Comparison of floating point numbers in bash


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# 1  
Comparison of floating point numbers in bash

I have the following code snippet in bash
Code:
        if [[ $diff < $minm ]]; then
		minm=`echo "$diff" | bc`
	fi

It works well for most of the cases. However lets say diff is -0.17 and minm is -0.0017. In such a case the comparison seems to fail. Is the correct way to compare a mixture of positive and negative numbers in bash.
Appreciate your help.
# 2  
bash doesn't handle floating point numbers, only integers. On top, (man bash)
Quote:
When used with [[, the < and > operators sort lexicographically using the current locale.
You might want to consider the -gt operator.
This User Gave Thanks to RudiC For This Post:
# 3  
Use bc

Code:
if (( $(echo "$num1 > $num2" |bc -l) )); then
  echo "ok"
fi


bc does floating point comparisons, in bash you have to surround it with (( )) to get a boolean (true/false) result.
These 3 Users Gave Thanks to jim mcnamara For This Post:
# 4  
You could also use awk:
Code:
if awk "BEGIN{exit !($diff < $minm)}"; then

This User Gave Thanks to Chubler_XL For This Post:
# 5  
Hi Chubler_XL...
Modified to suit OSX 10.14.6, default bash terminal:
Code:
Last login: Tue Oct 22 22:05:17 on ttys000
AMIGA:amiga~> bash --version
GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin18)
Copyright (C) 2007 Free Software Foundation, Inc.
AMIGA:amiga~> num1=1.2345
AMIGA:amiga~> num2=0.09876
AMIGA:amiga~> if awk 'BEGIN{exit !('"$num1"' > '"$num2"')}'; then echo "OK."; fi
OK.
AMIGA:amiga~> _

# 6  
As Python doesn't lend itself to one liners at all here is a Python version for Python Versions 2.7.x to 3.8.0.
Code:
if python -c 'if '"$num1"' > '"$num2"':exit(1)'; then :; else echo "OK."; fi

OSX 10.14.6, default bash terminal:
Code:
Last login: Tue Oct 22 23:15:20 on ttys000
AMIGA:amiga~> num1=1.2345
AMIGA:amiga~> num2=0.9876
AMIGA:amiga~> if python3.8 -c 'if '"$num1"' < '"$num2"':exit(1)'; then :; else echo "OK."; fi
AMIGA:amiga~> if python3.8 -c 'if '"$num1"' > '"$num2"':exit(1)'; then :; else echo "OK."; fi
OK.
AMIGA:amiga~> _

# 7  
Quote:
Originally Posted by wisecracker
Hi Chubler_XL...
Modified to suit OSX 10.14.6, default bash terminal:
Code:
Last login: Tue Oct 22 22:05:17 on ttys000
AMIGA:amiga~> bash --version
GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin18)
Copyright (C) 2007 Free Software Foundation, Inc.
AMIGA:amiga~> num1=1.2345
AMIGA:amiga~> num2=0.09876
AMIGA:amiga~> if awk 'BEGIN{exit !('"$num1"' > '"$num2"')}'; then echo "OK."; fi
OK.
AMIGA:amiga~> _


Thanks wisecracker, I'm curious does OSX 10.14.6, default bash terminal have an issue with
Code:
awk "BEGIN{exit !($num1 > $num2)}"; then echo "OK."; fi

The only thing I can think could be causing it trouble is the bracketed expressions within double quotes.
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