These examples all use UNIX extended regular expression syntax.
1. Find all trailing spaces:
finds one or more spaces or tabs followed by the end of line.
2. Find an empty line:
finds the beginning of a line immediately followed by its end.
3. Find everything on a line:
finds the beginning of a line, followed by zero or more of any characters, up to the end of the line.
4. Find “$12.34”:
Note that ‘.’ and ‘$’ have been escaped using the backslash to hide their regular expression meanings.
5. Find any valid C language variable name:
\<[ a-zA-Z][ a-zA-Z0-9]*
finds a word starting with an underscore or alphabetic character, followed by zero or more underscores or alphanumeric characters.
6. Find an inner-most bracketed expression:
finds a left bracket, followed by zero or more characters excluding left and right brackets, followed by a right bracket.
7. Find a repeated expression:
This uses a tagged expression “\(…\)” to find one or more digits, followed by a hyphen, followed by the string matched by the tagged expression. So this regular expression will find 12-12, but not 12-34.