Repeats

Scripts > Token definitions > Regular expressions > Repeats

Any atom (a single character, a marked sub-expression, or a character class) can be repeated with the *, +, ?, and {} operators.

*

The * operator will match the preceding atom zero or more times, for example the expression a*b will match any of the following:

b

ab

aaaaaaaab

+

The + operator will match the preceding atom one or more times, for example the expression a+b will match any of the following:

ab

aaaaaaaab

But will not match:

b

?

The ? operator will match the preceding atom zero or one times, for example the expression ca?b will match any of the following:

cb

cab

But will not match:

caab

{}

An atom can also be repeated with a bounded repeat:

a{n} Matches 'a' repeated exactly n times.

a{n,} Matches 'a' repeated n or more times.

a{n, m} Matches 'a' repeated between n and m times inclusive.

For example:

^a{2,3}$

Will match either of:

aa

aaa

But neither of:

a

aaaa

It is an error to use a repeat operator, if the preceding construct can not be repeated, for example:

a(*)

Will raise an error, as there is nothing for the * operator to be applied to.

All repeat expressions refer to the shortest possible previous sub-expression: a single character; a character set, or a sub-expression grouped with "()" for example.

The expression "ba*" doesn't match "baba".

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