1. The if...else statements
1.1 if...fi statement
Syntax:
if [ expression ]
then
Statement(s) to be executed if expression is true
fi if [ expression ]; then
Statement(s) to be executed if expression is true
fi
Ex:
#!/bin/sh
a=10
b=20
if [ $a == $b ]
then
echo "a is equal to b"
fi
if [ $a != $b ]
then
echo "a is not equal to b"
fi
$./test.sh
a is not equal to b
1.2 if...else...fi statement
Syntax:
if [ expression ]
then
Statement(s) to be executed if expression is true
else
Statement(s) to be executed if expression is not true
fi
Ex:
#!/bin/sh
a=10
b=20
if [ $a == $b ]
then
echo "a is equal to b"
else
echo "a is not equal to b"
fi
$./test.sh
a is not equal to b
1.3 if...elif...else...fi statement
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
Ex:
#!/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
$./test.sh
a is less than b
2. The case...esac Statement
Syntax:
case word in
pattern1)
Statement(s) to be executed if pattern1 matches
;;
pattern2)
Statement(s) to be executed if pattern2 matches
;;
pattern3)
Statement(s) to be executed if pattern3 matches
;;
esac
Ex1:
#!/bin/sh
FRUIT="kiwi"
case "$FRUIT" in
"apple") echo "Apple pie is quite tasty."
;;
"banana") echo "I like banana nut bread."
;;
"kiwi") echo "New Zealand is famous for kiwi."
;;
esac
$./test.sh
New Zealand is famous for kiwi.
Ex2:
#!/bin/sh
echo "Is it morning? Please answer yes or no"
read timeofday
case "$timeofday" in
yes | y | Yes | YES )
echo "Good Morning"
echo "Up bright and early this morning"
;;
[nN]*)
echo "Good Afternoon"
;;
*)
echo "Sorry, answer not recognized"
echo "Please answer yes or no"
exit 1
;;
esac
exit 0