Conditional Statements are those which execute different blocks of code depending upon whether a Boolean expression provided by the programmer evaluates to a true condition or a false one. In this article, we will learn Conditional Statements, its different types, their syntax and example of each of them. We have already seen these statements in some of our previous articles on Basic Linux Shell Scripting Language. So, most of the part of this article is self explanatory.
Here we go!
Types of Conditional Statements
- Simple If Statement
- 'If-else' Statement
- 'If-elif-else' Statement
- 'Nested If' Statement
1. Simple 'If' Statement
In simple 'if statements', the block of code is executed if and only if the
condition evaluates to 'true'. Otherwise, the block of code is skipped.Syntax:
if [ condition ]
then
-- Block of Commands --
fi
Example:
#!/bin/bash
echo "Enter an Even Number :"
read n
i=$(expr $n % 2)
if [ $i -ne 0 ]
then
echo "Its not Even!"
fi
Result:
Enter an Even Number :
3
Its not Even!
2. 'If - else' Statement
In 'if-else statements', if the
condition evaluates to 'true', the block of commands under 'if-then', i.e. 'Block of Commands 1', is executed while 'Block of Commands 2' is skipped. Otherwise, 'Block of Commands 1' is skipped and block of code under 'else', i.e. 'Block of Commands 2', is executed. Syntax:
if [ condition ]
then
-- Block of Commands 1 --
else
-- Block of Commands 2 --
fi
Example:
#!/bin/bash
echo "Enter a Natural Number :"
read n
i=$(expr $n % 2)
if [ $i -eq 0 ]
then
echo "Its Even!"
else
echo "Its Odd!"
fi
Result:
Enter a Natural Number :
7
Its Odd!
Enter a Natural Number :
12
Its Even!
3. 'If - elif - else' Statement
In case of 'if-elif-else' statements, '
condition 1' is checked and if 'true', 'Block of Commands 1' is executed. If condition 1 evaluates to be false, then condition 2 in 'elif' is checked, if it evaluates to be 'true', then 'Block of Commands 2' is executed. If both the conditions are evaluated to be 'false', then program jumps to the 'else' part and executes 'Block of Commands 3'. Syntax:
if [ condition1 ]
then
-- Block of Commands 1 --
elif [ condition2 ]
then
-- Block of Commands 2 --
else
-- Block of Commands 3 --
fi
Example:
#!/bin/bash
echo "Enter any Number :"
read n
if [ $n -lt 0 ]
then
echo "Its Negative!"
elif [ $n -eq 0 ]
then
echo "Its Neither Positive Nor Negative!!"
else
echo "Its Positive!"
fi
Result:
Enter any Number :
20
Its Positive!
Enter any Number :
-5
Its Negative!
Enter any Number :
0
Its Neither Positive Nor Negative!
4. 'Nested If' Statement
In 'nested-if' statements, there are one or more 'if-then-else' or 'if-elif-else' statements nested in one 'if-then-else' or 'if-elif-else' statement.
Syntax:
if [ condition ]
then
-- Block of Commands --
else
if [ condition ]
then
-- Block of Commands --
fi
fi
Example:
#!/bin/bash
echo "Balance = $1000"
echo "Enter the Amount You want to Withdraw."
read a
if [ $a -gt 1000 ]
then
echo "Insufficient Balance!"
else
if [ $a -gt 950 ]
then
echo "Warning! Keep $50 in your account to keep it active!"
fi
fi
Result:
Balance = $1000
Enter the Amount You want to Withdraw:
960
Warning! Keep $50 in your account to keep it active!
That's all about 'Conditional Statements'!
Also Read:
- Getting Started - Basic Linux Shell Scripting Language
- Basic Linux Shell Scripting Language - Part II
- Basic Linux Shell Scripting Language - Part III
- Basic Linux Shell Scripting Language : Introduction to 'FOR' Loops
- Basic Linux Shell Scripting Language : 'While' Loops
- Basic Linux Shell Scripting Language : 'Until' Loops
- Basic Linux Shell Scripting Language : 'Case' Statement
- Basic Linux Shell Scripting Language : 'Select Loop'
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