Rx

3.7: Counted Subexpressions

An interval expression, \{m,n\} where m and n are non-negative integers with n >= m, applies to the preceeding character, character set, subexpression or backreference. It indicates that the preceeding element must match at least m times and may match as many as n times.

For example:

c\([ad]\)\{1,4\}

matches

car
cdr
caar
cdar
...
caaar
cdaar
...
cadddr
cddddr