Regular expression

A regular expression is a search pattern, its very often used in the programming language Perl, but it is used in other programming languages too or Text editors.

 

Meta characters

char meaning
^ defines the end of the matching String
$ defines the end of the matching String
. matches any character but not newline
* matches from 0 to infinity times
+ matches from 1 to infinity times
? matches 0 or 1 times
{} matches exact the given number or range
| logical or operator
() makes a group to store the result
[] makes a character matching group

 

Matches

\t tabulator
\n new line
\r return (CR)
\w matches from a-z,A-Z,0-9 and “_”.
\W matches nothing from a-z,A-Z,0-9 and “_”.
\s matches space, tab and newline
\S matches nothing from space, tab and newline
\d matches from 0-9
\D matches nothing from 0-9

 

Examples

^a

This matches every string that starts with an “a”.

a$

This pattern matches every string that end with an “a”.

^schools?$

This regex would match “schools” and “school”.

^.{3,4}$

Would match every string with the length between 3 and 4.

^school$|^schools$

This also would match “schools” and “school”.

"(\w)+"

On this “this is an ‘test’.” the pattern would store “test”.

[aco]+

This regex matches every combination from “a”,”c” and “o” like the word “coca”.

 

For testing Regex you could test the JavaScript Regex tester.

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