Computer Science
PERLLOCALE(1) Perl Programmers Reference Guide PERLLOCALE(1)
NNAAMMEE
perllocale - Perl locale handling (internationalization
and localization)
DDEESSCCRRIIPPTTIIOONN
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
iinntteerrnnaattiioonnaalliizzaattiioonn (often abbreviated as ii1188nn); telling
such an application about a particular set of preferences
is known as llooccaalliizzaattiioonn (ll1100nn).
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.
NNOOTTEE: This feature is new in Perl 5.004, and does not
apply unless an application specifically requests it--see
the section on Backward compatibility. The one exception
is that write() now aallwwaayyss uses the current locale - see
the section on NOTES.
PPRREEPPAARRIINNGG TTOO UUSSEE LLOOCCAALLEESS
If Perl applications are to understand and present your
data correctly according a locale of your choice, aallll of
the following must be true:
o YYoouurr ooppeerraattiinngg ssyysstteemm mmuusstt ssuuppppoorrtt tthhee llooccaallee ssyysstteemm.
If it does, you should find that the setlocale()
function is a documented part of its C library.
o DDeeffiinniittiioonnss ffoorr llooccaalleess tthhaatt yyoouu uussee mmuusstt bbee
iinnssttaalllleedd. 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.
o PPeerrll mmuusstt bbeelliieevvee tthhaatt tthhee llooccaallee ssyysstteemm iiss ssuuppppoorrtteedd.
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 section
on The use locale pragma) where appropriate, and aatt lleeaasstt
oonnee of the following must be true:
o TThhee llooccaallee--ddeetteerrmmiinniinngg eennvviirroonnmmeenntt vvaarriiaabblleess ((sseeee tthhee
sseeccttiioonn oonn 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 TThhee aapppplliiccaattiioonn mmuusstt sseett iittss oowwnn llooccaallee using the
method described in the section on The setlocale
function.
UUSSIINNGG LLOOCCAALLEESS
TThhee uussee llooccaallee pprraaggmmaa
By default, Perl ignores the current locale. The use
locale pragma tells Perl to use the current locale for
some operations:
o TThhee ccoommppaarriissoonn ooppeerraattoorrss (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.
NNoottee:: 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 section on Category LC_COLLATE:
Collation.
o RReegguullaarr eexxpprreessssiioonnss aanndd ccaassee--mmooddiiffiiccaattiioonn ffuunnccttiioonnss
(uc(), lc(), ucfirst(), and lcfirst()) use LC_CTYPE
o TThhee ffoorrmmaattttiinngg ffuunnccttiioonnss (printf(), sprintf() and
write()) use LC_NUMERIC
o TThhee PPOOSSIIXX ddaattee ffoorrmmaattttiinngg ffuunnccttiioonn (strftime()) uses
LC_TIME.
LC_COLLATE, LC_CTYPE, and so on, are discussed further in
the section on 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 the section on SECURITY.
TThhee sseettllooccaallee ffuunnccttiioonn
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 ccaatteeggoorryy, the
second the llooccaallee. The category tells in what aspect of
data processing you want to apply locale-specific rules.
Category names are discussed in the section on LOCALE
CATEGORIES 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 the setlocale(3) manpage 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 the
setlocale(3) manpage.
FFiinnddiinngg llooccaalleess
For locales available in your system, consult also the
setlocale(3) manpage 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 IISSOO 33116666 and IISSOO 663399, the two-letter
abbreviations for the countries and the languages of the
world, respectively. The codeset part often mentions some
IISSOO 88885599 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 ddeeffaauulltt llooccaallee 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.
NNOOTTEE: 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.
LLOOCCAALLEE PPRROOBBLLEEMMSS
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.
TTeemmppoorraarriillyy ffiixxiinngg llooccaallee pprroobblleemmss
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 for the full list of relevant
environment variables and the section on USING LOCALES for
their effects in Perl. Effects in other programs are
easily deducible. For example, the variable LC_COLLATE
may well affect your ssoorrtt 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 (sshh, kksshh, bbaasshh, zzsshh):
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 (ccsshh, ttccsshh)
setenv LC_ALL en_US.ISO8859-1
If you do not know what shell you have, consult your local
helpdesk or the equivalent.
PPeerrmmaanneennttllyy ffiixxiinngg llooccaallee pprroobblleemmss
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 section on
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
eexxaaccttllyy (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 section on Permanently fixing system locale
configuration.
PPeerrmmaanneennttllyy ffiixxiinngg yyoouurr llooccaallee ccoonnffiigguurraattiioonn
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 section on Finding
locales about general rules.
FFiixxiinngg ssyysstteemm llooccaallee ccoonnffiigguurraattiioonn
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
section on Finding locales section is unfortunately a bit
vague about the exact commands and places because these
things are not that standardized.
TThhee llooccaalleeccoonnvv ffuunnccttiioonn
The POSIX::localeconv() function allows you to get
particulars of the locale-dependent numeric formatting
information specified by the current LC_NUMERIC and
LC_MONETARY locales. (If you just want the name of the
current locale for a particular category, use
POSIX::setlocale() with a single parameter--see the
section on 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 aa rreeffeerreennccee
ttoo 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 (3) 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";
LLOOCCAALLEE CCAATTEEGGOORRIIEESS
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.
CCaatteeggoorryy LLCC_<i>_CCOOLLLLAATTEE:: CCoollllaattiioonn
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 D 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 alphanumeric
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 section on USING LOCALES, 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::strcoll() if you don't want this fall-back:
use POSIX qw(strcoll);
$equal_in_locale =
!strcoll("space and case ignored", "SpaceAndCaseIgnored");
$equal_in_locale will be true if the collation locale
specifies a dictionary-like ordering that ignores space
characters completely and which folds case.
If you have a single string that you want to check for
"equality in locale" against several others, you might
think you could gain a little efficiency by using
POSIX::strxfrm() in conjunction with eq:
use POSIX qw(strxfrm);
$xfrm_string = strxfrm("Mixed-case string");
print "locale collation ignores spaces\n"
if $xfrm_string eq strxfrm("Mixed-casestring");
print "locale collation ignores hyphens\n"
if $xfrm_string eq strxfrm("Mixedcase string");
print "locale collation ignores case\n"
if $xfrm_string eq strxfrm("mixed-case string");
strxfrm() takes a string and maps it into a transformed
string for use in 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
section on Magic Variables 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.
CCaatteeggoorryy LLCC_<i>_CCTTYYPPEE:: CChhaarraacctteerr TTyyppeess
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 and numeric characters.
(Consult the perlre manpage 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 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().
NNoottee:: 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.
CCaatteeggoorryy LLCC_<i>_NNUUMMEERRIICC:: NNuummeerriicc FFoorrmmaattttiinngg
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 section on The localeconv function if you
care about these things.)
Output produced by print() is nneevveerr affected by the
current locale: it is independent of 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-independent conversion to string
print "half five is $n\n"; # Locale-independent 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
CCaatteeggoorryy LLCC_<i>_MMOONNEETTAARRYY:: FFoorrmmaattttiinngg ooff mmoonneettaarryy aammoouunnttss
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 section on 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.
LLCC_<i>_TTIIMMEE
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.
OOtthheerr ccaatteeggoorriieess
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.
SSEECCUURRIITTYY
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:
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 If the decimal point character in the LC_NUMERIC
locale is surreptitiously changed from a dot to a
comma, sprintf("%g", 0.123456e3) produces a string
result of "123,456". Many people would interpret this
as one hundred and twenty-three thousand, four hundred
and fifty-six.
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 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:
CCoommppaarriissoonn ooppeerraattoorrss (lt, le, ge, gt and cmp):
Scalar true/false (or less/equal/greater) result is
never tainted.
CCaassee--mmaappppiinngg iinntteerrppoollaattiioonn (with \l, \L, \u or \U)
Result string containing interpolated material is
tainted if use locale is in effect.
MMaattcchhiinngg ooppeerraattoorr (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.
SSuubbssttiittuuttiioonn ooppeerraattoorr (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.
IInn--mmeemmoorryy ffoorrmmaattttiinngg ffuunnccttiioonn (sprintf()):
Result is tainted if use locale is in effect.
OOuuttppuutt ffoorrmmaattttiinngg ffuunnccttiioonnss (printf() and write()):
Success/failure result is never tainted.
CCaassee--mmaappppiinngg ffuunnccttiioonnss (lc(), lcfirst(), uc(), ucfirst()):
Results are tainted if use locale is in effect.
PPOOSSIIXX llooccaallee--ddeeppeennddeenntt ffuunnccttiioonnss (localeconv(), strcoll(),
strftime(), strxfrm()):
Results are never tainted.
PPOOSSIIXX cchhaarraacctteerr ccllaassss tteessttss (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.
EENNVVIIRROONNMMEENNTT
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.
NNOOTTEE: 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 NNOOTTEE: 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_....
NNOOTTEESS
BBaacckkwwaarrdd ccoommppaattiibbiilliittyy
Versions of Perl prior to 5.004 mmoossttllyy 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 section on The
setlocale function). By default, Perl still behaves this
way for backward compatibility. If you want a Perl
application to pay attention to locale information, you
mmuusstt use the use locale pragma (see the section on 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.
II1188NN::CCoollllaattee oobbssoolleettee
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.
SSoorrtt ssppeeeedd aanndd mmeemmoorryy uussee iimmppaaccttss
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.
FFrreeeellyy aavvaaiillaabbllee llooccaallee ddeeffiinniittiioonnss
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.
II1188nn aanndd ll1100nn
"Internationalization" is often abbreviated as ii1188nn
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 ll1100nn.
AAnn iimmppeerrffeecctt ssttaannddaarrdd
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.
BBUUGGSS
BBrrookkeenn ssyysstteemmss
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.com>, 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.
SSEEEE AALLSSOO
the isalnum entry in the POSIX (3) manpage
the isalpha entry in the POSIX (3) manpage
the isdigit entry in the POSIX (3) manpage
the isgraph entry in the POSIX (3) manpage
the islower entry in the POSIX (3) manpage
the isprint entry in the POSIX (3) manpage,
the ispunct entry in the POSIX (3) manpage
the isspace entry in the POSIX (3) manpage
the isupper entry in the POSIX (3) manpage,
the isxdigit entry in the POSIX (3) manpage
the localeconv entry in the POSIX (3) manpage
the setlocale entry in the POSIX (3) manpage,
the strcoll entry in the POSIX (3) manpage
the strftime entry in the POSIX (3) manpage
the strtod entry in the POSIX (3) manpage,
the strxfrm entry in the POSIX (3) manpage
HHIISSTTOORRYY
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
23/Jan/1999 perl 5.005, patch 03 1
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