[SOLVED] bc in bash

ghantauke · 11-16-2010, 07:00 AM

echo 1/2 | bc -l = .50000000000000000000

Its a huge waste of space. Is there anyway I can change that to float i.e output = .500000

GrapefruiTgirl · 11-16-2010, 07:01 AM

Code:

sasha@reactor: echo "scale=6; 1/2" | bc -l
.500000
sasha@reactor:

ghantauke · 11-16-2010, 07:24 AM

Quote:

Originally Posted by GrapefruiTgirl

Code:

sasha@reactor: echo "scale=6; 1/2" | bc -l
.500000
sasha@reactor:

Is there anyway I could actually make bc calculate in float rather than skim the output by echo? The main reason I want to calculate in float is because bc is taking too long to calculate on the large amount of data that I have and it might take shorter time calculating if i calculate in float. Anyway thanks for your solution I learned something new

.

onebuck · 11-16-2010, 07:50 AM

Hi,

Links 4,5 & 6 below will provide some useful insight and understanding.

Just a few links to aid you to gaining some understanding;
  1 Linux Documentation Project 
2 Rute Tutorial & Exposition 
3 Linux Command Guide  
4 Bash Beginners Guide 
5 Bash Reference Manual 
6 Advanced Bash-Scripting Guide 
7 Linux Newbie Admin Guide 
8 LinuxSelfHelp 
9 Getting Started with Linux

The above links and others can be found at 'Slackware-Links'. More than just Slackware® links!

GrapefruiTgirl · 11-16-2010, 08:03 AM

Hi,

I'm not 100% sure I follow your last post.

We aren't using echo to "skim the output" here - we're giving `bc` an expression to evaluate, and telling it at what scale to do the evaluation.

About "float" or not.. Perhaps consulting the `bc` man page, near the beginning, in the section titled "NUMBERS", would answer your question about floats? I can't provide anything further than what it says there. But I believe using 'scale' is the way to achieve what you want as far as output. Does it make internal calculations any faster? I don't know, but I don't think so. A snippet from my bc (version 1.06.95) man page:

Code:

All numbers are represented internally in decimal and all computation is done in decimal.
This version truncates results from divide and multiply operations.

It is the second line which makes me suspect that 'scale' does not make calculations any faster, because to me, this line says bc is merely truncating the results of computations resulting in more places after the decimal than we want. Heh, 'scale' might even make it take longer

Sorry if I haven't quite answered your question; maybe someone else will have more to add.

Good luck!

w1k0 · 11-16-2010, 08:16 AM

Instead of bc you could use Perl to perform calculations:

Code:

alias c='perl -e '\''$_="@ARGV"; print eval $_, "\n"'\'''

Put the above alias into your ~/.bashrc to perform calculations in the command line or put it into the script to use it in the script.

In the thread Using Perl to perform calculations in Bash you’ll find the script explaining the possibilities of that alias.

ghantauke · 11-16-2010, 08:53 AM

Quote:

Originally Posted by GrapefruiTgirl

Hi,

I'm not 100% sure I follow your last post.

We aren't using echo to "skim the output" here - we're giving `bc` an expression to evaluate, and telling it at what scale to do the evaluation.

About "float" or not.. Perhaps consulting the `bc` man page, near the beginning, in the section titled "NUMBERS", would answer your question about floats? I can't provide anything further than what it says there. But I believe using 'scale' is the way to achieve what you want as far as output. Does it make internal calculations any faster? I don't know, but I don't think so. A snippet from my bc (version 1.06.95) man page:

Code:

All numbers are represented internally in decimal and all computation is done in decimal.
This version truncates results from divide and multiply operations.

It is the second line which makes me suspect that 'scale' does not make calculations any faster, because to me, this line says bc is merely truncating the results of computations resulting in more places after the decimal than we want. Heh, 'scale' might even make it take longer

Sorry if I haven't quite answered your question; maybe someone else will have more to add.

Good luck!

After doing all the research and finding facts about bc for 1 whole hour you state the exact facts that I found out

I shoulda checked your post beforehand. Might have saved me a lot of time. Thank you sooooo much for all your help.