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: