Math with the shell

Arithmetic operations are an essential requirement for every programming language. In this recipe, we will explore various methods for performing arithmetic operations in shell.

Getting ready

The Bash shell environment can perform basic arithmetic operations using the commands let, (( )), and []. The two utilities expr and bc are also very helpful in performing advanced operations.

How to do it...

1. A numeric value can be assigned as a regular variable assignment, which is stored as a string. However, we use methods to manipulate as numbers:

   #!/bin/bash
   no1=4;
   no2=5;
   

2. The let command can be used to perform basic operations directly. While using let, we use variable names without the $ prefix, for example:

   let result=no1+no2
   echo $result
   

   • Increment operation:

     	$ let no1++
     

   • Decrement operation:

     	$ let no1--
     

   • Shorthands:

     	let no+=6
     	let no-=6
     

   These are equal to let no=no+6 and let no=no-6 respectively.

   • Alternate methods:

     The [] operator can be used in the same way as the let command as follows:

     	result=$[ no1 + no2 ]
     

     Using the $ prefix inside [] operators are legal, for example:

     	result=$[ $no1 + 5 ]
     

     (( )) can also be used. $ prefixed with a variable name is used when (( )) operator is used, as follows:

     	result=$(( no1 + 50 ))
     

     expr can also be used for basic operations:

     	result=`expr 3 + 4`
     	result=$(expr $no1 + 5)
     

     All of the preceding methods do not support floating point numbers, and operate on integers only.

3. bc , the precision calculator is an advanced utility for mathematical operations. It has a wide range of options. We can perform floating point operations and use advanced functions as follows:

   echo "4 * 0.56" | bc
   2.24
   
   no=54; 
   result=`echo "$no * 1.5" | bc`
   echo $result
   81.0
   

   Additional parameters can be passed to bc with prefixes to the operation with semicolon as delimiters through stdin.

   • Decimal places scale with bc: In the following example the scale=2 parameter sets the number of decimal places to 2. Hence, the output of bc will contain a number with two decimal places:

     	echo "scale=2;3/8" | bc
     	0.37
     

   • Base conversion with bc: We can convert from one base number system to another one. Let us convert from decimal to binary, and binary to octal:

     	#!/bin/bash
     	Desc: Number conversion
     	
     	no=100
     	echo "obase=2;$no" | bc
     	1100100
     	no=1100100
     	echo "obase=10;ibase=2;$no" | bc
     	100
     

   • Calculating squares and square roots can be done as follows:

     	echo "sqrt(100)" | bc #Square root
     	echo "10^10" | bc #Square