PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
NAME
perllocale - Perl locale handling (internationalization and localization)
DESCRIPTION
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 in English. Perl is also aware that some character
other than '.' may be preferred as a decimal point, and that output date representations may be lan-guage-specific. language-specific.
guage-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 set-locale() setlocale()
locale() 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 appropri-ate, appropriate,
ate, and at least one of the following must be true:
The locale-determining environment variables (see "ENVIRONMENT") must be correctly set up at the
time the application is started, either by yourself or by whoever set up your system account.
The application must set its own locale using the method described in "The setlocale function".
USING LOCALES
The use locale pragma
By default, Perl ignores the current locale. The "use locale" pragma tells Perl to use the current
locale for some operations:
The comparison operators ("lt", "le", "cmp", "ge", and "gt") and the POSIX string collation func-tions functions
tions 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 compari-son, comparison,
son, and only returns 0 (equal) if the operands are char-for-char identical. If you really want
to know whether two strings--which "eq" and "cmp" may consider different--are equal as far as
collation in the locale is concerned, see the discussion in "Category LC_COLLATE: Collation".
Regular expressions and case-modification functions (uc(), lc(), ucfirst(), and lcfirst()) use
"LC_CTYPE"
The formatting functions (printf(), sprintf() and write()) use "LC_NUMERIC"
The POSIX date formatting function (strftime()) uses "LC_TIME".
"LC_COLLATE", "LC_CTYPE", and so on, are discussed further in "LOCALE CATEGORIES".
The default behavior is restored with the "no locale" pragma, or upon reaching the end of block
enclosing "use locale".
The string result of any operation that uses locale information is tainted, as it is possible for a
locale to be untrustworthy. See "SECURITY".
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 locales names (separator also implementation-dependent) or a sin-gle single
gle locale name. Please consult your setlocale(3) 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 lan-guage_territory.codeset, language_territory.codeset,
guage_territory.codeset, but the latter parts after language are not always present. The language
and country are usually from the standards ISO 3166 and ISO 639, the two-letter abbreviations for the
countries and the languages of the world, respectively. The codeset part often mentions some ISO
8859 character set, the Latin codesets. For example, "ISO 8859-1" is the so-called "Western European
codeset" that can be used to encode most Western European languages adequately. Again, there are
several ways to write even the name of that one standard. Lamentably.
Two special locales are worth particular mention: "C" and "POSIX". Currently these are effectively
the same locale: the difference is mainly that the first one is defined by the C standard, the second
by the POSIX standard. They define the default locale in which every program starts in the absence
of locale information in its environment. (The default default locale, if you will.) Its language
is (American) English and its character codeset ASCII.
NOTE: Not all systems have the "POSIX" locale (not all systems are POSIX-conformant), so use "C" when
you need explicitly to specify this default locale.
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 some-thing something
thing 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 pro-grams programs
grams 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 for-matting formatting
matting 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 vari-able variable
able names for formatting, such as "decimal_point" and "thousands_sep". The values are the corre-sponding, corresponding,
sponding, 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 cor-rectly correctly
rectly 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() func-tion, function,
tion, 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 ques-tion question
tion in the current locale.
use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
my ($abday_1, $yesstr, $nostr) = map { langinfo } qw(ABDAY_1 YESSTR NOSTR);
print "$abday_1? [$yesstr/$nostr] ";
In other words, in the "C" (or English) locale the above will probably print something like:
Sun? [yes/no]
See I18N::Langinfo for more information.
LOCALE CATEGORIES
The following subsections describe basic locale categories. Beyond these, some combination cate-gories categories
gories allow manipulation of more than one basic category at a time. See "ENVIRONMENT" for a discus-sion discussion
sion 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 compari-son comparison
son 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_COL-LATE" "LC_COLLATE"
LATE" locale.
Category LC_CTYPE: Character Types
In the scope of "use locale", Perl obeys the "LC_CTYPE" locale setting. This controls the applica-tion's application's
tion's notion of which characters are alphabetic. This affects Perl's "\w" regular expression metan-otation, metanotation,
otation, 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 reg-ular regular
ular expressions.) Thanks to "LC_CTYPE", depending on your locale setting, characters like 'ae',
'', 'ss', and 'o' may be understood as "\w" characters.
The "LC_CTYPE" locale also provides the map used in transliterating characters between lower and
uppercase. This affects the case-mapping functions--lc(), lcfirst, uc(), and ucfirst(); case-mapping
interpolation with "\l", "\L", "\u", or "\U" in double-quoted strings and "s///" substitutions; and
case-independent regular expression pattern matching using the "i" modifier.
Finally, "LC_CTYPE" affects the POSIX character-class test functions--isalpha(), islower(), and so
on. For example, if you move from the "C" locale to a 7-bit Scandinavian one, you may find--possibly
to your surprise--that "|" moves from the ispunct() class to isalpha().
Note: A broken or malicious "LC_CTYPE" locale definition may result in clearly ineligible characters
being considered to be alphanumeric by your application. For strict matching of (mundane) letters
and digits--for example, in command strings--locale-aware applications should use "\w" inside a "no
locale" block. See "SECURITY".
Category LC_NUMERIC: Numeric Formatting
In the scope of "use locale", Perl obeys the "LC_NUMERIC" locale information, which controls an
application's idea of how numbers should be formatted for human readability by the printf(),
sprintf(), and write() functions. String-to-numeric conversion by the POSIX::strtod() function is
also affected. In most implementations the only effect is to change the character used for the deci-mal decimal
mal point--perhaps from '.' to ','. These functions aren't aware of such niceties as thousands sep-aration separation
aration and so on. (See "The localeconv function" if you care about these things.)
Output produced by print() is also affected by the current locale: it depends on whether "use locale"
or "no locale" is in effect, and corresponds to what you'd get from printf() in the "C" locale. The
same is true for Perl's internal conversions between numeric and string formats:
use POSIX qw(strtod);
use locale;
$n = 5/2; # 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 no 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 informa-tion, information,
tion, 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 localedependent
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 implemen-tations) implementations)
tations) 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 util-ities. utilities.
ities. Note especially that the string value of $! and the error messages given by external utili-ties utilities
ties may be changed by "LC_MESSAGES". If you want to have portable error codes, use "%!". See
Errno.
SECURITY
Although the main discussion of Perl security issues can be found in perlsec, a discussion of Perl's
locale handling would be incomplete if it did not draw your attention to locale-dependent security
issues. Locales--particularly on systems that allow unprivileged users to build their own
locales--are untrustworthy. A malicious (or just plain broken) locale can make a locale-aware appli-cation application
cation give unexpected results. Here are a few possibilities:
Regular expression checks for safe file names or mail addresses using "\w" may be spoofed by an
"LC_CTYPE" locale that claims that characters such as ">" and "|" are alphanumeric.
String interpolation with case-mapping, as in, say, "$dest = "C:\U$name.$ext"", may produce dan-gerous dangerous
gerous 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 char-acter), character),
acter), "\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. Fail-ure Failure
ure can occur if the locale support in the operating system is lacking (broken) in some
way--or if you mistyped the name of a locale when you set up your environment. If this
environment variable is absent, or has a value that does not evaluate to integer
zero--that is, "0" or ""-- Perl will complain about locale setting failures.
NOTE: PERL_BADLANG only gives you a way to hide the warning message. The message tells
about some problem in your system's locale support, and you should investigate what the
problem is.
The following environment variables are not specific to Perl: They are part of the standardized (ISO
C, XPG4, POSIX 1.c) setlocale() method for controlling an application's opinion on data.
LC_ALL "LC_ALL" is the "override-all" locale environment variable. If set, it overrides all the
rest of the locale environment variables.
LANGUAGE NOTE: "LANGUAGE" is a GNU extension, it affects you only if you are using the GNU libc.
This is the case if you are using e.g. Linux. If you are using "commercial" UNIXes you
are most probably not using GNU libc and you can ignore "LANGUAGE".
However, in the case you are using "LANGUAGE": it affects the language of informational,
warning, and error messages output by commands (in other words, it's like "LC_MESSAGES")
but it has higher priority than LC_ALL. Moreover, it's not a single value but instead a
"path" (":"-separated list) of languages (not locales). See the GNU "gettext" library
documentation for more information.
LC_CTYPE In the absence of "LC_ALL", "LC_CTYPE" chooses the character type locale. In the absence
of both "LC_ALL" and "LC_CTYPE", "LANG" chooses the character type locale.
LC_COLLATE In the absence of "LC_ALL", "LC_COLLATE" chooses the collation (sorting) locale. In the
absence 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_...".
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") 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 partici-pated participated
pated 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 imple-mentation implementation
mentation of the locale system than by Perl.
write() and LC_NUMERIC
Formats are the only part of Perl that unconditionally use information from a program's locale; if a
program's environment specifies an LC_NUMERIC locale, it is always used to specify the decimal point
character in formatted output. Formatted output cannot be controlled by "use locale" because the
pragma is tied to the block structure of the program, and, for historical reasons, formats exist out-side outside
side that block structure.
Freely available locale definitions
There is a large collection of locale definitions at ftp://dkuug.dk/i18n/WG15-collection . 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 abbrevi-
ated.) 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. But, for now, it's the
only standard we've got. This may be construed as a bug.
Unicode and UTF-8
The support of Unicode is new starting from Perl version 5.6, and more fully implemented in the ver-
sion 5.8. See perluniintro and perlunicode for more details.
Usually locale settings and Unicode do not affect each other, but there are exceptions, see "Locales"
in perlunicode for examples.
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 the "use
locale" is in effect. When confronted with such a system, please report in excruciating detail to
<perlbug@perl.org>, and complain to your vendor: bug fixes may exist for these problems in your oper-
ating 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, "str-
coll" 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.
Last update: Thu Jun 11 08:44:13 MDT 1998
perl v5.8.8 2006-01-07 PERLLOCALE(1)
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