A script-enabled browser is required for this page to function properly.

Regular Expressions

Regular expressions are strings that can contain any of the following special wildcard characters:

.

Matches any single character. For example, .he would match both the and she.

( )

Used to force precedence of operators (e.g., +) when the default precedence is not desired. For example, concatenation of characters (e.g., the) precedes other operators such as +, so that the+A is equivalent to (the)+A. If instead you wished to match theeeeeeA, you can force + to precede concatenation using parentheses: th(e+)A.

[ ]

Matches any one of the single characters in the brackets. The brackets are a logical OR operator. For example, t[hr]e would match the in other and tre in trend.

|

Used between two regular expressions. Matches if either regular expression matches.

/

Matches the special character that follows the backslash. For example, /* would match *. The backslash is the escape character. Any special character following it is not treated as a special character.

Below are some special uses of the escape character:

/n matches a newline character

/t matches a tab character

/b matches a blank character

/w matches /n, /t, /b or /0

*

Matches 0 or more instances of the regular expression. For example, (the)*A would match A, theA, and thetheA.

+

Matches 1 or more instances of the regular expression. For example, (the)+A would match both theA and thetheA, but it would not match A by itself as (the)*A would.

Two characters have special meaning between square brackets:

~

As the first character, matches any characters not found in the characters or ranges inside the brackets. For example, t[~hr]e would match toe, but not the.

Between character pairs, matches any characters in the range. For example, [A-E] would match the letters A, B, C, D, and E. Character range pairs can be either of the following:

same case alphabetics, in which the first character comes before (or is equal to) the second character in the alphabet

digits, in which the first digit is less than or equal to the second digit (e.g., [4-9] or [0-3]).

You can use the escape character between brackets. For example, if you enter [/*/+], * or + would match.

 

Rules: The order of precedence of the regular expression special characters is as follows: ( ), [ ], concatenated characters (e.g., abc), *, +, ~, , |, .

The following examples show some of the implications of the order of precedence:

  • Start|Finish is equivalent to (Start)|(Finish)
  • Start* is equivalent to (Start)*
  • Start|Finish* is equivalent to (Start)|((Finish)*)