Regex : all greek letters with 5 unique letters (meaning that each letter only appears once)

Question

Another one I can't seem to solve : all greek letters with 5 unique letters (meaning that each letter only appears once).

my solution :

egrep '(.)([^/1])([^/1/2])([^/1/2/3])([^/1/2/3/4])' greek.txt

So What I think I am saying :

• match any first character

• every consecutive character can't be any of the previous patterns

But what comes out :

alpha
gamma
delta
epsilon
theta
kappa
lambda
omicron
sigma
upsilon
omega

Alpha, gamma, they have characters that are not unique. Any hints or tips on what I am doing wrong ?

Answer 1

I think you're on the right track but got your slashes going to wrong direction to be back-references. Use \1 not /1!