Bash – Subtract floating numbers in shell script

arithmeticbashkshlinuxshell-script

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 ")

Best Answer

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

Related Solutions

Bash – Limiting Precision of Floating Point Variables

A simple way is to use printf:

$ printf "%.3f\n" 0.005000000000
0.005

To remove the leading 0, just parse it out with sed:

$ printf "%.3f\n" 0.005000000000 | sed 's/^0//'
.005

Shell – String to integer in Shell

The regex below will extract the number of bytes, only the number:

contentlength=$(
  LC_ALL=C sed '
    /^[Cc]ontent-[Ll]ength:[[:blank:]]*0*\([0-9]\{1,\}\).*$/!d
    s//\1/; q' headers
)

After the above change, the contentlength variable will be only made of decimal digits (with leading 0s removes so the shell doesn't consider the number as octal), thus the 2 lines below will display the same result:

echo "$(($contentlength/9))"

echo "$((contentlength/9))"

Best Answer

Related Solutions

Bash – Limiting Precision of Floating Point Variables

Shell – String to integer in Shell

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