Pattern Matching

Pattern matching makes use of regular expressions to specify text by its characteristics rather than by its exact characters. A regular expression is composed of a sequence of sub-expressions. Each sub-expression must be in the form in the operators table displayed below. Entire expressions can be preceeded by a ^ character to indicate that the expression is only matched at the start of a line, or ended by a $ character to indicate that the expression can only exist at the end of a line.

Pattern matching examples:

Expression Matches Does Not Match

"one"|"two" one ONE

two TWO

\d(3)\.\d(2) 123.45 12.45

001.23 1.23

[a-zA-Z]\w* Word 2Words

""  <-- Not Comment -->

Expression	Matches	Does Not Match
"one"\|"two"	one	ONE
	two	TWO
\d(3)\.\d(2)	123.45	12.45
	001.23	1.23
[a-zA-Z]\w*	Word	2Words
"<!--".*"-->"	<!-- Comment -->	<-- Not Comment -->

The following chart displays each operator that can be used when pattern matching:

Operators Description

a+ One or more occurrences of a

a* Zero or more occurences of a

a? Zero or one (i.e. optional) occurence of a

a{n} Exactly n occurences of a

a{n,} n or more occurences of a

a{,m} Zero or at most m occurences of a

a{n,m} At least n but not more than m occurences of a

a|b Either a or b

a||b a or b or both a and b in any order

abc a followed by b followed by c

[abc] A single character, one of a or b or c

[a-b] A single character, ranging in value from a to b inclusive

[^abc] A single character, any except a, b or c

(abc) a followed by b followed by c

"abc" The letters a followed by b followed by c with no special significance attached to a, b or c

. Any character except a newline

\a The letter a, with no special significance attached to a, special forms:

\t The tab character

\n The newline character

\r The return character

\f The formfeed character

\b The backspace character

\xNN The hex character NN

\0ooo The octal character ooo

\w A single character, one of [a-zA-Z0-9_]

\W Any single character not matching \w

\d A single character [0-9]

\D A single character not matching \d

\s A whitespace character [\t\r\n\f\b\ ]

\S A single character not matching \s

Operators	Description
a+	One or more occurrences of a
a*	Zero or more occurences of a
a?	Zero or one (i.e. optional) occurence of a
a{n}	Exactly n occurences of a
a{n,}	n or more occurences of a
a{,m}	Zero or at most m occurences of a
a{n,m}	At least n but not more than m occurences of a
a\|b	Either a or b
a\|\|b	a or b or both a and b in any order
abc	a followed by b followed by c
[abc]	A single character, one of a or b or c
[a-b]	A single character, ranging in value from a to b inclusive
[^abc]	A single character, any except a, b or c
(abc)	a followed by b followed by c
"abc"	The letters a followed by b followed by c with no special significance attached to a, b or c
.	Any character except a newline
\a	The letter a, with no special significance attached to a, special forms:
\t	The tab character
\n	The newline character
\r	The return character
\f	The formfeed character
\b	The backspace character
\xNN	The hex character NN
\0ooo	The octal character ooo
\w	A single character, one of [a-zA-Z0-9_]
\W	Any single character not matching \w
\d	A single character [0-9]
\D	A single character not matching \d
\s	A whitespace character [\t\r\n\f\b\ ]
\S	A single character not matching \s