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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 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 the Backward compatibility entry
elsewhere in this document. The one exception is that write() now always
uses the current locale - see the section on "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 The use locale pragma entry elsewhere in this
document) where appropriate, and at least one of the following must be
true:
· The locale-determining environment variables (see the section on
"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 The setlocale function entry elsewhere in this document.
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 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
byte-by-byte 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
byte-by-byte comparison, and only returns 0 (equal) if the operands are
bit-for-bit 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 the
Category LC_COLLATE: Collation entry elsewhere in this document.
· 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 the LOCALE
CATEGORIES entry elsewhere in this document.
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 the section on
"SECURITY".
The setlocale function
You can switch locales as often as you wish at run time with the
POSIX:\fIs0: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 the LOCALE
CATEGORIES entry elsewhere in this document and the section on
"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 single 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
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.
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
the ENVIRONMENT manpage for the full list of relevant environment variables
and the USING LOCALES entry elsewhere in this document 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
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 the Finding locales entry
elsewhere in this document. 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 the
Permanently fixing your system's locale configuration entry elsewhere in
this document.
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 the
Finding locales entry elsewhere in this document 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 the Finding locales entry
elsewhere in this document section is unfortunately a bit vague about the
exact commands and places because these things are not that standardized.
The localeconv function
The POSIX:\fIs0: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:\fIs0:setlocale() with
a single parameter--see the The setlocale function entry elsewhere in this
document.)
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 the localeconv entry in the POSIX manpage 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";
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 the section on "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 the USING LOCALES entry elsewhere in this document, "cmp"
compares according to the current collation locale when "use locale" is in
effect, but falls back to a byte-by-byte comparison for strings that the
locale says are equal. You can use POSIX:\fIs0: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:\fIs0: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
byte-by-byte comparisons against other transformed strings during
collation. "Under the hood", locale-affected Perl comparison operators
call strxfrm() for both operands, then do a byte-by-byte 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
the Magic Variables entry in the perlguts manpage) 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 the perlre
manpage 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) letters and digits--for
example, in command strings--locale-aware applications should use "\w"
inside a "no locale" block. See the section on "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:\fIs0: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 The localeconv function entry elsewhere in this document
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
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 The localeconv function
entry elsewhere in this document--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.
LC_TIME
Output produced by POSIX:\fIs0: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, $_, 96);
}
Note: "use locale" isn't needed in this example: as a function that exists
only to generate locale-dependent results, strftime() always obeys the
current "LC_TIME" locale.
Other categories
The remaining locale category, "LC_MESSAGES" (possibly supplemented by
others in particular implementations) is not currently used by Perl--except
possibly to affect the behavior of library functions called by extensions
outside the standard Perl distribution and by the operating system and its
utilities. Note especially that the string value of "$!" and the error
messages given by external utilities may be changed by "LC_MESSAGES". If
you want to have portable error codes, use "%!". See the Errno manpage.
SECURITY
Although the main discussion of Perl security issues can be found in the
perlsec manpage, 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 the perlsec manpage) 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" (white-space character), or "\S"
(non white-space 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.
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 the LC_ALL manpage. 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 The
setlocale function entry elsewhere in this document). 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 The use locale pragma entry elsewhere in this
document) 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
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 outside 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 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. But, for now, it's the only standard we've got.
This may be construed as a bug.
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 operating system. Sometimes such bug fixes are
called an operating system upgrade.
SEE ALSO
the isalnum entry in the POSIX manpage, the isalpha entry in the POSIX
manpage, the isdigit entry in the POSIX manpage, the isgraph entry in the
POSIX manpage, the islower entry in the POSIX manpage, the isprint entry in
the POSIX manpage, the ispunct entry in the POSIX manpage, the isspace
entry in the POSIX manpage, the isupper entry in the POSIX manpage, the
isxdigit entry in the POSIX manpage, the localeconv entry in the POSIX
manpage, the setlocale entry in the POSIX manpage, the strcoll entry in the
POSIX manpage, the strftime entry in the POSIX manpage, the strtod entry in
the POSIX manpage, the strxfrm entry in the POSIX manpage.
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
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