assign command substitution output to a variable inside until test-CodePudding

I expect the following snippet

until [ MY_VAR=$(echo my_var_val) ]
do
 echo 'inside the loop'
done 

echo $MY_VAR

to produce the my_var_val output. However, this does not happen. How can I make this happen?

Long story

I want to perform a retry on a script producing some output. I need the output later in the script. Unfortunately, assigning the variable value in the until test fails - the variable has empty value, when I try to use it later in the script. How can I execute the external script with retry logic and have its output stored in a variable that I can use later in the script?

max_retry=10
counter=0
until [ IMPORTANT_SCRIPT_OUTPUT=$(python very_important_script_with_output.py) ]
do
 #retry logic
 if [[ counter -eq $max_retry ]]; then
   echo "Failed"
   exit 1
 fi
 ((counter  ))
 echo "very_important_script_with_output failed, retrying"
done 

python another_very_important_script_with_the_previous_script_output_as_parameter.py --important-parameter $IMPORTANT_SCRIPT_OUTPUT

CodePudding user response：

You can try this:

until MY_VAR=$(echo my_var_val); test -n "$MY_VAR"
do
 echo 'inside the loop'
done 

echo $MY_VAR

CodePudding user response：

[ is an ordinary command, not shell syntax, and its arguments are processed normally. So MY_VAR=$(echo my_var_val) is just a string beginning with MY_VAR=, not a variable assignment.

Do the assignment separately from testing the variable.

while :
do
    MY_VAR=$(command)
    if [[ -n "$MY_VAR" ]]
    then break
    fi
    echo 'inside the loop
done