Subtract floating numbers in shell script

Question

I'm trying to do some calculation in shell script with CPU usage. Which return floating point number. But when I subtract this number I'm getting error. See the following code and error.

Code

#!/bin/sh

CPU_IDLE=98.67
echo $CPU_IDLE
CPU_USAGE=$(( 100 - $CPU_IDLE ))
echo $CPU_USAGE

Error

./poc.sh: line 14: 100 - 98.67 : syntax error: invalid arithmetic operator (error token is ".67 ")

see How to do integer & float calculations, in bash or other languages/frameworks? — Evgeny, Aug 19 '15 at 15:03

jimmij · Accepted Answer · 2015-08-19T15:17:29.290

7

Neither bash nor ksh can perform floating point arithmetic (ksh93 supports that if I remember correctly). I recommend to switch to zsh or run external tool like bc:

$ CPU_IDLE=98.67
$ echo "$CPU_IDLE"
$ CPU_USAGE=$( bc <<< "100 - $CPU_IDLE" )
$ echo "$CPU_USAGE"
1.33

edited Aug 19 '15 at 15:17

answered Aug 19 '15 at 14:58

jimmij

47,140

score 1 · Answer 2 · answered Aug 20 '15 at 11:02

1

Even though you used the ksh tag in your question, the script starts with the #!/bin/sh hashbang, which will rarely give you a korn shell.

The rest of the code works fine with ksh (AT&T ksh93) on ubuntu 14.04:

$ ksh poc.sh
98.67
1.33

$ ls -lL /bin/ksh*
-rwxr-xr-x 1 root root 1509040 Jan  9  2013 /bin/ksh
-rwxr-xr-x 1 root root 1509040 Jan  9  2013 /bin/ksh93

answered Aug 20 '15 at 11:02

Henk Langeveld

772

1

It will only work in locales where the decimal separator is the dot (.). – Stéphane Chazelas Nov 30 '15 at 18:26
@StéphaneChazelas True. I guessed that a multi-locale solution was out-of-scope for this question. – Henk Langeveld Dec 01 '15 at 09:58
1

Still worth pointing out as it will affect most people in the non-english-speaking world. – Stéphane Chazelas Dec 01 '15 at 10:01

Subtract floating numbers in shell script

2 Answers2