bash script to find the difference between the 4th element of each line in 2 files

dontbugmeplz · 07-18-2008, 03:12 PM

Hi All,
I have 2 data files. I want a shell script to get the 4th element on each line of each file, and take the difference and store it in a variable. (1st line are junk description, it would be good if u could write code to ignore the 1st 2 line and start reading from the third line)

To read from one file is simple:

while read a

do

echo "$a" | 'awk [print $4]'

done <"filename"

sth like above.

Now, how do I read the other file simultaneously and pull out the 4th element and take the difference.

A quick solution will be very much appreciated.
Thanks much!

DM.

matthewg42 · 07-18-2008, 04:54 PM

Quickie in Perl:

Code:

#!/usr/bin/perl

use strict;
use warnings;

my $file1 = shift || die "please specify two files as arguments\n";
my $file2 = shift || die "please specify two files as arguments\n";

open(F1, "<$file1") || die "cannot open $file1 : $!\n";
open(F2, "<$file2") || die "cannot open $file2 : $!\n";

while(!eof(F1)&&!eof(F2)) {
        my $v1 = (split(/\s+/, <F1>))[3];
        my $v2 = (split(/\s+/, <F2>))[3];

        printf "%-4d - %-4d == %d\n",  $v2, $v1, ($v2 - $v1);
}
close(F1);
close(F2);

The program will terminate when the end of either file is detected. No checking is done to make sure the required values from the input files are actually numerical, so you'll get a warning or two if they are not.

dontbugmeplz · 07-19-2008, 05:41 PM

Thanks a lot matthewg42. I need a bash shell script. Appreciate ur efforts, though.

matthewg42 · 07-19-2008, 05:52 PM

how about this:

Code:

#!/bin/bash

have_data=1
line_number=0
while [ $have_data -eq 1 ]; do
        let line_number+=1
        read -u 2 d1_1 d1_2 d1_3 d1_4 d1_5
        read -u 3 d2_1 d2_2 d2_3 d2_4 d2_5
        if [ "$d1_4" = "" ] || [ "$d2_4" = "" ]; then
                echo "End of data at line $line_number"
                have_data=0
        else
                echo "at line $line_number : $d1_4 + $d2_4 == $(($d1_4 + $d2_4))"
        fi
done 2<one 3<two

dontbugmeplz · 07-19-2008, 06:48 PM

Thanks Matthew for the quick response. Will try it and let u know.

ghostdog74 · 07-19-2008, 09:10 PM

Code:

awk '{
 getline line <"file2"
 m=split(line,l," ")
 print "The difference is: " l[4]-$4
}' file

dontbugmeplz · 07-21-2008, 08:05 AM

Thanks ghostdog and matthew for ur help.