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This document is a mirror of the original which was written by Jukka Korpela.The original document can be accessed at the following URL: http://www.cs.tut.fi/~jkorpela/perl/regexp.html Regular expressions in PerlThis document presents a tabular summary of the regular expression (regexp) syntax in Perl, then illustrates it with a collection of annotated examples.
Special notations with
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\w |
matches any single character classified as a “word” character
(alphanumeric or “_”)
|
\W |
matches any non-“word” character |
\s |
matches any whitespace character (space, tab, newline) |
\S |
matches any non-whitespace character |
\d |
matches any digit character, equiv. to [0-9] |
\D |
matches any non-digit character |
Character sets: specialities inside [...]
Different meanings apply inside a
character set (“character class”) denoted by
[...] so that, instead of
the normal rules given here, the following apply:
[characters] |
matches any of the characters in the sequence |
[x-y] |
matches any of the characters from x to y (inclusively) in the ASCII code |
[\-] |
matches the hyphen character “-” |
[\n] |
matches the newline; other single character denotations with \
apply normally, too
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[^something] |
matches any character except those that
[something] denotes; that is,
immediately after the leading “[”, the circumflex
“^” means “not” applied to all of the rest
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Examples
| expression | matches... |
|---|---|
abc |
abc (that exact character sequence, but anywhere in the string) |
^abc |
abc at the beginning of the string |
abc$ |
abc at the end of the string |
a|b |
either of a and b |
^abc|abc$ |
the string abc at the beginning or at the end of the string |
ab{2,4}c |
an a followed by two, three or four b’s
followed by a c
|
ab{2,}c |
an a followed by at least two b’s followed by a c |
ab*c |
an a followed by any number (zero or more) of
b’s followed by a c
|
ab+c |
an a followed by one or more b’s followed by a c |
ab?c |
an a followed by an optional b followed
by a c; that is, either abc or ac
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a.c |
an a followed by any single character (not newline) followed by a c |
a\.c |
a.c exactly |
[abc] |
any one of a, b and c |
[Aa]bc |
either of Abc and abc |
[abc]+ |
any (nonempty) string of a’s, b’s
and c’s (such as a, abba,
acbabcacaa)
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[^abc]+ |
any (nonempty) string which does not contain any of a,
b and c (such as defg)
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\d\d |
any two decimal digits, such as 42; same as \d{2} |
\w+ |
a “word”: a nonempty sequence of alphanumeric characters and
low lines (underscores), such as foo and 12bar8
and foo_1
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100\s*mk |
the strings 100 and mk optionally separated by any amount of white space
(spaces, tabs, newlines)
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abc\b |
abc when followed by a word boundary (e.g. in abc! but not in abcd) |
perl\B |
perl when not followed by a word boundary (e.g. in perlert
but not in perl stuff)
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Examples of simple use in Perl statements
These examples use very simple regexps only. The
intent is just to show contexts where regexps might be
used, as well as the effect of some “flags” to matching
and replacements. Note in particular that matching is by default
case-sensitive (Abc does not match abc unless
specified otherwise).
s/foo/bar/;
replaces the first occurrence of the exact character sequence
foo in the “current string” (in special
variable $_) by the character sequence bar;
for example, foolish bigfoot would become barlish bigfoot
s/foo/bar/g;
replaces any occurrence of the exact character sequence
foo in the “current string”
by the character sequence bar;
for example, foolish bigfoot would become
barlish bigbart
s/foo/bar/gi;
replaces any occurrence of foo case-insensitively in the
“current string” by the character sequence bar
(e.g. Foo and FOO get replaced by
bar too)
if(m/foo/)...
tests whether the current string contains the string foo