In Bourne Shell if statement checks whether a condition is true or not. If so , the shell executes the block of code associated with the if statement. If the statement is not true , the shell jumps beyond the end of the if statement block & Continues on.
### Syntax of if Statement : ###
if [ condition_command ]
then
command1
command2
……..
last_command
fi
#### Example: ####
#!/bin/bash
number=150
if [ $number -eq 150 ]
then
echo "Number is 150"
fi
#### if-else Statement : ####
In addition to the normal if statement , we can extend the if statement with an else block. The basic idea is that if the statement is true , then execute the if block. If the statement is false , then execute the else block.
#### Syntax : ####
if [ condition_command ]
then
command1
command2
……..
last_command
else
command1
command2
……..
last_command
fi
#### Example: ####
#!/bin/bash
number=150
if [ $number -gt 250 ]
then
echo "Number is greater"
else
echo "Number is smaller"
fi
### If..elif..else..fi Statement (Short for else if) ###
The Bourne shell syntax for the if statement allows an else block that gets executed if the test is not true. We can nest if statement , allowing for multiple conditions. As an alternative, we can use the elif construct , shot for else if.
#### Syntax : ####
if [ condition_command ]
then
command1
command2
……..
last_command
elif [ condition_command2 ]
then
command1
command2
……..
last_command
else
command1
command2
……..
last_command
fi
#### Example : ####
#!/bin/bash
number=150
if [ $number -gt 300 ]
then
echo "Number is greater"
elif [ $number -lt 300 ]
then
echo "Number is Smaller"
else
echo "Number is equal to actual value"
fi
### Nested if statements : ###
If statement and else statement can be nested in a bash script. The keyword ‘fi’ shows the end of the inner if statement and all if statement should end with the keyword ‘fi’.
