I recently reviewed a pull request with a few commits focused on regular expression code changes. It's time to re-create a quick regular expression cheat sheet.

Common expressions

Category	Expression	Description
Special Characters	. \n \f \t \xhhhh	any character newline character form feed character tab character Unicode character defined by hexadecimal number, i.e. \xFFFF
Quantifiers	+ ? * {x,y}	1 or more 0 or one 0 or more at least ‘x’ but no more that ‘y’ occurrences
Character Sets	\s \S \d \D \w \W [a-x] [^a-x]	whitespace character non-whitespace character digit character (0-9) non-digit character any letter or digit or underscore (_) character non-word character characters in the range of a to x, excluding yz characters except in the range of a to x, i.e. y and z
Anchoring	^ $ \b \B	if the first character, indicates that the match starts at beginning of string Match must continue to end of string word boundary non-word boundary

An example

1. The first character ^ indicates that the next match (19|20) starts at beginning of string.
2. We either need a 19 or a 20 at the beginning of the string.
3. Next we have two digit character (0-9).
4. Next we have a range of valid characters, in this case minus, slash, space and dot.
5. Next we have two possible combinations of digits.
   5.1 Either we have a 0, followed by a digit in the range of 1-9, i.e. 01 to 09.
   5.2 Or we have a 1, followed by a zero, one or two, i.e. 10, 11 or 12.
6. The last character $ indicates that the next match must continue to end of string.
7. Next we have three possible combinations of digits.
   7.1 Either we have a 0, followed by a digit in the range of 1-9, i.e. 01 to 09.
   7.2 Or we have a 1 or a 2, followed by a digit in the range of 0-9, i.e. 10 to 29.
   7.3 Or we have a three, followed by a zero or a one, i.e. 30 - 31.

If you need more examples, go to regularexpressions.info.