Bash - [: =: unary operator expected during trap execution-CodePudding

I am trying to use trap in order to run a clean-app jar in case the main app jar exists successfully (0 exit code) :

trap "exit_code=$?; if [ "${exit_code}" = "0" ]; then java -jar /clean-app.jar; fi" EXIT

java -jar /main-app.jar

but I am getting the following error and not sure I'm getting the reason behind it :

/bin/bash: line 1: [: =: unary operator expected

Could someone share a pointer please ? Thank you

CodePudding user response：

You can't nest double quotes like this. Here, you can switch to single quotes for the outer layer. You'll want to do this anyway because you need to prevent $? from being expanded before trap is called.

trap 'exit_code=$?; if [ "${exit_code}" = "0" ]; then java -jar /clean-app.jar; fi' EXIT

Better yet, define a function first.

handler () {
    exit_code=$?
    if [ "$exit_code" = 0 ]; then java -jar /clean-app.jar; fi
}

trap handler EXIT

In either case, you don't really need exit_code, as you don't need the original exit code after the test. You can also use -eq, since $? is guaranteed to be an integer.

handler () {
    [ $? -eq 0 ] && java -jar /clean-app.jar
}