Specifications

Counted Subexpressions

We can specify how many times something can be repeated by using a numerical expression in

curly braces ( {} ).You can show an exact number of repetitions ({3} means exactly 3 repeti-

tions), a range of repetitions ({2, 4} means from 2 to 4 repetitions), or an open ended range of

repetitions ({2,} means at least two repetitions).

For example,

(very ){1, 3}

matches “very”, “very very” and “very very very”.

Anchoring to the Beginning or End of a String

You can specify whether a particular subexpression should appear at the start, the end, or both.

This is pretty useful when you want to make sure that only your search term and nothing else

appears in the string.

The caret symbol (^) is used at the start of a regular expression to show that it must appear at

the beginning of a searched string, and $ is used at the end of a regular expression to show that

it must appear at the end.

For example, this matches bob at the start of a string:

^bob

This matches com at the end of a string:

com$

Finally, this matches any single character from a to z, in the string on its own:

^[a-z]$

Branching

You can represent a choice in a regular expression with a vertical pipe. For example, if we

want to match com, edu, or net, we can use the expression:

(com)|(edu)|(net)

Matching Literal Special Characters

If you want to match one of the special characters mentioned in this section, such as ., {, or $,

you must put a slash (\) in front of it. If you want to represent a slash, you must replace it with

two slashes, \\.

Using PHP

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