[SOLVED] arithmetic in bash

xeon123 · 04-22-2011, 11:07 AM

Hi,

I've a txt file that contains values in 2 columns:

Code:

#field1  field2
324        2343
232        13434
213        453
54         231

I would like to apply the equation 1/(1-(field1/field2)) in bash. How can I do that?

kurumi · 04-22-2011, 11:11 AM

If this is not homework, try a different tool than bash.

Code:

$ ruby -ane 'puts $F[0].to_f/$F[1].to_f' file

you can use also awk,Perl, Python etc that can support decimals

xeon123 · 04-22-2011, 11:15 AM

This is not homework. I prefer in bash.

Here's the command that I use and it won't work.
expr 1/(`cat tmp.txt | awk '{ print $1/$2 }'`)

grail · 04-22-2011, 11:59 AM

Well you just said in bash but are using awk?? As kurumi said, awk can do it on its own.

Code:

awk 'NR>1{print 1/(1 - $1/$2)}' file

Bash does not do fractions so you will at least need to use bc.

arizonagroovejet · 04-22-2011, 01:12 PM

Code:

answer=$((1/(1-(field1/field2))))

answer will be rounded to the nearest integer.

http://tldp.org/LDP/abs/html/arithexp.html

grail · 04-23-2011, 01:18 AM

@arizonagroovejet - I do not see how your solution is of any use? All answers will be 1 as the fraction portion will always equate to 0 so it is just 1/1.

arizonagroovejet · 04-23-2011, 04:12 AM

Quote:

Originally Posted by grail

All answers will be 1 as the fraction portion will always equate to 0 so it is just 1/1.

Yeah... good point. What I posted works and meets the OP's original stated requirement/desire of doing it in bash but you're right, it isn't of any practical use in this case given the numbers being used.

xeon123 · 04-23-2011, 09:07 AM

Hi grail,

can you explain me what are you saying please? How the fraction part is always 0?

grail · 04-23-2011, 09:24 AM

All of the numbers in your file when column 1 is divided by column 2 will end up as a fraction less than 1. Bash does not actually round numbers to the nearest integer,
it actually truncates the decimal portion so all of your values will equate to 0.

Hope that helps.

xeon123 · 04-23-2011, 09:39 AM

Thanks, now I get it.