=head1 DESCRIPTION
-This page describes the syntax of regular expressions in Perl. For a
-description of how to I<use> regular expressions in matching
-operations, plus various examples of the same, see discussions
-of C<m//>, C<s///>, C<qr//> and C<??> in L<perlop/"Regexp Quote-Like Operators">.
+This page describes the syntax of regular expressions in Perl.
+
+if you haven't used regular expressions before, a quick-start
+introduction is available in L<perlrequick>, and a longer tutorial
+introduction is available in L<perlretut>.
+
+For reference on how regular expressions are used in matching
+operations, plus various examples of the same, see discussions of
+C<m//>, C<s///>, C<qr//> and C<??> in L<perlop/"Regexp Quote-Like
+Operators">.
Matching operations can have various modifiers. Modifiers
that relate to the interpretation of the regular expression inside
\pP Match P, named property. Use \p{Prop} for longer names.
\PP Match non-P
\X Match eXtended Unicode "combining character sequence",
- equivalent to C<(?:\PM\pM*)>
- \C Match a single C char (octet) even under utf8.
- (Currently this does not work correctly.)
-
-A C<\w> matches a single alphanumeric character or C<_>, not a whole word.
-Use C<\w+> to match a string of Perl-identifier characters (which isn't
-the same as matching an English word). If C<use locale> is in effect, the
-list of alphabetic characters generated by C<\w> is taken from the
-current locale. See L<perllocale>. You may use C<\w>, C<\W>, C<\s>, C<\S>,
+ equivalent to (?:\PM\pM*)
+ \C Match a single C char (octet) even under Unicode.
+ NOTE: breaks up characters into their UTF-8 bytes,
+ so you may end up with malformed pieces of UTF-8.
+
+A C<\w> matches a single alphanumeric character (an alphabetic
+character, or a decimal digit) or C<_>, not a whole word. Use C<\w+>
+to match a string of Perl-identifier characters (which isn't the same
+as matching an English word). If C<use locale> is in effect, the list
+of alphabetic characters generated by C<\w> is taken from the current
+locale. See L<perllocale>. You may use C<\w>, C<\W>, C<\s>, C<\S>,
C<\d>, and C<\D> within character classes, but if you try to use them
-as endpoints of a range, that's not a range, the "-" is understood literally.
-See L<utf8> for details about C<\pP>, C<\PP>, and C<\X>.
+as endpoints of a range, that's not a range, the "-" is understood
+literally. If Unicode is in effect, C<\s> matches also "\x{85}",
+"\x{2028}, and "\x{2029}", see L<perlunicode> for more details about
+C<\pP>, C<\PP>, and C<\X>, and L<perluniintro> about Unicode in general.
+You can define your own C<\p> and C<\P> propreties, see L<perlunicode>.
The POSIX character class syntax
word \w [3]
xdigit
- [1] A GNU extension equivalent to C<[ \t]>, `all horizontal whitespace'.
- [2] Not I<exactly equivalent> to C<\s> since the C<[[:space:]]> includes
- also the (very rare) `vertical tabulator', "\ck", chr(11).
- [3] A Perl extension.
+=over
+
+=item [1]
+
+A GNU extension equivalent to C<[ \t]>, `all horizontal whitespace'.
+
+=item [2]
+
+Not exactly equivalent to C<\s> since the C<[[:space:]]> includes
+also the (very rare) `vertical tabulator', "\ck", chr(11).
+
+=item [3]
+
+A Perl extension, see above.
+
+=back
For example use C<[:upper:]> to match all the uppercase characters.
Note that the C<[]> are part of the C<[::]> construct, not part of the
matches zero, one, any alphabetic character, and the percentage sign.
-If the C<utf8> pragma is used, the following equivalences to Unicode
-\p{} constructs and equivalent backslash character classes (if available),
-will hold:
+The following equivalences to Unicode \p{} constructs and equivalent
+backslash character classes (if available), will hold:
+
+ [:...:] \p{...} backslash
alpha IsAlpha
alnum IsAlnum
such but instead control the terminal somehow: for example newline and
backspace are control characters. All characters with ord() less than
32 are most often classified as control characters (assuming ASCII,
-the ISO Latin character sets, and Unicode).
+the ISO Latin character sets, and Unicode), as is the character with
+the ord() value of 127 (C<DEL>).
=item graph
=item print
-Any alphanumeric or punctuation (special) character or space.
+Any alphanumeric or punctuation (special) character or the space character.
=item punct
You can negate the [::] character classes by prefixing the class name
with a '^'. This is a Perl extension. For example:
- POSIX trad. Perl utf8 Perl
+ POSIX traditional Unicode
[:^digit:] \D \P{IsDigit}
[:^space:] \S \P{IsSpace}
[:^word:] \W \P{IsWord}
-The POSIX character classes [.cc.] and [=cc=] are recognized but
-B<not> supported and trying to use them will cause an error.
+Perl respects the POSIX standard in that POSIX character classes are
+only supported within a character class. The POSIX character classes
+[.cc.] and [=cc=] are recognized but B<not> supported and trying to
+use them will cause an error.
Perl defines the following zero-width assertions:
several patterns that you want to match against consequent substrings
of your string, see the previous reference. The actual location
where C<\G> will match can also be influenced by using C<pos()> as
-an lvalue. See L<perlfunc/pos>.
+an lvalue: see L<perlfunc/pos>. Currently C<\G> is only fully
+supported when anchored to the start of the pattern; while it
+is permitted to use it elsewhere, as in C</(?<=\G..)./g>, some
+such uses (C</.\G/g>, for example) currently cause problems, and
+it is recommended that you avoid such usage for now.
The bracketing construct C<( ... )> creates capture buffers. To
refer to the digit'th buffer use \<digit> within the
=item C<(?imsx-imsx)>
-One or more embedded pattern-match modifiers. This is particularly
-useful for dynamic patterns, such as those read in from a configuration
-file, read in as an argument, are specified in a table somewhere,
-etc. Consider the case that some of which want to be case sensitive
-and some do not. The case insensitive ones need to include merely
-C<(?i)> at the front of the pattern. For example:
+One or more embedded pattern-match modifiers, to be turned on (or
+turned off, if preceded by C<->) for the remainder of the pattern or
+the remainder of the enclosing pattern group (if any). This is
+particularly useful for dynamic patterns, such as those read in from a
+configuration file, read in as an argument, are specified in a table
+somewhere, etc. Consider the case that some of which want to be case
+sensitive and some do not. The case insensitive ones need to include
+merely C<(?i)> at the front of the pattern. For example:
$pattern = "foobar";
if ( /$pattern/i ) { }
$pattern = "(?i)foobar";
if ( /$pattern/ ) { }
-Letters after a C<-> turn those modifiers off. These modifiers are
-localized inside an enclosing group (if any). For example,
+These modifiers are restored at the end of the enclosing group. For example,
( (?i) blah ) \s+ \1
the time when used on a similar string with 1000000 C<a>s. Be aware,
however, that this pattern currently triggers a warning message under
the C<use warnings> pragma or B<-w> switch saying it
-C<"matches the null string many times">):
+C<"matches null string many times in regex">.
On simple groups, such as the pattern C<< (?> [^()]+ ) >>, a comparable
effect may be achieved by negative look-ahead, as in C<[^()]+ (?! [^()] )>.
got <d is under the >
Here's another example: let's say you'd like to match a number at the end
-of a string, and you also want to keep the preceding part the match.
+of a string, and you also want to keep the preceding part of the match.
So you write this:
$_ = "I have 2 numbers: 53147";
But that isn't going to match; at least, not the way you're hoping. It
claims that there is no 123 in the string. Here's a clearer picture of
-why it that pattern matches, contrary to popular expectations:
+why that pattern matches, contrary to popular expectations:
$x = 'ABC123' ;
$y = 'ABC445' ;
This is grandfathered for the RHS of a substitute to avoid shocking the
B<sed> addicts, but it's a dirty habit to get into. That's because in
-PerlThink, the righthand side of a C<s///> is a double-quoted string. C<\1> in
+PerlThink, the righthand side of an C<s///> is a double-quoted string. C<\1> in
the usual double-quoted string means a control-A. The customary Unix
meaning of C<\1> is kludged in for C<s///>. However, if you get into the habit
of doing that, you get yourself into trouble if you then add an C</e>
=head1 SEE ALSO
+L<perlrequick>.
+
+L<perlretut>.
+
L<perlop/"Regexp Quote-Like Operators">.
L<perlop/"Gory details of parsing quoted constructs">.