german@Debian:~$ cat <<EOF>holamundo
> hola
> EOF
german@Debian:~$ cat <<EOF>holamundo-0.1
> hola Mundo!
> EOF
german@Debian:~$ cat holamundo
hola
german@Debian:~$ cat holamundo-0.1
hola Mundo!
german@Debian:~$ diff holamundo-0.1 holamundo > holamundo.patch
german@Debian:~$ patch holamundo < holamundo.patch
patching file holamundo
Reversed (or previously applied) patch detected!  Assume -R? [n] y
german@Debian:~$ cat holamundo
hola Mundo!
german@Debian:~$