Question

How do I write a sed invocation to output only lines containing only numbers consisting of a repeated single digit (and containing at least two digits).

Example:

seq 1000 | sed ...

For which the output should be:

11
22
33
44
55
66
77
88
99
111
222
333
444
555
666
777
888
999

Answer 1

if sed is your favorite, here you go:

kent$  seq 1000|sed -nr '/^([0-9])\1+$/p'
11
22
33
44
55
66
77
88
99
111
222
333
444
555
666
777
888
999