The if...elif...fi statement is the one level advance form of control statement that allows Shell to make correct decision out of several conditions.
Syntax:
if [ expression 1 ]
then
Statement(s) to be executed if expression 1 is true
elif [ expression 2 ]
then
Statement(s) to be executed if expression 2 is true
elif [ expression 3 ]
then
Statement(s) to be executed if expression 3 is true
else
Statement(s) to be executed if no expression is true
fi
There is nothing special about this code. It is just a series of if statements, where each if is part of the else clause of the previous statement. Here statement(s) are executed based on the true condition, if non of the condition is true then else block is executed.
Example:
#!/bin/sh
a=10
b=20
if [ $a == $b ]
then
echo "a is equal to b"
elif [ $a -gt $b ]
then
echo "a is greater than b"
elif [ $a -lt $b ]
then
echo "a is less than b"
else
echo "None of the condition met"
fi