Comparing two files and applying the differences

Question

on a Linux based system, I can easily compare two files, e.g.:

diff file1.txt file2.txt

...and see the difference between them.

What if I want to take all lines that are unique to file2.txt and apply them to file1.txt so that file1.txt will now contain everything it had + lines from file2.txt that it didn't have before? Is there an easy way to do it?

Answer 1

Using patch

1. You can use diff's output to create a patch file.

   diff original_file file_with_new_lines > patch_file
   

2. You can edit patch_file to keep only the additions, since you only want the new lines.

3. Then you can use the patch command to apply this patch file:

   patch original_file patch_file