You can work around this by specifying the number field twice. Which makes no sense to me but hey, it works. > cat blah | sort -u -k 1n -k 1 1 a 5

You can work around this by specifying the number field twice. Which makes no sense to me but hey, it works. > cat blah | sort -u -k 1n -k 1 1 a 5 which 10 exotically 15 aerodynamically 15 differentiation 20 electroencephalogram