A brief analysis of subexpressions, subexpression counting, and branch usage (regular expressions)

Subexpressions

It is often useful to separate an expression into several subexpressions, for example, to mean "At least one of these strings needs to match exactly. "This can be done using parentheses, in the same way as in mathematical expressions.

For example:

(very) *large

can match "large", "very large", "very very large", etc.

Subexpression count

You can use a numeric expression in curly braces {} to specify the number of times the content is allowed to be repeated. You can specify an exact number of repetitions ({3} indicates the number of repetitions), or a range of repetitions ({2,4} indicates repetitions 2 to 4 times), or an open-bottom repetition range ({2,} means to repeat it at least twice).

For example:

(very){1,3}

means matching "very", "very very" and "very very very".

Branch

You can use a vertical bar in a regular expression to represent a selection. For example, if you want to match com, edu, or net, you can use the following expression:

com|edu|net

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