Regular expressions allow more complex search functions to be performed in a single operation.
Regular Expressions (Unix Syntax):
\ 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 character zero or more times.
+ Matches the preceding character one or more times. Does not match repeated newlines.
. 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.
\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 white space including space, tab, form-feed, etc but not newline.
\S Matches any nonwhite space character but not newline.
\t Matches a tab character.
\v Matches a vertical tab character.
\w Matches any word character including underscore.
\W Matches any nonword character.
Note - ^ refers to the character '^' NOT Control Key + value.
m.n matches "man", "men", "min" but not "moon".
Te+st matches "test", "teest", "teeeest" etc. BUT NOT "tst".
Te*st matches "test", "teest", "teeeest" etc. AND "tst".
[aeiou] matches every lowercase vowel
[,.?] matches a literal ",", "." or "?".
[0-9a-z] matches any digit, or lowercase letter
[^0-9] matches any character except a digit (^ means NOT the following)
You may search for an expression A or B as follow:
This will search for an occurrence of John or Tom. There should be nothing between the two expressions.
You may combine A or B and C or D in the same search as follows:
This will search for John or Tom followed by Smith or Jones.