from cover to cover, Perl does support many Unicode features.
People who want to learn to use Unicode in Perl, should probably read
-L<the Perl Unicode tutorial, perlunitut|perlunitut>, before reading
+the L<Perl Unicode tutorial, perlunitut|perlunitut>, before reading
this reference document.
+Also, the use of Unicode may present security issues that aren't obvious.
+Read L<Unicode Security Considerations|http://www.unicode.org/reports/tr36>.
+
=over 4
=item Input and Output Layers
semantics in a particular lexical scope. See L<bytes>.
The C<use feature 'unicode_strings'> pragma is intended to always, regardless
-of platform, force Unicode semantics in a particular lexical scope. In
-release 5.12, it is partially implemented, applying only to case changes.
+of platform, force character (Unicode) semantics in a particular lexical scope.
+In release 5.12, it is partially implemented, applying only to case changes.
See L</The "Unicode Bug"> below.
The C<utf8> pragma is primarily a compatibility device that enables
If strings operating under byte semantics and strings with Unicode
character data are concatenated, the new string will have
-character semantics. This can cause surprises: See L</BUGS>, below
+character semantics. This can cause surprises: See L</BUGS>, below.
+You can choose to be warned when this happens. See L<encoding::warnings>.
Under character semantics, many operations that formerly operated on
bytes now operate on characters. A character in Perl is
occur directly within the literal strings in UTF-8 encoding, or UTF-16.
(The former requires a BOM or C<use utf8>, the latter requires a BOM.)
-Unicode characters can also be added to a string by using the C<\x{...}>
+Unicode characters can also be added to a string by using the C<\N{U+...}>
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 works for all characters, but
-for characters under 0x100, note that Perl may use an 8 bit encoding
-internally, for optimization and/or backward compatibility.
+should be placed in the braces, after the C<U>. For instance, a smiley face is
+C<\N{U+263A}>.
+
+Alternatively, you can use the C<\x{...}> notation for characters 0x100 and
+above. For characters below 0x100 you may get byte semantics instead of
+character semantics; see L</The "Unicode Bug">. On EBCDIC machines there is
+the additional problem that the value for such characters gives the EBCDIC
+character rather than the Unicode one.
Additionally, if you
you can use the C<\N{...}> notation and put the official Unicode
character name within the braces, such as C<\N{WHITE SMILING FACE}>.
+See L<charnames>.
=item *
=item *
-Character classes in regular expressions match characters instead of
+Bracketed 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 a Japanese
ideograph, for instance.
=item *
-Named Unicode properties, scripts, and block ranges may be used like
-character classes via the C<\p{}> "matches property" construct and
+Named Unicode properties, scripts, and block ranges may be used (like bracketed
+character classes) by using the C<\p{}> "matches property" construct and
the C<\P{}> negation, "doesn't match property".
See L</"Unicode Character Properties"> for more details.
=item *
-You can define your own mappings to be used in lc(),
-lcfirst(), uc(), and ucfirst() (or their string-inlined versions).
+You can define your own mappings to be used in C<lc()>,
+C<lcfirst()>, C<uc()>, and C<ucfirst()> (or their double-quoted string inlined
+versions such as C<\U>).
See L</"User-Defined Case Mappings"> for more details.
=back
=head2 Unicode Character Properties
Most Unicode character properties are accessible by using regular expressions.
-They are used like character classes via the C<\p{}> "matches property"
-construct and the C<\P{}> negation, "doesn't match property".
+They are used (like bracketed character classes) by using the C<\p{}> "matches
+property" construct and the C<\P{}> negation, "doesn't match property".
+
+Note that the only time that Perl considers a sequence of individual code
+points as a single logical character is in the C<\X> construct, already
+mentioned above. Therefore "character" in this discussion means a single
+Unicode code point.
-For instance, C<\p{Uppercase}> matches any character with the Unicode
+For instance, C<\p{Uppercase}> matches any single character with the Unicode
"Uppercase" property, while C<\p{L}> matches any character with a
General_Category of "L" (letter) property. Brackets are not
-required for single letter properties, so C<\p{L}> is equivalent to C<\pL>.
+required for single letter property names, so C<\p{L}> is equivalent to C<\pL>.
-More formally, C<\p{Uppercase}> matches any character whose Unicode Uppercase
-property value is True, and C<\P{Uppercase}> matches any character whose
-Uppercase property value is False, and they could have been written as
-C<\p{Uppercase=True}> and C<\p{Uppercase=False}>, respectively
+More formally, C<\p{Uppercase}> matches any single character whose Unicode
+Uppercase property value is True, and C<\P{Uppercase}> matches any character
+whose Uppercase property value is False, and they could have been written as
+C<\p{Uppercase=True}> and C<\p{Uppercase=False}>, respectively.
This formality is needed when properties are not binary, that is if they can
take on more values than just True and False. For example, the Bidi_Class (see
L</"Bidirectional Character Types"> below), can take on a number of different
values, such as Left, Right, Whitespace, and others. To match these, one needs
to specify the property name (Bidi_Class), and the value being matched against
-(Left, Right, I<etc.>). This is done, as in the examples above, by having the
+(Left, Right, etc.). This is done, as in the examples above, by having the
two components separated by an equal sign (or interchangeably, a colon), like
C<\p{Bidi_Class: Left}>.
Zp Paragraph_Separator
C Other
- Cc Control (also Cntrl)
+ Cc Control (also Cntrl)
Cf Format
Cs Surrogate (not usable)
Co Private_Use
Single-letter properties match all characters in any of the
two-letter sub-properties starting with the same letter.
-C<LC> and C<L&> are special cases, which are aliases for the set of
-C<Ll>, C<Lu>, and C<Lt>.
+C<LC> and C<L&> are special cases, which are both aliases for the set consisting of everything matched by 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
=head3 B<Bidirectional Character Types>
-Because scripts differ in their directionality--Hebrew is
-written right to left, for example--Unicode supplies these properties in
+Because scripts differ in their directionality (Hebrew is
+written right to left, for example) Unicode supplies these properties in
the Bidi_Class class:
Property Meaning
Hiragana or Katakana. There are many more.
The Unicode Script property gives what script a given character is in,
-and can be matched with the compound form like C<\p{Script=Hebrew}> (short:
-C<\p{sc=hebr}>). Perl furnishes shortcuts for all script names. You can omit
-everything up through the equals (or colon), and simply write C<\p{Latin}> or
-C<\P{Cyrillic}>.
+and the property can be specified with the compound form like
+C<\p{Script=Hebrew}> (short: C<\p{sc=hebr}>). Perl furnishes shortcuts for all
+script names. You can omit everything up through the equals (or colon), and
+simply write C<\p{Latin}> or C<\P{Cyrillic}>.
A complete list of scripts and their shortcuts is in L<perluniprops>.
block is all characters whose ordinals are between 0 and 127, inclusive, in
other words, the ASCII characters. The "Latin" script contains some letters
from this block as well as several more, like "Latin-1 Supplement",
-"Latin Extended-A", I<etc.>, but it does not contain all the characters from
+"Latin Extended-A", etc., but it 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
the script called C<Common>. There is also a script called C<Inherited> for
necessary to know some basics about decomposition.
Consider a character, say H. It could appear with various marks around it,
such as an acute accent, or a circumflex, or various hooks, circles, arrows,
-I<etc.>, above, below, to one side and/or the other, I<etc.> There are many
+I<etc.>, above, below, to one side and/or the other, etc. There are many
possibilities among the world's languages. The number of combinations is
astronomical, and if there were a character for each combination, it would
soon exhaust Unicode's more than a million possible characters. So Unicode
syllabaries (hiragana and katakana), you can define
sub InKana {
- return <<END;
+ return <<END;
3040\t309F
30A0\t30FF
END
You could also have used the existing block property names:
sub InKana {
- return <<'END';
+ return <<'END';
+utf8::InHiragana
+utf8::InKatakana
END
the non-characters:
sub InKana {
- return <<'END';
+ return <<'END';
+utf8::InHiragana
+utf8::InKatakana
-utf8::IsCn
The negation is useful for defining (surprise!) negated classes.
sub InNotKana {
- return <<'END';
+ return <<'END';
!utf8::InHiragana
-utf8::InKatakana
+utf8::IsCn
=head2 User-Defined Case Mappings
-You can also define your own mappings to be used in the lc(),
-lcfirst(), uc(), and ucfirst() (or their string-inlined versions).
+You can also define your own mappings to be used in C<lc()>,
+C<lcfirst()>, C<uc()>, and C<ucfirst()> (or their string-inlined versions,
+C<\L>, C<\l>, C<\U>, and C<\u>).
The principle is similar to that of user-defined character
properties: to define subroutines
-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()).
+with names C<ToLower> (for C<lc()> and C<lcfirst()>); C<ToTitle> (for
+C<ucfirst()>); and C<ToUpper> (for C<uc()>).
The string returned by the subroutines needs to be two hexadecimal numbers
separated by two tabulators: the two numbers being, respectively, the source
code point and the destination code point. For example:
sub ToUpper {
- return <<END;
+ return <<END;
0061\t\t0041
END
}
-defines an uc() mapping that causes only the character "a"
+defines a mapping for C<uc()> (and C<\U>) that causes only the character "a"
to be mapped to "A"; all other characters will remain unchanged.
(For serious hackers only) The above means you have to furnish a complete
mapping; you can't just override a couple of characters and leave the rest
-unchanged. You can find all the mappings 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 "Digit" and
+unchanged. You can find all the official mappings in the directory
+C<$Config{privlib}>F</unicore/To/>. The mapping data is returned as the
+here-document. The C<utf8::ToSpecI<Foo>> hashes in those files are special
+exception mappings derived from
+C<$Config{privlib}>F</unicore/SpecialCasing.txt>. (The "Digit" and
"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 "Fold" mapping is used).
+user-accessible, one can use either the L<Unicode::UCD> module, or just match
+case-insensitively, which is what uses the "Fold" mapping. Neither are user
+overridable.)
+
+If you have many mappings to change, you can take the official mapping data,
+change by hand the affected code points, and place the whole thing into your
+subroutine. But this will only be valid on Perls that use the same Unicode
+version. Another option would be to have your subroutine read the official
+mapping file(s) and overwrite the affected code points.
+
+If you have only a few mappings to change, starting in 5.14 you can use the
+following trick, here illustrated for Turkish.
+
+ use Config;
+
+ sub ToUpper {
+ my $official = do "$Config{privlib}/unicore/To/Upper.pl";
+ $utf8::ToSpecUpper{'i'} =
+ "\N{LATIN CAPITAL LETTER I WITH DOT ABOVE}";
+ return $official;
+ }
-The mappings will only take effect on scalars that have been marked as having
-Unicode characters, for example by using C<utf8::upgrade()>.
-Old byte-style strings are not affected.
+This takes the official mappings and overrides just one, for "LATIN SMALL
+LETTER I". The keys to the hash must be in UTF-8 (or on EBCDIC platforms,
+UTF-EBCDIC), as illustrated by the inverse function.
+
+ sub ToLower {
+ my $official = do $lower;
+ $utf8::ToSpecLower{"\xc4\xb0"} = "i";
+ return $official;
+ }
+
+This example is for an ASCII platform, and C<\xc4\xb0> is the UTF-8 string that
+represents C<\N{LATIN CAPITAL LETTER I WITH DOT ABOVE}>, C<U+0130>.
+
+(The trick illustrated here does work in earlier releases, but only if all the
+characters you want to override have ordinal values of 256 or higher.)
+
+The mappings are in effect only for the package they are defined in, and only
+on scalars that have been marked as having Unicode characters, for example by
+using C<utf8::upgrade()>. You can get around the latter restriction in the
+scope of a C<S<use subs>>:
+
+ use subs qw(uc ucfirst lc lcfirst);
+
+ sub uc($) {
+ my $string = shift;
+ utf8::upgrade($string);
+ return CORE::uc($string);
+ }
+
+ sub lc($) {
+ my $string = shift;
+ utf8::upgrade($string);
+
+ # Unless an I is before a dot_above, it turns into a dotless i.
+ $string =~
+ s/I (?! [^\p{ccc=0}\p{ccc=Above}]* \x{0307} )/\x{131}/gx;
+
+ # But when the I is followed by a dot_above, remove the
+ # dot_above so the end result will be i.
+ $string =~ s/I ([^\p{ccc=0}\p{ccc=Above}]* ) \x{0307}/i$1/gx;
+ return CORE::lc($string);
+ }
-The mappings are in effect for the package they are defined in.
+These examples (also for Turkish) make sure the input is in UTF-8, and then
+call the corresponding official function, which will use the C<ToUpper()> and
+C<ToLower()> functions you have defined in the package. The C<lc()> example
+shows how you can add context-dependent casing. (For Turkish, there other
+required functions: C<ucfirst>, C<lcfirst>, and C<ToTitle>. These are very
+similar to the ones given above.)
=head2 Character Encodings for Input and Output
Level 1 - Basic Unicode Support
- RL1.1 Hex Notation - done [1]
- RL1.2 Properties - done [2][3]
- RL1.2a Compatibility Properties - done [4]
- RL1.3 Subtraction and Intersection - MISSING [5]
- RL1.4 Simple Word Boundaries - done [6]
- RL1.5 Simple Loose Matches - done [7]
- RL1.6 Line Boundaries - MISSING [8]
- RL1.7 Supplementary Code Points - done [9]
+ RL1.1 Hex Notation - done [1]
+ RL1.2 Properties - done [2][3]
+ RL1.2a Compatibility Properties - done [4]
+ RL1.3 Subtraction and Intersection - MISSING [5]
+ RL1.4 Simple Word Boundaries - done [6]
+ RL1.5 Simple Loose Matches - done [7]
+ RL1.6 Line Boundaries - MISSING [8]
+ RL1.7 Supplementary Code Points - done [9]
[1] \x{...}
[2] \p{...} \P{...}
- [3] supports not only minimal list, but all Unicode character
- properties (see L</Unicode Character Properties>)
+ [3] supports not only minimal list, but all Unicode character
+ properties (see L</Unicode Character Properties>)
[4] \d \D \s \S \w \W \X [:prop:] [:^prop:]
[5] can use regular expression look-ahead [a] or
- user-defined character properties [b] to emulate set operations
+ user-defined character properties [b] to emulate set
+ operations
[6] \b \B
- [7] note that Perl does Full case-folding in matching (but with bugs),
- not Simple: for example U+1F88 is equivalent to U+1F00 U+03B9,
- not with 1F80. This difference matters mainly 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.
- [8] should do ^ and $ also on U+000B (\v in C), FF (\f), CR (\r),
- CRLF (\r\n), NEL (U+0085), LS (U+2028), and PS (U+2029);
- should also affect <>, $., and script line numbers;
- should not split lines within CRLF [c] (i.e. there is no empty
- line between \r and \n)
- [9] UTF-8/UTF-EBDDIC used in perl allows not only U+10000 to U+10FFFF
- but also beyond U+10FFFF [d]
+ [7] note that Perl does Full case-folding in matching (but with
+ bugs), not Simple: for example U+1F88 is equivalent to
+ U+1F00 U+03B9, not with 1F80. This difference matters
+ mainly 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.
+ [8] should do ^ and $ also on U+000B (\v in C), FF (\f), CR
+ (\r), CRLF (\r\n), NEL (U+0085), LS (U+2028), and PS
+ (U+2029); should also affect <>, $., and script line
+ numbers; should not split lines within CRLF [c] (i.e. there
+ is no empty line between \r and \n)
+ [9] UTF-8/UTF-EBDDIC used in perl allows not only U+10000 to
+ U+10FFFF but also beyond U+10FFFF [d]
[a] You can mimic class subtraction using lookahead.
For example, what UTS#18 might write as
[12] have \X but we don't have a "Grapheme Cluster Mode"
[14] see UAX#29, Word Boundaries
[15] see UAX#21 "Case Mappings"
- [16] have \N{...} but neither compute names of CJK Ideographs
- and Hangul Syllables nor use a loose match [e]
+ [16] missing loose match [e]
[e] C<\N{...}> allows namespaces (see L<charnames>).
[17] see UAX#10 "Unicode Collation Algorithms"
[18] have Unicode::Collate but not integrated to regexes
- [19] have (?<=x) and (?=x), but look-aheads or look-behinds should see
- outside of the target substring
- [20] need insensitive matching for linguistic features other than case;
- for example, hiragana to katakana, wide and narrow, simplified Han
- to traditional Han (see UTR#30 "Character Foldings")
+ [19] have (?<=x) and (?=x), but look-aheads or look-behinds
+ should see outside of the target substring
+ [20] need insensitive matching for linguistic features other
+ than case; for example, hiragana to katakana, wide and
+ narrow, simplified Han to traditional Han (see UTR#30
+ "Character Foldings")
=back
The following table is from Unicode 3.2.
- Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
+ Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
- U+0000..U+007F 00..7F
+ U+0000..U+007F 00..7F
U+0080..U+07FF * C2..DF 80..BF
- U+0800..U+0FFF E0 * A0..BF 80..BF
+ U+0800..U+0FFF E0 * A0..BF 80..BF
U+1000..U+CFFF E1..EC 80..BF 80..BF
U+D000..U+D7FF ED 80..9F 80..BF
U+D800..U+DFFF +++++++ utf16 surrogates, not legal utf8 +++++++
U+E000..U+FFFF EE..EF 80..BF 80..BF
- U+10000..U+3FFFF F0 * 90..BF 80..BF 80..BF
- U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
- U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
+ U+10000..U+3FFFF F0 * 90..BF 80..BF 80..BF
+ U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
+ U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
Note the gaps before several of the byte entries above marked by '*'. These are
caused by legal UTF-8 avoiding non-shortest encodings: it is technically
surrogates> are the range C<U+D800..U+DBFF> and the I<low surrogates>
are the range C<U+DC00..U+DFFF>. The surrogate encoding is
- $hi = ($uni - 0x10000) / 0x400 + 0xD800;
- $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
+ $hi = ($uni - 0x10000) / 0x400 + 0xD800;
+ $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
and the decoding is
- $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);
+ $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);
If you try to generate surrogates (for example by using chr()), you
will get a warning, if warnings are turned on, because those code
=head2 The "Unicode Bug"
The term, the "Unicode bug" has been applied to an inconsistency with the
-Unicode characters whose code points are in the Latin-1 Supplement block, that
+Unicode characters whose ordinals are in the Latin-1 Supplement block, that
is, between 128 and 255. Without a locale specified, unlike all other
characters or code points, these characters have very different semantics in
byte semantics versus character semantics.
=item *
-Matching a number of properties in regular expressions, such as C<\w>
+Matching a number of properties in regular expressions, namely C<\b>,
+C<\B>, C<\s>, C<\S>, C<\w>, C<\W>, and all the Posix character classes
+I<except> C<[[:ascii:]]>.
=item *
problematic behaviors in later releases: you can't have one without them all.
In the meantime, a workaround is to always call utf8::upgrade($string), or to
-use the standard modules L<Encode> or L<charnames>.
+use the standard module L<Encode>. Also, a scalar that has any characters
+whose ordinal is above 0x100, or which were specified using either of the
+C<\N{...}> notations will automatically have character semantics.
=head2 Forcing Unicode in Perl (Or Unforcing Unicode in Perl)
Perl's internal representation like so:
sub my_escape_html ($) {
- my($what) = shift;
- return unless defined $what;
- Encode::decode_utf8(Foo::Bar::escape_html(Encode::encode_utf8($what)));
+ my($what) = shift;
+ return unless defined $what;
+ Encode::decode_utf8(Foo::Bar::escape_html(
+ Encode::encode_utf8($what)));
}
Sometimes, when the extension does not convert data but just stores
that is still true.
sub fetchrow {
- my($self, $sth, $what) = @_; # $what is one of fetchrow_{array,hashref}
+ # $what is one of fetchrow_{array,hashref}
+ my($self, $sth, $what) = @_;
if ($] < 5.007) {
return $sth->$what;
} else {
my $ret = $sth->$what;
if (ref $ret) {
for my $k (keys %$ret) {
- defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret->{$k};
+ defined
+ && /[^\000-\177]/
+ && Encode::_utf8_on($_) for $ret->{$k};
}
return $ret;
} else {
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