Symbol

Function

\

Indicates the next character has a special meaning.  "n" on it's own matches the character "n".  "\n" matches a linefeed or newline character.  See examples below (\d, \f, \n etc).

^

Matches/anchors the beginning of line.

$

Matches/anchors the end of line.

*

Matches the preceding single character/character set zero or more times.

+

Matches one or more of the preceding single character/character set.  At least one occurrence of the preceding character or one of the characters in preceding character set must be found.

. 

Matches any single character except a newline character.  Does not match repeated newlines.

(expression)

Brackets or tags an expression to use in the replace command.  A regular expression may have up to 9 tagged expressions, numbered according to their order in the regular expression.
  
The corresponding replacement expression is \x, for x in the range 1-9.  Example: If (h.*o) (f.*s) matches "hello folks", \2 \1 would replace it with "folks hello".

[xyz]

A character set.  Matches any characters between brackets.

[^xyz]

A negative character set.  Matches any characters NOT between brackets including newline characters.

\d

Matches a digit character.  Equivalent to [0-9].

\D

Matches a nondigit character.  Equivalent to [^0-9].

\f

Matches a form-feed character.

\n

Matches a linefeed character.

\r

Matches a carriage return character.

\s

Matches any whitespace including space, tab, form-feed, etc but not newline.

\S

Matches any non-whitespace character but not newline.

\t

Matches a tab character.

\v

Matches a vertical tab character.

\w

Matches any alphanumeric character including underscore.

\W

Matches any character except alphanumeric characters and underscore.

\p

Matches CR/LF (same as \r\n) to match a DOS line terminator.