Bash – How to add a number as a command line argument

bash

I'm trying to add 1 number from the command line, and one number as like a default.
For example:
When user types in the number 50 the script will add 10 ( as the default number). 

./script 50
The sum of 50+ 10 is 60.

This is what I have so far. 

echo -n "Please enter a number: " 
read number 
default = 10
sum = $((default + number)) // this line does not seem to work
echo "The sum of $number and 10 is $sum."

Do I have the syntax wrong? I'm not sure if I'm on the right track. Am I adding the numbers wrong? Should I use awk instead? 

let sum = $default + $number

Best Answer

Spaces are causing the errors.

If you want user to input the number when he is prompted as "Please enter a number:", you can use your script with some corrections as:

#!/bin/bash
echo -n "Please enter a number: " 
read number 
default=10
sum=`echo "$number + $default" | bc`
echo "The sum of $number and 10 is $sum."

Check:

./temp.sh
Please enter a number: 50
The sum of 50 and 10 is 60.

If you want the user to input the number as an argument to the script, you can use the script below:

#!/bin/bash
number="$1"
default=10
sum=`echo "$number + $default" | bc`
echo "The sum of $number and 10 is $sum."

Check:

./temp.sh 50
The sum of 50 and 10 is 60.
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