Regular expressions (regex) are a powerful method of pattern matching in character strings. This topic describes a few basic regex terms. For a full explanation of regular expressions, please refer to one of the many books or online resources available.
| Type of Match | Regex Example | Action | Explanation |
|---|---|---|---|
| Contains the sub-string (case sensitive) | this | Matches any string containing the sub-string this, respecting the case e.g.: Grab this thistle |
A sub-string on its own will be matched anywhere within the search string. |
| Contains the sub-string (case insensitive) | (?i)this | Matches any string containing the sub-string this, without regard to case e.g.: Grab ThiS thIstle |
The (?i) mode modifier turns off case sensitive matching |
| Starts with the sub-string | ^this | Matches any string starting with this e.g.: this is a tree |
The ^ anchor means the sub-string must appear at the start of the string being searched |
| Ends with the sub-string | that$ | Matches any string ending with that e.g.: don't touch that |
The $ anchor means the sub-string must appear at the end of the string being searched |
| Starts with any of the sub-strings | ^(this|that|other) | Matches any string starting with this or that or other e.g.: this time it matters and: that's life and: other types available |
The | alternation operator indicates any sub-string in brackets will be matched |
| Contains any of the sub-strings | (this|that) | Matches any string containing this or that e.g.: you can't touch this and: please don't do that |
The | alternation operator indicates either sub-string in brackets will be matched |
| Starts with sub-string 1 and ends with sub-string 2 | ^this.*that$ | Matches any string staring with this and ending with that e.g.: this is the answer to that |
The . metacharacter matches any character, then the * quantifier indicates that zero or more of them will be matched |