Conditional Statements

Use if else conditions in shell scripting. Compare numbers and strings. Test command and operators. Build decision making logic like real projects.

What is a Conditional Statement?

Conditional statements allow a script to make decisions based on conditions. The script executes different blocks of code depending on whether a condition is true or false.

Why Use Conditional Statements?

Decision Making

Control the flow of execution based on conditions.

Automation

Scripts can respond differently based on inputs.

Error Handling

Handle success and failure cases properly.

Syntax of if, elif, else

syntax

if [ condition ]; then
  commands
elif [ another_condition ]; then
  commands
else
  commands
fi

Examples

1. Basic if Statement

Executes a block of code only if the condition is true.

terminal — bash

if-else

age=18
 
if [ $age -ge 18 ]; then
  echo "You are eligible to vote"
fi

2. if-else Statement

Executes one block if condition is true, otherwise another.

terminal — bash

if-else

age=15
 
if [ $age -ge 18 ]; then
  echo "You can vote"
else
  echo "You are not eligible to vote"
fi

3. if-elif-else Statement

Used when checking multiple conditions.

terminal — bash

if-else

marks=75
 
if [ $marks -ge 90 ]; then
  echo "Grade A"
elif [ $marks -ge 60 ]; then
  echo "Grade B"
else
  echo "Grade C"
fi

4. String Comparison Example

Compare strings using = or != operators.

terminal — bash

if-else

name="admin"
 
if [ "$name" = "admin" ]; then
  echo "Welcome Admin"
else
  echo "Access Denied"
fi

Best Practices

Follow These Rules

Always leave space after [ and before ].
Use double quotes around variables.
Indent code for readability.
Use elif instead of multiple if statements.

Practice Task – Conditional Logic

Ask user for age and check eligibility.
Check if a number is positive or negative.
Check username and allow access.

Next lesson: Loops (for, while, until)