On 29 May 2022 21:47 -0700, from bakul(a)iitbombay.org (Bakul Shah): I was trying to do something very similar using procmail regexes some time ago, only with strings instead of individual characters (for parsing and matching on arbitrarily-ordered, comma-separated values within a header). I never did come up with a good solution. -- Michael Kjörling • https://michael.kjorling.se • michael(a)kjorling.se “Remember when, on the Internet, nobody cared that you were a dog?”

Hi Bakul, I know you know this and the error is just from typing an email, but in case other listeners are following along, all the greps need start and end-of-line anchors. Without them, grep '[^a]*a[^a]*' still matches ‘aa’ because there are zero non-a before the first a, then the first a matches, and there are zero non-a after it. Here's ‘aa’ with indexes between the characters. a a 0 1 2 [^a]* matches 0-0 a matches 0-1 [^a]* matches 1-1 And it's easier to invert the test into grep -v 'a.*a' I'll stop waffling on about regexps now. Though I do have a SNOBOL4 question for TUHS which I should get around to writing. :-) -- Cheers, Ralph.

Hi Bakul, 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}\ ladybug $ -- Cheers, Ralph.

Hi Bakul, I was thinking it looks like APL and it turns out to be a descendant. https://en.wikipedia.org/wiki/K_(programming_language) That pushed me into writing an awk-permutation generator. It's inefficient as it keeps altering $0 which cascades into re-working $1, etc., even if that's lazily done. Still, it sufficies for the small cases I typically need. $ cat perm #! /bin/awk -f function perm(s, f, l, t) { if (!NF) { print substr(s, 2) return } l = $0 for (f = 1; f <= NF; f++) { t = $f $f = ""; $0 = $0 perm(s " " t) $0 = l } } { perm("") } $ $ ./perm <<<'' $ ./perm <<<1 1 $ ./perm <<<'1 2' 1 2 2 1 $ ./perm <<<'1 2 3' 1 2 3 1 3 2 2 1 3 2 3 1 3 1 2 3 2 1 $ $ time ./perm <<<'1 2 3 4 5 6 7 8 9' | wc -l 362880 real 0m5.421s user 0m5.406s sys 0m0.082s $ $ dc <<<'9 8*7*6*5*4*3*2*p' 362880 $ -- Cheers, Ralph.

Hi again Dave, I wrote: Sorry, they use frames. Still. From that URL you need ‘Base Definitions’ in the top left, which I think is the default, and then ‘9. Regular Expressions’ in the bottom left. (This is as bad as reading one GUI uesr explain to the other where to click, click, click.) -- Cheers, Ralph.