Writing a do while loop in bash with multiple conditions

Question

I'm having some trouble writing a do-while loop in bash with multiple conditions.

My code currently works when it is like this:

    while
    count=$((count+1))
    ( MyFunction $arg1 $arg2 -eq 1 )
    do
       :
    done

But I want to add a second condition to the "do-while" loop like so:

    while
    count=$((count+1))
    ( MyFunction $arg1 $arg2 -eq 1 ) || ( $count -lt 20 )
    do
       :
    done

When I do this I get an "command not found error".

I've been trying some of the while loop examples from this post but had no luck and the do-while example I use is from here. In particular the answer with 137 likes.

chepner · Accepted Answer · 2019-10-07 12:47:48Z

2

The ( is part of syntax and $count is not a valid command. The test or [ is a valid command that is used to "test" expressions.

while
   count=$((count+1))
   [ "$(MyFunction "$arg1" "$arg2")" -eq 1 ] || [ "$count" -lt 20 ]
do
   :
done

The answer you mention uses arithmetic expressions with (( (not a single (, but double (( without anything between). You could also do:

while
   count=$((count+1))
   (( "$(MyFunction "$arg1" "$arg2")" == 1 || count < 20 ))
do
   :
done

edited Oct 7, 2019 at 12:47

chepner

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answered Oct 7, 2019 at 10:36

KamilCuk

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3 Comments

Bobybobp Over a year ago

I understand why this should work for me but I don't understand why I get a syntax error while using it. I get an error like: -eq 1 || count < 20 : syntax error in expression. It then mentions the error token being in my function, but it looks like the code runs through to completion.

chepner Over a year ago

Since bash is interpreted, parsing and evaluation/execution run somewhat in parallel. A syntax error becomes just another run-time error, and is interpreted as a failure, the same as if a command actually ran but had a non-zero exit status.

Bobybobp Over a year ago

Thanks for the explanation, I've tried it again using your edit @chepner and it runs without the syntax error as well now.

anubhava · Accepted Answer · 2019-10-07 10:25:52Z

0

You can use for loop:

for ((count=0; i<20 && $(MyFunction $arg1 $arg2) == 1; count++)); do
   echo $count
done

answered Oct 7, 2019 at 10:25

anubhava

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