We can use interval expressions to specify a minimum, maximum, or exact number of occurrences to match the preceding regular expression. The unary operator for repetition can specify a minimum number of occurrences, but we cannot specify the maximum number of occurrences of the preceding expression with them.
Interval expressions were not originally available in AWK. They were added as part of the POSIX standard to make AWK and egrep consistent with each other. In GAWK, they are available with version 4.0 and above.
Let's create a file to illustrate the interval expression: