Conditional statment

 

5. CONDITIONAL STATEMENTS :

The if construct is followed by a command. If an expression is to be tested, it is enclosed in square brackets. The then keyword is placed after the closing parenthesis. An if must end with a fi.

Syntax :

1.if

This is used to check a condition and if it satisfies the condition if then does the next action , if not it goes to the else part.

2.if…else

Syntax :

If cp $ source $ target

Then

Echo File copied successfully

Else

Echo Failed to copy the file.

3.nested if

here sequence of condition are checked and the corresponding

performed accordingly.

Syntax :

if condition

then

command

if condition

then

command

else

command

fi

fi

4.case ….. esac

This construct helps in execution of the shell script based on Choice.

EXAMPLE

The if construct is: if command then block of statements fi -------------------------------------- if [ expression ] then block of statements fi -------------------------------------- The if/else/else if construct is: if command then block of statements elif command then block of statements elif command then block of statements else block of statements fi ------------------------------ if [ expression ] then block of statements elif [ expression ] then block of statements elif [ expression ] then block of statements else block of statements fi --------------------------------------

The case command construct is: case variable_name in pattern1) statements ;; pattern2) statements ;; pattern3) ;; *) default value ;; esac case "$color" in blue) echo $color is blue ;; green) echo $color is green ;; red|orange) echo $color is red or orange ;; *) echo "Not a color" # default esac The if/else construct is: if [ expression ] then block of statements else block of statements fi --------------------------------------