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. Different blocks of code execute depending on whether a condition is true or false.

In shell scripting, conditions are commonly written usingif,elif, andelse.

Why Use Conditional Statements?

Decision Making

Control script flow based on conditions.

Automation

Scripts respond dynamically to user input and data.

Error Handling

Handle success and failure conditions properly.

Syntax of if, elif, else

syntax

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

Comparison Operators

Numeric Comparison Operators

Operator	Meaning
-eq	Equal to
-ne	Not equal to
-gt	Greater than
-lt	Less than
-ge	Greater than or equal to
-le	Less than or equal to

String Comparison Operators

Operator	Meaning
=	Strings are equal
!=	Strings are not equal
-z	String is empty
-n	String is not empty

File Test Operators

Operator	Meaning
-f	Check if file exists
-d	Check if directory exists
-r	Check read permission
-w	Check write permission
-x	Check execute permission

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

5. File Check Example

Check whether a file exists.

terminal — bash

if-else

file="test.txt"
 
if [ -f "$file" ]; then
  echo "File exists"
else
  echo "File not found"
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.
Use meaningful conditions.
Test scripts with different inputs.

Practice Task – Conditional Logic

Ask user for age and check eligibility.
Check if a number is positive or negative.
Check username and allow access.
Check whether a file exists.
Check if a string is empty.

Next lesson: Loops (for, while, until)