We all know how to make an if then else decision in programming or scripting languages. In bash , and most other languages it is possible to reduce several lines of code to a one-liners. Lets call that short-hand.
A typical if then else
if [ $num -eq 4 ] then echo "variable num equals 4" else echo "variable num contains a different value" fi
This can also written down in short-hand. The basic construct is [[ test ]] && actions_if_true || action_if_false
The code looks like this;
[[ $num -eq 4 ]] && echo "variable num equals 4" || echo "variable num contains a different value"