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 Informa-
tion Interchange", which works quite well for Americans with their English
alphabet and dollar-denominated currency (as long as they don't need the
cents "A" symbol, as it is not in ASCII)). But it doesn't work so well
even for other English speakers, who may use different currencies, such as
the pound sterling "A" (as the symbol for that currency is also 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 (for-
mally the ISO C, XPG4, POSIX 1.c "locale system"). These allow for users
to interface with their computer more according to their preferences. Ap-
plications were and are being written that use the locale mechanism. The
process of making such an application take account of its users' prefer-
ences in these kinds of matters is called internationalization (often ab-
breviated as i18n); telling such an application about a particular set of
preferences is known as localization (l10n).
Perl has been extended to support certain types of locales available in the
locale system. This is controlled per application by using one pragma, one
function call, and several environment variables.
Perl supports single-byte locales that are supersets of ASCII, such as the
ISO 8859 ones, and one multi-byte-type locale, UTF-8 ones, described in the
next paragraph. Perl doesn't support any other multi-byte locales, such as
the ones for East Asian languages.
Unfortunately, there are quite a few deficiencies with the design (and of-
ten, the implementations) of locales. Unicode was invented (see perlunitut
for an introduction to that) in part to address these design deficiencies,
and nowadays, there is a series of "UTF-8 locales", based on Unicode.
These are locales whose character set is Unicode, encoded in UTF-8. Start-
ing in v5.20, Perl fully supports UTF-8 locales, except for sorting and
string comparisons like "lt" and "ge". Starting in v5.26, Perl can handle
these reasonably as well, depending on the platform's implementation. How-
ever, for earlier releases or for better control, use Unicode::Collate.
There are actually two slightly different types of UTF-8 locales: one for
Turkic languages and one for everything else. Starting in Perl v5.30, Perl
detects UTF-8 Turkic locales by their behaviour, and seamlessly handles
both types; previously only the non-Turkic one was supported. The name of
the locale is ignored; if your system has a "tr_TR.UTF-8" locale and it
doesn't behave like a Turkic locale, perl will treat it like a non-Turkic
locale.
Perl continues to support the old non UTF-8 locales as well. There are
currently no UTF-8 locales for EBCDIC platforms.
The perl interpreter is a C language program. At least stub locale support
is required by the C language specification. So any instance of perl auto-
matically has this. Later, the POSIX standard added more capabilities be-
yond the ones required by C. Perl supports these on the platforms where
they are available. And Unicode supports a database of more types of in-
formation than the basic locale systems have. This database is called
"CLDR", the "Common Locale Data Repository", .
There are various CPAN modules that provide access to this XML-encoded
data, such as Locale::CLDR, CLDR::Number, and DateTime::Format::CLDR.
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 bro-
ken 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_COLLATE": Collation
This indicates the ordering of letters for comparison 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.
Category "LC_MESSAGES": Error and other messages
This is a POSIX extension beyond the basic C language required cate-
gories. On Windows and other non-POSIX platforms, perl uses
workarounds to simulate it.
Category "LC_TIME": Date/Time formatting
Category "LC_ALL"
This is not an actual category, but a convenience short-hand to refer
to all of the actual ones.
Other categories
Some platforms have other categories, dealing with such things as mea-
surement units and paper sizes. None of these are used directly by
Perl, but outside operations that Perl interacts with may use these.
See "Not within the scope of "use locale"" below.
More details on the categories used by Perl are given below in "LOCALE CAT-
EGORIES".
Together, these categories go a long way towards being able to customize a
single program to run in many different locations. And adding Unicode CLDR
goes further. But there are deficiencies, so keep reading.
PREPARING TO USE LOCALES
Perl itself (outside the POSIX module) will not use locales unless specifi-
cally requested to (but again note that Perl may interact with code that
does use them). Even if there is such a request, all of the following must
be true for it to work properly:
* 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 "de-
fine".
* Definitions for the locales that you use must be installed. All plat-
forms that perl runs on are required to support at least one locale,
named "C", which is essentially ASCII, and typical American prefer-
ences.
Most platforms allow for additional locales, but these must be specifi-
cally installed. You, or your system administrator, must make sure
that any locales you want are installed. The available locales, the
location in which they are kept, and the manner in which they are in-
stalled all vary from system to system. Some systems provide only a
few, hard-wired locales and do not allow more to be added. Others al-
low you to add "canned" locales provided by the system supplier. Still
others allow you or the system administrator to define and add arbi-
trary 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.
If you want a Perl application to process and present your data according
to a particular locale, the application code should include the "use lo-
cale" 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 itself (outside the POSIX module) ignores the current lo-
cale. The "use locale" pragma tells Perl to use the current locale for
some operations. Starting in v5.16, there are optional parameters to this
pragma, described below, which restrict which operations are affected by
it.
Starting in Perl 5.28, this pragma may be used in multi-threaded applica-
tions on systems that have thread-safe locale ability. Some caveats apply,
see "Multi-threaded" below. On systems without this capability, or in ear-
lier Perls, do NOT use this pragma in scripts that have multiple threads
active. The locale in these cases is not local to a single thread. An-
other thread may change the locale at any time, which could cause at a min-
imum that a given thread is operating in a locale it isn't expecting to be
in. On some platforms, segfaults can also occur. The locale change need
not be explicit; some operations cause perl itself to change the locale.
You are vulnerable simply by having done a "use locale".
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 exe-
cution, the current locale is that which was determined by the "ENVIRON-
MENT" in effect at the start of the program. If there is no valid environ-
ment, the current locale is whatever the system default has been set to.
On POSIX systems, it is likely, but not necessarily, the "C" locale. On
Windows, the default is set via the computer's "Control Panel->Re-
gional and Language Options" (or its current equivalent).
The operations that are affected by locale are:
Not within the scope of "use locale"
Only certain operations (all originating outside Perl) should be af-
fected, as follows:
* The current locale is used when going outside of Perl with opera-
tions like system() or qx//, if those operations are locale-sensi-
tive.
* Also Perl gives access to various C library functions through the
POSIX module. Some of those functions are always affected by the
current locale. For example, POSIX::strftime() uses "LC_TIME";
POSIX::strtod() uses "LC_NUMERIC"; POSIX::strcoll() and
POSIX::strxfrm() use "LC_COLLATE". All such functions will behave
according to the current underlying locale, even if that locale
isn't exposed to Perl space.
This applies as well to I18N::Langinfo.
* XS modules for all categories but "LC_NUMERIC" get the underlying
locale, and hence any C library functions they call will use that
underlying locale. For more discussion, see "Dealing with locales"
in perlclib.
Note that all C programs (including the perl interpreter, which is
written in C) always have an underlying locale. That locale is the "C"
locale unless changed by a call to setlocale(). When Perl starts up,
it changes the underlying locale to the one which is indicated by the
"ENVIRONMENT". When using the POSIX module or writing XS code, it is
important to keep in mind that the underlying locale may be something
other than "C", even if the program hasn't explicitly changed it.
Lingering effects of "use locale"
Certain Perl operations that are set-up within the scope of a "use lo-
cale" retain that effect even outside the scope. These include:
* The output format of a write() is determined by an earlier format
declaration ("format" in perlfunc), so whether or not the output is
affected by locale is determined by if the format() is within the
scope of a "use locale", not whether the write() is.
* Regular expression patterns can be compiled using qr// with actual
matching deferred to later. Again, it is whether or not the compi-
lation was done within the scope of "use locale" that determines
the match behavior, not if the matches are done within such a scope
or not.
Under ""use locale";"
* All the above operations
* Format declarations ("format" in perlfunc) and hence any subsequent
write()s use "LC_NUMERIC".
* stringification and output use "LC_NUMERIC". These include the re-
sults of print(), printf(), say(), and sprintf().
* The comparison operators ("lt", "le", "cmp", "ge", and "gt") 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 variables $! (and its synonyms $ERRNO and $OS_ERROR) and $^E>
(and its synonym $EXTENDED_OS_ERROR) when used as strings use
"LC_MESSAGES". On platforms that lack this category "LC_CTYPE" is
used instead.
The default behavior is restored with the "no locale" pragma, or upon
reaching the end of the block enclosing "use locale". Note that "use lo-
cale" calls may be nested, and that what is in effect within an inner scope
will revert to the outer scope's rules at the end of the inner scope.
The string result of any operation that uses locale information is tainted
(if your perl supports taint checking), as it is possible for a locale to
be untrustworthy. See "SECURITY".
Starting in Perl v5.16 in a very limited way, and more generally in v5.22,
you can restrict which category or categories are enabled by this particu-
lar instance of the pragma by adding parameters to it. (This capability
was to enable you to write code to work around deficiencies in perl's lo-
cale handling, which have since been corrected, so it is unlikely that new
code will need to use it.)
For example,
use locale qw(:ctype :numeric);
enables locale awareness within its scope of only those operations (listed
above) that are affected by "LC_CTYPE" and "LC_NUMERIC".
The possible categories are: ":collate", ":ctype", ":messages", ":mone-
tary", ":numeric", ":time", and the pseudo category ":characters" (de-
scribed below).
Thus you can say
use locale ':messages';
and only "$!" and "$^E" will be locale aware. Everything else is unaf-
fected.
Since Perl doesn't currently do anything with the "LC_MONETARY" category,
specifying ":monetary" does effectively nothing. Some systems have other
categories, such as "LC_PAPER", but the perl core doesn't do anything with
them, and there is no way to specify them in this pragma's arguments.
You can also easily say to use all categories but one, by either, for exam-
ple,
use locale ':!ctype';
use locale ':not_ctype';
both of which mean to enable locale awareness of all categories but
"LC_CTYPE". Only one category argument may be specified in a "use locale"
if it is of the negated form.
Prior to v5.22 only one form of the pragma with arguments is available:
use locale ':not_characters';
(and you have to say "not_"; you can't use the bang "!" form). This pseudo
category is a shorthand for specifying both ":collate" and ":ctype".
Hence, in the negated form, it is nearly the same thing as saying
use locale qw(:messages :monetary :numeric :time);
We use the term "nearly", because ":not_characters" also turns on "use fea-
ture 'unicode_strings'" within its scope. This form is less useful in
v5.20 and later, and is described fully in "Unicode and UTF-8", but
briefly, it tells Perl to not use the character portions of the locale def-
inition, that is the "LC_CTYPE" and "LC_COLLATE" categories. Instead it
will use the native character set (extended by Unicode). 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 setlocale function
WARNING! Prior to Perl 5.28 or on a system that does not support
thread-safe locale operations, do NOT use this function in a thread. The
locale will change in all other threads at the same time, and should your
thread get paused by the operating system, and another started, that thread
will not have the locale it is expecting. On some platforms, there can be
a race leading to segfaults if two threads call this function nearly simul-
taneously. This warning does not apply on unthreaded builds, or on perls
where "${^SAFE_LOCALES}" exists and is non-zero; namely Perl 5.28 and later
unthreaded or compiled to be locale-thread-safe. On z/OS systems, this
function becomes a no-op once any thread is started. Thus, on that system,
you can set up the locale before creating any threads, and that locale will
be the one in effect for the entire program.
Otherwise, you can switch locales as often as you wish at run time with the
POSIX::setlocale() function:
# Import locale-handling tool set from POSIX module.
# This example uses: setlocale -- the function call
# LC_CTYPE -- explained below
# (Showing the testing for success/failure of operations is
# omitted in these examples to avoid distracting from the main
# point)
use POSIX qw(locale_h);
use locale;
my $old_locale;
# 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 the default defined by the
# LC_ALL/LC_CTYPE/LANG environment variables, or to the system
# default. See below for documentation.
# restore the old locale
setlocale(LC_CTYPE, $old_locale);
The first argument of setlocale() gives the category, the second the lo-
cale. The category tells in what aspect of data processing you want to ap-
ply locale-specific rules. Category names are discussed in "LOCALE CATE-
GORIES" and "ENVIRONMENT". The locale is the name of a collection of cus-
tomization information corresponding to a particular combination of lan-
guage, 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 other 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(), but on some platforms the string is opaque, not some-
thing that most people would be able to decipher as to what locale it
means.
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 lo-
cale 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 dif-
fer 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 cate-
gory's locale is returned to the default specified by the corresponding en-
vironment 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.
Note that when a form of "use locale" that doesn't include all categories
is specified, Perl ignores the excluded categories.
If setlocale() fails for some reason (for example, an attempt to set to a
locale unknown to the system), the locale for the category is not changed,
and the function returns "undef".
Starting in Perl 5.28, on multi-threaded perls compiled on systems that im-
plement POSIX 2008 thread-safe locale operations, this function doesn't ac-
tually call the system "setlocale". Instead those thread-safe operations
are used to emulate the "setlocale" function, but in a thread-safe manner.
You can force the thread-safe locale operations to always be used (if
available) by recompiling perl with
-Accflags='-DUSE_THREAD_SAFE_LOCALE'
added to your call to Configure.
For further information about the categories, consult setlocale(3).
Multi-threaded operation
Beginning in Perl 5.28, multi-threaded locale operation is supported on
systems that implement either the POSIX 2008 or Windows-specific
thread-safe locale operations. Many modern systems, such as various Unix
variants do have this. Others, such as most *BSD-derived variants, includ-
ing Darwin, claim to have it, but are buggy as of May 2024, so Perl avoids
their use.
You can tell if using locales is safe on your system by looking at the
read-only variable "${^SAFE_LOCALES}". The value is 1 if the perl is not
threaded, or if it is using thread-safe locale operations.
Thread-safe operations are supported in Windows starting in Visual Studio
2005, in cygwin, in MingW compiled to use UCRT (the Universal C Run Time
library), and in systems compatible with POSIX 2008. "${^SAFE_LOCALES}"
will be 0 on threaded builds on platforms that Perl knows to have buggy im-
plementations.
Be aware that writing a multi-threaded application will not be portable to
a platform which lacks the native thread-safe locale support. On systems
that do have it, you automatically get this behavior for threaded perls,
without having to do anything. If for some reason, you don't want to use
this capability (perhaps the POSIX 2008 support turns out to be buggy on
your system), you can manually compile Perl to use the old non-thread-safe
implementation by passing the argument "-Accflags='-DNO_THREAD_SAFE_LO-
CALE'" to Configure. Except on Windows, this will continue to use certain
of the POSIX 2008 functions in some situations. If these are buggy, you
can pass the following to Configure instead or additionally: "-Ac-
cflags='-DNO_POSIX_2008_LOCALE'". This will also keep the code from using
thread-safe locales. "${^SAFE_LOCALES}" will be 0 on systems that turn off
the thread-safe operations.
Normally on unthreaded builds, Perl uses the traditional setlocale() to
change the locale, and not the alternate POSIX 2008 thread-safe lo-
cale-changing functions. You can force the use of these on systems that
have them by adding the "-Accflags='-DUSE_THREAD_SAFE_LOCALE'" to Config-
ure.
The initial program is started up using the locale specified from the envi-
ronment, as currently, described in "ENVIRONMENT". All newly created
threads start with "LC_ALL" set to "C". Each thread may use POSIX::setlo-
cale() to query or switch its locale at any time, without affecting any
other thread. All locale-dependent operations automatically use their
thread's locale.
This should be completely transparent to any applications written entirely
in Perl (minus a few rarely encountered caveats given in the
"Multi-threaded" section). Information for XS module writers is given in
"Dealing with locales" in perlclib.
Finding locales
For locales available in your system, consult also setlocale(3) to see
whether it leads to the list of available locales (search for the SEE ALSO
section). If that fails, try the following command lines:
locale -a
nlsinfo
ls /usr/lib/nls/loc
ls /usr/lib/locale
ls /usr/lib/nls
ls /usr/share/locale
and see whether they list something resembling these
en_US.ISO8859-1 de_DE.ISO8859-1 ru_RU.ISO8859-5
en_US.iso88591 de_DE.iso88591 ru_RU.iso88595
en_US de_DE ru_RU
en de ru
english german russian
english.iso88591 german.iso88591 russian.iso88595
english.roman8 russian.koi8r
Sadly, even though the calling interface for setlocale() has been standard-
ized, names of locales and the directories where the configuration resides
have not been. The basic form of the name is language[_territory[.code-
set]][@modifier]. 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. modifier is very
individualized to the rest of the locale, naming some variant, such as a
different currency symbol than the locale would normally contain.
Two special locales are worth particular mention: "C" and "POSIX". Cur-
rently 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 stan-
dard. They define the default locale in which every program starts in the
absence of locale information in its environment. (The default default lo-
cale, if you will.) Its language is (American) English and its character
codeset ASCII or, rarely, a superset thereof (such as the "DEC Multina-
tional Character Set (DEC-MCS)"). 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 de-
fault 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. In-
stead, Perl gave up and fell back to the "C" locale, the default locale
that is supposed to work no matter what. (On Windows, it first tries
falling back to the system default locale.) 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.
Testing for broken locales
If you are building Perl from source, the Perl test suite file lib/locale.t
can be used to test the locales on your system. Setting the environment
variable "PERL_DEBUG_FULL_TEST" to 1 will cause it to output detailed re-
sults. For example, on Linux, you could say
PERL_DEBUG_FULL_TEST=1 ./perl -T -Ilib lib/locale.t > locale.log 2>&1
Besides many other tests, it will test every locale it finds on your system
to see if they conform to the POSIX standard. If any have errors, it will
include a summary near the end of the output of which locales passed all
its tests, and which failed, and why.
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 envi-
ronment variable "PERL_BADLANG" to "0" or "". 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 "US-
ING LOCALES" for their effects in Perl. Effects in other programs are eas-
ily deducible. For example, the variable "LC_COLLATE" may well affect your
sort program (or whatever the program that arranges "records" alphabeti-
cally in your system is called).
You can test out changing these variables temporarily, and if the new set-
tings seem to help, put those settings into your shell startup files. Con-
sult your local documentation for the exact details. For 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 Csh-ish 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)configu-
ration of the whole system's locales usually requires the help of your sys-
tem administrator.
First, see earlier in this document about "Finding locales". That tells
how to find which locales are really supported--and more importantly, in-
stalled--on your system. In our example error message, environment vari-
ables 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 "Per-
manently 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 standardization is weak in this area. See again the "Finding
locales" about general rules.
Fixing system locale configuration
Contact a system administrator (preferably your own) and report the exact
error message you get, and ask them to read this same 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 localeconv function
The POSIX::localeconv() function allows you to get particulars of the lo-
cale-dependent numeric formatting information specified by the current un-
derlying "LC_NUMERIC" and "LC_MONETARY" locales (regardless of whether
called from within the scope of "use locale" or not). (If you just want
the name of the current locale for a particular category, use POSIX::setlo-
cale() with a single parameter--see "The setlocale function".)
use POSIX qw(locale_h);
# Get a reference to a hash of locale-dependent info
$locale_values = localeconv();
# Output sorted list of the values
for (sort keys %$locale_values) {
printf "%-20s = %s\n", $_, $locale_values->{$_}
}
localeconv() takes no arguments, and returns a reference to a hash. The
keys of this hash are variable names for formatting, such as "deci-
mal_point" and "thousands_sep". The values are the corresponding, er, val-
ues. See "localeconv" in POSIX for a longer example listing the categories
an implementation might be expected to provide; some provide more and oth-
ers 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 para-
meters as integers correctly formatted in the current locale:
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";
Note that if the platform doesn't have "LC_NUMERIC" and/or "LC_MONETARY"
available or enabled, the corresponding elements of the hash will be miss-
ing.
I18N::Langinfo
Another interface for querying locale-dependent information is the
I18N::Langinfo::langinfo() function.
The following example will import the langinfo() function itself and three
constants to be used as arguments to langinfo(): a constant for the abbre-
viated 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 ques-
tion in the current locale.
use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
my ($abday_1, $yesstr, $nostr)
= map { langinfo } qw(ABDAY_1 YESSTR NOSTR);
print "$abday_1? [$yesstr/$nostr] ";
In other words, in the "C" (or English) locale the above will probably
print something like:
Sun? [yes/no]
See I18N::Langinfo for more information.
LOCALE CATEGORIES
The following subsections describe basic locale categories. Beyond these,
some combination categories allow manipulation of more than one basic cate-
gory at a time. See "ENVIRONMENT" for a discussion of these.
Category "LC_COLLATE": Collation: Text Comparisons and Sorting
In the scope of a "use locale" form that includes collation, Perl looks to
the "LC_COLLATE" environment variable to determine the application's no-
tions on collation (ordering) of characters. For example, "b" likely fol-
lows "a" in Latin alphabets, but where do "A" and "A" belong? And while
"color" follows "chocolate" in English, what about in traditional 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 colla-
tion 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 dictio-
nary-like ordering that ignores space characters completely and which folds
case.
Perl uses the platform's C library collation functions strcoll() and
strxfrm(). That means you get whatever they give. On some platforms,
these functions work well on UTF-8 locales, giving a reasonable default
collation for the code points that are important in that locale. (And if
they aren't working well, the problem may only be that the locale defini-
tion is deficient, so can be fixed by using a better definition file. Uni-
code's definitions (see "Freely available locale definitions") provide rea-
sonable UTF-8 locale collation definitions.) Starting in Perl v5.26,
Perl's use of these functions has been made more seamless. This may be
sufficient for your needs. For more control, and to make sure strings con-
taining any code point (not just the ones important in the locale) collate
properly, the Unicode::Collate module is suggested.
In non-UTF-8 locales (hence single byte), code points above 0xFF are tech-
nically invalid. But if present, again starting in v5.26, they will col-
late to the same position as the highest valid code point does. This gen-
erally gives good results, but the collation order may be skewed if the
valid code point gets special treatment when it forms particular sequences
with other characters as defined by the locale. When two strings collate
identically, the code point order is used as a tie breaker.
If Perl detects that there are problems with the locale collation order, it
reverts to using non-locale collation rules for that locale.
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 colla-
tion. "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 lo-
cale-affected comparison, the example attempts to save a couple of trans-
formations. 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() are POSIX:: functions which use the stan-
dard system-supplied "libc" functions that always obey the current "LC_COL-
LATE" locale.
Category "LC_CTYPE": Character Types
In the scope of a "use locale" form that includes "LC_CTYPE", Perl obeys
the "LC_CTYPE" locale setting. This controls the application's notion of
which characters are alphabetic, numeric, punctuation, etc. This affects
Perl's "\w" regular expression metanotation, which stands for alphanumeric
characters--that is, alphabetic, numeric, and the platform's native under-
score. (Consult perlre for more information about regular expressions.)
Thanks to "LC_CTYPE", depending on your locale setting, characters like
"A", "A", "A", and "A" may be understood as "\w" characters. It also af-
fects things like "\s", "\D", and the POSIX character classes, like
"[[:graph:]]". (See perlrecharclass for more information on all these.)
The "LC_CTYPE" locale also provides the map used in transliterating charac-
ters between lower and uppercase. This affects the case-mapping func-
tions--fc(), lc(), lcfirst(), uc(), and ucfirst(); case-mapping interpola-
tion with "\F", "\l", "\L", "\u", or "\U" in double-quoted strings and
"s///" substitutions; and case-insensitive regular expression pattern
matching using the "i" modifier.
Starting in v5.20, Perl supports UTF-8 locales for "LC_CTYPE", but other-
wise Perl only supports single-byte locales, such as the ISO 8859 series.
This means that wide character locales, for example for Asian languages,
are not well-supported. Use of these locales may cause core dumps. If the
platform has the capability for Perl to detect such a locale, starting in
Perl v5.22, Perl will warn, default enabled, using the "locale" warning
category, whenever such a locale is switched into. The UTF-8 locale sup-
port is actually a superset of POSIX locales, because it is really full
Unicode behavior as if no "LC_CTYPE" locale were in effect at all (except
for tainting; see "SECURITY"). POSIX locales, even UTF-8 ones, are lacking
certain concepts in Unicode, such as the idea that changing the case of a
character could expand to be more than one character. Perl in a UTF-8 lo-
cale, will give you that expansion. Prior to v5.20, Perl treated a UTF-8
locale on some platforms like an ISO 8859-1 one, with some restrictions,
and on other platforms more like the "C" locale. For releases v5.16 and
v5.18, "use locale 'not_characters" could be used as a workaround for this
(see "Unicode and UTF-8").
Note that there are quite a few things that are unaffected by the current
locale. Any literal character is the native character for the given plat-
form. Hence 'A' means the character at code point 65 on ASCII platforms,
and 193 on EBCDIC. That may or may not be an 'A' in the current locale, if
that locale even has an 'A'. Similarly, all the escape sequences for par-
ticular characters, "\n" for example, always mean the platform's native
one. This means, for example, that "\N" in regular expressions (every
character but new-line) works on the platform character set.
Starting in v5.22, Perl will by default warn when switching into a locale
that redefines any ASCII printable character (plus "\t" and "\n") into a
different class than expected. This is likely to happen on modern locales
only on EBCDIC platforms, where, for example, a CCSID 0037 locale on a CC-
SID 1047 machine moves "[", but it can happen on ASCII platforms with the
ISO 646 and other 7-bit locales that are essentially obsolete. Things may
still work, depending on what features of Perl are used by the program.
For example, in the example from above where "|" becomes a "\w", and there
are no regular expressions where this matters, the program may still work
properly. The warning lists all the characters that it can determine could
be adversely affected.
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 dig-
its--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, and within the scope of a "use lo-
cale" form that includes numerics, Perl obeys the "LC_NUMERIC" locale in-
formation, which controls an application's idea of how numbers should be
formatted for human readability. In most implementations the only effect
is to change the character used for the decimal point--perhaps from "." to
",". The functions aren't aware of such niceties as thousands separation
and so on. (See "The localeconv function" if you care about these things.)
use POSIX qw(strtod setlocale LC_NUMERIC);
use locale;
setlocale LC_NUMERIC, "";
$n = 5/2; # Assign numeric 2.5 to $n
$x = " $n"; # Locale-dependent conversion to string
print "half five is $n\n"; # Locale-dependent output
printf "half five is %g\n", $n; # Locale-dependent output
print "DECIMAL POINT IS COMMA\n"
if $n == (strtod("2,5"))[0]; # Locale-dependent conversion
See also I18N::Langinfo and "RADIXCHAR".
Category "LC_MONETARY": Formatting of monetary amounts
The C standard defines the "LC_MONETARY" category, but not a function that
is affected by its contents. (Those with experience of standards commit-
tees will recognize that the working group decided to punt on the issue.
POSIX 2001 added the strfmon() function to format currency amounts, but
there is no official function to parse strings representing currency val-
ues.)
Perl essentially takes no notice of this category. On POSIX systems, you
can call strfmon() from XS code to create formatted strings, and/or you can
query the "LC_MONETARY" locale-specific values with "The localeconv func-
tion" and use the information that it returns in your application's own
formatting of currency amounts. However, you may well find that the infor-
mation, voluminous and complex though it may be, still does not quite meet
your requirements: currency formatting is a hard nut to crack.
See also "CRNCYSTR" in I18N::Langinfo.
Category "LC_TIME": Representation of time
Output produced by POSIX::strftime(), which builds a formatted human-read-
able 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, $_, 96);
}
Note: "use locale" isn't needed in this example: strftime() is a POSIX::
function which uses the standard system-supplied "libc" function that al-
ways obeys the current "LC_TIME" locale.
See also I18N::Langinfo and "ABDAY_1".."ABDAY_7", "DAY_1".."DAY_7", "AB-
MON_1".."ABMON_12", and "ABMON_1".."ABMON_12".
There is also the libc strptime() function defined starting in POSIX 2001
(it's not in Windows) that parses formatted time strings. There is cur-
rently no pure perl access to this function, so you need to write XS code
to use it.
Category "LC_MESSAGES": System messages
This category is used by perl to create a string describing a system error
number, such as what you would get by saying "$!" or "$^E". On some sys-
tems and locales, the string will be in the language of the locale given by
"LC_MESSAGES". But not many systems have bothered to install such transla-
tions for all locales available on the system. If no translation is avail-
able for a given locale, the string will be in English. See Errno for in-
formation about portably using error codes.
The other categories mentioned so far are required to exist in any platform
on which Perl can run. But this category is a POSIX extension, and Perl
runs on platforms, Windows, for example, that don't have it. On such plat-
forms the underlying language for the system errors will be whatever
"LC_CTYPE" gives, or English.
This category in conjunction with I18N::Langinfo can be used to output
yes/no in its locale's language, and to parse strings that contain "yes" or
"no" in that language.
Other categories
Some platforms have additional categories. These are not used by Perl it-
self. I18N::Langinfo may be used to query them, yielding stub values on
platforms where they don't exist. But again note that things Perl inter-
acts with may use these, including extensions outside the standard Perl
distribution, and by the operating system and its utilities.
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. Lo-
cales--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.
* An application that takes the trouble to use information in "LC_MONE-
TARY" 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 in-
stead of Hong Kong dollars.
* The date and day names in dates formatted by strftime() could be manip-
ulated to advantage by a malicious user able to subvert the "LC_TIME"
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 appli-
cation's environment which may be modified maliciously presents similar
challenges. Similarly, they are not specific to Perl: any programming lan-
guage that allows you to write programs that take account of their environ-
ment 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 ef-
fect, Perl uses the tainting mechanism (see perlsec) to mark string results
that become locale-dependent, and which may be untrustworthy in conse-
quence.
Note that it is possible to compile Perl without taint support, in which
case all taint features silently do nothing.
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", "\U", or "\F")
The result string containing interpolated material is tainted if a "use
locale" form that includes "LC_CTYPE" is in effect.
* Matching operator ("m//"):
Scalar true/false result never tainted.
All subpatterns, either delivered as a list-context result or as $1
etc., are tainted if a "use locale" form that includes "LC_CTYPE" is in
effect, and the subpattern regular expression contains a locale-depen-
dent construct. These constructs include "\w" (to match an alphanu-
meric character), "\W" (non-alphanumeric character), "\b" and "\B"
(word-boundary and non-boundary, which depend on what "\w" and "\W"
match), "\s" (whitespace character), "\S" (non whitespace character),
"\d" and "\D" (digits and non-digits), and the POSIX character classes,
such as "[:alpha:]" (see "POSIX Character Classes" in perlrecharclass).
Tainting is also likely if the pattern is to be matched case-insensi-
tively (via "/i"). The exception is if all the code points to be
matched this way are above 255 and do not have folds under Unicode
rules to below 256. Tainting is not done for these because Perl only
uses Unicode rules for such code points, and those rules are the same
no matter what the current locale.
The matched-pattern variables, $&, "$`" (pre-match), "$'" (post-match),
and $+ (last match) also are tainted.
* Substitution operator ("s///"):
Has the same behavior as the match operator. Also, the left operand of
"=~" becomes tainted when a "use locale" form that includes "LC_CTYPE"
is in effect, if modified as a result of a substitution based on a reg-
ular expression match involving any of the things mentioned in the pre-
vious item, or of case-mapping, such as "\l", "\L","\u", "\U", or "\F".
* 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 a "use locale" form that includes "LC_CTYPE" is
in effect.
* POSIX locale-dependent functions (localeconv(), strcoll(), strftime(),
strxfrm()):
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 com-
mand line may not be used to name an output file when taint checks are en-
abled.
#/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 $tainted_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 informa-
tion--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_SKIP_LOCALE_INIT
This environment variable, available starting in Perl v5.20, if
set (to any value), tells Perl to not use the rest of the envi-
ronment variables to initialize with. Instead, Perl uses what-
ever the current locale settings are. This is particularly
useful in embedded environments, see "Using embedded Perl with
POSIX locales" in perlembed.
PERL_BADLANGA 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 environ-
ment. If this environment variable is absent, or has a value
other than "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 con-
trolling an application's opinion on data. Windows is non-POSIX, but Perl
arranges for the following to work as described anyway. If the locale
given by an environment variable is not valid, Perl tries the next lower
one in priority. If none are valid, on Windows, the system default locale
is then tried. If all else fails, the "C" locale is used. If even that
doesn't work, something is badly broken, but Perl tries to forge ahead with
whatever the locale settings might be.
"LC_ALL" "LC_ALL" is the "override-all" locale environment variable. If
set, it overrides all the rest of the locale environment vari-
ables.
"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 prob-
ably 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 of both "LC_ALL" and "LC_COL-
LATE", "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_NU-
MERIC", "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_foo".
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
String "eval" and "LC_NUMERIC"
A string eval parses its expression as standard Perl. It is therefore ex-
pecting the decimal point to be a dot. If "LC_NUMERIC" is set to have this
be a comma instead, the parsing will be confused, perhaps silently.
use locale;
use POSIX qw(locale_h);
setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
my $x = 1.2;
print eval "$x + 1.5";
print "\n";
prints "13,5". This is because in that locale, the comma is the decimal
point character. The "eval" thus expands to:
eval "1,2 + 1.5"
and the result is not what you likely expected. No warnings are generated.
If you do string "eval"'s within the scope of "use locale", you should in-
stead change the "eval" line to do something like:
print eval "no locale; $x + 1.5";
This prints 2.7.
You could also exclude "LC_NUMERIC", if you don't need it, by
use locale ':!numeric';
Backward compatibility
Versions of Perl prior to 5.004 mostly ignored locale information, gener-
ally behaving as if something similar to the "C" locale were always in
force, even if the program environment suggested otherwise (see "The setlo-
cale function"). By default, Perl still behaves this way for backward com-
patibility. If you want a Perl application to pay attention to locale in-
formation, 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 modi-
fiers" 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 down-
sides are dictated more by the operating system's implementation of the lo-
cale system than by Perl.
Freely available locale definitions
The Unicode CLDR project extracts the POSIX portion of many of its locales,
available at
https://unicode.org/Public/cldr/2.0.1/
(Newer versions of CLDR require you to compute the POSIX data yourself.
See .)
There is a large collection of locale definitions at:
http://std.dkuug.dk/i18n/WG15-collection/locales/
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 de-
velopment 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 in-
ternalin ... 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 crit-
icized as incomplete and ungainly. They also have a tendency, like stan-
dards 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 versions v5.8 and later. See perluniintro.
Starting in Perl v5.20, UTF-8 locales are supported in Perl, except
"LC_COLLATE" is only partially supported; collation support is improved in
Perl v5.26 to a level that may be sufficient for your needs (see "Category
"LC_COLLATE": Collation: Text Comparisons and Sorting").
If you have Perl v5.16 or v5.18 and can't upgrade, you can 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 (actu-
ally 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 Uni-
code from the current locale as specified in the environment (see "ENVIRON-
MENT"), 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::lo-
cale module, or the Encode::Locale module, both available from CPAN. The
latter module also has methods to ease the handling of "ARGV" and environ-
ment variables, and can be used on individual strings. 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 by Unicode code point order.
Unicode::Collate can be used to get Unicode rules collation.
All the modules and switches just described can be used in v5.20 with just
plain "use locale", and, should the input locales not be UTF-8, you'll get
the less than ideal behavior, described below, that you get with pre-v5.16
Perls, or when you use the locale pragma without the ":not_characters" pa-
rameter in v5.16 and v5.18. If you are using exclusively UTF-8 locales in
v5.20 and higher, the rest of this section does not apply to you.
There are two cases, multi-byte and single-byte locales. First multi-byte:
The only multi-byte (or wide character) locale that Perl is ever likely to
support is UTF-8. This is due to the difficulty of implementation, the
fact that high quality UTF-8 locales are now published for every area of
the world ( for ones that are al-
ready set-up, but from an earlier version; for the most up-to-date, but you have to extract the
POSIX information yourself), and failing all that, you can use the Encode
module to translate to/from your locale. So, you'll have to do one of
those things if you're using one of these locales, such as Big5 or Shift
JIS. For UTF-8 locales, in Perls (pre v5.20) that don't have full UTF-8
locale support, they may work reasonably well (depending on your C library
implementation) 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 isal-
num(). Your C library may not work for UTF-8 locales with those functions,
instead only working under the newer wide library functions like iswal-
num(), which Perl does not use. These multi-byte locales are treated like
single-byte locales, and will have the restrictions described below.
Starting in Perl v5.22 a warning message is raised when Perl detects a
multi-byte locale that it doesn't fully support.
For single-byte locales, 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 mag-
ically match 0xD7 in the Greek locale but not in the Latin one.
However, there are places where this breaks down. Certain Perl constructs
are for Unicode only, such as "\p{Alpha}". They assume that 0xD7 always
has its Unicode meaning (or the equivalent on EBCDIC platforms). Since
Latin1 is a subset of Unicode and 0xD7 is the multiplication sign in both
Latin1 and Unicode, "\p{Alpha}" will never match it, regardless of locale.
A similar issue occurs with "\N{...}". Prior to v5.20, it is therefore a
bad idea to use "\p{}" or "\N{}" under plain "use locale"--unless you can
guarantee that the locale will be ISO8859-1. Use POSIX character classes
instead.
Another problem with this approach is that operations that cross the single
byte/multiple byte boundary are not well-defined, and so are disallowed.
(This boundary is between the codepoints at 255/256.) For example, lower
casing LATIN CAPITAL LETTER Y WITH DIAERESIS (U+0178) should return LATIN
SMALL LETTER Y WITH DIAERESIS (U+00FF). But in the Greek locale, for exam-
ple, there is no character at 0xFF, and Perl has no way of knowing what the
character at 0xFF is really supposed to represent. Thus it disallows the
operation. In this mode, 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 pres-
ence 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 mul-
tiplication sign, won't be interpreted by Perl that way under the Greek lo-
cale. 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 defi-
cient C library, a UTF-8 locale.
Still another problem is that this approach can lead to two code points
meaning the same character. Thus in a Greek locale, both U+03A7 and U+00D7
are GREEK CAPITAL LETTER CHI.
Because of all these problems, starting in v5.22, Perl will raise a warning
if a multi-byte (hence Unicode) code point is used when a single-byte lo-
cale is in effect. (Although it doesn't check for this if doing so would
unreasonably slow execution down.)
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 lo-
cales that work, using them may be worthwhile for certain specific pur-
poses, as long as you keep in mind the gotchas already mentioned. For ex-
ample, if the collation for your locales works, it runs faster under lo-
cales 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 con-
sistently 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 so
far, the system's strxfrm() function is called, and whatever it does is
what you get. Starting in v5.26, various bugs are fixed with the way perl
uses this function.
BUGS
Collation of strings containing embedded "NUL" characters
"NUL" characters will sort the same as the lowest collating control charac-
ter does, or to "\001" in the unlikely event that there are no control
characters at all in the locale. In cases where the strings don't contain
this non-"NUL" control, the results will be correct, and in many locales,
this control, whatever it might be, will rarely be encountered. But there
are cases where a "NUL" should sort before this control, but doesn't. If
two strings do collate identically, the one containing the "NUL" will sort
to earlier. Prior to 5.26, there were more bugs.
"LANGUAGE"
As stated above, Perl ignores this environment variable.
Embedded perls and multi-threaded
You should not change the locale after startup on a platform where
"${^SAFE_LOCALES}" is 0. It will always be 1 on an unthreaded platform.
XS writers should refer to "Dealing with embedded perls and threads" in
perlclib.
Broken systems
On a few remaining 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
<>, 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. If you have the
source for Perl, include in the bug report the output of the test described
above in "Testing for broken locales".
SEE ALSO
I18N::Langinfo, perluniintro, perlunicode, open, "localeconv" in POSIX,
"setlocale" in POSIX, "strcoll" in POSIX, "strftime" in POSIX, "strtod" in
POSIX, "strxfrm" in POSIX.
For special considerations when Perl is embedded in a C program, see "Using
embedded Perl with POSIX locales" in perlembed.
HISTORY
Jarkko Hietaniemi's original perli18n.pod heavily hacked by Dominic Dunlop,
assisted by the perl5-porters. Prose worked over a bit by Tom Chris-
tiansen, and now maintained by Perl 5 porters.
perl v5.44.0 2026-06-22 PERLLOCALE(1)