\A Beginning of string. Not in [].
\b Word/non-word boundary. (Backspace in []).
\B Not a word/non-word boundary. Not in [].
- \cX Control-X
+ \cX Control-X.
\C Single octet, even under UTF-8. Not in [].
\d Character class for digits.
\D Character class for non-digits.
\E Turn off \Q, \L and \U processing. Not in [].
\f Form feed.
\F Foldcase till \E. Not in [].
- \g{}, \g1 Named, absolute or relative backreference. Not in []
+ \g{}, \g1 Named, absolute or relative backreference.
+ Not in [].
\G Pos assertion. Not in [].
\h Character class for horizontal whitespace.
\H Character class for non horizontal whitespace.
\l Lowercase next character. Not in [].
\L Lowercase till \E. Not in [].
\n (Logical) newline character.
- \N Any character but newline. Experimental. Not in [].
+ \N Any character but newline. Not in [].
\N{} Named or numbered (Unicode) character or sequence.
\o{} Octal escape sequence.
\p{}, \pP Character with the given Unicode property.
\P{}, \PP Character without the given Unicode property.
- \Q Quotemeta till \E. Not in [].
+ \Q Quote (disable) pattern metacharacters till \E. Not
+ in [].
\r Return character.
\R Generic new line. Not in [].
\s Character class for whitespace.
$str = "Perl";
$str =~ /\o{120}/; # Match, "\120" is "P".
$str =~ /\120/; # Same.
- $str =~ /\o{120}+/; # Match, "\120" is "P", it's repeated at least once
+ $str =~ /\o{120}+/; # Match, "\120" is "P",
+ # it's repeated at least once.
$str =~ /\120+/; # Same.
$str =~ /P\053/; # No match, "\053" is "+" and taken literally.
/\o{23073}/ # Black foreground, white background smiling face.
- /\o{4801234567}/ # Raises a warning, and yields chr(4)
+ /\o{4801234567}/ # Raises a warning, and yields chr(4).
=head4 Disambiguation rules between old-style octal escapes and backreferences
Octal escapes of the C<\000> form outside of bracketed character classes
-potentially clash with old-style backreferences. (see L</Absolute referencing>
+potentially clash with old-style backreferences (see L</Absolute referencing>
below). They both consist of a backslash followed by numbers. So Perl has to
use heuristics to determine whether it is a backreference or an octal escape.
Perl uses the following rules to disambiguate:
$pat .= ")" x 999;
/^($pat)\1000$/; # Matches 'aa'; there are 1000 capture groups.
/^$pat\1000$/; # Matches 'a@0'; there are 999 capture groups
- # and \1000 is seen as \100 (a '@') and a '0'
+ # and \1000 is seen as \100 (a '@') and a '0'.
=back
C<\E>, whichever comes first. They provide functionality similar to what
the functions C<lc> and C<uc> provide.
-C<\Q> is used to escape all characters following, up to the next C<\E>
-or the end of the pattern. C<\Q> adds a backslash to any character that
-isn't a letter, digit, or underscore. This ensures that any character
-between C<\Q> and C<\E> shall be matched literally, not interpreted
-as a metacharacter by the regex engine.
+C<\Q> is used to quote (disable) pattern metacharacters, up to the next
+C<\E> or the end of the pattern. C<\Q> adds a backslash to any character
+that could have special meaning to Perl. In the ASCII range, it quotes
+every character that isn't a letter, digit, or underscore. See
+L<perlfunc/quotemeta> for details on what gets quoted for non-ASCII
+code points. Using this ensures that any character between C<\Q> and
+C<\E> will be matched literally, not interpreted as a metacharacter by
+the regex engine.
C<\F> can be used to casefold all characters following, up to the next C<\E>
or the end of the pattern. It provides the functionality similar to
=head4 Examples
/(\w+) \g1/; # Finds a duplicated word, (e.g. "cat cat").
- /(\w+) \1/; # Same thing; written old-style
+ /(\w+) \1/; # Same thing; written old-style.
/(.)(.)\g2\g1/; # Match a four letter palindrome (e.g. "ABBA").
C<\C> always matches a single octet, even if the source string is encoded
in UTF-8 format, and the character to be matched is a multi-octet character.
-C<\C> was introduced in perl 5.6. This is very dangerous, because it violates
+This is very dangerous, because it violates
the logical character abstraction and can cause UTF-8 sequences to become malformed.
Mnemonic: oI<C>tet.
=item \N
-This is an experimental feature new to perl 5.12.0. It matches any character
+This feature, available starting in v5.12, matches any character
that is B<not> a newline. It is a short-hand for writing C<[^\n]>, and is
identical to the C<.> metasymbol, except under the C</s> flag, which changes
the meaning of C<.>, but not C<\N>.
inside a bracketed character class; C</[\R]/> is an error; use C<\v>
instead. C<\R> was introduced in perl 5.10.0.
+Note that this does not respect any locale that might be in effect; it
+matches according to the platform's native character set.
+
Mnemonic: none really. C<\R> was picked because PCRE already uses C<\R>,
and more importantly because Unicode recommends such a regular expression
metacharacter, and suggests C<\R> as its notation.
=head4 Examples
- "\x{256}" =~ /^\C\C$/; # Match as chr (0x256) takes 2 octets in UTF-8.
+ "\x{256}" =~ /^\C\C$/; # Match as chr (0x256) takes
+ # 2 octets in UTF-8.
$str =~ s/foo\Kbar/baz/g; # Change any 'bar' following a 'foo' to 'baz'
$str =~ s/(.)\K\g1//g; # Delete duplicated characters.
https://perl5.git.perl.org / perl5.git / blobdiff