`0a1` in the output of diff file1 and file2

Upon comparing two files and get the result:

 diff alpha_rsa.pub authorized_keys
0a1
> ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDBj3chjFnpxtHfeSUJVFv6fIN4CPZmIlBzuhMOOJNpovQqBc5JAhrz9uRiQIMHPD2vW+QJYiK08+6pCHthQSFrSLokLXTJfqEvb+frNEc6HvPPglGY3//97lbxR+CQYTjB/XgvnrP8sWKRt4VLfCwtCE6TqdVMx1y9SUmf7FghbHWhUioezdJaFJmfR+WVtELrUSwsc5eXcF+RS74eXEys2/v7LJF2JNYZxu0+Et7EwgxliA/5bOo6jTKBSZttBZPlsn2N7/GXnDilfAy06Iuc8MzMFCrAajQx8Nd4DG5Y33YyNVfU7eat9btUqNhpKGC+b5FGY4mkIPA2tammnjkx

I am aware that the output is the difference.

What does 0a1 mean? which cannot be found from the manual.

1 Answer

After line 0 (i.e., beginning) of the first file, a dd the following line (1 st line from the second file).

Note: Since these are ed commands, you should look at the ed man page:

Also, google diff command tutorial for more examples.