PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)NAMEperllocale - 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' prefer-
ences 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 standard-
ized (ISO C, XPG4, POSIX 1.c) method called "the locale sys-
tem". The locale system is controlled per application using
one pragma, one function call, and several environment vari-
ables.
NOTE: This feature is new in Perl 5.004, and does not apply
unless an application specifically requests it--see "Back-
ward 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 fol-
lowing must be true:
+ Your operating system must support the locale system.
If it does, you should find that the setlocale() func-
tion 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
perl v5.8.8 2006-06-30 1
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
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 follow-
ing 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 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"
+ The formatting functions (printf(), sprintf() and
write()) use "LC_NUMERIC"
+ The POSIX date formatting function (strftime()) uses
perl v5.8.8 2006-06-30 2
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
"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 informa-
tion 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 com-
bination 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 some-
thing else than LC_ALL, the function returns a string naming
the current locale for the category. You can use this value
perl v5.8.8 2006-06-30 3
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
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. Gen-
erally, 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 setlo-
cale(3).
Finding locales
For locales available in your system, consult also setlo-
cale(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
perl v5.8.8 2006-06-30 4
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
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 sys-
tems are POSIX-conformant), so use "C" when you need expli-
citly 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
perl v5.8.8 2006-06-30 5
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
to work no matter what. This usually means your locale set-
tings 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 miss-
ing). There are quick and temporary fixes to these prob-
lems, 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 set-
ting 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 environ-
ment 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 dedu-
cible. 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
perl v5.8.8 2006-06-30 6
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
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
perl v5.8.8 2006-06-30 7
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
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 com-
mands and places because these things are not that standard-
ized.
The localeconv function
The POSIX::localeconv() function allows you to get particu-
lars 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 format-
ting, 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 $thousands_sep;
perl v5.8.8 2006-06-30 8
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
# grouping and mon_grouping are packed lists
# of small integers (characters) telling the
# grouping (thousand_seps and mon_thousand_seps
# being the group dividers) of numbers and
# monetary quantities. The integers' meanings:
# 255 means no more grouping, 0 means repeat
# the previous grouping, 1-254 means use that
# as the current grouping. Grouping goes from
# right to left (low to high digits). In the
# below we cheat slightly by never using anything
# else than the first grouping (whatever that is).
if ($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 lan-
ginfo(): 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.
perl v5.8.8 2006-06-30 9
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)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 "ENVIRON-
MENT" 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");
perl v5.8.8 2006-06-30 10
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
$equal_in_locale will be true if the collation locale speci-
fies a dictionary-like ordering that ignores space charac-
ters 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 ver-
sion 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 pro-
duces to be portable across systems--or even from one revi-
sion 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
perl v5.8.8 2006-06-30 11
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
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 transli-
terating 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 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 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
perl v5.8.8 2006-06-30 12
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
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 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 format-
ted 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 func-
tion 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".
perl v5.8.8 2006-06-30 13
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
Other categories
The remaining locale category, "LC_MESSAGES" (possibly sup-
plemented 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
$! and the error messages given by external utilities may be
changed by "LC_MESSAGES". If you want to have portable
error codes, use "%!". See Errno.
SECURITY
Although the main discussion of Perl security issues can be
found in perlsec, a discussion of Perl's locale handling
would be incomplete if it did not draw your attention to
locale-dependent security issues. Locales--particularly on
systems that allow unprivileged users to build their own
locales--are untrustworthy. A malicious (or just plain bro-
ken) locale can make a locale-aware application give unex-
pected results. Here are a few possibilities:
+ Regular expression checks for safe file names or mail
addresses using "\w" may be spoofed by an "LC_CTYPE"
locale that claims that characters such as ">" and "|"
are alphanumeric.
+ String interpolation with case-mapping, as in, say,
"$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 sub-
verted. 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
perl v5.8.8 2006-06-30 14
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
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 conse-
quence. 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()):
perl v5.8.8 2006-06-30 15
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
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(), isdi-
git(), 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";
perl v5.8.8 2006-06-30 16
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
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 vari-
able 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 environ-
ment 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, warn-
ing, 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.
perl v5.8.8 2006-06-30 17
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
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 infor-
mation, generally behaving as if something similar to the
"C" locale were always in force, even if the program
environment suggested otherwise (see "The setlocale func-
tion"). By default, Perl still behaves this way for back-
ward 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 vari-
ables. 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",
perl v5.8.8 2006-06-30 18
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
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 environ-
ment 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 stan-
dards, 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
perl v5.8.8 2006-06-30 19
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
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 con-
strued 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 version 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 perlun-
icode 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 deficien-
cies can and will result in mysterious hangs and/or Perl
core dumps when the "use locale" is in effect. When con-
fronted 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
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.
Last update: Thu Jun 11 08:44:13 MDT 1998
perl v5.8.8 2006-06-30 20
