NAME¶
perllocale - Perl locale handling (internationalization and localization)
DESCRIPTION¶
Locales these days have been mostly been supplanted by Unicode, but Perl
continues to support them. See "Unicode and UTF-8" below.
Perl supports language-specific notions of data such as "is this a
letter", "what is the uppercase equivalent of this letter", and
"which of these letters comes first". These are important issues,
especially for languages other than English--but also for English: it would be
naieve to imagine that "A-Za-z" defines all the "letters"
needed to write correct English. Perl is also aware that some character other
than "." may be preferred as a decimal point, and that output date
representations may be language-specific. The process of making an application
take account of its users' preferences in such matters is called
internationalization (often abbreviated as
i18n); telling such
an application about a particular set of preferences is known as
localization (
l10n).
Perl can understand language-specific data via the standardized (ISO C, XPG4,
POSIX 1.c) method called "the locale system". The locale system is
controlled per application using one pragma, one function call, and several
environment variables.
NOTE: This feature is new in Perl 5.004, and does not apply unless an
application specifically requests it--see "Backward compatibility".
The one exception is that
write() now
always uses the current
locale - see "NOTES".
PREPARING TO USE LOCALES¶
If Perl applications are to understand and present your data correctly according
a locale of your choice,
all of the following must be true:
- •
- Your operating system must support the locale
system. If it does, you should find that the setlocale()
function is a documented part of its C library.
- •
- Definitions for locales that you use must be
installed. You, or your system administrator, must make sure that this
is the case. The available locales, the location in which they are kept,
and the manner in which they are installed all vary from system to system.
Some systems provide only a few, hard-wired locales and do not allow more
to be added. Others allow you to add "canned" locales provided
by the system supplier. Still others allow you or the system administrator
to define and add arbitrary locales. (You may have to ask your supplier to
provide canned locales that are not delivered with your operating system.)
Read your system documentation for further illumination.
- •
- Perl must believe that the locale system is
supported. If it does, "perl -V:d_setlocale" will say that
the value for "d_setlocale" is "define".
If you want a Perl application to process and present your data according to a
particular locale, the application code should include the
"use locale" pragma (see "The use locale pragma")
where appropriate, and
at least one of the following must be true:
- 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 whoever set up your
system account; or
- 2.
- The application must set its own locale using the
method described in "The setlocale function".
USING LOCALES¶
The use locale pragma¶
By default, Perl ignores the current locale. The "use locale"
pragma and the "/l" regular expression modifier tell Perl to use the
current locale for some operations ("/l" for just pattern matching).
The current locale is set at execution time by
setlocale() described
below. If that function hasn't yet been called in the course of the program's
execution, the current locale is that which was determined by the
"ENVIRONMENT" in effect at the start of the program, except that
"LC_NUMERIC" is always initialized to the C locale (mentioned under
"Finding locales"). If there is no valid environment, the current
locale is undefined. It is likely, but not necessarily, the "C"
locale.
The operations that are affected by locale are:
- •
- The comparison operators ("lt",
"le", "cmp", "ge", and "gt") and
the POSIX string collation functions strcoll() and strxfrm()
use "LC_COLLATE". sort() is also affected if used without
an explicit comparison function, because it uses "cmp" by
default.
Note: "eq" and "ne" are unaffected by locale:
they always perform a char-by-char comparison of their scalar operands.
What's more, if "cmp" finds that its operands are equal
according to the collation sequence specified by the current locale, it
goes on to perform a char-by-char comparison, and only returns 0
(equal) if the operands are char-for-char identical. If you really want to
know whether two strings--which "eq" and "cmp" may
consider different--are equal as far as collation in the locale is
concerned, see the discussion in "Category LC_COLLATE:
Collation".
- •
- Regular expressions and case-modification functions
( uc(), lc(), ucfirst(), and lcfirst()) use
"LC_CTYPE"
- •
- Format declarations (format()) use
"LC_NUMERIC"
- •
- The POSIX date formatting function
(strftime()) uses "LC_TIME".
"LC_COLLATE", "LC_CTYPE", and so on, are discussed further
in "LOCALE CATEGORIES".
The default behavior is restored with the "no locale" pragma, or
upon reaching the end of block enclosing "use locale".
The string result of any operation that uses locale information is tainted, as
it is possible for a locale to be untrustworthy. See "SECURITY".
The setlocale function¶
You can switch locales as often as you wish at run time with the
POSIX::setlocale() function:
# This functionality not usable prior to Perl 5.004
require 5.004;
# Import locale-handling tool set from POSIX module.
# This example uses: setlocale -- the function call
# LC_CTYPE -- explained below
use POSIX qw(locale_h);
# query and save the old locale
$old_locale = setlocale(LC_CTYPE);
setlocale(LC_CTYPE, "fr_CA.ISO8859-1");
# LC_CTYPE now in locale "French, Canada, codeset ISO 8859-1"
setlocale(LC_CTYPE, "");
# LC_CTYPE now reset to default defined by LC_ALL/LC_CTYPE/LANG
# environment variables. See below for documentation.
# restore the old locale
setlocale(LC_CTYPE, $old_locale);
The first argument of
setlocale() gives the
category, the second
the
locale. The category tells in what aspect of data processing you
want to apply locale-specific rules. Category names are discussed in
"LOCALE CATEGORIES" and "ENVIRONMENT". The locale is the
name of a collection of customization information corresponding to a
particular combination of language, country or territory, and codeset. Read on
for hints on the naming of locales: not all systems name locales as in the
example.
If no second argument is provided and the category is something else than
LC_ALL, the function returns a string naming the current locale for the
category. You can use this value as the second argument in a subsequent call
to
setlocale().
If no second argument is provided and the category is LC_ALL, the result is
implementation-dependent. It may be a string of concatenated locale names
(separator also implementation-dependent) or a single locale name. Please
consult your
setlocale(3) man page for details.
If a second argument is given and it corresponds to a valid locale, the locale
for the category is set to that value, and the function returns the
now-current locale value. You can then use this in yet another call to
setlocale(). (In some implementations, the return value may sometimes
differ from the value you gave as the second argument--think of it as an alias
for the value you gave.)
As the example shows, if the second argument is an empty string, the category's
locale is returned to the default specified by the corresponding environment
variables. Generally, this results in a return to the default that was in
force when Perl started up: changes to the environment made by the application
after startup may or may not be noticed, depending on your system's C library.
If the second argument does not correspond to a valid locale, the locale for the
category is not changed, and the function returns
undef.
For further information about the categories, consult
setlocale(3).
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.
Warning. The C locale
delivered by some vendors may not actually exactly match what the C standard
calls for. So beware.
NOTE: Not all systems have the "POSIX" locale (not all systems
are POSIX-conformant), so use "C" when you need explicitly to
specify this default locale.
LOCALE PROBLEMS¶
You may encounter the following warning message at Perl startup:
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
LC_ALL = "En_US",
LANG = (unset)
are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
This means that your locale settings had LC_ALL set to "En_US" and
LANG exists but has no value. Perl tried to believe you but could not.
Instead, Perl gave up and fell back to the "C" locale, the default
locale that is supposed to work no matter what. This usually means your locale
settings were wrong, they mention locales 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.
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 a zero value, for example "0". This method
really just sweeps the problem under the carpet: you tell Perl to shut up even
when Perl sees that something is wrong. Do not be surprised if later something
locale-dependent misbehaves.
Perl can be run under the "C" locale by setting the environment
variable LC_ALL to "C". This method is perhaps a bit more civilized
than the PERL_BADLANG approach, but setting LC_ALL (or other locale variables)
may affect other programs as well, not just Perl. In particular, external
programs run from within Perl will see these changes. If you make the new
settings permanent (read on), all programs you run see the changes. See
"ENVIRONMENT" for the full list of relevant environment variables
and "USING LOCALES" for their effects in Perl. Effects in other
programs are easily deducible. For example, the variable LC_COLLATE may well
affect your
sort program (or whatever the program that arranges
"records" alphabetically in your system is called).
You can test out changing these variables temporarily, and if the new settings
seem to help, put those settings into your shell startup files. Consult your
local documentation for the exact details. For in Bourne-like shells (
sh,
ksh,
bash,
zsh):
LC_ALL=en_US.ISO8859-1
export LC_ALL
This assumes that we saw the locale "en_US.ISO8859-1" using the
commands discussed above. We decided to try that instead of the above faulty
locale "En_US"--and in Cshish shells (
csh,
tcsh)
setenv LC_ALL en_US.ISO8859-1
or if you have the "env" application you can do in any shell
env LC_ALL=en_US.ISO8859-1 perl ...
If you do not know what shell you have, consult your local helpdesk or the
equivalent.
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
"LC_NUMERIC" and "LC_MONETARY" locales. (If you just want
the name of the current locale for a particular category, use
POSIX::setlocale() with a single parameter--see "The setlocale
function".)
use POSIX qw(locale_h);
# Get a reference to a hash of locale-dependent info
$locale_values = localeconv();
# Output sorted list of the values
for (sort keys %$locale_values) {
printf "%-20s = %s\n", $_, $locale_values->{$_}
}
localeconv() takes no arguments, and returns
a reference to a
hash. The keys of this hash are variable names for formatting, such as
"decimal_point" and "thousands_sep". The values are the
corresponding, er, values. See "localeconv" in POSIX for a longer
example listing the categories an implementation might be expected to provide;
some provide more and others fewer. You don't need an explicit "use
locale", because
localeconv() always observes the current locale.
Here's a simple-minded example program that rewrites its command-line parameters
as integers correctly formatted in the current locale:
# See comments in previous example
require 5.004;
use POSIX qw(locale_h);
# Get some of locale's numeric formatting parameters
my ($thousands_sep, $grouping) =
@{localeconv()}{'thousands_sep', 'grouping'};
# Apply defaults if values are missing
$thousands_sep = ',' unless $thousands_sep;
# grouping and mon_grouping are packed lists
# of small integers (characters) telling the
# grouping (thousand_seps and mon_thousand_seps
# being the group dividers) of numbers and
# monetary quantities. The integers' meanings:
# 255 means no more grouping, 0 means repeat
# the previous grouping, 1-254 means use that
# as the current grouping. Grouping goes from
# right to left (low to high digits). In the
# below we cheat slightly by never using anything
# else than the first grouping (whatever that is).
if ($grouping) {
@grouping = unpack("C*", $grouping);
} else {
@grouping = (3);
}
# Format command line params for current locale
for (@ARGV) {
$_ = int; # Chop non-integer part
1 while
s/(\d)(\d{$grouping[0]}($|$thousands_sep))/$1$thousands_sep$2/;
print "$_";
}
print "\n";
I18N::Langinfo¶
Another interface for querying locale-dependent information is the
I18N::Langinfo::langinfo() function, available at least in Unix-like
systems and VMS.
The following example will import the
langinfo() function itself and
three constants to be used as arguments to
langinfo(): a constant for
the abbreviated first day of the week (the numbering starts from Sunday = 1)
and two more constants for the affirmative and negative answers for a yes/no
question in the current locale.
use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
my ($abday_1, $yesstr, $nostr) = map { langinfo } qw(ABDAY_1 YESSTR NOSTR);
print "$abday_1? [$yesstr/$nostr] ";
In other words, in the "C" (or English) locale the above will probably
print something like:
Sun? [yes/no]
See I18N::Langinfo for more information.
LOCALE CATEGORIES¶
The following subsections describe basic locale categories. Beyond these, some
combination categories allow manipulation of more than one basic category at a
time. See "ENVIRONMENT" for a discussion of these.
Category LC_COLLATE: Collation¶
In the scope of "use locale", Perl looks to the
"LC_COLLATE" environment variable to determine the application's
notions on collation (ordering) of characters. For example, "b"
follows "a" in Latin alphabets, but where do "a" and
"aa" belong? And while "color" follows
"chocolate" in English, what about in Spanish?
The following collations all make sense and you may meet any of them if you
"use locale".
A B C D E a b c d e
A a B b C c D d E e
a A b B c C d D e E
a b c d e A B C D E
Here is a code snippet to tell what "word" characters are in the
current locale, in that locale's order:
use locale;
print +(sort grep /\w/, map { chr } 0..255), "\n";
Compare this with the characters that you see and their order if you state
explicitly that the locale should be ignored:
no locale;
print +(sort grep /\w/, map { chr } 0..255), "\n";
This machine-native collation (which is what you get unless
"use locale" has appeared earlier in the same block) must be
used for sorting raw binary data, whereas the locale-dependent collation of
the first example is useful for natural text.
As noted in "USING LOCALES", "cmp" compares according to the
current collation locale when "use locale" is in effect, but falls
back to a char-by-char comparison for strings that the locale says are equal.
You can use
POSIX::strcoll() if you don't want this fall-back:
use POSIX qw(strcoll);
$equal_in_locale =
!strcoll("space and case ignored", "SpaceAndCaseIgnored");
$equal_in_locale will be true if the collation locale specifies a
dictionary-like ordering that ignores space characters completely and which
folds case.
If you have a single string that you want to check for "equality in
locale" against several others, you might think you could gain a little
efficiency by using
POSIX::strxfrm() in conjunction with
"eq":
use POSIX qw(strxfrm);
$xfrm_string = strxfrm("Mixed-case string");
print "locale collation ignores spaces\n"
if $xfrm_string eq strxfrm("Mixed-casestring");
print "locale collation ignores hyphens\n"
if $xfrm_string eq strxfrm("Mixedcase string");
print "locale collation ignores case\n"
if $xfrm_string eq strxfrm("mixed-case string");
strxfrm() takes a string and maps it into a transformed string for use in
char-by-char comparisons against other transformed strings during collation.
"Under the hood", locale-affected Perl comparison operators call
strxfrm() for both operands, then do a char-by-char comparison of the
transformed strings. By calling
strxfrm() explicitly and using a non
locale-affected comparison, the example attempts to save a couple of
transformations. But in fact, it doesn't save anything: Perl magic (see
"Magic Variables" in perlguts) creates the transformed version of a
string the first time it's needed in a comparison, then keeps this version
around in case it's needed again. An example rewritten the easy way with
"cmp" runs just about as fast. It also copes with null characters
embedded in strings; if you call
strxfrm() directly, it treats the
first null it finds as a terminator. don't expect the transformed strings it
produces to be portable across systems--or even from one revision of your
operating system to the next. In short, don't call
strxfrm() directly:
let Perl do it for you.
Note: "use locale" isn't shown in some of these examples because it
isn't needed:
strcoll() and
strxfrm() exist only to generate
locale-dependent results, and so always obey the current
"LC_COLLATE" locale.
Category LC_CTYPE: Character Types¶
In the scope of "use locale", Perl obeys the "LC_CTYPE"
locale setting. This controls the application's notion of which characters are
alphabetic. This affects Perl's "\w" regular expression
metanotation, which stands for alphanumeric characters--that is, alphabetic,
numeric, and including other special characters such as the underscore or
hyphen. (Consult perlre for more information about regular expressions.)
Thanks to "LC_CTYPE", depending on your locale setting, characters
like "ae", "d`", "ss", and "o" may be
understood as "\w" characters.
The "LC_CTYPE" locale also provides the map used in transliterating
characters between lower and uppercase. This affects the case-mapping
functions--
lc(), lcfirst,
uc(), and
ucfirst();
case-mapping interpolation with "\l", "\L",
"\u", or "\U" in double-quoted strings and
"s///" substitutions; and case-independent regular expression
pattern matching using the "i" modifier.
Finally, "LC_CTYPE" affects the POSIX character-class test functions--
isalpha(),
islower(), and so on. For example, if you move from
the "C" locale to a 7-bit Scandinavian one, you may find--possibly
to your surprise--that "|" moves from the
ispunct() class to
isalpha().
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".
After a proper
POSIX::setlocale() call, Perl obeys the
"LC_NUMERIC" locale information, which controls an application's
idea of how numbers should be formatted for human readability by the
printf(),
sprintf(), and
write() functions.
String-to-numeric conversion by the
POSIX::strtod() function is also
affected. In most implementations the only effect is to change the character
used for the decimal point--perhaps from "." to ",". These
functions aren't aware of such niceties as thousands separation and so on.
(See "The localeconv function" if you care about these things.)
Output produced by
print() is also affected by the current locale: it
corresponds to what you'd get from
printf() in the "C"
locale. The same is true for Perl's internal conversions between numeric and
string formats:
use POSIX qw(strtod setlocale LC_NUMERIC);
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".
The C standard defines the "LC_MONETARY" category, but not a function
that is affected by its contents. (Those with experience of standards
committees will recognize that the working group decided to punt on the
issue.) Consequently, Perl takes no notice of it. If you really want to use
"LC_MONETARY", you can query its contents--see "The localeconv
function"--and use the information that it returns in your application's
own formatting of currency amounts. However, you may well find that the
information, voluminous and complex though it may be, still does not quite
meet your requirements: currency formatting is a hard nut to crack.
See also I18N::Langinfo and "CRNCYSTR".
LC_TIME¶
Output produced by
POSIX::strftime(), which builds a formatted
human-readable date/time string, is affected by the current
"LC_TIME" locale. Thus, in a French locale, the output produced by
the %B format element (full month name) for the first month of the year would
be "janvier". Here's how to get a list of long month names in the
current locale:
use POSIX qw(strftime);
for (0..11) {
$long_month_name[$_] =
strftime("%B", 0, 0, 0, 1, $_, 96);
}
Note: "use locale" isn't needed in this example: as a function that
exists only to generate locale-dependent results,
strftime() always
obeys the current "LC_TIME" locale.
See also I18N::Langinfo and "ABDAY_1".."ABDAY_7",
"DAY_1".."DAY_7",
"ABMON_1".."ABMON_12", and
"ABMON_1".."ABMON_12".
Other categories¶
The remaining locale category, "LC_MESSAGES" (possibly supplemented by
others in particular implementations) is not currently used by Perl--except
possibly to affect the behavior of library functions called by extensions
outside the standard Perl distribution and by the operating system and its
utilities. Note especially that the string value of $! and the error messages
given by external utilities may be changed by "LC_MESSAGES". If you
want to have portable error codes, use "%!". See Errno.
SECURITY¶
Although the main discussion of Perl security issues can be found in perlsec, a
discussion of Perl's locale handling would be incomplete if it did not draw
your attention to locale-dependent security issues. Locales--particularly on
systems that allow unprivileged users to build their own locales--are
untrustworthy. A malicious (or just plain broken) locale can make a
locale-aware application give unexpected results. Here are a few
possibilities:
- •
- Regular expression checks for safe file names or mail
addresses using "\w" may be spoofed by an "LC_CTYPE"
locale that claims that characters such as ">" and
"|" are alphanumeric.
- •
- String interpolation with case-mapping, as in, say,
"$dest = "C:\U$name.$ext"", may produce dangerous
results if a bogus LC_CTYPE case-mapping table is in effect.
- •
- A sneaky "LC_COLLATE" locale could result in the
names of students with "D" grades appearing ahead of those with
"A"s.
- •
- 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.
- •
- 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.
Here is a summary of the tainting behavior of operators and functions that may
be affected by the locale:
- •
- Comparison operators ("lt",
"le", "ge", "gt" and "cmp"):
Scalar true/false (or less/equal/greater) result is never tainted.
- •
- Case-mapping interpolation (with "\l",
"\L", "\u" or "\U")
Result string containing interpolated material is tainted if "use
locale" is in effect.
- •
- Matching operator ("m//"):
Scalar true/false result never tainted.
Subpatterns, either delivered as a list-context result or as $1 etc. are
tainted if "use locale" is in effect, and the subpattern regular
expression contains "\w" (to match an alphanumeric character),
"\W" (non-alphanumeric character), "\s" (whitespace
character), or "\S" (non whitespace character). The
matched-pattern variable, $&, $` (pre-match), $' (post-match), and $+
(last match) are also tainted if "use locale" is in effect and
the regular expression contains "\w", "\W",
"\s", or "\S".
- •
- Substitution operator ("s///"):
Has the same behavior as the match operator. Also, the left operand of
"=~" becomes tainted when "use locale" in effect if
modified as a result of a substitution based on a regular expression match
involving "\w", "\W", "\s", or
"\S"; or of case-mapping with "\l",
"\L","\u" or "\U".
- •
- Output formatting functions (printf() and
write()):
Results are never tainted because otherwise even output from print, for
example "print(1/7)", should be tainted if "use
locale" is in effect.
- •
- Case-mapping functions (lc(),
lcfirst(), uc(), ucfirst()):
Results are tainted if "use locale" is in effect.
- •
- POSIX locale-dependent functions
(localeconv(), strcoll(), strftime(),
strxfrm()):
Results are never tainted.
- •
- POSIX character class tests (isalnum(),
isalpha(), isdigit(), isgraph(), islower(),
isprint(), ispunct(), isspace(), isupper(),
isxdigit()):
True/false results are never tainted.
Three examples illustrate locale-dependent tainting. The first program, which
ignores its locale, won't run: a value taken directly from the command line
may not be used to name an output file when taint checks are enabled.
#/usr/local/bin/perl -T
# Run with taint checking
# Command line sanity check omitted...
$tainted_output_file = shift;
open(F, ">$tainted_output_file")
or warn "Open of $untainted_output_file failed: $!\n";
The program can be made to run by "laundering" the tainted value
through a regular expression: the second example--which still ignores locale
information--runs, creating the file named on its command line if it can.
#/usr/local/bin/perl -T
$tainted_output_file = shift;
$tainted_output_file =~ m%[\w/]+%;
$untainted_output_file = $&;
open(F, ">$untainted_output_file")
or warn "Open of $untainted_output_file failed: $!\n";
Compare this with a similar but locale-aware program:
#/usr/local/bin/perl -T
$tainted_output_file = shift;
use locale;
$tainted_output_file =~ m%[\w/]+%;
$localized_output_file = $&;
open(F, ">$localized_output_file")
or warn "Open of $localized_output_file failed: $!\n";
This third program fails to run because $& is tainted: it is the result of a
match involving "\w" while "use locale" is in effect.
ENVIRONMENT¶
- PERL_BADLANG
- A string that can suppress Perl's warning about failed
locale settings at startup. Failure can occur if the locale support in the
operating system is lacking (broken) in some way--or if you mistyped the
name of a locale when you set up your environment. If this environment
variable is absent, or has a value that does not evaluate to integer
zero--that is, "0" or ""-- Perl will complain about
locale setting failures.
NOTE: PERL_BADLANG only gives you a way to hide the warning message.
The message tells about some problem in your system's locale support, and
you should investigate what the problem is.
- DPKG_RUNNING_VERSION
- On Debian systems, if the DPKG_RUNNING_VERSION environment
variable is set (to any value), the locale failure warnings will be
suppressed just like with a zero PERL_BADLANG setting. This is done to
avoid floods of spurious warnings during system upgrades. See
<http://bugs.debian.org/508764>.
The following environment variables are not specific to Perl: They are part of
the standardized (ISO C, XPG4, POSIX 1.c)
setlocale() method for
controlling an application's opinion on data.
- LC_ALL
- "LC_ALL" is the "override-all" locale
environment variable. If set, it overrides all the rest of the locale
environment variables.
- LANGUAGE
- NOTE: "LANGUAGE" is a GNU extension, it
affects you only if you are using the GNU libc. This is the case if you
are using e.g. Linux. If you are using "commercial" Unixes you
are most probably not using GNU libc and you can ignore
"LANGUAGE".
However, in the case you are using "LANGUAGE": it affects the
language of informational, warning, and error messages output by commands
(in other words, it's like "LC_MESSAGES") but it has higher
priority than "LC_ALL". Moreover, it's not a single value but
instead a "path" (":"-separated list) of
languages (not locales). See the GNU "gettext" library
documentation for more information.
- LC_CTYPE
- In the absence of "LC_ALL", "LC_CTYPE"
chooses the character type locale. In the absence of both
"LC_ALL" and "LC_CTYPE", "LANG" chooses the
character type locale.
- LC_COLLATE
- In the absence of "LC_ALL",
"LC_COLLATE" chooses the collation (sorting) locale. In the
absence 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_...".
Examples¶
The LC_NUMERIC controls the numeric output:
use locale;
use POSIX qw(locale_h); # Imports setlocale() and the LC_ constants.
setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
printf "%g\n", 1.23; # If the "fr_FR" succeeded, probably shows 1,23.
and also how strings are parsed by
POSIX::strtod() as numbers:
use locale;
use POSIX qw(locale_h strtod);
setlocale(LC_NUMERIC, "de_DE") or die "Entschuldigung";
my $x = strtod("2,34") + 5;
print $x, "\n"; # Probably shows 7,34.
NOTES¶
Backward compatibility¶
Versions of Perl prior to 5.004
mostly ignored locale information,
generally behaving as if something similar to the "C" locale were
always in force, even if the program environment suggested otherwise (see
"The setlocale function"). By default, Perl still behaves this way
for backward compatibility. If you want a Perl application to pay attention to
locale information, you
must use the "use locale" pragma
(see "The use locale pragma") or for just pattern matching, the
"/l" regular expression modifier (see "Character set
modifiers" in perlre) to instruct it to do so.
Versions of Perl from 5.002 to 5.003 did use the "LC_CTYPE"
information if available; that is, "\w" did understand what were the
letters according to the locale environment variables. The problem was that
the user had no control over the feature: if the C library supported locales,
Perl used them.
I18N:Collate obsolete¶
In versions of Perl prior to 5.004, per-locale collation was possible using the
"I18N::Collate" library module. This module is now mildly obsolete
and should be avoided in new applications. The "LC_COLLATE"
functionality is now integrated into the Perl core language: One can use
locale-specific scalar data completely normally with "use locale",
so there is no longer any need to juggle with the scalar references of
"I18N::Collate".
Sort speed and memory use impacts¶
Comparing and sorting by locale is usually slower than the default sorting;
slow-downs of two to four times have been observed. It will also consume more
memory: once a Perl scalar variable has participated in any string comparison
or sorting operation obeying the locale collation rules, it will take 3-15
times more memory than before. (The exact multiplier depends on the string's
contents, the operating system and the locale.) These downsides are dictated
more by the operating system's implementation of the locale system than by
Perl.
write() and LC_NUMERIC¶
If a program's environment specifies an LC_NUMERIC locale and "use
locale" is in effect when the format is declared, the locale is used to
specify the decimal point character in formatted output. Formatted output
cannot be controlled by "use locale" at the time when
write()
is called.
Freely available locale definitions¶
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, ungainly, and having too large a granularity. (Locales apply to
a whole process, when it would arguably be more useful to have them apply to a
single thread, window group, or whatever.) They also have a tendency, like
standards groups, to divide the world into nations, when we all know that the
world can equally well be divided into bankers, bikers, gamers, and so on.
Unicode and UTF-8¶
The support of Unicode is new starting from Perl version 5.6, and more fully
implemented in version 5.8 and later. See perluniintro. Perl tries to work
with both Unicode and locales--but of course, there are problems.
Perl does not handle multi-byte locales, such as have been used for various
Asian languages, such as Big5 or Shift JIS. However, the increasingly common
multi-byte UTF-8 locales, if properly implemented, tend to work reasonably
well in Perl, simply because both they and Perl store characters that take up
multiple bytes the same way.
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 wasn't
uniformly applied prior to Perl 5.14). 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, even if the string is encoded in UTF-8, which would normally
imply Unicode semantics. (The "U" in UTF-8 stands for Unicode.)
However, there are places where this breaks down. Certain 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{...}". It is therefore a bad idea to
use "\p{}" or "\N{}" under "use locale"--
unless you can guarantee that the locale will be a ISO8859-1 or UTF-8
one. Use POSIX character classes instead.
The same problem ensues 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. Again, this is not a problem
provided you make certain that all
locales will always and only be either an ISO8859-1 or a UTF-8 locale.
Vendor locales are notoriously buggy, and it is difficult for Perl to test its
locale-handling code because this interacts with code that Perl has no control
over; therefore the locale-handling code in Perl may be buggy as well. But if
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, collation runs faster under locales than under Unicode::Collate
(albeit with less flexibility), and you gain access to such things as the
local currency symbol and the names of the months and days of the week.
BUGS¶
Broken systems¶
In certain systems, the operating system's locale support is broken and cannot
be fixed or used by Perl. Such deficiencies can and will result in mysterious
hangs and/or Perl core dumps when "use locale" is in effect. When
confronted with such a system, please report in excruciating detail to <
perlbug@perl.org>, and also contact your vendor: bug fixes may exist
for these problems in your operating system. Sometimes such bug fixes are
called an operating system upgrade.
SEE ALSO¶
I18N::Langinfo, perluniintro, perlunicode, open, "isalnum" in POSIX,
"isalpha" in POSIX, "isdigit" in POSIX,
"isgraph" in POSIX, "islower" in POSIX,
"isprint" in POSIX, "ispunct" in POSIX,
"isspace" in POSIX, "isupper" in POSIX,
"isxdigit" in POSIX, "localeconv" in POSIX,
"setlocale" in POSIX, "strcoll" in POSIX,
"strftime" in POSIX, "strtod" in POSIX,
"strxfrm" in POSIX.
HISTORY¶
Jarkko Hietaniemi's original
perli18n.pod heavily hacked by Dominic
Dunlop, assisted by the perl5-porters. Prose worked over a bit by Tom
Christiansen, and updated by Perl 5 porters.