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' preferences in such matters is called internation
alization (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 stan
dardized (ISO C, XPG4, POSIX 1.c) method called "the
locale system". The locale system is controlled per appli
cation using one pragma, one function call, and several
environment variables.
NOTE: This feature is new in Perl 5.004, and does not
apply unless an application specifically requests it--see
the Backward compatibility entry elsewhere in this docu
ment. The one exception is that write() now always uses
the current locale - see the section on "NOTES".
PREPARING TO USE LOCALES
If Perl applications are to understand and present your
data correctly according a locale of your choice, all of
the following must be true:
Your operating system must support the locale system.
If it does, you should find that the setlocale() 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 sys
tem to system. Some systems provide only a few, hard-
wired locales and do not allow more to be added. Oth
ers allow you to add "canned" locales provided by the
system supplier. Still others allow you or the system
administrator to define and add arbitrary locales.
(You may have to ask your supplier to provide canned
locales that are not delivered with your operating
system.) Read your system documentation for further
illumination.
Perl must believe that the locale system is supported.
If it does, "perl -V:d_setlocale" will say that the
value for "d_setlocale" is "define".
If you want a Perl application to process and present your
data according to a particular locale, the application
code should include the "use locale" pragma (see the The
use locale pragma entry elsewhere in this document) where
appropriate, and at least one of the following must be
true:
The locale-determining environment variables (see the
section on "ENVIRONMENT") must be correctly set up at
the time the application is started, either by your
self or by whoever set up your system account.
The application must set its own locale using the
method described in the The setlocale function entry
elsewhere in this document.
USING LOCALES
The use locale pragma
By default, Perl ignores the current locale. The
"use locale" pragma tells Perl to use the current locale
for some operations:
The comparison operators ("lt", "le", "cmp", "ge", and
"gt") and the POSIX string collation functions str_
coll() and strxfrm() use "LC_COLLATE". sort() is also
affected if used without an explicit comparison func
tion, because it uses "cmp" by default.
Note: "eq" and "ne" are unaffected by locale: they
always perform a byte-by-byte comparison of their
scalar operands. What's more, if "cmp" finds that its
operands are equal according to the collation sequence
specified by the current locale, it goes on to perform
a byte-by-byte comparison, and only returns 0 (equal)
if the operands are bit-for-bit identical. If you
really want to know whether two strings--which "eq"
and "cmp" may consider different--are equal as far as
collation in the locale is concerned, see the discus
sion in the Category LC_COLLATE: Collation entry else
where in this document.
Regular expressions and case-modification functions
(uc(), lc(), ucfirst(), and lcfirst()) use "LC_CTYPE"
The formatting functions (printf(), sprintf() and
write()) use "LC_NUMERIC"
The POSIX date formatting function (strftime()) uses
"LC_TIME".
"LC_COLLATE", "LC_CTYPE", and so on, are discussed further
in the LOCALE CATEGORIES entry elsewhere in this document.
The default behavior is restored with the "no locale"
pragma, or upon reaching the end of block enclosing "use
locale".
The string result of any operation that uses locale infor
mation is tainted, as it is possible for a locale to be
untrustworthy. See the section on "SECURITY".
The setlocale function
You can switch locales as often as you wish at run time
with the POSIX:\fIs0:setlocale() function:
# This functionality not usable prior to Perl 5.004
require 5.004;
# Import locale-handling tool set from POSIX module.
# This example uses: setlocale -- the function call
# LC_CTYPE -- explained below
use POSIX qw(locale_h);
# query and save the old locale
$old_locale = setlocale(LC_CTYPE);
setlocale(LC_CTYPE, "fr_CA.ISO8859-1");
# LC_CTYPE now in locale "French, Canada, codeset ISO 8859-1"
setlocale(LC_CTYPE, "");
# LC_CTYPE now reset to default defined by LC_ALL/LC_CTYPE/LANG
# environment variables. See below for documentation.
# restore the old locale
setlocale(LC_CTYPE, $old_locale);
The first argument of setlocale() gives the category, the
second the locale. The category tells in what aspect of
data processing you want to apply locale-specific rules.
Category names are discussed in the LOCALE CATEGORIES
entry elsewhere in this document and the section on "ENVI
RONMENT". The locale is the name of a collection of cus
tomization 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 sys
tems 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 set_
locale(). (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 environ
ment 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 set_
locale(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
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 directo
ries where the configuration resides have not been. The
basic form of the name is language_territory.codeset, but
the latter parts after language are not always present.
The language and country are usually from the standards
ISO 3166 and ISO 639, the two-letter abbreviations for the
countries and the languages of the world, respectively.
The codeset part often mentions some ISO 8859 character
set, the Latin codesets. For example, "ISO 8859-1" is the
so-called "Western European codeset" that can be used to
encode most Western European languages adequately. Again,
there are several ways to write even the name of that one
standard. Lamentably.
Two special locales are worth particular mention: "C" and
"POSIX". Currently these are effectively the same locale:
the difference is mainly that the first one is defined by
the C standard, the second by the POSIX standard. They
define the default locale in which every program starts in
the absence of locale information in its environment.
(The default default locale, if you will.) Its language
is (American) English and its character codeset ASCII.
NOTE: Not all systems have the "POSIX" locale (not all
systems are POSIX-conformant), so use "C" when you need
explicitly to specify this default locale.
LOCALE PROBLEMS
You may encounter the following warning message at Perl
startup:
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
LC_ALL = "En_US",
LANG = (unset)
are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").
This means that your locale settings had LC_ALL set to
"En_US" and LANG exists but has no value. Perl tried to
believe you but could not. Instead, Perl gave up and fell
back to the "C" locale, the default locale that is sup
posed to work no matter what. This usually means your
locale settings were wrong, they mention locales your sys
tem 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 envi
ronment 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 ENVI
RONMENT manpage for the full list of relevant environment
variables and the USING LOCALES entry elsewhere in this
document for their effects in Perl. Effects in other pro
grams are easily deducible. For example, the variable
LC_COLLATE may well affect your sort program (or whatever
the program that arranges `records' alphabetically in your
system is called).
You can test out changing these variables temporarily, and
if the new settings seem to help, put those settings into
your shell startup files. Consult your local documenta
tion for the exact details. For in Bourne-like shells
(sh, ksh, bash, zsh):
LC_ALL=en_US.ISO8859-1
export LC_ALL
This assumes that we saw the locale "en_US.ISO8859-1"
using the commands discussed above. We decided to try
that instead of the above faulty locale "En_US"--and in
Cshish shells (csh, tcsh)
setenv LC_ALL en_US.ISO8859-1
If you do not know what shell you have, consult your local
helpdesk or the equivalent.
Permanently fixing locale problems
The slower but superior fixes are when you may be able to
yourself fix the misconfiguration of your own environment
variables. The mis(sing)configuration of the whole sys
tem's locales usually requires the help of your friendly
system administrator.
First, see earlier in this document about the Finding
locales entry elsewhere in this document. That tells how
to find which locales are really supported--and more
importantly, installed--on your system. In our example
error message, environment variables affecting the locale
are listed in the order of decreasing importance (and
unset variables do not matter). Therefore, having LC_ALL
set to "En_US" must have been the bad choice, as shown by
the error message. First try fixing locale settings
listed first.
Second, if using the listed commands you see something
exactly (prefix matches do not count and case usually
counts) like "En_US" without the quotes, then you should
be okay because you are using a locale name that should be
installed and available in your system. In this case, see
the Permanently fixing your system's locale configuration
entry elsewhere in this document.
Permanently fixing your system's locale configuration
This is when you see something like:
perl: warning: Please check that your locale settings:
LC_ALL = "En_US",
LANG = (unset)
are supported and installed on your system.
but then cannot see that "En_US" listed by the above-men
tioned commands. You may see things like
"en_US.ISO8859-1", but that isn't the same. In this case,
try running under a locale that you can list and which
somehow matches what you tried. The rules for matching
locale names are a bit vague because standardization is
weak in this area. See again the the Finding locales
entry elsewhere in this document about general rules.
Fixing system locale configuration
Contact a system administrator (preferably your own) and
report the exact error message you get, and ask them to
read this same documentation you are now reading. They
should be able to check whether there is something wrong
with the locale configuration of the system. The the
Finding locales entry elsewhere in this document section
is unfortunately a bit vague about the exact commands and
places because these things are not that standardized.
The localeconv function
The POSIX:\fIs0:localeconv() function allows you to get
particulars of the locale-dependent numeric formatting
information specified by the current "LC_NUMERIC" and
"LC_MONETARY" locales. (If you just want the name of the
current locale for a particular category, use
POSIX:\fIs0:setlocale() with a single parameter--see the
The setlocale function entry elsewhere in this document.)
use POSIX qw(locale_h);
# Get a reference to a hash of locale-dependent info
$locale_values = localeconv();
# Output sorted list of the values
for (sort keys %$locale_values) {
printf "%-20s = %s\n", $_, $locale_values->{$_}
}
localeconv() takes no arguments, and returns a reference
to a hash. The keys of this hash are variable names for
formatting, such as "decimal_point" and "thousands_sep".
The values are the corresponding, er, values. See the
localeconv entry in the POSIX manpage for a longer example
listing the categories an implementation might be expected
to provide; some provide more and others fewer. You don't
need an explicit "use locale", because localeconv() always
observes the current locale.
Here's a simple-minded example program that rewrites its
command-line parameters as integers correctly formatted in
the current locale:
# See comments in previous example
require 5.004;
use POSIX qw(locale_h);
# Get some of locale's numeric formatting parameters
my ($thousands_sep, $grouping) =
@{localeconv()}{'thousands_sep', 'grouping'};
# Apply defaults if values are missing
$thousands_sep = ',' unless $thousands_sep;
# grouping and mon_grouping are packed lists
# of small integers (characters) telling the
# grouping (thousand_seps and mon_thousand_seps
# being the group dividers) of numbers and
# monetary quantities. The integers' meanings:
# 255 means no more grouping, 0 means repeat
# the previous grouping, 1-254 means use that
# as the current grouping. Grouping goes from
# right to left (low to high digits). In the
# below we cheat slightly by never using anything
# else than the first grouping (whatever that is).
if ($grouping) {
@grouping = unpack("C*", $grouping);
} else {
@grouping = (3);
}
# Format command line params for current locale
for (@ARGV) {
$_ = int; # Chop non-integer part
1 while
s/(\d)(\d{$grouping[0]}($|$thousands_sep))/$1$thousands_sep$2/;
print "$_";
}
print "\n";
LOCALE CATEGORIES
The following subsections describe basic locale cate
gories. Beyond these, some combination categories allow
manipulation of more than one basic category at a time.
See the section on "ENVIRONMENT" for a discussion of
these.
Category LC_COLLATE: Collation
In the scope of "use locale", Perl looks to the "LC_COL
LATE" environment variable to determine the application's
notions on collation (ordering) of characters. For exam
ple, 'b' follows 'a' in Latin alphabets, but where do 'a'
and 'aa' belong? And while 'color' follows 'chocolate' in
English, what about in Spanish?
The following collations all make sense and you may meet
any of them if you "use locale".
A B C D E a b c d e
A a B b C c D d E e
a A b B c C d D e E
a b c d e A B C D E
Here is a code snippet to tell what "word" characters are
in the current locale, in that locale's order:
use locale;
print +(sort grep /\w/, map { chr } 0..255), "\n";
Compare this with the characters that you see and their
order if you state explicitly that the locale should be
ignored:
no locale;
print +(sort grep /\w/, map { chr } 0..255), "\n";
This machine-native collation (which is what you get
unless "use locale" has appeared earlier in the same
block) must be used for sorting raw binary data, whereas
the locale-dependent collation of the first example is
useful for natural text.
As noted in the USING LOCALES entry elsewhere in this doc
ument, "cmp" compares according to the current collation
locale when "use locale" is in effect, but falls back to a
byte-by-byte comparison for strings that the locale says
are equal. You can use POSIX:\fIs0:strcoll() if you don't
want this fall-back:
use POSIX qw(strcoll);
$equal_in_locale =
!strcoll("space and case ignored", "SpaceAndCaseIgnored");
$equal_in_locale will be true if the collation locale
specifies a dictionary-like ordering that ignores space
characters completely and which folds case.
If you have a single string that you want to check for
"equality in locale" against several others, you might
think you could gain a little efficiency by using
POSIX:\fIs0:strxfrm() in conjunction with "eq":
use POSIX qw(strxfrm);
$xfrm_string = strxfrm("Mixed-case string");
print "locale collation ignores spaces\n"
if $xfrm_string eq strxfrm("Mixed-casestring");
print "locale collation ignores hyphens\n"
if $xfrm_string eq strxfrm("Mixedcase string");
print "locale collation ignores case\n"
if $xfrm_string eq strxfrm("mixed-case string");
strxfrm() takes a string and maps it into a transformed
string for use in byte-by-byte comparisons against other
transformed strings during collation. "Under the hood",
locale-affected Perl comparison operators call strxfrm()
for both operands, then do a byte-by-byte comparison of
the transformed strings. By calling strxfrm() explicitly
and using a non locale-affected comparison, the example
attempts to save a couple of transformations. But in
fact, it doesn't save anything: Perl magic (see the Magic
Variables entry in the perlguts manpage) creates the
transformed version of a string the first time it's needed
in a comparison, then keeps this version around in case
it's needed again. An example rewritten the easy way with
"cmp" runs just about as fast. It also copes with null
characters embedded in strings; if you call strxfrm()
directly, it treats the first null it finds as a termina
tor. don't expect the transformed strings it produces to
be portable across systems--or even from one revision of
your operating system to the next. In short, don't call
strxfrm() directly: let Perl do it for you.
Note: "use locale" isn't shown in some of these examples
because it isn't needed: strcoll() and strxfrm() exist
only to generate locale-dependent results, and so always
obey the current "LC_COLLATE" locale.
Category LC_CTYPE: Character Types
In the scope of "use locale", Perl obeys the "LC_CTYPE"
locale setting. This controls the application's notion of
which characters are alphabetic. This affects Perl's "\w"
regular expression metanotation, which stands for alphanu
meric characters--that is, alphabetic, numeric, and
including other special characters such as the underscore
or hyphen. (Consult the perlre manpage for more informa
tion 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().
Note: A broken or malicious "LC_CTYPE" locale definition
may result in clearly ineligible characters being consid
ered 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 "SECU
RITY".
Category LC_NUMERIC: Numeric Formatting
In the scope of "use locale", Perl obeys the "LC_NUMERIC"
locale information, which controls an application's idea
of how numbers should be formatted for human readability
by the printf(), sprintf(), and write() functions.
String-to-numeric conversion by the POSIX:\fIs0:strtod()
function is also affected. In most implementations the
only effect is to change the character used for the deci
mal point--perhaps from '.' to ','. These functions
aren't aware of such niceties as thousands separation and
so on. (See the The localeconv function entry elsewhere
in this document if you care about these things.)
Output produced by print() is also affected by the current
locale: it depends on whether "use locale" or "no locale"
is in effect, and corresponds to what you'd get from
printf() in the "C" locale. The same is true for Perl's
internal conversions between numeric and string formats:
use POSIX qw(strtod);
use locale;
$n = 5/2; # Assign numeric 2.5 to $n
$a = " $n"; # Locale-dependent conversion to string
print "half five is $n\n"; # Locale-dependent output
printf "half five is %g\n", $n; # Locale-dependent output
print "DECIMAL POINT IS COMMA\n"
if $n == (strtod("2,5"))[0]; # Locale-dependent conversion
Category LC_MONETARY: Formatting of monetary amounts
The C standard defines the "LC_MONETARY" category, but no
function that is affected by its contents. (Those with
experience of standards committees will recognize that the
working group decided to punt on the issue.) Conse
quently, Perl takes no notice of it. If you really want
to use "LC_MONETARY", you can query its contents--see the
The localeconv function entry elsewhere in this docu
ment--and use the information that it returns in your
application's own formatting of currency amounts. How
ever, you may well find that the information, voluminous
and complex though it may be, still does not quite meet
your requirements: currency formatting is a hard nut to
crack.
LC_TIME
Output produced by POSIX:\fIs0:strftime(), which builds a
formatted human-readable date/time string, is affected by
the current "LC_TIME" locale. Thus, in a French locale,
the output produced by the "%B" format element (full month
name) for the first month of the year would be "janvier".
Here's how to get a list of long month names in the cur
rent locale:
use POSIX qw(strftime);
for (0..11) {
$long_month_name[$_] =
strftime("%B", 0, 0, 0, 1, $_, 96);
}
Note: "use locale" isn't needed in this example: as a
function that exists only to generate locale-dependent
results, strftime() always obeys the current "LC_TIME"
locale.
Other categories
The remaining locale category, "LC_MESSAGES" (possibly
supplemented by others in particular implementations) is
not currently used by Perl--except possibly to affect the
behavior of library functions called by extensions outside
the standard Perl distribution and by the operating system
and its utilities. Note especially that the string value
of "$!" and the error messages given by external utilities
may be changed by "LC_MESSAGES". If you want to have
portable error codes, use "%!". See the Errno manpage.
SECURITY
Although the main discussion of Perl security issues can
be found in the perlsec manpage, a discussion of Perl's
locale handling would be incomplete if it did not draw
your attention to locale-dependent security issues.
Locales--particularly on systems that allow unprivileged
users to build their own locales--are untrustworthy. A
malicious (or just plain broken) locale can make a locale-
aware application give unexpected results. Here are a few
possibilities:
Regular expression checks for safe file names or mail
addresses using "\w" may be spoofed by an "LC_CTYPE"
locale that claims that characters such as ">" and "|"
are alphanumeric.
String interpolation with case-mapping, as in, say,
"$dest = "C:\U$name.$ext"", may produce dangerous
results if a bogus LC_CTYPE case-mapping table is in
effect.
A sneaky "LC_COLLATE" locale could result in the names
of students with "D" grades appearing ahead of those
with "A"s.
An application that takes the trouble to use informa
tion in "LC_MONETARY" may format debits as if they
were credits and vice versa if that locale has been
subverted. Or it might make payments in US dollars
instead of Hong Kong dollars.
The date and day names in dates formatted by strf_
time() could be manipulated to advantage by a mali
cious 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 modi
fied 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 vigi
lance--but, when "use locale" is in effect, Perl uses the
tainting mechanism (see the perlsec manpage) to mark
string results that become locale-dependent, and which may
be untrustworthy in consequence. Here is a summary of the
tainting behavior of operators and functions that may be
affected by the locale:
Comparison operators ("lt", "le", "ge", "gt" and
"cmp"):
Scalar true/false (or less/equal/greater) result is
never tainted.
Case-mapping interpolation (with "\l", "\L", "\u" or
"\U")
Result string containing interpolated material is
tainted if "use locale" is in effect.
Matching operator ("m//"):
Scalar true/false result never tainted.
Subpatterns, either delivered as a list-context result
or as $1 etc. are tainted if "use locale" is in
effect, and the subpattern regular expression contains
"\w" (to match an alphanumeric character), "\W" (non-
alphanumeric character), "\s" (white-space character),
or "\S" (non white-space character). The matched-pat
tern 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 substi
tution 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 out
put from print, for example "print(1/7)", should be
tainted if "use locale" is in effect.
Case-mapping functions (lc(), lcfirst(), uc(),
ucfirst()):
Results are tainted if "use locale" is in effect.
POSIX locale-dependent functions (localeconv(), str_
coll(), strftime(), strxfrm()):
Results are never tainted.
POSIX character class tests (isalnum(), isalpha(),
isdigit(), isgraph(), islower(), isprint(), ispunct(),
isspace(), isupper(), isxdigit()):
True/false results are never tainted.
Three examples illustrate locale-dependent tainting. The
first program, which ignores its locale, won't run: a
value taken directly from the command line may not be used
to name an output file when taint checks are enabled.
#/usr/local/bin/perl -T
# Run with taint checking
# Command line sanity check omitted...
$tainted_output_file = shift;
open(F, ">$tainted_output_file")
or warn "Open of $untainted_output_file failed: $!\n";
The program can be made to run by "laundering" the tainted
value through a regular expression: the second exam
ple--which still ignores locale information--runs, creat
ing the file named on its command line if it can.
#/usr/local/bin/perl -T
$tainted_output_file = shift;
$tainted_output_file =~ m%[\w/]+%;
$untainted_output_file = $&;
open(F, ">$untainted_output_file")
or warn "Open of $untainted_output_file failed: $!\n";
Compare this with a similar but locale-aware program:
#/usr/local/bin/perl -T
$tainted_output_file = shift;
use locale;
$tainted_output_file =~ m%[\w/]+%;
$localized_output_file = $&;
open(F, ">$localized_output_file")
or warn "Open of $localized_output_file failed: $!\n";
This third program fails to run because $& is tainted: it
is the result of a match involving "\w" while "use locale"
is in effect.
ENVIRONMENT
PERL_BADLANG
A string that can suppress Perl's warning
about failed locale settings at startup.
Failure can occur if the locale support in the
operating system is lacking (broken) in some
way--or if you mistyped the name of a locale
when you set up your environment. If this
environment variable is absent, or has a value
that does not evaluate to integer zero--that
is, "0" or ""-- Perl will complain about
locale setting failures.
NOTE: PERL_BADLANG only gives you a way to
hide the warning message. The message tells
about some problem in your system's locale
support, and you should investigate what the
problem is.
The following environment variables are not specific to
Perl: They are part of the standardized (ISO C, XPG4,
POSIX 1.c) setlocale() method for controlling an applica
tion'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,
warning, and error messages output by commands
(in other words, it's like "LC_MESSAGES") but
it has higher priority than the LC_ALL man
page. Moreover, it's not a single value but
instead a "path" (":"-separated list) of lan_
guages (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_MONE
TARY", "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 cat
egory-specific "LC_...".
NOTES
Backward compatibility
Versions of Perl prior to 5.004 mostly ignored locale
information, generally behaving as if something similar to
the ""C"" locale were always in force, even if the program
environment suggested otherwise (see the The setlocale
function entry elsewhere in this document). By default,
Perl still behaves this way for backward compatibility.
If you want a Perl application to pay attention to locale
information, you must use the "use locale" pragma (see the
The use locale pragma entry elsewhere in this document) to
instruct it to do so.
Versions of Perl from 5.002 to 5.003 did use the
"LC_CTYPE" information if available; that is, "\w" did
understand what were the letters according to the locale
environment variables. The problem was that the user had
no control over the feature: if the C library supported
locales, Perl used them.
I18N:Collate obsolete
In versions of Perl prior to 5.004, per-locale collation
was possible using the "I18N::Collate" library module.
This module is now mildly obsolete and should be avoided
in new applications. The "LC_COLLATE" functionality is
now integrated into the Perl core language: One can use
locale-specific scalar data completely normally with "use
locale", so there is no longer any need to juggle with the
scalar references of "I18N::Collate".
Sort speed and memory use impacts
Comparing and sorting by locale is usually slower than the
default sorting; slow-downs of two to four times have been
observed. It will also consume more memory: once a Perl
scalar variable has participated in any string comparison
or sorting operation obeying the locale collation rules,
it will take 3-15 times more memory than before. (The
exact multiplier depends on the string's contents, the
operating system and the locale.) These downsides are dic
tated 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 envi
ronment specifies an LC_NUMERIC locale, it is always used
to specify the decimal point character in formatted out
put. 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 eigh
teen others. (You may guess why the internalin ... inter
naliti ... 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 hav
ing too large a granularity. (Locales apply to a whole
process, when it would arguably be more useful to have
them apply to a single thread, window group, or whatever.)
They also have a tendency, like standards groups, to
divide the world into nations, when we all know that the
world can equally well be divided into bankers, bikers,
gamers, and so on. But, for now, it's the only standard
we've got. This may be construed as a bug.
BUGS
Broken systems
In certain systems, the operating system's locale support
is broken and cannot be fixed or used by Perl. Such defi
ciencies 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 excruciat
ing detail to <perlbug@perl.org>, and complain to your
vendor: bug fixes may exist for these problems in your
operating system. Sometimes such bug fixes are called an
operating system upgrade.
SEE ALSO
the isalnum entry in the POSIX manpage, the isalpha entry
in the POSIX manpage, the isdigit entry in the POSIX man
page, the isgraph entry in the POSIX manpage, the islower
entry in the POSIX manpage, the isprint entry in the POSIX
manpage, the ispunct entry in the POSIX manpage, the iss
pace entry in the POSIX manpage, the isupper entry in the
POSIX manpage, the isxdigit entry in the POSIX manpage,
the localeconv entry in the POSIX manpage, the setlocale
entry in the POSIX manpage, the strcoll entry in the POSIX
manpage, the strftime entry in the POSIX manpage, the str
tod entry in the POSIX manpage, the strxfrm entry in the
POSIX manpage.
HISTORY
Jarkko Hietaniemi's original perli18n.pod heavily hacked
by Dominic Dunlop, assisted by the perl5-porters. Prose
worked over a bit by Tom Christiansen.
Last update: Thu Jun 11 08:44:13 MDT 1998
2001-03-18 perl v5.6.1 PERLLOCALE(1)
