[Solved] Bash and Floating point arithmetic

Question

I didn't realize how troublesome floating point numbers can be until now.
What I want to do should be simple I dare say:
properRounding( ( currentTime - downloadTime ) / ( dueTime - downloadTime ) * 100 )
however best I've been able to achieve so far is this:
echo "($currentTime-$downloadTime)/($dueTime-$downloadTime)*100" | bc -l
Which prints the correct floating point value.
I've tried to put the result in a variable, but I must be doing it wrong as I get the most peculiar error. I can live without it, but it would make life easier.
As for the rounding, that is a must. I've read that if you remove the -l param from bc, then it will round, but in my case something goes wrong as I just get the value 0 in return and besides, concluded after a simple test, bc always rounds down as in integer division, which I can not use.
So of course I'll continue reading and hopefully someday arrive at a solution, but I would very much appreciate if someone could lend me a hand.
This after all is not just a learning experience, I'm trying to create something useful.
Best regards.
edit:
nb:
all variables are integers.
Last edited by zacariaz (2012-09-09 14:50:18)

Answer 1

Just for the fun of it, here's my progress thus far... Well, there really isn't much more to do. The rest is a conky thing.
#!/bin/bash
# Variables from unitinfo.txt - date as unix timestamps.
dueTime="$(date +%s -d "$(grep 'Due time: ' ~/unitinfo.txt | cut -c11-)")"
if [ "$1" = "end" ]
then echo $dueTime
fi
downloadTime="$(date +%s -d "$(grep 'Download time: ' ~/unitinfo.txt | cut -c16-)")"
if [ "$1" = "start" ]
then echo $downloadTime
fi
progress="$(grep 'Progress: ' ~/unitinfo.txt | cut -c11-12 | sed 's/ *$//')"
if [ "$1" = "prog1" ]
then echo $progress
fi
# The rest
#progress valued 0-1 for use with conky proress bars
progress2=$( echo 2k $progress 100 / f | dc )
if [ "$1" = "prog2" ]
then echo $progress2
fi
# Current time - unix timestamp.
currentTime="$(date +%s)"
# Remaining time - unix timestamp
remainingTime=$(( dueTime-$currentTime ))
if [ "$1" = "remain" ]
then echo $remainingTime
fi
# Elapsed time - unix timestamp
elapsedTime=$(( currentTime-downloadTime ))
if [ "$1" = "elap1" ]
then echo $elapsedTime
fi
# Total amount of time available - unix timestamp
totalTime=$(( dueTime-downloadTime ))
if [ "$1" = "total" ]
then echo $totalTime
fi
# How much time has elapsed in percent
progress3="$(echo 3k $elapsedTime $totalTime / 100 \* 0k 0.5 + 1 / f | dc)"
if [ "$1" = "elap2" ]
then echo $progress3
fi
# Like the above bur 0-1
progress4=$( echo 2k $progress3 100 / f | dc )
if [ "$1" = "elap3" ]
then echo $progress4
fi
# In percent, expected completion vs $dueTime - less than 100 is better.
expectedCompletion="$( echo 3k $elapsedTime 10000 \* $progress / $totalTime / 0k 0.5 + 1 / f | dc )"
if [ "$1" = "exp1" ]
then echo $expectedCompletion
fi
# Same as above, but unix timestamp
expectedCompletion2=$(( downloadTime+(expectedCompletion*totalTime/100) ))
if [ "$1" = "exp2" ]
then echo $expectedCompletion2
fi
#efficiency
if [ "$1" = "ef1" ]; then
if [ $progress -lt $progress3 ]
then echo "you're behind schedule."
elif [ $progress -eq $progress3 ]
then echo "You're right on schedule."
else
echo "You're ahead of schedule."
fi
fi
if [ "$1" = "ef2" ]; then
if [ $expectedCompletion -gt 100 ]
then echo "You're not going to make it!"
else
echo "You're going to make it!"
fi
fi