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 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
often, 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. Starting 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. However, 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 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.
(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, it is possible to compute the POSIX locale data
from them, and earlier CLDR versions had these already extracted for
you as UTF-8 locales <http://unicode.org/Public/cldr/2.0.1/>.)
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 is used by Perl itself only for accessing operating system
error messages via $! and $^E.
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.
Other categories
Some platforms have other categories, dealing with such things as
measurement 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
CATEGORIES".
Together, these categories go a long way towards being able to
customize a single program to run in many different locations. But
there are deficiencies, so keep reading.
PREPARING TO USE LOCALES
Perl itself (outside the POSIX module) will not use locales unless
specifically 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:
o Your operating system must support the locale system. If it does,
you should find that the setlocale() function is a documented part
of its C library.
o Definitions for locales that you use must be installed. You, or
your system administrator, must make sure that this is the case.
The available locales, the location in which they are kept, and the
manner in which they are installed all vary from system to system.
Some systems provide only a few, hard-wired locales and do not
allow more to be added. Others allow you to add "canned" locales
provided by the system supplier. Still others allow you or the
system administrator to define and add arbitrary locales. (You may
have to ask your supplier to provide canned locales that are not
delivered with your operating system.) Read your system
documentation for further illumination.
o 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
Starting in Perl 5.28, this pragma may be used in multi-threaded
applications on systems that have thread-safe locale ability. Some
caveats apply, see "Multi-threaded" below. On systems without this
capability, or in earlier 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. Another thread may change the locale at any time,
which could cause at a minimum 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".
By default, Perl itself (outside the POSIX module) ignores the current
locale. 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.
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. If there is
no valid environment, 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->Regional 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
affected, as follows:
o The current locale is used when going outside of Perl with
operations like system() or qx//, if those operations are
locale-sensitive.
o 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.
o 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
"CAVEATS" in perlxs.
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
locale" retain that effect even outside the scope. These include:
o 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.
o Regular expression patterns can be compiled using qr// with
actual matching deferred to later. Again, it is whether or not
the compilation 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";"
o All the above operations
o Format declarations ("format" in perlfunc) and hence any
subsequent write()s use "LC_NUMERIC".
o stringification and output use "LC_NUMERIC". These include the
results of print(), printf(), say(), and sprintf().
o 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".
o Regular expressions and case-modification functions (uc(),
lc(), ucfirst(), and lcfirst()) use "LC_CTYPE"
o The variables $! (and its synonyms $ERRNO and $OS_ERROR) and
$^E> (and its synonym $EXTENDED_OS_ERROR) when used as strings
use "LC_MESSAGES".
The default behavior is restored with the "no locale" pragma, or upon
reaching the end of the block enclosing "use locale". Note that "use
locale" 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 particular instance of the pragma by adding parameters to 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",
":monetary", ":numeric", ":time", and the pseudo category ":characters"
(described below).
Thus you can say
use locale ':messages';
and only $! and $^E will be locale aware. Everything else is
unaffected.
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 Perl also
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
example,
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 feature '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 definition, 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 simultaneously. 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
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 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 something 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
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.
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
implement POSIX 2008 thread-safe locale operations, this function
doesn't actually 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 and Darwin do have this.
You can tell if using locales is safe on your system by looking at the
read-only boolean 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, and in systems compatible with POSIX 2008. Some platforms
claim to support POSIX 2008, but have buggy implementations, so that
the hints files for compiling to run on them turn off attempting to use
thread-safety. "${^SAFE_LOCALES}" will be 0 on them.
Be aware that writing a multi-threaded application will not be portable
to a platform which lacks the native thread-safe locale support. On
systems that do have it, you automatically get this behavior for
threaded perls, without having to do anything. If for some reason, you
don't want to use this capability (perhaps the POSIX 2008 support is
buggy on your system), you can manually compile Perl to use the old
non-thread-safe implementation by passing the argument
"-Accflags='-DNO_THREAD_SAFE_LOCALE'" to Configure. Except on Windows,
this will continue to use certain of the POSIX 2008 functions in some
situations. If these are buggy, you can pass the following to
Configure instead or additionally:
"-Accflags='-DNO_POSIX_2008_LOCALE'". This will also keep the code
from using thread-safe locales. "${^SAFE_LOCALES}" will be 0 on
systems that turn off the thread-safe operations.
Normally on unthreaded builds, the traditional setlocale() is used and
not the thread-safe locale functions. You can force the use of these
on systems that have them by adding the
"-Accflags='-DUSE_THREAD_SAFE_LOCALE'" to Configure.
The initial program is started up using the locale specified from the
environment, as currently, described in "ENVIRONMENT". All newly
created threads start with "LC_ALL" set to "C". Each thread may use
POSIX::setlocale() 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 "Locale-aware XS code" in perlxs.
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
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 or, rarely, a superset thereof
(such as the "DEC Multinational 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
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. (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 results. 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
environment 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 "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
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 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
locale-dependent numeric formatting information specified by the
current underlying "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::setlocale() 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
"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:
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 missing.
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 abbreviated first day of the week (the numbering starts from Sunday
= 1) and two more constants for the affirmative and negative answers
for a yes/no question in the current locale.
use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
my ($abday_1, $yesstr, $nostr)
= map { langinfo } qw(ABDAY_1 YESSTR NOSTR);
print "$abday_1? [$yesstr/$nostr] ";
In other words, in the "C" (or English) locale the above will probably
print something like:
Sun? [yes/no]
See 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: 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
notions on collation (ordering) of characters. For example, "b"
follows "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
collation locale when "use locale" is in effect, but falls back to a
char-by-char comparison for strings that the locale says are equal. You
can use POSIX::strcoll() if you don't want this fall-back:
use POSIX qw(strcoll);
$equal_in_locale =
!strcoll("space and case ignored", "SpaceAndCaseIgnored");
$equal_in_locale will be true if the collation locale specifies a
dictionary-like ordering that ignores space characters completely and
which folds case.
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
definition is deficient, so can be fixed by using a better definition
file. Unicode's definitions (see "Freely available locale
definitions") provide reasonable 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 containing 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
technically invalid. But if present, again starting in v5.26, they
will collate to the same position as the highest valid code point does.
This generally 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
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() are POSIX functions which use the
standard system-supplied "libc" functions that always obey the current
"LC_COLLATE" 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 underscore. (Consult perlre for more information
about regular expressions.) Thanks to "LC_CTYPE", depending on your
locale setting, characters like "ae", "dh", "ss", and "o" may be
understood as "\w" characters. It also affects 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
characters between lower and uppercase. This affects the case-mapping
functions--fc(), lc(), lcfirst(), uc(), and ucfirst(); case-mapping
interpolation 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
otherwise 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 support 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 locale, 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 platform. 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 particular 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 CCSID 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
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, and within the scope of a "use
locale" form that includes numerics, Perl obeys the "LC_NUMERIC" locale
information, 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
$a = " $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
committees will recognize that the working group decided to punt on the
issue.) Consequently, Perl essentially 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".
Category "LC_TIME": Respresentation of 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: strftime() is a POSIX
function which uses the standard system-supplied "libc" function that
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 categories are not currently used by Perl itself.
But again note that things Perl interacts with may use these, including
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:
o 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.
o 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.
o A sneaky "LC_COLLATE" locale could result in the names of students
with "D" grades appearing ahead of those with "A"s.
o An application that takes the trouble to use information in
"LC_MONETARY" may format debits as if they were credits and vice
versa if that locale has been subverted. Or it might make payments
in US dollars instead of Hong Kong dollars.
o The date and day names in dates formatted by strftime() could be
manipulated to advantage by a malicious user able to subvert the
"LC_DATE" locale. ("Look--it says I wasn't in the building on
Sunday.")
Such dangers are not peculiar to the locale system: any aspect of an
application's environment which may be modified maliciously presents
similar challenges. Similarly, they are not specific to Perl: any
programming language that allows you to write programs that take
account of their environment exposes you to these issues.
Perl cannot protect you from all possibilities shown in the
examples--there is no substitute for your own vigilance--but, when "use
locale" is in effect, Perl uses the tainting mechanism (see perlsec) to
mark string results that become locale-dependent, and which may be
untrustworthy in consequence.
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:
o Comparison operators ("lt", "le", "ge", "gt" and "cmp"):
Scalar true/false (or less/equal/greater) result is never tainted.
o 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.
o 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-dependent construct. These constructs include "\w" (to
match an alphanumeric character), "\W" (non-alphanumeric
character), "\b" and "\B" (word-boundary and non-boundardy, 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-
insensitively (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.
o 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 regular expression match involving any of
the things mentioned in the previous item, or of case-mapping, such
as "\l", "\L","\u", "\U", or "\F".
o 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.
o Case-mapping functions (lc(), lcfirst(), uc(), ucfirst()):
Results are tainted if a "use locale" form that includes "LC_CTYPE"
is in effect.
o 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 command line may not be used to name an output file when taint
checks are enabled.
#/usr/local/bin/perl -T
# Run with taint checking
# Command line sanity check omitted...
$tainted_output_file = shift;
open(F, ">$tainted_output_file")
or warn "Open of $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 information--runs, creating the file named on its command line
if it can.
#/usr/local/bin/perl -T
$tainted_output_file = shift;
$tainted_output_file =~ m%[\w/]+%;
$untainted_output_file = $&;
open(F, ">$untainted_output_file")
or warn "Open of $untainted_output_file failed: $!\n";
Compare this with a similar but locale-aware program:
#/usr/local/bin/perl -T
$tainted_output_file = shift;
use locale;
$tainted_output_file =~ m%[\w/]+%;
$localized_output_file = $&;
open(F, ">$localized_output_file")
or warn "Open of $localized_output_file failed: $!\n";
This third program fails to run because $& is tainted: it is the result
of a match involving "\w" while "use locale" is in effect.
ENVIRONMENT
PERL_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 environment variables to initialize with.
Instead, Perl uses whatever the current locale settings
are. This is particularly useful in embedded environments,
see "Using embedded Perl with POSIX locales" in perlembed.
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 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 controlling 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
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 of both
"LC_ALL" and "LC_COLLATE", "LANG" chooses the collation
locale.
"LC_MONETARY"
In the absence of "LC_ALL", "LC_MONETARY" chooses the
monetary formatting locale. In the absence of both
"LC_ALL" and "LC_MONETARY", "LANG" chooses the monetary
formatting locale.
"LC_NUMERIC"
In the absence of "LC_ALL", "LC_NUMERIC" chooses the
numeric format locale. In the absence of both "LC_ALL" and
"LC_NUMERIC", "LANG" chooses the numeric format.
"LC_TIME" In the absence of "LC_ALL", "LC_TIME" chooses the date and
time formatting locale. In the absence of both "LC_ALL"
and "LC_TIME", "LANG" chooses the date and time formatting
locale.
"LANG" "LANG" is the "catch-all" locale environment variable. If
it is set, it is used as the last resort after the overall
"LC_ALL" and the category-specific "LC_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
expecting 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 $a = 1.2;
print eval "$a + 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 instead change the "eval" line to do something like:
print eval "no locale; $a + 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,
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.
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 <http://unicode.org/Public/cldr/latest/>.)
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 development of your own locales.
I18n and l10n
"Internationalization" is often abbreviated as i18n because its first
and last letters are separated by eighteen others. (You may guess why
the internalin ... internaliti ... i18n tends to get abbreviated.) In
the same way, "localization" is often abbreviated to l10n.
An imperfect standard
Internationalization, as defined in the C and POSIX standards, can be
criticized as incomplete and ungainly. 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 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 (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. 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" parameter 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 (<https://unicode.org/Public/cldr/2.0.1/> for ones
that are already set-up, but from an earlier version;
<https://unicode.org/Public/cldr/latest/> 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 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(), 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 magically 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 example, 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 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.
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 locale 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 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 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
character 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.
Multi-threaded
XS code or C-language libraries called from it that use the system
setlocale(3) function (except on Windows) likely will not work from a
multi-threaded application without changes. See "Locale-aware XS code"
in perlxs.
An XS module that is locale-dependent could have been written under the
assumption that it will never be called in a multi-threaded
environment, and so uses other non-locale constructs that aren't multi-
thread-safe. See "Thread-aware system interfaces" in perlxs.
POSIX does not define a way to get the name of the current per-thread
locale. Some systems, such as Darwin and FreeBSD do implement a
function, querylocale(3) to do this. On non-Windows systems without
it, such as Linux, there are some additional caveats:
o An embedded perl needs to be started up while the global locale is
in effect. See "Using embedded Perl with POSIX locales" in
perlembed.
o It becomes more important for perl to know about all the possible
locale categories on the platform, even if they aren't apparently
used in your program. Perl knows all of the Linux ones. If your
platform has others, you can submit an issue at
<https://github.com/Perl/perl5/issues> for inclusion of it in the
next release. In the meantime, it is possible to edit the Perl
source to teach it about the category, and then recompile. Search
for instances of, say, "LC_PAPER" in the source, and use that as a
template to add the omitted one.
o It is possible, though hard to do, to call "POSIX::setlocale" with
a locale that it doesn't recognize as syntactically legal, but
actually is legal on that system. This should happen only with
embedded perls, or if you hand-craft a locale name yourself.
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 <<https://github.com/Perl/perl5/issues>>, 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(3), perluniintro(1), perlunicode(1), open(3),
localeconv(3) in POSIX, setlocale(3) in POSIX, strcoll(3) in POSIX,
strftime(3) in POSIX, strtod(3) in POSIX, strxfrm(3) in POSIX.
For special considerations when Perl is embedded in a C program, see
"Using embedded Perl with POSIX locales" in perlembed(1).
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 now maintained by Perl 5 porters.
perl v5.38.2 2023-11-28 perllocale(1)
perl 5.38.2 - Generated Sat Nov 30 09:59:24 CST 2024