Using grep to compare files and extract the difference to another output file

spartan22 · #1 (**permalink**) 02-20-2009

I have two files with dumps of DNS zones. One old and one new. I need to take the new file to find out what was added to the zone's since the old file was given to me. and output that data into another file so we can import it to our DNS server.

I'm extremely new at Unix and am not sure how to go about doing this...

I attemped to use grep -n -f olddump newdump > output.txt but it's only outputting like two domain names when i know there are hundreds of differences.

Ikon · #2 (**permalink**) 02-20-2009

Check out the diff command.

Code:

man diff

sunadmn · #3 (**permalink**) 02-20-2009

sdiff will do a side by side compare also if that makes things easier for you.

spartan22 · #4 (**permalink**) 02-20-2009

Ok, i gave it a shot with Sdiff. Now is there a way to have Sdiff only display what data actually changed in the output file?

sunadmn · #5 (**permalink**) 02-20-2009

so what I do is just run it through a grep like this:

sdiff orig_file new_file |grep ">"

That should show you everything that is in the new file and not in the original. You may need to just run the sdiff without the grep to see what I am talking about and you will see how it works.

-Stephen

treesloth · #6 (**permalink**) 02-20-2009

I did something along these lines not so long ago. From the comm man page:

Quote:

The comm utility reads file1 and file2, which should be sorted lexically,
and produces three text columns as output: lines only in file1; lines
only in file2; and lines in both files.

The following options are available:
-1 Suppress printing of column 1.
-2 Suppress printing of column 2.
-3 Suppress printing of column 3.

It sounds like column 2 is what you're interested in. So, first I sorted my lists:

Code:

sort previouslist > previouslist.sorted
sort newlist > newlist.sorted

Then:

Code:

comm -1 -3 previouslist.sorted newlist.sorted > file.containing.just.new.zones

It seems like comm is not a commonly-used command, so I don't know if there's a lot of variation from one UNIXy system to another. Check your man page.

spartan22 · #7 (**permalink**) 02-23-2009

Below is the script i'm using. I chose grep because it's dumping the contents of all the files in the directory into one file while putting the name of the original file next to each entry.

Everything works great until I get to the point of comparing the files and outputting the difference. It seems like it's doing it line for line... for example

www macklaw.com 1.x.x.x ftp macklaw.com 1.x.x.x
ftp macklaw.com 1.x.x.x www macklaw.com 1.x.x.x

If the above data is the way it is output it shows them as being different data, i guess because they aren't on the same line. A few of the lines got swapped around when the new dump was sent out and this is prevalent throughout the file. Is there any clean way to get an exact difference either from two different files, or two directories with a whole listing of other files into one sheet that only list the difference between the two?

Quote:

#
cd new
grep -v -e 'rr.com' -e 'comcastmailservice.com' *.db > ../newzones.txt
cd ..
cd old
grep -v -e 'rr.com' -e 'comcastmailservice.com' *.db > ../oldzones.txt
cd ..
sort newzones.txt > newzonessorted.txt | sort oldzones.txt > oldzonessorted.txt | sdiff oldzonessorted.txt newzonessorted.txt > diff.txt
#

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