not uniformly applied. Pre-v5.12, it was somewhat haphazard; in v5.12 it was applied fairly
consistently to regular expression matching except for bracketed character classes; in v5.14 it was extended
to all regex matches; and in v5.16 to the casing operations such as "\L" and "uc()". For collation, in all
releases, the system's "strxfrm()" function is called, and whatever it does is what you get.
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 "use locale" is in effect.
When confronted with such a system, please report in excruciating detail to <[email protected]>, and also
contact 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, "setlocale" 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, and updated by Perl 5 porters.
perl v5.16.3 2013-03-04 PERLLOCALE(1)
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