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From: Ralph Corderoy <ralph@inputplus.co.uk>
To: Computer Old Farts Followers <coff@tuhs.org>
Subject: [COFF] Re: Grep has gone overboard
Date: Mon, 30 May 2022 09:16:04 +0100	[thread overview]
Message-ID: <20220530081604.A9FBF21F8A@orac.inputplus.co.uk> (raw)
In-Reply-To: <F83DB452-12EA-4EA4-8193-76B8FB5644D2@iitbombay.org>

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.

  parent reply	other threads:[~2022-05-30  8:16 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-30  4:12 [COFF] " Dave Horsfall
2022-05-30  4:47 ` [COFF] " Bakul Shah
2022-05-30  6:35   ` Michael Kjörling
2022-05-30  6:51     ` Bakul Shah
2022-05-30  8:26       ` Ralph Corderoy
2022-05-30  8:01     ` Ralph Corderoy
2022-05-30  8:16   ` Ralph Corderoy [this message]
2022-05-30  8:43     ` Bakul Shah
2022-05-30  9:19       ` Ralph Corderoy
2022-05-30  7:38 ` Ralph Corderoy
2022-05-30  7:44   ` Ralph Corderoy

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