Online experimenting
Here is an amazingly useful online tool to experiment with Regexps: Rubular
Top Regexp expressions
\[abc\] A single character of: a, b, or c
\[^abc\] Any single character except: a, b, or c
\[a-z\] Any single character in the range a-z
\[a-zA-Z\] Any single character in the range a-z or A-Z
^ Start of line
$ End of line
\A Start of string
\z End of string
. Any single character
\s Any whitespace character
\S Any non-whitespace character
\d Any digit
\D Any non-digit
\w Any word character (letter, number, underscore)
\W Any non-word character
\b Any word boundary
(...) Capture everything enclosed
(a|b) a or b
a? Zero or one of a
a* Zero or more of a
a+ One or more of a
a{3} Exactly 3 of a
a{3,} 3 or more of a
a{3,6} Between 3 and 6 of a