Table of Contents

OPERATORS: Bash Arithmetic Operators

 

Arithmetic Operators

Arithmetic Operators
 Operator Symbol Meaning
+  Addition
– Subtraction
* Multiplication
/ Division
% Mod Operator
** Exponent Operator

 

 

Arithmetic evaluation using let command

Arithmetic evaluation using let command
The let statement can be used to do mathematical functions:
 let X=10+2*7

 echo $X

 24

 let Y=X+2*4

 echo $Y

  32
An arithmetic expression can be evaluated  by $[expression] or $((expression))
  echo “$((123+20))”

  143

  VALORE=$[123+20]

  echo “$[123*$VALORE]”

  17589

 

 

Example of arithmetic evaluation – 1

Another example of arithmetic evaluation
 #!/bin/bash

x=10

 y=5

let sum=$x+$y

diff=$(($x – $y))

let mul=$x*$y

let div=$x/$y

let mod=$x%$y

let exp=$x**$y

echo “$x + $y = $sum”

echo “$x – $y = $diff”

echo “$x * $y = $mul”

echo “$x / $y = $div”

echo “$x ** $y = $exp“

exit

 

 

Another example of arithmetic evaluation

 

 

Example of arithmetic evaluation – 2

Another example of arithmetic evaluation
 #!/bin/bash

echo -n “Enter the first number: ”; read x

echo -n “Enter the second number: ”; read y

add=$(($x + $y))

sub=$(($x – $y))

mul=$(($x * $y))

div=$(($x / $y))

mod=$(($x % $y))

# print out the answers:

echo “Sum: $add”

echo “Difference: $sub”

echo “Product: $mul”

echo “Quotient: $div”

echo “Remainder: $mod”

 

 

example of arithmetic evaluation
example of arithmetic evaluation

 

 

Declaring variable

Declaring variable
We can declare variables in bash, providing some form of typing.

For example, we can declare a constant variable (cannot be changed after definition) or declare an integer or even a variable whose scope will extend beyond the script.
Example
  x=1

 declare -r x

 x=2

 –bash: x: readonly variable

echo $x

1

 y=2

 declare –i y

 echo $y

2

 

 

Declaring variable
Declaring variable

 

 

Passing arguments with a script

Passing arguments with a script
  • We can also pass arguments while executing the script.
  •  There arguments are mapped to built-in shell parameters.
  •  We can use these to manipulate these built-in shell parameters in our script.
Example
While executing script pass the argument

./script   Epictetus Socrates Marcus

$0  is assigned  ./script

$1  is assigned    Epictetus

$2  is  assigned   Socrates

$3  is assigned    Marcus

 

 

Built-in shell parameter with special meanings

Several built-in shell parameter that has special meanings:
Variable Name Meaning
$* $* is the list of arguments passed to the current process.

All arguments as a single word.
$@ $@ is the list of arguments passed to the current process. Excluding script name ie., parameter $0
$# $# is the number of arguments in $*.
$0, $1, $2, … Arguments
$$  $$ variable will hold your current process ID (of shell)

Actually $$ is a shell parameter and not a variable, you cannot assign a value to it.
$PPID  (Not a shell parameter ..) $PPID contains the parent PID.
$? $? is the return value of the last executed command.
Note :  $* $$ , $# , $? , $0, $1, $2… are shell parameter and not a variable, you cannot assign a  value to it.

 

 

Shell Parameter $* $@ $# $0, $1, $2, ... $$ $PPID $?
Shell Parameter $* $@ $# $0, $1, $2, …
$$ $PPID $?