Absolute value of a number

Question

I want to take the absolute of a number by the following code in bash:

#!/bin/bash
echo \"Enter the first file name: \"
read first

echo \"Enter the second f         


        

Answer 1

A workaround: try to eliminate the minus sign.

1. with sed

x=-12
x=$( sed "s/-//" <<< $x )
echo $x

12

2. Checking the first character with parameter expansion

x=-12
[[ ${x:0:1} = '-' ]] && x=${x:1} || :
echo $x

12

This syntax is a ternary opeartor. The colon ':' is the do-nothing instruction.

3. or substitute the '-' sign with nothing (again parameter expansion)

x=-12
echo ${x/-/}

12

Personally, scripting bash appears easier to me when I think string-first.