Diff generated patch

Baby diff could return commands for "ed", the editor:
diff -e <oldfile> <newfile>
In his youth, he learnt to show context around differences
            to be more pleasant for men:
diff -c <oldfile> <newfile>
Once grown up, he learnt to be terse
            to be more pleasant for machines and networks:
diff -u <oldfile> <newfile>

The "patch" command, initially written by Larry Wall, uses
           diff's output to change <oldfile> into <newfile>
It's used to "patch" a wrong file into a correct one
Patch files are just diff's output saved to file