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PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
NAME
perllocale - Perl locale handling (internationalization and localiza-
tion)
DESCRIPTION
Perl supports language-specific notions of data such as "is this a let-
ter", "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 interna-
tionalization (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:
o Your operating system must support the locale system. If it does,
you should find that the setlocale() function is a documented part
of its C library.
o Definitions for locales that you use must be installed. You, or
your system administrator, must make sure that this is the case.
The available locales, the location in which they are kept, and the
manner in which they are installed all vary from system to system.
Some systems provide only a few, hard-wired locales and do not
allow more to be added. Others allow you to add "canned" locales
provided by the system supplier. Still others allow you or the
system administrator to define and add arbitrary locales. (You may
have to ask your supplier to provide canned locales that are not
delivered with your operating system.) Read your system documenta-
tion for further illumination.
o Perl must believe that the locale system is supported. If it does,
"perl -V:d_setlocale" will say that the value for "d_setlocale" is
"define".
If you want a Perl application to process and present your data accord-
ing to a particular locale, the application code should include the
"use locale" pragma (see "The use locale pragma") where appropriate,
and at least one of the following must be true:
o 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.
o 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:
o 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".
o Regular expressions and case-modification functions (uc(), lc(),
ucfirst(), and lcfirst()) use "LC_CTYPE"
o The formatting functions (printf(), sprintf() and write()) use
"LC_NUMERIC"
o 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 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 corre-
sponding 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 stan-
dardized, names of locales and the directories where the configuration
resides have not been. The basic form of the name is language_terri-
tory.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 men-
tions 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 pro-
gram 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 vari-
able LC_ALL to "C". This method is perhaps a bit more civilized than
the PERL_BADLANG approach, but setting LC_ALL (or other locale vari-
ables) may affect other programs as well, not just Perl. In particu-
lar, external programs run from within Perl will see these changes. If
you make the new settings permanent (read on), all programs you run see
the changes. See ENVIRONMENT for the full list of relevant environment
variables and "USING LOCALES" for their effects in Perl. Effects in
other programs are easily deducible. For example, the variable LC_COL-
LATE 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 com-
mands 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 impor-
tantly, installed--on your system. In our example error message, envi-
ronment 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 com-
mands. 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 documenta-
tion you are now reading. They should be able to check whether there
is something wrong with the locale configuration of the system. The
"Finding locales" section is unfortunately a bit vague about the exact
commands and places because these things are not that standardized.
The localeconv function
The POSIX::localeconv() function allows you to get particulars of the
locale-dependent numeric formatting information specified by the cur-
rent "LC_NUMERIC" and "LC_MONETARY" locales. (If you just want the
name of the current locale for a particular category, use POSIX::setlo-
cale() with a single parameter--see "The setlocale function".)
use POSIX qw(locale_h);
# Get a reference to a hash of locale-dependent info
$locale_values = localeconv();
# Output sorted list of the values
for (sort keys %$locale_values) {
printf "%-20s = %s\n", $_, $locale_values->{$_}
}
localeconv() takes no arguments, and returns a reference to a hash.
The keys of this hash are variable names for formatting, such as "deci-
mal_point" and "thousands_sep". The values are the corresponding, er,
values. See "localeconv" in POSIX for a longer example listing the
categories an implementation might be expected to provide; some provide
more and others fewer. You don't need an explicit "use locale",
because localeconv() always observes the current locale.
Here's a simple-minded example program that rewrites its command-line
parameters as integers correctly formatted in the current locale:
# See comments in previous example
require 5.004;
use POSIX qw(locale_h);
# Get some of locale's numeric formatting parameters
my ($thousands_sep, $grouping) =
@{localeconv()}{'thousands_sep', 'grouping'};
# Apply defaults if values are missing
$thousands_sep = ',' unless $thousands_sep;
# grouping and mon_grouping are packed lists
# of small integers (characters) telling the
# grouping (thousand_seps and mon_thousand_seps
# being the group dividers) of numbers and
# monetary quantities. The integers' meanings:
# 255 means no more grouping, 0 means repeat
# the previous grouping, 1-254 means use that
# as the current grouping. Grouping goes from
# right to left (low to high digits). In the
# below we cheat slightly by never using anything
# else than the first grouping (whatever that is).
if ($grouping) {
@grouping = unpack("C*", $grouping);
} else {
@grouping = (3);
}
# Format command line params for current locale
for (@ARGV) {
$_ = int; # Chop non-integer part
1 while
s/(\d)(\d{$grouping[0]}($|$thousands_sep))/$1$thousands_sep$2/;
print "$_";
}
print "\n";
I18N::Langinfo
Another interface for querying locale-dependent information is the
I18N::Langinfo::langinfo() function, available at least in UNIX-like
systems and VMS.
The following example will import the langinfo() function itself and
three constants to be used as arguments to langinfo(): a constant for
the abbreviated first day of the week (the numbering starts from Sunday
= 1) and two more constants for the affirmative and negative answers
for a yes/no question in the current locale.
use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
my ($abday_1, $yesstr, $nostr) = map { langinfo } qw(ABDAY_1 YESSTR NOSTR);
print "$abday_1? [$yesstr/$nostr] ";
In other words, in the "C" (or English) locale the above will probably
print something like:
Sun? [yes/no]
See I18N::Langinfo for more information.
LOCALE CATEGORIES
The following subsections describe basic locale categories. Beyond
these, some combination categories allow manipulation of more than one
basic category at a time. See "ENVIRONMENT" for a discussion of these.
Category LC_COLLATE: Collation
In the scope of "use locale", Perl looks to the "LC_COLLATE" environ-
ment variable to determine the application's notions on collation
(ordering) of characters. For example, 'b' follows 'a' in Latin alpha-
bets, 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 cur-
rent 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 dic-
tionary-like ordering that ignores space characters completely and
which folds case.
If you have a single string that you want to check for "equality in
locale" against several others, you might think you could gain a little
efficiency by using POSIX::strxfrm() in conjunction with "eq":
use POSIX qw(strxfrm);
$xfrm_string = strxfrm("Mixed-case string");
print "locale collation ignores spaces\n"
if $xfrm_string eq strxfrm("Mixed-casestring");
print "locale collation ignores hyphens\n"
if $xfrm_string eq strxfrm("Mixedcase string");
print "locale collation ignores case\n"
if $xfrm_string eq strxfrm("mixed-case string");
strxfrm() takes a string and maps it into a transformed string for use
in char-by-char comparisons against other transformed strings during
collation. "Under the hood", locale-affected Perl comparison operators
call strxfrm() for both operands, then do a char-by-char comparison of
the transformed strings. By calling strxfrm() explicitly and using a
non locale-affected comparison, the example attempts to save a couple
of transformations. But in fact, it doesn't save anything: Perl magic
(see "Magic Variables" in perlguts) creates the transformed version of
a string the first time it's needed in a comparison, then keeps this
version around in case it's needed again. An example rewritten the
easy way with "cmp" runs just about as fast. It also copes with null
characters embedded in strings; if you call strxfrm() directly, it
treats the first null it finds as a terminator. don't expect the
transformed strings it produces to be portable across systems--or even
from one revision of your operating system to the next. In short,
don't call strxfrm() directly: let Perl do it for you.
Note: "use locale" isn't shown in some of these examples because it
isn't needed: strcoll() and strxfrm() exist only to generate locale-
dependent results, and so always obey the current "LC_COLLATE" locale.
Category LC_CTYPE: Character Types
In the scope of "use locale", Perl obeys the "LC_CTYPE" locale setting.
This controls the application's notion of which characters are alpha-
betic. This affects Perl's "\w" regular expression metanotation, which
stands for alphanumeric characters--that is, alphabetic, numeric, and
including other special characters such as the underscore or hyphen.
(Consult perlre for more information about regular expressions.)
Thanks to "LC_CTYPE", depending on your locale setting, characters like
'ae', '`', '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 interpola-
tion 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 func-
tions--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 dig-
its--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 infor-
mation, 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() func-
tion 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 sepa-
ration 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 corre-
sponds to what you'd get from printf() in the "C" locale. The same is
true for Perl's internal conversions between numeric and string for-
mats:
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 com-
mittees 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 applica-
tion's own formatting of currency amounts. However, you may well find
that the information, voluminous and complex though it may be, still
does not quite meet your requirements: currency formatting is a hard
nut to crack.
See also I18N::Langinfo and "CRNCYSTR".
LC_TIME
Output produced by POSIX::strftime(), which builds a formatted human-
readable date/time string, is affected by the current "LC_TIME" locale.
Thus, in a French locale, the output produced by the %B format element
(full month name) for the first month of the year would be "janvier".
Here's how to get a list of long month names in the current locale:
use POSIX qw(strftime);
for (0..11) {
$long_month_name[$_] =
strftime("%B", 0, 0, 0, 1, $_, 96);
}
Note: "use locale" isn't needed in this example: as a function that
exists only to generate locale-dependent results, strftime() always
obeys the current "LC_TIME" locale.
See also I18N::Langinfo and "ABDAY_1".."ABDAY_7", "DAY_1".."DAY_7",
"ABMON_1".."ABMON_12", and "ABMON_1".."ABMON_12".
Other categories
The remaining locale category, "LC_MESSAGES" (possibly supplemented by
others in particular implementations) is not currently used by
Perl--except possibly to affect the behavior of library functions
called by extensions outside the standard Perl distribution and by the
operating system and its utilities. Note especially that the string
value of $! and the error messages given by external utilities may be
changed by "LC_MESSAGES". If you want to have portable error codes,
use "%!". See Errno.
SECURITY
Although the main discussion of Perl security issues can be found in
perlsec, a discussion of Perl's locale handling would be incomplete if
it did not draw your attention to locale-dependent security issues.
Locales--particularly on systems that allow unprivileged users to build
their own locales--are untrustworthy. A malicious (or just plain bro-
ken) locale can make a locale-aware application give unexpected
results. Here are a few possibilities:
o Regular expression checks for safe file names or mail addresses
using "\w" may be spoofed by an "LC_CTYPE" locale that claims that
characters such as ">" and "|" are alphanumeric.
o String interpolation with case-mapping, as in, say, "$dest =
"C:\U$name.$ext"", may produce dangerous results if a bogus
LC_CTYPE case-mapping table is in effect.
o A sneaky "LC_COLLATE" locale could result in the names of students
with "D" grades appearing ahead of those with "A"s.
o An application that takes the trouble to use information in
"LC_MONETARY" may format debits as if they were credits and vice
versa if that locale has been subverted. Or it might make payments
in US dollars instead of Hong Kong dollars.
o The date and day names in dates formatted by strftime() could be
manipulated to advantage by a malicious user able to subvert the
"LC_DATE" locale. ("Look--it says I wasn't in the building on Sun-
day.")
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 pro-
gramming 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 exam-
ples--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 behav-
ior of operators and functions that may be affected by the locale:
o Comparison operators ("lt", "le", "ge", "gt" and "cmp"):
Scalar true/false (or less/equal/greater) result is never tainted.
o Case-mapping interpolation (with "\l", "\L", "\u" or "\U")
Result string containing interpolated material is tainted if "use
locale" is in effect.
o 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 charac-
ter), "\W" (non-alphanumeric character), "\s" (whitespace charac-
ter), 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".
o Substitution operator ("s///"):
Has the same behavior as the match operator. Also, the left oper-
and 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".
o Output formatting functions (printf() and write()):
Results are never tainted because otherwise even output from print,
for example "print(1/7)", should be tainted if "use locale" is in
effect.
o Case-mapping functions (lc(), lcfirst(), uc(), ucfirst()):
Results are tainted if "use locale" is in effect.
o POSIX locale-dependent functions (localeconv(), strcoll(), strf-
time(), strxfrm()):
Results are never tainted.
o 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 pro-
gram, 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 sys-
tem'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_MES-
SAGES") 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 charac-
ter 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 colla-
tion (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 mone-
tary 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, gen-
erally 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 atten-
tion 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 participated
in any string comparison or sorting operation obeying the locale colla-
tion 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 char-
acter 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 defi-
nitions 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 use-
ful 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 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 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 excruci-
ating 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, "setlo-
cale" 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 2006-01-07 PERLLOCALE(1)
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