Character classes
. – Matches any character except newline
\d – Digit (0-9)
\D – Not a digit (0-9) – opposite of \d
\w, [A-Za-z0-9_], [:word:] – Word character (a-z, A-Z, 0-9 and _)
\W, [^A-Za-z0-9], [^:word:] – Not a word character
\s – Whitespace (space, tab, newline)
\S – Not whitespace (space, tab, newline) – opposite of \s
[] – Matches characters in brackets
[^ ] – Matches characters NOT in brackets
[a-z] – lowercase characters or [:lower:] in POSIX notation
[A-Z] – uppercase characters or [:upper:] in POSIX notation
[a-zA-Z] – lowercase and uppercase characters or [:alpha:] in POSIX notation
Anchors
\b – Word boundary
\B – Not a word boundary – opposite of \b
^ – Start of a string (or start of line in multiline pattern)
$ – End of a string (or end of line in multiline pattern)
| – Either Or
( ) – Group
Quantifiers:
- – 0 or More
eg: ab* – where b is optional (if present, must match 1 or more) - – 1 or More
eg: ab+ – where the character b pattern must be present (or required) 1 or more
? – 0 or 1
eg: ab? – where the character b pattern is optional (if present only 1 character is required)
{N} – Exactly N, where N usually a number
eg: {3} – Exactly 3
{N,} – N or more
eg: {3,} – 3 or more
{MIN_N,MAX_N} – Range of Numbers (Minimum, Maximum)
eg: {3,5} – Minimum of 3 and maximum of 5
