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Old 04-22-2011, 11:07 AM   #1
xeon123
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arithmetic in bash


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?

Last edited by xeon123; 04-22-2011 at 11:11 AM.
 
Old 04-22-2011, 11:11 AM   #2
kurumi
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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
 
Old 04-22-2011, 11:15 AM   #3
xeon123
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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 }'`)
 
Old 04-22-2011, 11:59 AM   #4
grail
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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.
 
Old 04-22-2011, 01:12 PM   #5
arizonagroovejet
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Code:
answer=$((1/(1-(field1/field2))))
answer will be rounded to the nearest integer.

http://tldp.org/LDP/abs/html/arithexp.html
 
Old 04-23-2011, 01:18 AM   #6
grail
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@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.
 
Old 04-23-2011, 04:12 AM   #7
arizonagroovejet
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Quote:
Originally Posted by grail View Post
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.
 
Old 04-23-2011, 09:07 AM   #8
xeon123
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Hi grail,

can you explain me what are you saying please? How the fraction part is always 0?
 
Old 04-23-2011, 09:24 AM   #9
grail
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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.
 
Old 04-23-2011, 09:39 AM   #10
xeon123
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Thanks, now I get it.
 
  


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