Regular expressions

grep man

A regular expression may be followed by one of several repetition operators:

? The preceding item is optional and matched at most once.
* The preceding item will be matched zero or more times.
+ The preceding item will be matched one or more times.
{n} The preceding item is matched exactly n times.
{n,} The preceding item is matched n or more times.
{,m} The preceding item is matched at most m times.
{n,m} The preceding item is matched at least n times, but not more than m times.