The $? variable is the exit status of the last command. $1 is the first command line argument passed to the script.

For example, make a script like the following (give it some name I used test.sh):

#!/bin/bash
echo $1
exit 23


Make it executable: chmod 755 test.sh
Then run it with an argument, for example: ./test.sh "Hello"
Then after that run: echo $?
You'll see that "echo $1" in the script returned the argument you passed, while "echo $?" returned the number after "exit" in the script (the exit status).

I used an exit status other then 0 (true) or 1 (false) to hopefully make the example clearer.

Good tip Thanks,

but how does the ? in echo$? work
IS it like $1 ?