Bash scripting - Decision Making

 

Decision Making

In programming, Decision Making is one of the important concepts. The programmer provides one or more conditions for the execution of a block of code. If the conditions are satisfied then those block of codes only gets executed.

 

Two types of decision-making statements are used within shell scripting. They are –

1. If-else statement:

If else statement is a conditional statement. It can be used to execute two different codes based on whether the given condition is satisfied or not.

There are a couple of varieties present within the if-else statement. They are –

• if-fi 

• if-else-fi 

• if-elif-else-fi 

• nested if-else

The syntax for the simplest one will be –

 

Syntax of If-else statement:

 

if [ expression ]; then

    statements

fi

Example Script:

Name="Satyajit"
if [ "$Name" = "Satyajit" ]; then
  echo "His name is Satyajit. It is true."
fi

Output of if-else statement:

His name is Satyajit. It is true.

In the above example, during the condition checking the name matches and the condition becomes true. Hence, the block of code present within the if block gets executed. In case the name doesn’t match then will not have an output. Below is the terminal shell pictorial depiction after executing the following script --

 

2. case-sac statement:

case-sac is basically working the same as switch statement in programming. Sometimes if we have to check multiple conditions, then it may get complicated using if statements. At those moments we can use a case-sac statement. The syntax will be –

 

Syntax of case-sac statement:

case $var in
   Pattern 1) Statement 1;;
   Pattern n) Statement n;;
esac

Example Script:

Name="Satyajit"
case "$Name" in
    #case 1
    "Rajib") echo "Profession : Software Engineer" ;;
    
    #case 2
    "Vikas") echo "Profession : Web Developer" ;;
    
    #case 3
    "Satyajit") echo "Profession : Technical Content Writer" ;;
esac

Output of case-sac statement:

Profession : Technical Content Writer

In the above example, the case-sac statement executed the statement which is a part of the matched pattern here the ‘Name’. Below is the terminal shell pictorial depiction after executing the following script –