Update a bash variable in the while loop test from within the loop?

Question

I have a very-long-oneliner that outputs true or false whose I want to wait to be true to process further. My until loop works OK this way:

var=$(very-long|oneliner)
until [[ $var = true ]]; do sleep 5
var=$(very-long|oneliner); done

But when I want get it lighter:

var=$(very-long|oneliner)
until [[ $var = true ]]; do sleep 5
var=$var; done

it fails when initial $var is false because var after do is never updated as I hoped. I learned this is because at some point the loop goes in a sub shell, then var is no more the output of the oneliner, but get stuck to false. Is there a way to do it ? Maybe the first line would be declare -g var=$(very-long|oneliner) (I never used this and am afraid it spreads I don't know where in the system),or declare -x var=$(very-long|oneliner)?

Thanks in advance for hints.

Paul Hodges · Accepted Answer · 2020-05-15 19:31:17Z

1

Simplify. Make sure your one-liner exits with a valid code.

until very-long|oneliner
do sleep 5
done

as long as very-long|oneliner returns 0 then true, it'll work.

answered May 15, 2020 at 19:31

Paul Hodges

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1 Comment

useful Over a year ago

Thanks Paul, but I don't understand: the end of the oneliner is awk that searches a specific line in a file and ouputs the last word, false or true, then it always exits with 0. Even when I drive it where it won't find true or false... OK, I got it work this way, with the help of grep to get a reliable 0|1 exit code. I wasn't able with awk only + 1 week reading the excellent gawk manual :

until [[ `$verylongcurl/command.org|awk -v DID=$DevID '$0~DID,/}/ {if ($0~/online/) print}'|grep "\"online\": true,"` ]]; do sleep 5; done

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