Floating Point Calculation¶
This is an example represent how to compute Floating point in bash.
Using in Script for Comparision¶
To use bc in our bash scripts we'll package it up into a couple of functions:
float_eval writes the result of the expression evaluation to standard out, float_cond assumes the expression is a conditional expression and sets the return/status code to zero if the expression is true and one if it's false.
Usage is quite simple:
float_eval '12.0 / 3.0'
if float_cond '10.0 > 9.0'; then
echo 'As expected, 10.0 is greater than 9.0'
fi
a=12.0
b=3.0
c=$(float_eval "$a / $b")
#!/bin/bash
#
# Floating point number functions.
#####################################################################
# Default scale used by float functions.
float_scale=2
#####################################################################
# Evaluate a floating point number expression.
function float_eval()
{
local stat=0
local result=0.0
if [[ $# -gt 0 ]]; then
result=$(echo "scale=$float_scale; $*" | bc -q 2>/dev/null)
stat=$?
if [[ $stat -eq 0 && -z "$result" ]]; then stat=1; fi
fi
echo $result
return $stat
}
#####################################################################
# Evaluate a floating point number conditional expression.
function float_cond()
{
local cond=0
if [[ $# -gt 0 ]]; then
cond=$(echo "$*" | bc -q 2>/dev/null)
if [[ -z "$cond" ]]; then cond=0; fi
if [[ "$cond" != 0 && "$cond" != 1 ]]; then cond=0; fi
fi
local stat=$((cond == 0))
return $stat
}
# Test code if invoked directly.
if [[ $(basename $0 .sh) == 'float' ]]; then
# Use command line arguments if there are any.
if [[ $# -gt 0 ]]; then
echo $(float_eval $*)
else
# Turn off pathname expansion so * doesn't get expanded
set -f
e="12.5 / 3.2"
echo $e is $(float_eval "$e")
e="100.4 / 4.2 + 3.2 * 6.5"
echo $e is $(float_eval "$e")
if float_cond '10.0 > 9.3'; then
echo "10.0 is greater than 9.3"
fi
if float_cond '10.0 < 9.3'; then
echo "Oops"
else
echo "10.0 is not less than 9.3"
fi
a=12.0
b=3.0
c=$(float_eval "$a / $b")
echo "$a / $b" is $c
set +f
fi
fi
# vim: tabstop=4: shiftwidth=4: noexpandtab:
# kate: tab-width 4; indent-width 4; replace-tabs false;
bc:
By default bc outputs its result with no digits to the right of the decimal point and without a decimal point. To change this you have to change one of bc's builtin variables: scale. This is where the "language" features of bc are relevant, in bc as in C statements are separated by semi-colons. We set bc's scale variable by preceding the expression that we pass to bc with scale=$float_scale;. This sets the scale in bc to the value of the bash global variable float_scale, which is by default set to two (near the top of the script).
The main gotcha here has to do with the fact that "", "<", and ">" have other meanings in bash. You can eliminate the problem of "<" and ">" by quoting your expressions, but this only works with "" if you use single quotes and that would mean you couldn't include bash variables in the expression. The other option is to bracket your code with "set -f" and "set +f" to turn off pathname/wildcard expansion.
If you save the script as float.sh and run it directly it will execute the test code at the bottom:
$ sh float.sh
12.5 / 3.2 is 3.90
100.4 / 4.2 + 3.2 * 6.5 is 44.70
10.0 is greater than 9.3
10.0 is not less than 9.3
12.0 / 3.0 is 4.00
Ref : Linux Journal
Doing Calculation¶
Details
If you are like me and you like to use the bash shell as much as possible, you have probably run into the situation where you wanted to have a calculator built into your bash shell. So with a 2 line script and an edit to your .bashrc file, your bash shell can become a useful basic calculator. No more firing up kcalc to do simple math. With the program bc and a very small bash script, you can now get those decimal places to show up.
The two line script.
Now save the script as bashcalc.shNow, you can do a couple of things at this point.
METHOD #1 If you're like me, you have a /home/crouse/Scripts directory (ok, so yours probably doesn't say crouse lol) and you put most of your scripts in there. The benefit of this is that it doesn't require any special privledges to accomplish.
Now that the script is in your script directory, you need an alias in the .bashrc file in order to make it work. Here is the alias in my .bashrc file for example:alias calc='sh /home/crouse/scripts/bashcalc.sh'
METHOD #2 Alternatively, you can put the script into /usr/bin and there is no need to edit the .bashrc file as /usr/bin is in your bash shell's path. You at least need the ability to sudo or install as root to accomplish this method.
Once all of this text editing, moving, and assorted stuff is done, you can use calc and do floating point math with your bash shell!Examples:
[crouse@localhost ~]$ calc 2.55*2.6666
6.7998
[crouse@localhost ~]$ calc 25.55/3.6666666
6.9681
[crouse@localhost ~]$ calc 25.2222+6.33333
31.55553
[crouse@localhost ~]$ calc 99-1.333333333
97.666666667
Here is an adaptation of the first script that allows you to keep inputing calculations (kind of like a calculator) without having to restart the script every time:
FILE DOWNLOAD: http://www.bashscripts.org/downloads/Scripts/crouse/calc.sh
You can use the function above and extend it to create a sort of bash adding machine. It's a calculator that constantly runs in a bash shell.
You can edit the script to suit your needs, but it basically allows you to key in your problems, gives the results and waits for another problem to be input.
The default scale for division is to go 4 decimal places, this can be adjusted in the script to whatever length you wish to use. This was because I sometimes needed to enter in alot of individual calculations and was tired of typing the word calc :)
This could be extended even further and store individual calculations if you wanted it to, but that's beyond the scope of this article at the moment.
#!/bin/bash
#######################################################
# Bash CALCulator 2
#######################################################
#
#
# FILE: bashcalc2.sh
# VERSION: 1.1
# DATE: 06-19-2006
#
# AUTHOR: Crouse - Please visit bashscripts.org and usalug.org
#
#
########################################################
header ()
{
clear; echo "Bash Calculator - Enter a calculation and hit enter";
echo "---------------------------------------------------";
}
calc ()
{
header
while true
do read -p "" bashcalc;
if [ "$bashcalc" = "quit" ]
then
exit
fi
if [ "$bashcalc" = "clear" ]
then
calc
fi
if [ "$bashcalc" = "help" ]
then
clear
echo "Options include:"
echo " help - This help file"
echo " clear - Clears the screen"
echo " quit - Quits the program"
echo " "
read -p "Hit any key to continue" temp;
calc
fi
echo "scale=4; ${bashcalc}" | bc ;
echo "---------------------";
done
}
# Program run starts here
calc
exit 0