The if statement

There are three shells available in shell command. All the three shells support and maintain nested if...then...else statements. These statements give a way of performing complicated conditional tests in shell programs.

Syntax

if [ expression ]

then commands

elif [ expression ]

then commands

else commands

fi

Practice 1

The given shell program will search if the '.profile' file is present in the current directory

# vi checkprofile

echo -e "Enter the filename to search :\\c"

read fname

if [ -f $fname ]

then

echo "An $fname file is available within current directory"

else

echo "Could not find the .profile file"

fi

# sh checkprofile

The given program will check for the file. Profile in the current directory by using the test option -f.it will show the message there is if the file is found. Profile file in the current directory otherwise it will show the message could not search the .profile file.

Practice 2

The given shell program will find of the 3 numbers.

# vi greatnum

echo -e "Enter the value of a, b and c:"

read a read b read c

if [ $a -gt $b -a $a -gt $c ]

then

echo $a is greater than $b and $c elif [ $b -gt $c ]

then

echo $b is greater than $a and $c else

echo $c is greater than $a and $b fi

# sh greatnum

Enter the value for a, b and c:

12

34

56

56 is greater than 12 and 34