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From: Ralph Corderoy <ralph@inputplus.co.uk>
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Subject: [COFF] Re: Grep has gone overboard
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Hi Bakul,

> You can write a program to generate all permutations and use that as
> your regexp.  For example abc maps to abc|acb|bac|bca|cab|cba.

Being lazy, I tend to use a shell's brace expansion and then whittle it
down to generate permutations.  I keep thinking it's surprising there's
no Bell Labs program to produce them given there's things like
factor(1).

The brace expansion is wasteful as it's going from n**l down to n! and
it can result in the old bash here not responding to SIGINT for a while
if it's producing gazillions.

    $ printf '%s\n' {b,a,d,u,g,l,y}{b,a,d,u,g,l,y}{b,a,d,u,g,l,y}\
    > {b,a,d,u,g,l,y}{b,a,d,u,g,l,y}{b,a,d,u,g,l,y}{b,a,d,u,g,l,y} |
    > egrep -v '(.).*\1' |
    > fgrep -x -f - /usr/share/dict/words
    ladybug
    $

-- 
Cheers, Ralph.