Matt's Perl Reference

Regular Expressions

Syntax

Examples

Operators

=~ m/expr/	matches (contains) expr, and returns number of times matched in the source string
!~ m/expr/	does not match (contain) expr
=~ s/expr1/expr2/	substitute expr2 for expr1
=~ tr/abc/xyz/	not really a regular expression, but exchanges 'x' for 'a', 'y' for 'b', and 'z' for 'c' in the source string.

Options

s/ / /g	Global Match	Substitute all matching text, instead of first occurrence.
s/ / /i	Ignore Case	Case-insensitive pattern matching
s/ / /x	Ignore whitespace	Ignores whitespace when matching
s/ / /e	Evaluate	Right side is evaluated as code
s/ / /s	Newline wildcarding	Allows . to match \n
s/ / /m	Carriage return inclusion	Considers embedded \n's when matching ^ and $
s/ / /o	Once	Compiles search pattern only once

Special Characters

\n	newline
\t	tab
\s	whitespace (space, tab, or newline)
\S	non-whitespace
\w	word character (letter, number, or underscore)
\W	non-word character (anything other than letter, number, or underscore)
\b	word boundary
\B	non-word boundary
\d	digit
\D	non-digit
^	beginning of line
$	end of line
.	single character wildcard
|	an or relationship between two patterns (/me|you/)
(abc)	treats abc as a single unit (for quantifiers), and stores it in \1 and $1
(?:abc)	treats abc as a single unit (for quantifiers), but does not store it
(?=abc)	matches abc without including it in the matched string (for picky backreferences or substitutions-- for example, s/abc(?=def)/xyz/ will substitute 'xyz' for any occurrence of 'abc' which is followed by 'def', without clobbering the 'def')
(?!abc)	matches anything other than 'abc', without including that text in the mathed string
\1 \2	backreference to the first, second, and so on, already matched parenthesized group (for example /(h.) \1 \1/ would match 'ha ha ha')
[abc]	one of any of the enclosed characters
[a-z]	one of any of the range of enclosed characters
[^abc]	anything other than the specified characters
$1, $2	(Perl variable) text matched in the first, second, and so on, back reference (parenthesized expression)
$&	(Perl variable) text matched in last pattern match
$`	(Perl variable) text before the matched pattern in the source string
$'	(Perl variable) text after the matched pattern in the source string
$+	(Perl variable) contents of last successful back reference (parenthesized expression) -- useful if multiple back references are set, and you don't know whether to address $1 or $2

Quantifiers

*	0 or more of preceding character or parenthesized expression
+	1 or more
?	0 or 1 (optional)
{3}	exactly 3
{3,7}	3 to 7
{5,}	5 or more

$string  =~ s/\n$//	Remove trailing newline (much like chomp).
$string  =~ s/\b(\w)/uc($1)/eg	Capitalize first letter of all words in a string
$string  =~ tr/[a-z]/[A-Z]/	Capitalize all letters (version 1)
$string =~ s/([a-z])/uc($1)/e	Capitalize all letters (version 2)
$string =~ s/([A-Z])|([a-z])/lc($1).uc($2)/eg	One way to transpose case of all characters
$string =~ /(\(?\d{3}\)?[\- ]*)?\d{3}\-\d{4}/	match a US phone number, with optional area code (parentheses or dash notation)