+=encoding utf8
+
=head1 NAME
perllocale - Perl locale handling (internationalization and localization)
=head1 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 naE<iuml>ve to imagine that C<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 B<internationalization> (often abbreviated as B<i18n>); telling
-such an application about a particular set of preferences is known as
-B<localization> (B<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.
-
-B<NOTE>: This feature is new in Perl 5.004, and does not apply unless an
-application specifically requests it--see L<Backward compatibility>.
-The one exception is that write() now B<always> uses the current locale
-- see L<"NOTES">.
+In the beginning there was ASCII, the "American Standard Code for
+Information Interchange", which works quite well for Americans with
+their English alphabet and dollar-denominated currency. But it doesn't
+work so well even for other English speakers, who may use different
+currencies, such as the pound sterling (as the symbol for that currency
+is not in ASCII); and it's hopelessly inadequate for many of the
+thousands of the world's other languages.
+
+To address these deficiencies, the concept of locales was invented
+(formally the ISO C, XPG4, POSIX 1.c "locale system"). And applications
+were and are being written that use the locale mechanism. The process of
+making such an application take account of its users' preferences in
+these kinds of matters is called B<internationalization> (often
+abbreviated as B<i18n>); telling such an application about a particular
+set of preferences is known as B<localization> (B<l10n>).
+
+Perl was extended to support the locale system. This
+is controlled per application by using one pragma, one function call,
+and several environment variables.
+
+Unfortunately, there are quite a few deficiencies with the design (and
+often, the implementations) of locales, and their use for character sets
+has mostly been supplanted by Unicode (see L<perlunitut> for an
+introduction to that, and keep on reading here for how Unicode interacts
+with locales in Perl).
+
+Perl continues to support the old locale system, and starting in v5.16,
+provides a hybrid way to use the Unicode character set, along with the
+other portions of locales that may not be so problematic.
+(Unicode is also creating C<CLDR>, the "Common Locale Data Repository",
+L<http://cldr.unicode.org/> which includes more types of information than
+are available in the POSIX locale system. At the time of this writing,
+there was no CPAN module that provides access to this XML-encoded data.
+However, many of its locales have the POSIX-only data extracted, and are
+available at L<http://unicode.org/Public/cldr/latest/>.)
+
+=head1 WHAT IS A LOCALE
+
+A locale is a set of data that describes various aspects of how various
+communities in the world categorize their world. These categories are
+broken down into the following types (some of which include a brief
+note here):
+
+=over
+
+=item Category LC_NUMERIC: Numeric formatting
+
+This indicates how numbers should be formatted for human readability,
+for example the character used as the decimal point.
+
+=item Category LC_MONETARY: Formatting of monetary amounts
+
+=for comment
+The nbsp below makes this look better
+
+E<160>
+
+=item Category LC_TIME: Date/Time formatting
+
+=for comment
+The nbsp below makes this look better
+
+E<160>
+
+=item Category LC_MESSAGES: Error and other messages
+
+This for the most part is beyond the scope of Perl
+
+=item Category LC_COLLATE: Collation
+
+This indicates the ordering of letters for comparision and sorting.
+In Latin alphabets, for example, "b", generally follows "a".
+
+=item Category LC_CTYPE: Character Types
+
+This indicates, for example if a character is an uppercase letter.
+
+=back
+
+More details on the categories are given below in L</LOCALE CATEGORIES>.
+
+Together, these categories go a long way towards being able to customize
+a single program to run in many different locations. But there are
+deficiencies, so keep reading.
=head1 PREPARING TO USE LOCALES
-If Perl applications are to understand and present your data
-correctly according a locale of your choice, B<all> of the following
-must be true:
+Perl will not use locales unless specifically requested to (see L</NOTES> below
+for the partial exception of C<write()>). But even if there is such a
+request, B<all> of the following must be true for it to work properly:
=over 4
=over 4
-=item *
+=item 1
-B<The locale-determining environment variables (see L<"ENVIRONMENT">)
+B<The locale-determining environment variables (see L</"ENVIRONMENT">)
must be correctly set up> at the time the application is started, either
-by yourself or by whoever set up your system account.
+by yourself or by whomever set up your system account; or
-=item *
+=item 2
B<The application must set its own locale> using the method described in
L<The setlocale function>.
=head2 The use locale pragma
By default, Perl ignores the current locale. The S<C<use locale>>
-pragma tells Perl to use the current locale for some operations:
+pragma tells Perl to use the current locale for some operations.
+Starting in v5.16, there is an optional parameter to this pragma:
+
+ use locale ':not_characters';
+
+This parameter allows better mixing of locales and Unicode, and is
+described fully in L</Unicode and UTF-8>, but briefly, it tells Perl to
+not use the character portions of the locale definition, that is
+the C<LC_CTYPE> and C<LC_COLLATE> categories. Instead it will use the
+native (extended by Unicode) character set. When using this parameter,
+you are responsible for getting the external character set translated
+into the native/Unicode one (which it already will be if it is one of
+the increasingly popular UTF-8 locales). There are convenient ways of
+doing this, as described in L</Unicode and UTF-8>.
+
+The current locale is set at execution time by
+L<setlocale()|/The setlocale function> described below. If that function
+hasn't yet been called in the course of the program's execution, the
+current locale is that which was determined by the L</"ENVIRONMENT"> in
+effect at the start of the program, except that
+C<L<LC_NUMERIC|/Category LC_NUMERIC: Numeric Formatting>> is always
+initialized to the C locale (mentioned under L<Finding locales>).
+If there is no valid environment, the current locale is undefined. It
+is likely, but not necessarily, the "C" locale.
+
+The operations that are affected by locale are:
+
+=over 4
+
+=item B<Under C<use locale ':not_characters';>>
+
+=over 4
+
+=item *
+
+B<Format declarations> (format()) use C<LC_NUMERIC>
+
+=item *
+
+B<The POSIX date formatting function> (strftime()) uses C<LC_TIME>.
+
+=back
+
+=for comment
+The nbsp below makes this look better
+
+E<160>
+
+=item B<Under just plain C<use locale;>>
+
+The above operations are affected, as well as the following:
=over 4
explicit comparison function, because it uses C<cmp> by default.
B<Note:> C<eq> and C<ne> are unaffected by locale: they always
-perform a byte-by-byte comparison of their scalar operands. What's
+perform a char-by-char comparison of their scalar operands. What's
more, if C<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 I<0> (equal) if the
-operands are bit-for-bit identical. If you really want to know whether
+perform a char-by-char comparison, and only returns I<0> (equal) if the
+operands are char-for-char identical. If you really want to know whether
two strings--which C<eq> and C<cmp> may consider different--are equal
as far as collation in the locale is concerned, see the discussion in
L<Category LC_COLLATE: Collation>.
B<Regular expressions and case-modification functions> (uc(), lc(),
ucfirst(), and lcfirst()) use C<LC_CTYPE>
-=item *
-
-B<The formatting functions> (printf(), sprintf() and write()) use
-C<LC_NUMERIC>
-
-=item *
-
-B<The POSIX date formatting function> (strftime()) uses C<LC_TIME>.
-
=back
-C<LC_COLLATE>, C<LC_CTYPE>, and so on, are discussed further in
-L<LOCALE CATEGORIES>.
+=back
The default behavior is restored with the S<C<no locale>> pragma, or
-upon reaching the end of block enclosing C<use locale>.
+upon reaching the end of the block enclosing C<use locale>.
+Note that C<use locale> and C<use locale ':not_characters'> may be
+nested, and that what is in effect within an inner scope will revert to
+the outer scope's rules at the end of the inner scope.
The string result of any operation that uses locale
information is tainted, as it is possible for a locale to be
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
The first argument of setlocale() gives the B<category>, the second the
B<locale>. The category tells in what aspect of data processing you
want to apply locale-specific rules. Category names are discussed in
-L<LOCALE CATEGORIES> and L<"ENVIRONMENT">. The locale is the name of a
+L</LOCALE CATEGORIES> and L</"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
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 L<setlocale(3)> for
+concatenated locale names (separator also implementation-dependent)
+or a single locale name. Please consult your setlocale(3) man page for
details.
If a second argument is given and it corresponds to a valid locale,
If the second argument does not correspond to a valid locale, the locale
for the category is not changed, and the function returns I<undef>.
-For further information about the categories, consult L<setlocale(3)>.
+Note that Perl ignores the current C<LC_CTYPE> and C<LC_COLLATE> locales
+within the scope of a C<use locale ':not_characters'>.
+
+For further information about the categories, consult setlocale(3).
=head2 Finding locales
-For locales available in your system, consult also L<setlocale(3)> to
+For locales available in your system, consult also setlocale(3) to
see whether it leads to the list of available locales (search for the
I<SEE ALSO> section). If that fails, try the following command lines:
every program starts in the absence of locale information in its
environment. (The I<default> default locale, if you will.) Its language
is (American) English and its character codeset ASCII.
+B<Warning>. The C locale delivered by some vendors may not
+actually exactly match what the C standard calls for. So beware.
B<NOTE>: Not all systems have the "POSIX" locale (not all systems are
POSIX-conformant), so use "C" when you need explicitly to specify this
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 L<ENVIRONMENT> for
+programs you run see the changes. See L<"ENVIRONMENT"> for
the full list of relevant environment variables and L<USING LOCALES>
-for their effects in Perl. Effects in other programs are
+for their effects in Perl. Effects in other programs are
easily deducible. For example, the variable LC_COLLATE may well affect
-your B<sort> program (or whatever the program that arranges `records'
+your B<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
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
+standardization is weak in this area. See again the
L<Finding locales> about general rules.
=head2 Fixing system locale configuration
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";
+ 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";
=head2 I18N::Langinfo
Another interface for querying locale-dependent information is the
-I18N::Langinfo::langinfo() function, available at least in UNIX-like
+I18N::Langinfo::langinfo() function, available at least in Unix-like
systems and VMS.
The following example will import the langinfo() function itself and
use I18N::Langinfo qw(langinfo ABDAY_1 YESSTR NOSTR);
- my ($abday_1, $yesstr, $nostr) = map { langinfo } qw(ABDAY_1 YESSTR NOSTR);
+ my ($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]
+ Sun? [yes/no]
See L<I18N::Langinfo> for more information.
=head2 Category LC_COLLATE: Collation
-In the scope of S<C<use locale>>, Perl looks to the C<LC_COLLATE>
+In the scope of S<C<use locale>> (but not a
+C<use locale ':not_characters'>), Perl looks to the C<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 'E<aacute>' and 'E<aring>' belong? And while
-'color' follows 'chocolate' in English, what about in Spanish?
+(ordering) of characters. For example, "b" follows "a" in Latin
+alphabets, but where do "E<aacute>" and "E<aring>" belong? And while
+"color" follows "chocolate" in English, what about in traditional Spanish?
The following collations all make sense and you may meet any of them
if you "use locale".
As noted in L<USING LOCALES>, C<cmp> compares according to the current
collation locale when C<use locale> is in effect, but falls back to a
-byte-by-byte comparison for strings that the locale says are equal. You
+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);
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
+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 byte-by-byte
+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
=head2 Category LC_CTYPE: Character Types
-In the scope of S<C<use locale>>, Perl obeys the C<LC_CTYPE> locale
+In the scope of S<C<use locale>> (but not a
+C<use locale ':not_characters'>), Perl obeys the C<LC_CTYPE> locale
setting. This controls the application's notion of which characters are
alphabetic. This affects Perl's C<\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 L<perlre> for more information about
regular expressions.) Thanks to C<LC_CTYPE>, depending on your locale
-setting, characters like 'E<aelig>', 'E<eth>', 'E<szlig>', and
-'E<oslash>' may be understood as C<\w> characters.
+setting, characters like "E<aelig>", "E<eth>", "E<szlig>", and
+"E<oslash>" may be understood as C<\w> characters.
The C<LC_CTYPE> locale also provides the map used in transliterating
characters between lower and uppercase. This affects the case-mapping
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().
+Unfortunately, this creates big problems for regular expressions. "|" still
+means alternation even though it matches C<\w>.
+
+Note that there are quite a few things that are unaffected by the
+current locale. All the escape sequences for particular characters,
+C<\n> for example, always mean the platform's native one. This means,
+for example, that C<\N> in regular expressions (every character
+but new-line) work on the platform character set.
B<Note:> A broken or malicious C<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
+your application. For strict matching of (mundane) ASCII letters and
digits--for example, in command strings--locale-aware applications
-should use C<\w> inside a C<no locale> block. See L<"SECURITY">.
+should use C<\w> with the C</a> regular expression modifier. See L<"SECURITY">.
=head2 Category LC_NUMERIC: Numeric Formatting
-In the scope of S<C<use locale>>, Perl obeys the C<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()
+After a proper POSIX::setlocale() call, Perl obeys the C<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 ','.
+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 L<The localeconv function> if you care about these things.)
+so on. (See L<The localeconv function> if you care about these things.)
Output produced by print() is also affected by the current locale: it
-depends on whether C<use locale> or C<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;
+ use POSIX qw(strtod setlocale LC_NUMERIC);
+
+ setlocale LC_NUMERIC, "";
$n = 5/2; # Assign numeric 2.5 to $n
=head2 Category LC_MONETARY: Formatting of monetary amounts
-The C standard defines the C<LC_MONETARY> category, but no function
+The C standard defines the C<LC_MONETARY> category, but not a 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 C<LC_MONETARY>, you can query its contents--see
-L<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 use C<LC_MONETARY>, you can query its contents--see
+L<The localeconv function>--and use the information that it returns in your
+application's own formatting of currency amounts. However, you may well
+find that the information, voluminous and complex though it may be, still
+does not quite meet your requirements: currency formatting is a hard nut
to crack.
See also L<I18N::Langinfo> and C<CRNCYSTR>.
B<Case-mapping interpolation> (with C<\l>, C<\L>, C<\u> or C<\U>)
Result string containing interpolated material is tainted if
-C<use locale> is in effect.
+C<use locale> (but not S<C<use locale ':not_characters'>>) is in effect.
=item *
Scalar true/false result never tainted.
Subpatterns, either delivered as a list-context result or as $1 etc.
-are tainted if C<use locale> is in effect, and the subpattern regular
+are tainted if C<use locale> (but not S<C<use locale ':not_characters'>>)
+is in effect, and the subpattern regular
expression contains C<\w> (to match an alphanumeric character), C<\W>
-(non-alphanumeric character), C<\s> (white-space character), or C<\S>
-(non white-space character). The matched-pattern variable, $&, $`
+(non-alphanumeric character), C<\s> (whitespace character), or C<\S>
+(non whitespace character). The matched-pattern variable, $&, $`
(pre-match), $' (post-match), and $+ (last match) are also tainted if
C<use locale> is in effect and the regular expression contains C<\w>,
C<\W>, C<\s>, or C<\S>.
B<Substitution operator> (C<s///>):
Has the same behavior as the match operator. Also, the left
-operand of C<=~> becomes tainted when C<use locale> in effect
-if modified as a result of a substitution based on a regular
+operand of C<=~> becomes tainted when C<use locale>
+(but not S<C<use locale ':not_characters'>>) is in effect if modified as
+a result of a substitution based on a regular
expression match involving C<\w>, C<\W>, C<\s>, or C<\S>; or of
case-mapping with C<\l>, C<\L>,C<\u> or C<\U>.
B<Case-mapping functions> (lc(), lcfirst(), uc(), ucfirst()):
-Results are tainted if C<use locale> is in effect.
+Results are tainted if C<use locale> (but not
+S<C<use locale ':not_characters'>>) is in effect.
=item *
$tainted_output_file = shift;
open(F, ">$tainted_output_file")
- or warn "Open of $untainted_output_file failed: $!\n";
+ or warn "Open of $tainted_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
B<NOTE>: C<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 I<not>
+If you are using "commercial" Unixes you are most probably I<not>
using GNU libc and you can ignore C<LANGUAGE>.
However, in the case you are using C<LANGUAGE>: it affects the
language of informational, warning, and error messages output by
commands (in other words, it's like C<LC_MESSAGES>) but it has higher
-priority than L<LC_ALL>. Moreover, it's not a single value but
+priority than C<LC_ALL>. Moreover, it's not a single value but
instead a "path" (":"-separated list) of I<languages> (not locales).
See the GNU C<gettext> library documentation for more information.
=back
+=head2 Examples
+
+The LC_NUMERIC controls the numeric output:
+
+ use locale;
+ use POSIX qw(locale_h); # Imports setlocale() and the LC_ constants.
+ setlocale(LC_NUMERIC, "fr_FR") or die "Pardon";
+ printf "%g\n", 1.23; # If the "fr_FR" succeeded, probably shows 1,23.
+
+and also how strings are parsed by POSIX::strtod() as numbers:
+
+ use locale;
+ use POSIX qw(locale_h strtod);
+ setlocale(LC_NUMERIC, "de_DE") or die "Entschuldigung";
+ my $x = strtod("2,34") + 5;
+ print $x, "\n"; # Probably shows 7,34.
+
=head1 NOTES
=head2 Backward compatibility
(see L<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 B<must> use the S<C<use locale>>
-pragma (see L<The use locale pragma>) to instruct it to do so.
+pragma (see L<The use locale pragma>) or, in the unlikely event
+that you want to do so for just pattern matching, the
+C</l> regular expression modifier (see L<perlre/Character set
+modifiers>) to instruct it to do so.
Versions of Perl from 5.002 to 5.003 did use the C<LC_CTYPE>
information if available; that is, C<\w> did understand what
=head2 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
-C<use locale> because the pragma is tied to the block structure of the
-program, and, for historical reasons, formats exist outside that block
-structure.
+If a program's environment specifies an LC_NUMERIC locale and C<use
+locale> is in effect when the format is declared, the locale is used
+to specify the decimal point character in formatted output. Formatted
+output cannot be controlled by C<use locale> at the time when write()
+is called.
=head2 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
+The Unicode CLDR project extracts the POSIX portion of many of its
+locales, available at
+
+ http://unicode.org/Public/cldr/latest/
+
+There is a large collection of locale definitions at:
+
+ http://std.dkuug.dk/i18n/WG15-collection/locales/
+
+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
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.
+into bankers, bikers, gamers, and so on.
=head1 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 L<perluniintro> and
-L<perlunicode> for more details.
-
-Usually locale settings and Unicode do not affect each other, but
-there are exceptions, see L<perlunicode/Locales> for examples.
+The support of Unicode is new starting from Perl version v5.6, and more fully
+implemented in version v5.8 and later. See L<perluniintro>. It is
+strongly recommended that when combining Unicode and locale (starting in
+v5.16), you use
+
+ use locale ':not_characters';
+
+When this form of the pragma is used, only the non-character portions of
+locales are used by Perl, for example C<LC_NUMERIC>. Perl assumes that
+you have translated all the characters it is to operate on into Unicode
+(actually the platform's native character set (ASCII or EBCDIC) plus
+Unicode). For data in files, this can conveniently be done by also
+specifying
+
+ use open ':locale';
+
+This pragma arranges for all inputs from files to be translated into
+Unicode from the current locale as specified in the environment (see
+L</ENVIRONMENT>), and all outputs to files to be translated back
+into the locale. (See L<open>). On a per-filehandle basis, you can
+instead use the L<PerlIO::locale> module, or the L<Encode::Locale>
+module, both available from CPAN. The latter module also has methods to
+ease the handling of C<ARGV> and environment variables, and can be used
+on individual strings. Also, if you know that all your locales will be
+UTF-8, as many are these days, you can use the L<B<-C>|perlrun/-C>
+command line switch.
+
+This form of the pragma allows essentially seamless handling of locales
+with Unicode. The collation order will be Unicode's. It is strongly
+recommended that when you need to order and sort strings that you use
+the standard module L<Unicode::Collate> which gives much better results
+in many instances than you can get with the old-style locale handling.
+
+For pre-v5.16 Perls, or if you use the locale pragma without the
+C<:not_characters> parameter, Perl tries to work with both Unicode and
+locales--but there are problems.
+
+Perl does not handle multi-byte locales in this case, such as have been
+used for various
+Asian languages, such as Big5 or Shift JIS. However, the increasingly
+common multi-byte UTF-8 locales, if properly implemented, may work
+reasonably well (depending on your C library implementation) in this
+form of the locale pragma, simply because both
+they and Perl store characters that take up multiple bytes the same way.
+However, some, if not most, C library implementations may not process
+the characters in the upper half of the Latin-1 range (128 - 255)
+properly under LC_CTYPE. To see if a character is a particular type
+under a locale, Perl uses the functions like C<isalnum()>. Your C
+library may not work for UTF-8 locales with those functions, instead
+only working under the newer wide library functions like C<iswalnum()>.
+
+Perl generally takes the tack to use locale rules on code points that can fit
+in a single byte, and Unicode rules for those that can't (though this
+isn't uniformly applied, see the note at the end of this section). This
+prevents many problems in locales that aren't UTF-8. Suppose the locale
+is ISO8859-7, Greek. The character at 0xD7 there is a capital Chi. But
+in the ISO8859-1 locale, Latin1, it is a multiplication sign. The POSIX
+regular expression character class C<[[:alpha:]]> will magically match
+0xD7 in the Greek locale but not in the Latin one.
+
+However, there are places where this breaks down. Certain constructs are
+for Unicode only, such as C<\p{Alpha}>. They assume that 0xD7 always has its
+Unicode meaning (or the equivalent on EBCDIC platforms). Since Latin1 is a
+subset of Unicode and 0xD7 is the multiplication sign in both Latin1 and
+Unicode, C<\p{Alpha}> will never match it, regardless of locale. A similar
+issue occurs with C<\N{...}>. It is therefore a bad idea to use C<\p{}> or
+C<\N{}> under plain C<use locale>--I<unless> you can guarantee that the
+locale will be a ISO8859-1. Use POSIX character classes instead.
+
+Another problem with this approach is that operations that cross the
+single byte/multiple byte boundary are not well-defined, and so are
+disallowed. (This boundary is between the codepoints at 255/256.).
+For example, lower casing LATIN CAPITAL LETTER Y WITH DIAERESIS (U+0178)
+should return LATIN SMALL LETTER Y WITH DIAERESIS (U+00FF). But in the
+Greek locale, for example, there is no character at 0xFF, and Perl
+has no way of knowing what the character at 0xFF is really supposed to
+represent. Thus it disallows the operation. In this mode, the
+lowercase of U+0178 is itself.
+
+The same problems ensue if you enable automatic UTF-8-ification of your
+standard file handles, default C<open()> layer, and C<@ARGV> on non-ISO8859-1,
+non-UTF-8 locales (by using either the B<-C> command line switch or the
+C<PERL_UNICODE> environment variable; see L<perlrun>).
+Things are read in as UTF-8, which would normally imply a Unicode
+interpretation, but the presence of a locale causes them to be interpreted
+in that locale instead. For example, a 0xD7 code point in the Unicode
+input, which should mean the multiplication sign, won't be interpreted by
+Perl that way under the Greek locale. This is not a problem
+I<provided> you make certain that all locales will always and only be either
+an ISO8859-1, or, if you don't have a deficient C library, a UTF-8 locale.
+
+Vendor locales are notoriously buggy, and it is difficult for Perl to test
+its locale-handling code because this interacts with code that Perl has no
+control over; therefore the locale-handling code in Perl may be buggy as
+well. (However, the Unicode-supplied locales should be better, and
+there is a feed back mechanism to correct any problems. See
+L</Freely available locale definitions>.)
+
+If you have Perl v5.16, the problems mentioned above go away if you use
+the C<:not_characters> parameter to the locale pragma (except for vendor
+bugs in the non-character portions). If you don't have v5.16, and you
+I<do> have locales that work, using them may be worthwhile for certain
+specific purposes, as long as you keep in mind the gotchas already
+mentioned. For example, if the collation for your locales works, it
+runs faster under locales than under L<Unicode::Collate>; and you gain
+access to such things as the local currency symbol and the names of the
+months and days of the week. (But to hammer home the point, in v5.16,
+you get this access without the downsides of locales by using the
+C<:not_characters> form of the pragma.)
+
+Note: The policy of using locale rules for code points that can fit in a
+byte, and Unicode rules for those that can't is not uniformly applied.
+Pre-v5.12, it was somewhat haphazard; in v5.12 it was applied fairly
+consistently to regular expression matching except for bracketed
+character classes; in v5.14 it was extended to all regex matches; and in
+v5.16 to the casing operations such as C<"\L"> and C<uc()>. For
+collation, in all releases, the system's C<strxfrm()> function is called,
+and whatever it does is what you get.
=head1 BUGS
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
+and will result in mysterious hangs and/or Perl core dumps when
C<use locale> is in effect. When confronted with such a system,
please report in excruciating detail to <F<perlbug@perl.org>>, and
-complain to your vendor: bug fixes may exist for these problems
+also contact your vendor: bug fixes may exist for these problems
in your operating system. Sometimes such bug fixes are called an
operating system upgrade.
Jarkko Hietaniemi's original F<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
+Tom Christiansen, and updated by Perl 5 porters.
https://perl5.git.perl.org / perl5.git / blobdiff