Bash If-Else Statement With Examples

If-else statements in bash scripting is similar to any other programming languages; it is a method for a program to make decisions.

In if-else statements, the execution of a block of statement is decided based on the result of the if condition.

Bash If-Else Statement Syntax

The syntax of the if-else statement in bash is:

if [condition]
then
    //if block code
else
   // else block code
fi

If the condition evaluates to true, the if block code is executed, and if the condition evaluates to false then the else block code is executed.

Note: The if block only gets executed if the condition evaluates to true.
The else statement and the else code block is optional.

We have to finish the if statement with the fi keyword.

Conditional Comparisons

The expression used by the conditional construct must evaluate to either true or false. The expression can be a single string or variable.

less than - denoted by: $a -lt $b or $a < $b
greater than - denoted by: $a -gt $b or $a > $b
less than or equal to - denoted by: $a -le $b or $a <= $b
greater than or equal to - denoted by: $a -ge $b or $a >= $b
equal to - denoted by: $a -eq $b or $a == $b
not equal to - denoted by: $a -ne $b or $a != $b

Logical Operators

The expression within the if statement can also be a logical combination of multiple comparisons.

The logical operators are:

logical and - denoted by $a AND $b or $a && $b evaluates to true when both variables or statements are true.
logical or - denoted by $a OR $b or $a || $b evaluates to true when one of the variables or statements are true.

Note: When using logical operators, conditional expressions should be surrounded by double brackets [[ ]].

For example:

#!/bin/bash

first_name="John"
last_name="Doe"

if [[ $first_name = "John" && $last_name = "Doe" ]]
then
echo 'hello John Doe'
fi

Bash if Example

The if statement is just a simple conditional statement. If the condition within the if[] evaluates to true then the if code block is executed.

Example:

#!/bin/bash

read -p "Enter a number: " mynumber

if [ $mynumber -gt 10 ]
then
    echo "The number you entered is greater than 10"
fi

Note: In the above example, if we enter a number which is less than 10, then nothing gets printed.

Bash if-else Example

When the result of the if condition is false then the code in the else block is executed, provided there is one.

For example:

#!/bin/bash

read -p "Enter a number: " mynumber

if [ $mynumber -gt 10 ]
then
    echo "The number you entered is greater than 10"
else
    echo "The number you entered is less than 10"
fi

Bash if-elif-else Example

The elif (else if) is used when there are multiple if conditions.

For example:

#!/bin/bash

read -p "Enter your exam grade: " grade

if [ $grade -ge 80 ]
then
    echo "You got A"

elif [ $grade -ge 70 ]
then
    echo "You got B"

elif [ $grade -ge 60 ]
then
    echo "You got C"
else
    echo "Fail"
fi

Bash Nested if Example

We can also have nested if statements.

For example:

#!/bin/bash

read -p "Enter value of a :" a
read -p "Enter value of b :" b
read -p "Enter value of c :" c

if [ $a -gt $b ]
then
    if [ $a -gt $c ]
    then
        echo "a is greatest"
    else
        echo "c is greatest"
    fi
else
    if [ $b -gt $c ]
    then
        echo "b is greatest"
    else
 echo "c is greatest"
    fi
fi