=over 4
-=item Input and Output Disciplines
+=item Input and Output Layers
Perl knows when a filehandle uses Perl's internal Unicode encodings
-(UTF-8 or UTF-EBCDIC) if the filehandle is opened with the ":utf8"
-layer. Other encodings can be converted to Perl's encoding on input
-or from Perl's encoding on output by use of the ":encoding(...)"
-layer. See L<open>.
+(UTF-8, or UTF-EBCDIC if in EBCDIC) if the filehandle is opened with
+the ":utf8" layer. Other encodings can be converted to Perl's
+encoding on input or from Perl's encoding on output by use of the
+":encoding(...)" layer. See L<open>.
To indicate that Perl source itself is using a particular encoding,
see L<encoding>.
As a compatibility measure, the C<use utf8> pragma must be explicitly
included to enable recognition of UTF-8 in the Perl scripts themselves
-on ASCII-based machines or to recognize UTF-EBCDIC on EBCDIC-based
+(in string or regular expression literals, or in identifier names) on
+ASCII-based machines or to recognize UTF-EBCDIC on EBCDIC-based
machines. B<These are the only times when an explicit C<use utf8>
-is needed.>
+is needed.> See L<utf8>.
You can also use the C<encoding> pragma to change the default encoding
of the data in your script; see L<encoding>.
+=item BOM-marked scripts and UTF-16 scripts autodetected
+
+If a Perl script begins marked with the Unicode BOM (UTF-16LE, UTF16-BE,
+or UTF-8), or if the script looks like non-BOM-marked UTF-16 of either
+endianness, Perl will correctly read in the script as Unicode.
+(BOMless UTF-8 cannot be effectively recognized or differentiated from
+ISO 8859-1 or other eight-bit encodings.)
+
+=item C<use encoding> needed to upgrade non-Latin-1 byte strings
+
+By default, there is a fundamental asymmetry in Perl's unicode model:
+implicit upgrading from byte strings to Unicode strings assumes that
+they were encoded in I<ISO 8859-1 (Latin-1)>, but Unicode strings are
+downgraded with UTF-8 encoding. This happens because the first 256
+codepoints in Unicode happens to agree with Latin-1.
+
+If you wish to interpret byte strings as UTF-8 instead, use the
+C<encoding> pragma:
+
+ use encoding 'utf8';
+
+See L</"Byte and Character Semantics"> for more details.
+
=back
=head2 Byte and Character Semantics
external programs, from information provided by the system (such as %ENV),
or from literals and constants in the source text.
-On Windows platforms, if the C<-C> command line switch is used or the
-${^WIDE_SYSTEM_CALLS} global flag is set to C<1>, all system calls
-will use the corresponding wide-character APIs. This feature is
-available only on Windows to conform to the API standard already
-established for that platform.
-
The C<bytes> pragma will always, regardless of platform, force byte
semantics in a particular lexical scope. See L<bytes>.
for Unicode data and byte semantics for non-Unicode data.
The decision to use character semantics is made transparently. If
input data comes from a Unicode source--for example, if a character
-encoding discipline is added to a filehandle or a literal Unicode
+encoding layer is added to a filehandle or a literal Unicode
string constant appears in a program--character semantics apply.
Otherwise, byte semantics are in effect. The C<bytes> pragma should
be used to force byte semantics on Unicode data.
If strings operating under byte semantics and strings with Unicode
-character data are concatenated, the new string will be upgraded to
-I<ISO 8859-1 (Latin-1)>, even if the old Unicode string used EBCDIC.
-This translation is done without regard to the system's native 8-bit
-encoding, so to change this for systems with non-Latin-1 and
-non-EBCDIC native encodings use the C<encoding> pragma. See
-L<encoding>.
+character data are concatenated, the new string will be created by
+decoding the byte strings as I<ISO 8859-1 (Latin-1)>, even if the
+old Unicode string used EBCDIC. This translation is done without
+regard to the system's native 8-bit encoding. To change this for
+systems with non-Latin-1 and non-EBCDIC native encodings, use the
+C<encoding> pragma. See L<encoding>.
Under character semantics, many operations that formerly operated on
bytes now operate on characters. A character in Perl is
as such and converted to Perl's internal representation only if the
appropriate L<encoding> is specified.
-Unicode characters can also be added to a string by using the C<\x{...}>
-notation. The Unicode code for the desired character, in
+Unicode characters can also be added to a string by using the
+C<\x{...}> notation. The Unicode code for the desired character, in
hexadecimal, should be placed in the braces. For instance, a smiley
face is C<\x{263A}>. This encoding scheme only works for characters
with a code of 0x100 or above.
use charnames ':full';
-you can use the C<\N{...}> notation and put the official Unicode character
-name within the braces, such as C<\N{WHITE SMILING FACE}>.
+you can use the C<\N{...}> notation and put the official Unicode
+character name within the braces, such as C<\N{WHITE SMILING FACE}>.
=item *
=item *
-Regular expressions match characters instead of bytes.
-"." matches a character instead of a byte. The C<\C> pattern
-is provided to force a match a single byte--a "C<char>" in C, hence C<\C>.
+Regular expressions match characters instead of bytes. "." matches
+a character instead of a byte. The C<\C> pattern is provided to force
+a match a single byte--a C<char> in C, hence C<\C>.
=item *
Character classes in regular expressions match characters instead of
bytes and match against the character properties specified in the
-Unicode properties database. C<\w> can be used to match an
+Unicode properties database. C<\w> can be used to match a Japanese
ideograph, for instance.
+(However, and as a limitation of the current implementation, using
+C<\w> or C<\W> I<inside> a C<[...]> character class will still match
+with byte semantics.)
+
=item *
Named Unicode properties, scripts, and block ranges may be used like
character classes via the C<\p{}> "matches property" construct and
the C<\P{}> negation, "doesn't match property".
-For instance, C<\p{Lu}> matches any
-character with the Unicode "Lu" (Letter, uppercase) property, while
-C<\p{M}> matches any character with an "M" (mark--accents and such)
-property. Brackets are not required for single letter properties, so
-C<\p{M}> is equivalent to C<\pM>. Many predefined properties are
-available, such as C<\p{Mirrored}> and C<\p{Tibetan}>.
+
+For instance, C<\p{Lu}> matches any character with the Unicode "Lu"
+(Letter, uppercase) property, while C<\p{M}> matches any character
+with an "M" (mark--accents and such) property. Brackets are not
+required for single letter properties, so C<\p{M}> is equivalent to
+C<\pM>. Many predefined properties are available, such as
+C<\p{Mirrored}> and C<\p{Tibetan}>.
The official Unicode script and block names have spaces and dashes as
separators, but for convenience you can use dashes, spaces, or
-underbars, and case is unimportant. It is
-recommended, however, that for consistency you use the following naming:
-the official Unicode script, property, or block name (see below for the
-additional rules that apply to block names) with whitespace and dashes
-removed, and the words "uppercase-first-lowercase-rest". "C<Latin-1
-Supplement>" thus becomes "C<Latin1Supplement>".
+underbars, and case is unimportant. It is recommended, however, that
+for consistency you use the following naming: the official Unicode
+script, property, or block name (see below for the additional rules
+that apply to block names) with whitespace and dashes removed, and the
+words "uppercase-first-lowercase-rest". C<Latin-1 Supplement> thus
+becomes C<Latin1Supplement>.
You can also use negation in both C<\p{}> and C<\P{}> by introducing a caret
(^) between the first brace and the property name: C<\p{^Tamil}> is
equal to C<\P{Tamil}>.
+B<NOTE: the properties, scripts, and blocks listed here are as of
+Unicode 3.2.0, March 2002, or Perl 5.8.0, July 2002. Unicode 4.0.0
+came out in April 2003, and Perl 5.8.1 in September 2003.>
+
Here are the basic Unicode General Category properties, followed by their
-long form. You can use either; C<\p{Lu}> and C<\p{LowercaseLetter}>,
+long form. You can use either; C<\p{Lu}> and C<\p{UppercaseLetter}>,
for instance, are identical.
Short Long
L Letter
+ LC CasedLetter
Lu UppercaseLetter
Ll LowercaseLetter
Lt TitlecaseLetter
Single-letter properties match all characters in any of the
two-letter sub-properties starting with the same letter.
-C<L&> is a special case, which is an alias for C<Ll>, C<Lu>, and C<Lt>.
+C<LC> and C<L&> are special cases, which are aliases for the set of
+C<Ll>, C<Lu>, and C<Lt>.
Because Perl hides the need for the user to understand the internal
-representation of Unicode characters, there is no need to implement the
-somewhat messy concept of surrogates. C<Cs> is therefore not
+representation of Unicode characters, there is no need to implement
+the somewhat messy concept of surrogates. C<Cs> is therefore not
supported.
Because scripts differ in their directionality--Hebrew is
-written right to left, for example--Unicode supplies these properties:
+written right to left, for example--Unicode supplies these properties in
+the BidiClass class:
Property Meaning
- BidiL Left-to-Right
- BidiLRE Left-to-Right Embedding
- BidiLRO Left-to-Right Override
- BidiR Right-to-Left
- BidiAL Right-to-Left Arabic
- BidiRLE Right-to-Left Embedding
- BidiRLO Right-to-Left Override
- BidiPDF Pop Directional Format
- BidiEN European Number
- BidiES European Number Separator
- BidiET European Number Terminator
- BidiAN Arabic Number
- BidiCS Common Number Separator
- BidiNSM Non-Spacing Mark
- BidiBN Boundary Neutral
- BidiB Paragraph Separator
- BidiS Segment Separator
- BidiWS Whitespace
- BidiON Other Neutrals
-
-For example, C<\p{BidiR}> matches characters that are normally
+ L Left-to-Right
+ LRE Left-to-Right Embedding
+ LRO Left-to-Right Override
+ R Right-to-Left
+ AL Right-to-Left Arabic
+ RLE Right-to-Left Embedding
+ RLO Right-to-Left Override
+ PDF Pop Directional Format
+ EN European Number
+ ES European Number Separator
+ ET European Number Terminator
+ AN Arabic Number
+ CS Common Number Separator
+ NSM Non-Spacing Mark
+ BN Boundary Neutral
+ B Paragraph Separator
+ S Segment Separator
+ WS Whitespace
+ ON Other Neutrals
+
+For example, C<\p{BidiClass:R}> matches characters that are normally
written right to left.
=back
Common Any character (or unassigned code point)
not explicitly assigned to a script
-For backward compatibility, all properties mentioned so far may have C<Is>
-prepended to their name, so C<\P{IsLu}>, for example, is equal to C<\P{Lu}>.
+For backward compatibility (with Perl 5.6), all properties mentioned
+so far may have C<Is> prepended to their name, so C<\P{IsLu}>, for
+example, is equal to C<\P{Lu}>.
=head2 Blocks
-In addition to B<scripts>, Unicode also defines B<blocks> of characters.
-The difference between scripts and blocks is that the concept of
-scripts is closer to natural languages, while the concept of blocks
-is more of an artificial grouping based on groups of around 256
+In addition to B<scripts>, Unicode also defines B<blocks> of
+characters. The difference between scripts and blocks is that the
+concept of scripts is closer to natural languages, while the concept
+of blocks is more of an artificial grouping based on groups of 256
Unicode characters. For example, the C<Latin> script contains letters
-from many blocks but does not contain all the characters from those
+from many blocks but does not contain all the characters from those
blocks. It does not, for example, contain digits, because digits are
shared across many scripts. Digits and similar groups, like
punctuation, are in a category called C<Common>.
Katakana block is referenced via C<\p{InKatakana}>. The C<In>
prefix may be omitted if there is no naming conflict with a script
or any other property, but it is recommended that C<In> always be used
-to avoid confusion.
+for block tests to avoid confusion.
These block names are supported:
Most operators that deal with positions or lengths in a string will
automatically switch to using character positions, including
-C<chop()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>,
+C<chop()>, C<chomp()>, C<substr()>, C<pos()>, C<index()>, C<rindex()>,
C<sprintf()>, C<write()>, and C<length()>. Operators that
specifically do not switch include C<vec()>, C<pack()>, and
-C<unpack()>. Operators that really don't care include C<chomp()>,
+C<unpack()>. Operators that really don't care include
operators that treats strings as a bucket of bits such as C<sort()>,
and operators dealing with filenames.
=item *
-The C<pack()>/C<unpack()> letters "C<c>" and "C<C>" do I<not> change,
+The C<pack()>/C<unpack()> letters C<c> and C<C> do I<not> change,
since they are often used for byte-oriented formats. Again, think
-"C<char>" in the C language. There is a new "C<U>" specifier
-that converts between Unicode characters and integers.
+C<char> in the C language.
+
+There is a new C<U> specifier that converts between Unicode characters
+and code points.
=item *
=back
-The following cases do not yet work:
+Things to do with locales (Lithuanian, Turkish, Azeri) do B<not> work
+since Perl does not understand the concept of Unicode locales.
-=over 8
-
-=item *
-
-the "final sigma" (Greek), and
-
-=item *
-
-anything to with locales (Lithuanian, Turkish, Azeri).
+See the Unicode Technical Report #21, Case Mappings, for more details.
=back
-See the Unicode Technical Report #21, Case Mappings, for more details.
+=over 4
=item *
=head2 User-Defined Character Properties
You can define your own character properties by defining subroutines
-whose names begin with "In" or "Is". The subroutines must be
-visible in the package that uses the properties. The user-defined
-properties can be used in the regular expression C<\p> and C<\P>
-constructs.
+whose names begin with "In" or "Is". The subroutines can be defined in
+any package. The user-defined properties can be used in the regular
+expression C<\p> and C<\P> constructs; if you are using a user-defined
+property from a package other than the one you are in, you must specify
+its package in the C<\p> or C<\P> construct.
+
+ # assuming property IsForeign defined in Lang::
+ package main; # property package name required
+ if ($txt =~ /\p{Lang::IsForeign}+/) { ... }
+
+ package Lang; # property package name not required
+ if ($txt =~ /\p{IsForeign}+/) { ... }
+
+
+Note that the effect is compile-time and immutable once defined.
The subroutines must return a specially-formatted string, with one
or more newline-separated lines. Each line must be one of the following:
=item *
Something to include, prefixed by "+": a built-in character
-property (prefixed by "utf8::"), to represent all the characters in that
-property; two hexadecimal code points for a range; or a single
-hexadecimal code point.
+property (prefixed by "utf8::") or a user-defined character property,
+to represent all the characters in that property; two hexadecimal code
+points for a range; or a single hexadecimal code point.
=item *
Something to exclude, prefixed by "-": an existing character
-property (prefixed by "utf8::"), for all the characters in that
-property; two hexadecimal code points for a range; or a single
-hexadecimal code point.
+property (prefixed by "utf8::") or a user-defined character property,
+to represent all the characters in that property; two hexadecimal code
+points for a range; or a single hexadecimal code point.
=item *
Something to negate, prefixed "!": an existing character
-property (prefixed by "utf8::") for all the characters except the
-characters in the property; two hexadecimal code points for a range;
-or a single hexadecimal code point.
+property (prefixed by "utf8::") or a user-defined character property,
+to represent all the characters in that property; two hexadecimal code
+points for a range; or a single hexadecimal code point.
+
+=item *
+
+Something to intersect with, prefixed by "&": an existing character
+property (prefixed by "utf8::") or a user-defined character property,
+for all the characters except the characters in the property; two
+hexadecimal code points for a range; or a single hexadecimal code point.
=back
END
}
+Intersection is useful for getting the common characters matched by
+two (or more) classes.
+
+ sub InFooAndBar {
+ return <<'END';
+ +main::Foo
+ &main::Bar
+ END
+ }
+
+It's important to remember not to use "&" for the first set -- that
+would be intersecting with nothing (resulting in an empty set).
+
+You can also define your own mappings to be used in the lc(),
+lcfirst(), uc(), and ucfirst() (or their string-inlined versions).
+The principle is the same: define subroutines in the C<main> package
+with names like C<ToLower> (for lc() and lcfirst()), C<ToTitle> (for
+the first character in ucfirst()), and C<ToUpper> (for uc(), and the
+rest of the characters in ucfirst()).
+
+The string returned by the subroutines needs now to be three
+hexadecimal numbers separated by tabulators: start of the source
+range, end of the source range, and start of the destination range.
+For example:
+
+ sub ToUpper {
+ return <<END;
+ 0061\t0063\t0041
+ END
+ }
+
+defines an uc() mapping that causes only the characters "a", "b", and
+"c" to be mapped to "A", "B", "C", all other characters will remain
+unchanged.
+
+If there is no source range to speak of, that is, the mapping is from
+a single character to another single character, leave the end of the
+source range empty, but the two tabulator characters are still needed.
+For example:
+
+ sub ToLower {
+ return <<END;
+ 0041\t\t0061
+ END
+ }
+
+defines a lc() mapping that causes only "A" to be mapped to "a", all
+other characters will remain unchanged.
+
+(For serious hackers only) If you want to introspect the default
+mappings, you can find the data in the directory
+C<$Config{privlib}>/F<unicore/To/>. The mapping data is returned as
+the here-document, and the C<utf8::ToSpecFoo> are special exception
+mappings derived from <$Config{privlib}>/F<unicore/SpecialCasing.txt>.
+The C<Digit> and C<Fold> mappings that one can see in the directory
+are not directly user-accessible, one can use either the
+C<Unicode::UCD> module, or just match case-insensitively (that's when
+the C<Fold> mapping is used).
+
+A final note on the user-defined property tests and mappings: they
+will be used only if the scalar has been marked as having Unicode
+characters. Old byte-style strings will not be affected.
+
=head2 Character Encodings for Input and Output
See L<Encode>.
The following list of Unicode support for regular expressions describes
all the features currently supported. The references to "Level N"
and the section numbers refer to the Unicode Technical Report 18,
-"Unicode Regular Expression Guidelines".
+"Unicode Regular Expression Guidelines", version 6 (Unicode 3.2.0,
+Perl 5.8.0).
=over 4
[ 1] \x{...}
[ 2] \N{...}
[ 3] . \p{...} \P{...}
- [ 4] now scripts (see UTR#24 Script Names) in addition to blocks
+ [ 4] support for scripts (see UTR#24 Script Names), blocks,
+ binary properties, enumerated non-binary properties, and
+ numeric properties (as listed in UTR#18 Other Properties)
[ 5] have negation
[ 6] can use regular expression look-ahead [a]
or user-defined character properties [b] to emulate subtraction
[ 7] include Letters in word characters
[ 8] note that Perl does Full case-folding in matching, not Simple:
- for example U+1F88 is equivalent with U+1F000 U+03B9,
+ for example U+1F88 is equivalent with U+1F00 U+03B9,
not with 1F80. This difference matters for certain Greek
capital letters with certain modifiers: the Full case-folding
decomposes the letter, while the Simple case-folding would map
it to a single character.
- [ 9] see UTR#13 Unicode Newline Guidelines
- [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029})
+ [ 9] see UTR #13 Unicode Newline Guidelines
+ [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029}
(should also affect <>, $., and script line numbers)
(the \x{85}, \x{2028} and \x{2029} do match \s)
[a] You can mimic class subtraction using lookahead.
-For example, what TR18 might write as
+For example, what UTR #18 might write as
[{Greek}-[{UNASSIGNED}]]
But in this particular example, you probably really want
- \p{Greek}
+ \p{GreekAndCoptic}
which will match assigned characters known to be part of the Greek script.
-[b] See L</User-defined Character Properties>.
+Also see the Unicode::Regex::Set module, it does implement the full
+UTR #18 grouping, intersection, union, and removal (subtraction) syntax.
+
+[b] See L</"User-Defined Character Properties">.
=item *
Level 2 - Extended Unicode Support
- 3.1 Surrogates - MISSING
- 3.2 Canonical Equivalents - MISSING [11][12]
- 3.3 Locale-Independent Graphemes - MISSING [13]
- 3.4 Locale-Independent Words - MISSING [14]
- 3.5 Locale-Independent Loose Matches - MISSING [15]
+ 3.1 Surrogates - MISSING [11]
+ 3.2 Canonical Equivalents - MISSING [12][13]
+ 3.3 Locale-Independent Graphemes - MISSING [14]
+ 3.4 Locale-Independent Words - MISSING [15]
+ 3.5 Locale-Independent Loose Matches - MISSING [16]
- [11] see UTR#15 Unicode Normalization
- [12] have Unicode::Normalize but not integrated to regexes
- [13] have \X but at this level . should equal that
- [14] need three classes, not just \w and \W
- [15] see UTR#21 Case Mappings
+ [11] Surrogates are solely a UTF-16 concept and Perl's internal
+ representation is UTF-8. The Encode module does UTF-16, though.
+ [12] see UTR#15 Unicode Normalization
+ [13] have Unicode::Normalize but not integrated to regexes
+ [14] have \X but at this level . should equal that
+ [15] need three classes, not just \w and \W
+ [16] see UTR#21 Case Mappings
=item *
=item *
-UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks)
+UTF-16, UTF-16BE, UTF-16LE, Surrogates, and BOMs (Byte Order Marks)
-The followings items are mostly for reference, Perl doesn't
-use them internally.
+The followings items are mostly for reference and general Unicode
+knowledge, Perl doesn't use these constructs internally.
UTF-16 is a 2 or 4 byte encoding. The Unicode code points
-C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code points
-C<U+10000..U+10FFFF> in two 16-bit units. The latter case is
+C<U+0000..U+FFFF> are stored in a single 16-bit unit, and the code
+points C<U+10000..U+10FFFF> in two 16-bit units. The latter case is
using I<surrogates>, the first 16-bit unit being the I<high
surrogate>, and the second being the I<low surrogate>.
The way this trick works is that the character with the code point
C<U+FFFE> is guaranteed not to be a valid Unicode character, so the
sequence of bytes C<0xFF 0xFE> is unambiguously "BOM, represented in
-little-endian format" and cannot be "C<U+FFFE>, represented in big-endian
+little-endian format" and cannot be C<U+FFFE>, represented in big-endian
format".
=item *
-UTF-32, UTF-32BE, UTF32-LE
+UTF-32, UTF-32BE, UTF-32LE
The UTF-32 family is pretty much like the UTF-16 family, expect that
the units are 32-bit, and therefore the surrogate scheme is not
more letters according to your language and country.
In the second case, the C<\w> set of characters is much, much larger.
-Most importantly, even in the set of the first 256 characters, it
-will probably match different characters: unlike most locales,
-which are specific to a language and country pair, Unicode classifies all
-the characters that are letters as C<\w>. For example, your locale might
-not think that LATIN SMALL LETTER ETH is a letter (unless you happen
-to speak Icelandic), but Unicode does.
+Most importantly, even in the set of the first 256 characters, it will
+probably match different characters: unlike most locales, which are
+specific to a language and country pair, Unicode classifies all the
+characters that are letters I<somewhere> as C<\w>. For example, your
+locale might not think that LATIN SMALL LETTER ETH is a letter (unless
+you happen to speak Icelandic), but Unicode does.
As discussed elsewhere, Perl has one foot (two hooves?) planted in
-each of two worlds: the old world of bytes and the new
-world of characters, upgrading from bytes to characters when necessary.
+each of two worlds: the old world of bytes and the new world of
+characters, upgrading from bytes to characters when necessary.
If your legacy code does not explicitly use Unicode, no automatic
switch-over to characters should happen. Characters shouldn't get
-downgraded to bytes, either. It is possible to accidentally mix
-bytes and characters, however (see L<perluniintro>), in which case
-C<\w> in regular expressions might start behaving differently. Review
-your code.
+downgraded to bytes, either. It is possible to accidentally mix bytes
+and characters, however (see L<perluniintro>), in which case C<\w> in
+regular expressions might start behaving differently. Review your
+code. Use warnings and the C<strict> pragma.
=back
=item *
-If your locale environment variables (LANGUAGE, LC_ALL, LC_CTYPE, LANG)
-contain the strings 'UTF-8' or 'UTF8' (case-insensitive matching),
-the default encodings of your STDIN, STDOUT, and STDERR, and of
-B<any subsequent file open>, are considered to be UTF-8.
+You can enable automatic UTF-8-ification of your standard file
+handles, default C<open()> layer, and C<@ARGV> by using either
+the C<-C> command line switch or the C<PERL_UNICODE> environment
+variable, see L<perlrun> for the documentation of the C<-C> switch.
=item *
=back
+=head2 When Unicode Does Not Happen
+
+While Perl does have extensive ways to input and output in Unicode,
+and few other 'entry points' like the @ARGV which can be interpreted
+as Unicode (UTF-8), there still are many places where Unicode (in some
+encoding or another) could be given as arguments or received as
+results, or both, but it is not.
+
+The following are such interfaces. For all of these interfaces Perl
+currently (as of 5.8.3) simply assumes byte strings both as arguments
+and results, or UTF-8 strings if the C<encoding> pragma has been used.
+
+One reason why Perl does not attempt to resolve the role of Unicode in
+this cases is that the answers are highly dependent on the operating
+system and the file system(s). For example, whether filenames can be
+in Unicode, and in exactly what kind of encoding, is not exactly a
+portable concept. Similarly for the qx and system: how well will the
+'command line interface' (and which of them?) handle Unicode?
+
+=over 4
+
+=item *
+
+chmod, chmod, chown, chroot, exec, link, lstat, mkdir,
+rename, rmdir, stat, symlink, truncate, unlink, utime, -X
+
+=item *
+
+%ENV
+
+=item *
+
+glob (aka the <*>)
+
+=item *
+
+open, opendir, sysopen
+
+=item *
+
+qx (aka the backtick operator), system
+
+=item *
+
+readdir, readlink
+
+=back
+
+=head2 Forcing Unicode in Perl (Or Unforcing Unicode in Perl)
+
+Sometimes (see L</"When Unicode Does Not Happen">) there are
+situations where you simply need to force Perl to believe that a byte
+string is UTF-8, or vice versa. The low-level calls
+utf8::upgrade($bytestring) and utf8::downgrade($utf8string) are
+the answers.
+
+Do not use them without careful thought, though: Perl may easily get
+very confused, angry, or even crash, if you suddenly change the 'nature'
+of scalar like that. Especially careful you have to be if you use the
+utf8::upgrade(): any random byte string is not valid UTF-8.
+
=head2 Using Unicode in XS
-If you want to handle Perl Unicode in XS extensions, you may find
-the following C APIs useful. See L<perlapi> for details.
+If you want to handle Perl Unicode in XS extensions, you may find the
+following C APIs useful. See also L<perlguts/"Unicode Support"> for an
+explanation about Unicode at the XS level, and L<perlapi> for the API
+details.
=over 4
=item *
-C<DO_UTF8(sv)> returns true if the C<UTF8> flag is on and the bytes pragma
-is not in effect. C<SvUTF8(sv)> returns true is the C<UTF8> flag is on; the
-bytes pragma is ignored. The C<UTF8> flag being on does B<not> mean that
-there are any characters of code points greater than 255 (or 127) in
-the scalar or that there are even any characters in the scalar.
-What the C<UTF8> flag means is that the sequence of octets in the
-representation of the scalar is the sequence of UTF-8 encoded
-code points of the characters of a string. The C<UTF8> flag being
-off means that each octet in this representation encodes a single
-character with code point 0..255 within the string. Perl's Unicode
-model is not to use UTF-8 until it is absolutely necessary.
+C<DO_UTF8(sv)> returns true if the C<UTF8> flag is on and the bytes
+pragma is not in effect. C<SvUTF8(sv)> returns true is the C<UTF8>
+flag is on; the bytes pragma is ignored. The C<UTF8> flag being on
+does B<not> mean that there are any characters of code points greater
+than 255 (or 127) in the scalar or that there are even any characters
+in the scalar. What the C<UTF8> flag means is that the sequence of
+octets in the representation of the scalar is the sequence of UTF-8
+encoded code points of the characters of a string. The C<UTF8> flag
+being off means that each octet in this representation encodes a
+single character with code point 0..255 within the string. Perl's
+Unicode model is not to use UTF-8 until it is absolutely necessary.
=item *
-C<uvuni_to_utf8(buf, chr>) writes a Unicode character code point into a
-buffer encoding the code point as UTF-8, and returns a pointer
+C<uvuni_to_utf8(buf, chr)> writes a Unicode character code point into
+a buffer encoding the code point as UTF-8, and returns a pointer
pointing after the UTF-8 bytes.
=item *
C<sv_uni_display(dsv, ssv, pvlim, flags)> are useful for debugging the
output of Unicode strings and scalars. By default they are useful
only for debugging--they display B<all> characters as hexadecimal code
-points--but with the flags C<UNI_DISPLAY_ISPRINT> and
-C<UNI_DISPLAY_BACKSLASH> you can make the output more readable.
+points--but with the flags C<UNI_DISPLAY_ISPRINT>,
+C<UNI_DISPLAY_BACKSLASH>, and C<UNI_DISPLAY_QQ> you can make the
+output more readable.
=item *
Some functions are slower when working on UTF-8 encoded strings than
on byte encoded strings. All functions that need to hop over
-characters such as length(), substr() or index() can work B<much>
-faster when the underlying data are byte-encoded. Witness the
-following benchmark:
-
- % perl -e '
- use Benchmark;
- use strict;
- our $l = 10000;
- our $u = our $b = "x" x $l;
- substr($u,0,1) = "\x{100}";
- timethese(-2,{
- LENGTH_B => q{ length($b) },
- LENGTH_U => q{ length($u) },
- SUBSTR_B => q{ substr($b, $l/4, $l/2) },
- SUBSTR_U => q{ substr($u, $l/4, $l/2) },
- });
- '
- Benchmark: running LENGTH_B, LENGTH_U, SUBSTR_B, SUBSTR_U for at least 2 CPU seconds...
- LENGTH_B: 2 wallclock secs ( 2.36 usr + 0.00 sys = 2.36 CPU) @ 5649983.05/s (n=13333960)
- LENGTH_U: 2 wallclock secs ( 2.11 usr + 0.00 sys = 2.11 CPU) @ 12155.45/s (n=25648)
- SUBSTR_B: 3 wallclock secs ( 2.16 usr + 0.00 sys = 2.16 CPU) @ 374480.09/s (n=808877)
- SUBSTR_U: 2 wallclock secs ( 2.11 usr + 0.00 sys = 2.11 CPU) @ 6791.00/s (n=14329)
-
-The numbers show an incredible slowness on long UTF-8 strings. You
-should carefully avoid using these functions in tight loops. If you
-want to iterate over characters, the superior coding technique would
-split the characters into an array instead of using substr, as the following
-benchmark shows:
-
- % perl -e '
- use Benchmark;
- use strict;
- our $l = 10000;
- our $u = our $b = "x" x $l;
- substr($u,0,1) = "\x{100}";
- timethese(-5,{
- SPLIT_B => q{ for my $c (split //, $b){} },
- SPLIT_U => q{ for my $c (split //, $u){} },
- SUBSTR_B => q{ for my $i (0..length($b)-1){my $c = substr($b,$i,1);} },
- SUBSTR_U => q{ for my $i (0..length($u)-1){my $c = substr($u,$i,1);} },
- });
- '
- Benchmark: running SPLIT_B, SPLIT_U, SUBSTR_B, SUBSTR_U for at least 5 CPU seconds...
- SPLIT_B: 6 wallclock secs ( 5.29 usr + 0.00 sys = 5.29 CPU) @ 56.14/s (n=297)
- SPLIT_U: 5 wallclock secs ( 5.17 usr + 0.01 sys = 5.18 CPU) @ 55.21/s (n=286)
- SUBSTR_B: 5 wallclock secs ( 5.34 usr + 0.00 sys = 5.34 CPU) @ 123.22/s (n=658)
- SUBSTR_U: 7 wallclock secs ( 6.20 usr + 0.00 sys = 6.20 CPU) @ 0.81/s (n=5)
-
-Even though the algorithm based on C<substr()> is faster than
-C<split()> for byte-encoded data, it pales in comparison to the speed
-of C<split()> when used with UTF-8 data.
+characters such as length(), substr() or index(), or matching regular
+expressions can work B<much> faster when the underlying data are
+byte-encoded.
+
+In Perl 5.8.0 the slowness was often quite spectacular; in Perl 5.8.1
+a caching scheme was introduced which will hopefully make the slowness
+somewhat less spectacular, at least for some operations. In general,
+operations with UTF-8 encoded strings are still slower. As an example,
+the Unicode properties (character classes) like C<\p{Nd}> are known to
+be quite a bit slower (5-20 times) than their simpler counterparts
+like C<\d> (then again, there 268 Unicode characters matching C<Nd>
+compared with the 10 ASCII characters matching C<d>).
+
+=head2 Porting code from perl-5.6.X
+
+Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer
+was required to use the C<utf8> pragma to declare that a given scope
+expected to deal with Unicode data and had to make sure that only
+Unicode data were reaching that scope. If you have code that is
+working with 5.6, you will need some of the following adjustments to
+your code. The examples are written such that the code will continue
+to work under 5.6, so you should be safe to try them out.
+
+=over 4
+
+=item *
+
+A filehandle that should read or write UTF-8
+
+ if ($] > 5.007) {
+ binmode $fh, ":utf8";
+ }
+
+=item *
+
+A scalar that is going to be passed to some extension
+
+Be it Compress::Zlib, Apache::Request or any extension that has no
+mention of Unicode in the manpage, you need to make sure that the
+UTF-8 flag is stripped off. Note that at the time of this writing
+(October 2002) the mentioned modules are not UTF-8-aware. Please
+check the documentation to verify if this is still true.
+
+ if ($] > 5.007) {
+ require Encode;
+ $val = Encode::encode_utf8($val); # make octets
+ }
+
+=item *
+
+A scalar we got back from an extension
+
+If you believe the scalar comes back as UTF-8, you will most likely
+want the UTF-8 flag restored:
+
+ if ($] > 5.007) {
+ require Encode;
+ $val = Encode::decode_utf8($val);
+ }
+
+=item *
+
+Same thing, if you are really sure it is UTF-8
+
+ if ($] > 5.007) {
+ require Encode;
+ Encode::_utf8_on($val);
+ }
+
+=item *
+
+A wrapper for fetchrow_array and fetchrow_hashref
+
+When the database contains only UTF-8, a wrapper function or method is
+a convenient way to replace all your fetchrow_array and
+fetchrow_hashref calls. A wrapper function will also make it easier to
+adapt to future enhancements in your database driver. Note that at the
+time of this writing (October 2002), the DBI has no standardized way
+to deal with UTF-8 data. Please check the documentation to verify if
+that is still true.
+
+ sub fetchrow {
+ my($self, $sth, $what) = @_; # $what is one of fetchrow_{array,hashref}
+ if ($] < 5.007) {
+ return $sth->$what;
+ } else {
+ require Encode;
+ if (wantarray) {
+ my @arr = $sth->$what;
+ for (@arr) {
+ defined && /[^\000-\177]/ && Encode::_utf8_on($_);
+ }
+ return @arr;
+ } else {
+ my $ret = $sth->$what;
+ if (ref $ret) {
+ for my $k (keys %$ret) {
+ defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret->{$k};
+ }
+ return $ret;
+ } else {
+ defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret;
+ return $ret;
+ }
+ }
+ }
+ }
+
+
+=item *
+
+A large scalar that you know can only contain ASCII
+
+Scalars that contain only ASCII and are marked as UTF-8 are sometimes
+a drag to your program. If you recognize such a situation, just remove
+the UTF-8 flag:
+
+ utf8::downgrade($val) if $] > 5.007;
+
+=back
=head1 SEE ALSO
L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>,
-L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}">
+L<perlretut>, L<perlvar/"${^UNICODE}">
=cut
projects / p5sagit/p5-mst-13.2.git / blobdiff