If given condition is true then command1 is executed otherwise command2 is executed.
if condition then condition is zero (true - 0) execute all commands up to else statement else if condition is not true then execute all commands up to fi fi
example of nested if else
echo "1. Unix (Sun Os)" echo "2. Linux (Red Hat)" echo -n "Select your os choice [1 or 2]? " read osch if [ $osch -eq 1 ] ; then echo "You Pick up Unix (Sun Os)" else #### nested if i.e. if within if ###### if [ $osch -eq 2 ] ; then echo "You Pick up Linux (Red Hat)" else echo "What you don't like Unix/Linux OS." fi fi