Question

is it possible to assign variable inside if conditional in bash 4? ie. in the function below I want to assign output of executing cmd to output and check whether it is an empty string – both inside test conditional. The function should output

“command returned: bar”

myfunc() {

local cmd="echo bar"
local output=

while [[ -z output=`$cmd` ]];
do
    #cmd is failing so far, wait and try again
    sleep 5
done

# great success
echo "command returned: $output"
}

why the above?

i prefer to run scripts with ‘set -e’ – which will cause script to terminate on first non-0 return/exit code that’s not in an if/loop conditional.

with that in mind, imagine cmd is an unstable command that may exit with > 1 from time to time, and I want to keep calling it until it succeeds and i get some output.

Answer 1

You can try something like this:

myfunc() {

    local cmd="echo bar"
    local output=

    while ! output=$($cmd) || [[ -z output ]];
    do
        #cmd is failing so far, wait and try again
        sleep 5
    done

    # great success
    echo "command returned: $output"
}

Note that it is strongly recommended to avoid the use of set -e.