. (dot) Atom matches with any character.
^ (caret) Atom matches with the beginning of a line.
$ (dollar sign) Atom matches with the end of a line.
{1,30} String must be 1 to 30 characters long. Example: ^[a-z]{1,3}$ (abc is valid, abcd not)
[0-9] Matches digits from 0 to 9.
[a-z] Matches any lowercase letter.
[A-Z] Matches any uppercase letter.
[A-Za-z0-9] Combinations are also possible.
Bracket expression lists also accept classes instead of just single characters and ranges. Traditional character classes are:
[:alnum:] Represents an alphanumeric character.
[:alpha:] Represents an alphabetic character.
[:ascii:] Represents a character that fits into the ASCII character set.
[:blank:] Represents a blank character, that is, a space or a tab.
[:cntrl:] Represents a control character.
[:digit:] Represents a digit (0 through 9).
[:graph:] Represents any printable character except space.
[:lower:] Represents a lowercase character.
[:print:] Represents any printable character including space.
[:punct:] Represents any printable character which is not a space or an alphanumeric character.
[:space:] Represents white-space characters: space, form-feed (\f), newline (\n), carriage return (\r), horizontal tab (\t), and vertical tab (\v).
[:upper:] Represents an uppercase letter.
[:xdigit:] Represents hexadecimal digits (0 through F).
- regex.help - generate a matching pattern