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Top Forums Shell Programming and Scripting Simple awk command to compare two files and print first difference Post 302996490 by LMHmedchem on Wednesday 26th of April 2017 05:34:54 PM
Old 04-26-2017
Simple awk command to compare two files and print first difference

Hello,

I have two text files, each with a single column,
file 1:
Code:
124152970
123899868
123476854
54258288
123117283

file 2:
Code:
124152970
123899868
54258288
123117283
122108330

I am trying to identify the value in red above which is the first value that doesn't match the second file. I need to print that value and exit.

At first I tried diff,

diff file1 file2 | head -n 2

This gives what I want, but there are multiple lines of output and so it was more steps to get the value into a bash variable, which is what I need.

I then tried awk,

awk ' NR==FNR { a[NR]=$0; next } !($0 in a){ print $1; exit } ' file2 file1

Note that the order of input files is reversed because I want the first line of file1 that does not match file2. This just prints the first line of file1. Even if it did work, I think that this just tells me that the value is, or is not, in the file, not if the lines match.

Code:
awk ' NR==FNR { a[NR]=$0; next } $0 != a[FNR] { print a[FNR]; exit } file1 file2

I am sure I could do a loop with read, but that would be slow.

This seems like a very simple task. Are there any suggestions?

LMHmedchem

Last edited by Scrutinizer; 04-26-2017 at 07:17 PM..
 

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COMBINE(1)																COMBINE(1)

NAME
combine - combine sets of lines from two files using boolean operations SYNOPSIS
combine file1 and file2 combine file1 not file2 combine file1 or file2 combine file1 xor file2 _ file1 and file2 _ _ file1 not file2 _ _ file1 or file2 _ _ file1 xor file2 _ DESCRIPTION
combine combines the lines in two files. Depending on the boolean operation specified, the contents will be combined in different ways: and Outputs lines that are in file1 if they are also present in file2. not Outputs lines that are in file1 but not in file2. or Outputs lines that are in file1 or file2. xor Outputs lines that are in either file1 or file2, but not in both files. "-" can be specified for either file to read stdin for that file. The input files need not be sorted, and the lines are output in the order they occur in file1 (followed by the order they occur in file2 for the two "or" operations). Bear in mind that this means that the operations are not commutative; "a and b" will not necessarily be the same as "b and a". To obtain commutative behavior sort and uniq the result. Note that this program can be installed as "_" to allow for the syntactic sugar shown in the latter half of the synopsis (similar to the test/[ command). It is not currently installed as "_" by default, but you can alias it to that if you like. SEE ALSO
join(1) AUTHOR
Copyright 2006 by Joey Hess <joey@kitenet.net> Licensed under the GNU GPL. moreutils 2012-04-09 COMBINE(1)
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