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

I know this thread is WAY old at this point, but I wanted to share a function I wrote that could help with this:

abs() { 
    [[ $[ $@ ] -lt 0 ]] && echo "$[ ($@) * -1 ]" || echo "$[ $@ ]"
}

This will take any mathematical/numeric expression as an argument and return the absolute value. For instance: abs -4 => 4 or abs 5-8 => 3

Answer 2

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.

Answer 3

You might just take ${var#-}.

${var#Pattern} Remove from $var the shortest part of $Pattern that matches the front end of $var. tdlp

---

Example:

s2=5; s1=4
s3=$((s1-s2))

echo $s3
-1

echo ${s3#-}
1

Answer 4

$ s2=5 s1=4
$ echo $s2 $s1
5 4
$ res= expr $s2 - $s1
1
$ echo $res

What's actually happening on the fourth line is that res is being set to nothing and exported for the expr command. Thus, when you run [ "$res" -lt 0 ] res is expanding to nothing and you see the error.

You could just use an arithmetic expression:

$ (( res=s2-s1 ))
$ echo $res
1

Arithmetic context guarantees the result will be an integer, so even if all your terms are undefined to begin with, you will get an integer result (namely zero).

$ (( res = whoknows - whocares )); echo $res
0

Alternatively, you can tell the shell that res is an integer by declaring it as such:

$ declare -i res
$ res=s2-s1

The interesting thing here is that the right hand side of an assignment is treated in arithmetic context, so you don't need the $ for the expansions.