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
"this"|"that" this This
that That
\d{2}\.\d{2} 23.45 2.4
03.22 0.1
[a-zA-Z_]\w* Identifier 2Identifiers
\(\*[\x01-\x7F]+\*\) (* a
comment *) ( No comment *)