On 7/4/20 7:54 AM, Chris Elvidge wrote: > On 03/07/2020 11:16 pm, Eli Schwartz wrote: >> On 7/3/20 2:00 PM, Chris Elvidge wrote: >>> I've used 'return $((!$#))' and 'return $[!$#]' to return an error if no >>> parameters given to function. >>> >>> Tested in a bash script 'exit $((!$#)) / $[!$#]' - both work. >>> >>> 'echo $((!$#)) / $[!$#]' - both echo 1 when no params, 0 when any >>> number of params. >>> >>> I'm told ( https://wiki.bash-hackers.org/scripting/obsolete ) that >>> $[...] is obsolete and that $((...)) should be used instead. OK so far. >>> >>> However 'N=0; echo $((!$N))' gives an error at the bash prompt. 'echo >>> $[!$N]' echo's 1 as expected. >> >> "gives an error" is a useless bug report. It works for me. >> >> $ N=0; echo $((!$N)) >> 1 >> >> My initial reaction to reading this thread is head scratching! >> >> As the other reply mentioned, there's actually a good explanation for >> why we get different results -- I disabled an annoying feature. >> >> $ set -o histexpand >> >> Now here's a useful bug report. "When I run this, I get the following >> incorrect results or error message": >> >> $ N=0; echo $((!$N)) >> N=0; echo $((histexpandN)) >> 0 >> $ N=0; echo $((!$N)) >> N=0; echo $(()N)) >> -bash: syntax error near unexpected token `)' >> $ N=0 >> $ echo $((!$N)) >> echo $((N=0N)) >> -bash: N=0N: value too great for base (error token is "0N") >> >> ... >> >> From there, people can give useful advice for solving the problem. (My >> preferred advice is "disable histexpand".) >> > > Thanks for the pointers to a better bug report. > And thanks for the info on histexpand. I obviously should read the > manual more carefully - I'd never come across it - as it's set by > default, not in any profile or bashrc file.
It's the section "HISTORY EXPANSION", and set -o histexpand is equivalent to set -H, which controls this option. Many people first realize it exists only when they've been bitten by it. :) > Did you mean set +o histexpand to disable the feature? "set +o histexpand" is in my bashrc to disable the feature. "set -o histexpand" is what I used at the console to temporarily re-enable it, in order to reproduce your issue. As you can see from $ N=0; echo $((!$N)) N=0; echo $((histexpandN)) 0 the first history expansion inserted the word "histexpand" into my command, because the previous command used the word. -- Eli Schwartz Arch Linux Bug Wrangler and Trusted User
signature.asc
Description: OpenPGP digital signature
