character(s){m,n}

Where one or more characters is followed by {m,n}

Use it to match the preceding character at least m and not more than n times.

[character- range]{m,n}

Where a character range is followed by {m,n}

Use it to match the preceding character range at least m and not more than n times.

a{3,5}

only 'aaa', 'aaaa', 'aaaaa'

ba{2,3}b

'baab', 'baaab', but not 'bab', 'baaaaab'

ba{0,3}b

'bb', 'bab', 'baab', 'baaab', but not 'baaaab', 'baaaaaab'

[0-9]{2,7}

23, 601, 060615 and all other combinations from 2 to 7 numbers.

2{1,3}

2, 22, 22-4-1999