Doing arithmetic operations in bash is not similar to other standard programming languages. One of the limitations of bash is that it can’t handle floating point or double numbers like other scripting languages. Another command tool is used in bash to solve this problem. Different types of arithmetic operations are shown in this tutorial by using different examples.
Example – 1: Using ‘expr’ Command
The oldest command for doing arithmetic operations in bash is ‘expr‘. This command can work with integer values only and prints the output directly in the terminal. You have to use space with each operand when you want to use the ‘expr’ command to do any mathematical operations. Create a bash file named expr.bash with the following script to know the use of ‘expr’ command.
#!/bin/bash
# Works as the string
expr ’10 30′
# Works as the string
expr 10 30
#Perform the addition
expr 10 30
#Find out the remainder value
expr 30 % 9
#Using expr with backtick
myVal1=`expr 30 / 10`
echo $myVal1
#Using expr within command substitute
myVal2=$( expr 30 – 10 )
echo $myVal2
Run the following command to execute the script.
Output:
The output shows that arithmetic operators worked only when space is used with each numeric value and no single quotation is used with the expr command. You can also assign the output of the expr command into a variable and print the variable later by using backtick or command substitute. 30/10 is calculated by using backtick and 30-10 is calculated by using command substitute.
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Example – 2: Using ‘let’ Command
‘let’ is another built-in command to do arithmetic operations in bash. ‘let’ command can’t print the output to the terminal without storing the value in a variable. But the ‘let’ command can be used to remove the other limitations of the ‘expr’ command. Create a bash file named let.bash with the following script to know the use of the ‘let’ command.
#!/bin/bash
# Multiplying 9 by 8
let val1=9*3
echo $val1
# Dividing 8 by 3
let “val2 = 8 / 3”
echo $val2
# Subtracting 3 from 9
let val3=9–3
echo $val3
# Applying increment
let val4=7
let val4
echo $val4
# Using argument value in arithmetic operation
let “val5=50 $1”
echo $val5
Run the following command to execute the script.
Output:
The output shows that the ‘let’ command is more flexible than the ‘expr’ command. You can evaluate any arithmetic expression with or without quotations. But you can’t use space within any mathematical expression. The increment or decrement operator can be used in the ‘let’ command. How the arithmetic operation can be done with the argument values using the ‘let‘ command is shown in the last part of the example.
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Example – 3: Using Double Brackets
Any arithmetic operation can be done in bash without using any command. Here, double brackets are used to do the arithmetic tasks, and using double brackets for executing mathematical expressions is more flexible than the command like the ‘expr’ or ‘let’. Create a bash file named dbl.bash with the following script to test the arithmetic operations by using double brackets.
#!/bin/bash
# Calculate the mathematical expression
val1=$((10*5 15))
echo $val1
# Using post or pre increment/decrement operator
((val1 ))
echo $val1
val2=41
((–val2))
echo $val2
# Using shorthand operator
(( val2 = 60 ))
echo $val2
# Dividing 40 by 6
(( val3 = 40/6 ))
echo $val3
Run the following command to execute the script.
Output:
The output shows that double brackets can execute any mathematical expression with space or without space and you can also use increment/decrement and shorthand operators in double brackets expressions.
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Example – 4: Using ‘bc’ Command for Float or Double Numbers
One of the major limitations of the above ways of doing arithmetic operations in bash is that ‘expr’ or ‘let’ or double brackets expressions are not able to produce floating-point or double numbers. The output of division operations of the above examples are integers. ‘bc’ command can be used to solve this problem and it works as a basic calculator for the Linux operating system. Create a bash file named bc.bash with the following script to know the use of the ‘bc’ command in arithmetic operations.
#!/bin/bash
# Dividing 55 by 3 with bc only
echo “55/3” | bc
# Dividing 55 by 3 with bc and -l option
echo “55/3” | bc -l
# Dividing 55 by 3 with bc and scale value
echo “scale=2; 55/3” | bc
Run the following command to execute the script.
Output:
The output shows that the simple ‘bc’ command produces integer value like other options when any division expression is executed. ‘bc -l’ command generates the exact output of the division and you can limit the fractional part by using scale value. Here, scale=2 is used. So the output shows 2 digits after the decimal point.
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Example-5: Using the printf Command for Float or Double Number
The `printf` command is another way to work with fractional data. This command can be used to generate the floating-point value more efficiently than the `bc` command after the arithmetic operation. This command can also be used to calculate the power of a number. The uses of the `printf` command for different arithmetic operations have shown in this example. Create a bash file named prn.bash with the following script to check the use of the `printf` command for the fractional output of the division of two numbers.
#!/bin/bash
# Take the dividend value from the user
read -p “Enter the dividend value: “ n1
# Take the divisor value from the user
read -p “Enter the divisor value: “ n2
# Find the division using `echo` and `bc`
echo “scale=2; $n1/$n2“|bc
# Find the division using `printf`
printf “%.2fn“ “$((10**2 * $n1/$n2))e-2″
Run the following command to execute the script.
Output:
The following output shows that the division value generated by the `bc` and `printf` commands of two integer numbers are the same.
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The following output shows that when the dividend value is a floating-point number then the division value generated by the `bc` command is correct but the `printf` command generated an error.
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Create a bash file named prn2.bash with the following script to know the use of the `printf` command for the correct fractional output when the dividend value is a floating-point number.
#!/bin/bash
# Take the dividend value from the user
read -p “Enter the dividend value: “ n1
# Take the divisor value from the user
read -p “Enter the divisor value: “ n2
# Find the division using `printf`, `echo` and `bc`
printf “%.2fn“ `echo $n1/$n2|bc -l`
Run the following command to execute the script.
Output:
The output shows that the `printf` with ‘`bc` command generates the correct output.
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Example-6: Using the awk Command for Arithmetic Operation
Using the `awk` command is another way to perform the arithmetic operation that can generate output properly for floating-point numbers. The arithmetic operations using the `awk` command without formatting and with formatting have shown in this example. Create a bash file named awk.bash with the following script to check the use of the `awk` command for arithmetic operation.
#!/bin/bash
# Initialize the dividend value
n1=90
# Initialize the divisor value
n2=43
# Print the output without formating
awk “BEGIN {print $n1/$n2}”
# Print the output with formatting
awk “BEGIN {printf “%.2fn“, $n1/$n2}”
Run the following command to execute the script.
Output:
The output shows that the `awk` command can generate appropriate fractional output.
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Example-7: Calculate the Percentage of a Value
Sometimes we need to calculate the percentage value of particular criteria. The percentage can be calculated in bash by using the `printf` command and `echo` command. Suppose, we need to find out the percentage of passed students on an exam based on the total number of students and total passed students. The solution to this problem has shown in this example. Create a bash file with the following script to calculate the percentage value of passed students using the `printf` command.
#!/bin/bash
# Take the total number of students from the user
read -p “Total number of students: “ total_std
# Take the total number of passed students from the user
read -p “Total number of passed students: “ passed_std
# Calculate the percentage of passed students
printf “The percentage of passed students: %.2f%%n“ “$((10**3 * 100 * $passed_std/$total_std))e-3″
Run the following command to execute the script.
Output:
The output shows the percentage of passing students based on the total number of students and passed students.
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Conclusion
The uses of different arithmetic operators in bash and the ways to perform the arithmetic operations using different commands have shown in this tutorial by using multiple examples to help the bash users.
