Re: Diff: obtain only the different lines of the newest file

[Bob Proulx]

Kimahri Ronso wrote:
> My question is about the diff command.
> 
> I have 2 files containing almost the same information with around 70.000
> records.
> 
> What I would like to know is if there is a possibility to obtain only the
> different lines from the second file without anything else.

Instead of using 'diff' you might find 'comm' more the right tool
there.

       Compare sorted files FILE1 and FILE2 line by line.

       With  no  options,  produce  three-column  output.  Column one contains
       lines unique to FILE1, column two contains lines unique to  FILE2,  and
       column three contains lines common to both files.

       -1     suppress lines unique to FILE1

       -2     suppress lines unique to FILE2

       -3     suppress lines that appear in both files

Here is an example.  Given:

  $ cat /tmp/a
  one
  two
  three

  $ cat /tmp/b
  one
  two
  three
  four
  five
  six

Then:

  $ comm -13 /tmp/a /tmp/b
  four
  five
  six

> I just need to know the content of the changed lines in the newest file.

For that you would need to determine the newest file first and then
handle it appropriately.  Something like this, untested:

  if [ $(stat --format %Y /tmp/a) -lt $(stat --format %Y /tmp/b) ]; then
    comm -13 /tmp/a /tmp/b
  else
    comm -13 /tmp/b /tmp/a
  fi

The stat with %Y emits the modification time as an integer number of
seconds and that is compared to determine the newest file.

Bob