|You question is vague. Since you are using Linux, I am assuming you are asking about the bash shell? |
Below is an example of a nexted if statement, but I don't know in what context you are asking about "lookup" and "match":
if [[ $x -eq 5 ]]
if [[ "$y" == "z" ]]
echo "x is 5 with y equal z"
echo "x does not 5"