Linux – Listing lines from just one file in DIFF

diff()linux

I would like to get (GNU)DIFF to printout only lines that are different in one file.
So given

    ==> diffa.txt <==
    line1
    line2 - in a only
    line3
    line4 changed
    line5

    ==> diffb.txt <==
    line1
    line3
    line4 changed in b
    line5
    line6 in b only

i would like diff --someoption diffa.txt diffb.txt to produce

    line2 - in a only

    line4 changed

The following looks as though it should be helpful but it is a bit cryptic :

   --GTYPE-group-format=GFMT
          Similar, but format GTYPE input groups with GFMT.

   --line-format=LFMT
          Similar, but format all input lines with LFMT.

   --LTYPE-line-format=LFMT
          Similar, but format LTYPE input lines with LFMT.

   LTYPE is `old', `new', or `unchanged'.
          GTYPE is LTYPE or `changed'.

          GFMT may contain:

   %<     lines from FILE1

   %>     lines from FILE2

Best Answer

Not sure diff alone can do it but you can always use the power of other GNU utilities to help you.

diff -u diffa.txt diffb.txt | grep '^-[^-]' | sed 's/^-//'

It does the diff, then selects only the lines that begins with '-' - those are changed and have values from diffa.txt file, then sed just remove those '-' signs.

Edit: After few experiments with diff, looks like the below command produces what you want:

diff --changed-group-format='%<' --unchanged-group-format='' diffa.txt diffb.txt
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