Regular expressions and syntax
A regular expression is a pattern that describes a set of strings. A regular expression is a sequence of any of the following items:
- literal character
- matching character
- repetition clause
- alternation clause
- subpattern grouped with parenthesis
Regular expressions syntax
The following table lists the regular expression syntax with it's corresponding descriptions:
Syntax | Description |
. | Matches any character; used as a wildcard when creating a search string. |
*** | Matches zero or more instances of the previous pattern item. |
+ | Matches one or more instances of the previous pattern item. |
? | Matches zero or one instances of the previous pattern item. |
( ) | Groups subpattern; repetition and alternation operators apply to the entire preceding subpattern. |
| | Allows for alternation of a pattern. For example, to match Hello or hello in a string, the regular expression should read: Hello|hello. |
[ ] | Delimits a set of characters; the range is specified as [x-y]. If the first character in the set is ^, there is a match only when the remaining characters in the set are not present. |
^ | Anchors the pattern to the beginning of the string; this character must be the first character in the set. |
$ | Anchors the pattern to the end of the string; this character must be the last character in the set. |