How to check the stdout of a command in a Bash while conditionality check? - bash

Question

I am trying to check for the output of a command as a breakout condition for while loop in Bash, but it keeps skipping past the block, even while the last echo confirms the value as "DELETE_IN_PROGRESS".
This is what I have:
stackname=cf_test
while [[ $(aws cloudformation describe-stacks --stack-name ${stackname} | jq '.Stacks | .[0] | .StackStatus') == "DELETE_IN_PROGRESS" ]]; do
echo -e " $(aws cloudformation describe-stacks --stack-name ${stackname} | jq '.Stacks | .[0] | .StackStatus'): waiting for current stack to delete before re-deploying..."
sleep 30
done
echo -e $(aws cloudformation describe-stacks --stack-name ${stackname} | jq '.Stacks | .[0] | .StackStatus')
What should I change?
edit:
Adding -x debug flag, gives:
▶ bash -x ~/Downloads/test_script.sh
+ stackname=cf_test
++ aws cloudformation describe-stacks --stack-name cf_test
++ jq '.Stacks | .[0] | .StackStatus'
+ [[ "DELETE_IN_PROGRESS" == \D\E\L\E\T\E\_\I\N\_\P\R\O\G\R\E\S\S ]]
++ aws cloudformation describe-stacks --stack-name cf_test
++ jq '.Stacks | .[0] | .StackStatus'
+ echo -e '"DELETE_IN_PROGRESS"'
"DELETE_IN_PROGRESS"

Answer 1

I would move the comparison inside jq. By default, jq will succeed, regardless of the logical status of the comparison you make.
% jq -n '3 == 3'; echo $?
true
0
% jq -n '3 != 3'; echo $?
false
0
To change this, use the -e option.
% jq -en '3 == 3'; echo $?
true
0
% jq -en '3 != 3'; echo $?
false
1
Doing this eliminates the need for the [[ ... ]] command.
while x=$(aws cloudformation describe-stacks --stack-name ${stackname});
jq -ne --arg x "$x" '$x.Stacks.[0].StackStatus == "DELETE_IN_PROGRESS"'; do
printf '%s: waiting for current stack to delete before re-deploying...\n' "$x"
sleep 30
done
printf '%s\n' "$x"

Answer 2

Your debug log shows the problem (even though the [[ line itself weirdly obscures it):
+ echo -e '"DELETE_IN_PROGRESS"'
The value you are comparing contains literal double quotes. That's why the match fails. Your right-hand side of == contains syntactical double quotes that are not treated as part of the string.
To fix it, use jq -r to output the string without JSON formatting and escaping:
json='{ "foo": "bar" }'
jq '.foo' <<< "$json" # Shows bad 5 character value: "bar"
jq -r '.foo' <<< "$json" # Shows good 3 character value: bar
In your case:
while [[ $(aws cloudformation describe-stacks --stack-name ${stackname} | jq -r '.Stacks | .[0] | .StackStatus') == "DELETE_IN_PROGRESS" ]]; doq -r '.Stacks | .[0] | .StackStatus') == "DELETE_IN_PROGRESS" ]]; do
echo "Still deleting"
sleep 30
done