Bash Script 'if-else' Statements - Conditional Statements are those which help us take certain decisive actions against certain different conditions. These statements execute different blocks of code, depending upon whether a condition (or a boolean expression) provided by the programmer evaluates to true or false. In this article, we will learn Conditional Statements, their different types, their syntax and example of each of them. Most of the part of this article is straight forward and self explanatory.
Here we go!
Types of Conditional Statements
Below are different types of Conditional statements those can be used in bash script.
- Simple
if
statement if-else
statementif-elif-else
statement- Nested
if
statement
Let us now see each of them, with their syntax and examples.
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 [ $i -ne 0 ] then echo "Its not Even!" fi
Result:
Enter an Even Number : 3 Its not Even!
Note :
read
statement used in above example, is used to get input from the user. In this case, the user input will be stored into a variable n
.
2. if-else
Statement
In
if-else
statements, if the condition evaluates to 'True', the block of commands under if-then
, i.e. Block of Commands 1
, is executed while Block of Commands 2
is skipped. If the condition evaluates to 'False', Block of Commands 1
is skipped and block of code under else
, i.e. Block of Commands 2
, is executed. Syntax:
if [ condition ] then -- Block of Commands 1 -- else -- Block of Commands 2 -- fi
Example:
#!/bin/bash echo "Enter a Natural Number :" read n i=$(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 it evaluates to 'True', Block of Commands 1
is executed. If 'condition 1' evaluates to 'False', then 'condition 2' in elif
block is checked. If it evaluates to 'True', then Block of Commands 2
is executed. If both the conditions are evaluated to '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-else
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'! After reading this article, one should be able to decide which statement must be used given a scenario and write those statements. Although very basic examples are provides, those should have given you a clear idea about how the control flow is switched depending on what the condition evaluates to. Thanks for reading this article, share your views and feedback in the comment section below and stay tuned.
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