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Accepted
Max
Asked: 2011-11-30 03:59:36 +0800 CST

Only show what's new in a file

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I want to find out what was added to a log file between 2 tasks. Right now the way I do it is:

content of test.log initially

aaa
bbb

saving content of the log

$ cp test.log test.log.before

doing something

content of test.log after doing something

aaa
bbb
ccc

saving content of the log

$ cp test.log test.log.after

showing the difference

$ diff test.log.before test.log.after
2a3
> ccc

What I don't like with this method is that I get some noise from diff (2a3 and >) whereas I just want ccc.

Q: Is there a way I can just get the difference between the 2 log files (i.e. what is new in test.log.after, ccc)?

I had a look at diff's man page but I don't see anything obvious there.

ubuntu diff

2 Answers

  1. If you always do a before and after such that the end of the after file will contain the new content then you could use comm. 

    $ cat before 
aaa
bbb

$ cat after
aaa
bbb
ccc

$ comm -3  after before
ccc
    • 4
  2. Best Answer

    If you want to get the additions only you can filter the output such as:

    $ diff test.log.before test.log.after | grep "^>" | cut -c 3-

    However, you will lose the deletions if any.

    • 3