How to get the difference (only additions) between two files in linux

All of the below is copied directly from @TomOnTime's serverfault answer here:

Show lines that only exist in file a: (i.e. what was deleted from a)

comm -23 a b

Show lines that only exist in file b: (i.e. what was added to b)

comm -13 a b

Show lines that only exist in one file or the other: (but not both)

comm -3 a b | sed 's/^\t//'

(Warning: If file a has lines that start with TAB, it (the first TAB) will be removed from the output.)

NOTE: Both files need to be sorted for "comm" to work properly. If they aren't already sorted, you should sort them:

sort <a >a.sortedsort <b >b.sortedcomm -12 a.sorted b.sorted

If the files are extremely long, this may be quite a burden as it requires an extra copy and therefore twice as much disk space.

Edit: note that the command can be written more concisely using process substitution (thanks to @phk for the comment):

comm -12 <(sort < a) <(sort < b)

diff and then grep for the edit type you want.

diff -u A1 A2 | grep -E "^\+"

You can try this

diff --changed-group-format='%>' --unchanged-group-format='' A1 A2

The options are documented in man diff:

       --GTYPE-group-format=GFMT              format GTYPE input groups with GFMT

and:

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

and:

              GFMT (only) may contain:       %<     lines from FILE1       %>     lines from FILE2       [...]