bash scripts, success and failure

All this might be trivial, but it's good to have it written down somewhere.


false and true can be used to simulate a command which failed or succeeded(respectively)

false
echo $?
1
true
echo $?
0

You can use || to run a command only if the previous failed:

false || echo "it failed"

it failed 

true || echo "it didn't fail"

(nothing is printed here) 

You can use && to run a command only if the previous succeeded:

true && echo "It succeeded"

It succeeded

false && echo "It succeeded"

(nothing is printed here)  

You can chain as many command as you want with && and || (normally you do this only with &&).

set -e  will make sure your script stops execution as soon as a command returns something != 0