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

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  • Use one grep to filter all lines with length != 5.
  • Use the second grep to filter all words, where any character repeats.

egrep '^.{5}$' greek.txt | egrep -v '^.*(.).*\1.*$'

Thanks to @StephaneChazelas for pointing out optimizations in a comment:

grep -x '.\{5\}' | grep -v '\(.\).*\1'

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Note that egrep is not required to support backreferences (traditional implementations don't). grep is. So grep -x '.\{5\}' | grep -v '\(.\).*\1' – Stéphane Chazelas Aug 17 '15 at 12:55

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

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indeed, backrefs are \1 and not /1 – Goez Aug 8 '11 at 12:44
still not working unfortunately :( – Lucas Kauffman Aug 8 '11 at 13:24
I'll have a look when I get home... – Goez Aug 8 '11 at 13:41
[^\1] is any character but backslash and 1. You can't use back references like that (egrep is not meant to support backreferences at all anyway) – Stéphane Chazelas Aug 17 '15 at 13:00
@StéphaneChazelas : I only ever remember seeing egrep implemented as a wrapper script for 'grep -E', and was not aware, that it isn't supposed to support backreferences. OP had used egrep, so I just went with that. – Alex Stragies Aug 17 '15 at 18:22

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