I am working in a situation where I have an automatable task that
includes patching a bunch of files. However, I do not know apriori
whether or not a particular patch has already been applied.
If I use the patch option, "--batch" it assumes (incorrectly)
that I want to reverse the patch. If I don't use the option,
then it reads from /dev/tty, making the whole thing interactive
instead of being an automated script.
So there really need to be four modes of operation:
force -- do the best you can
batch -- approximately the same, but apply in reverse if
it seems like it might be reversed
cautious-batch -- silently quit if anything looks awry
do *not* query /dev/tty for anything.
otherwise -- ask /dev/tty about anything unusual
patch forthcoming, unless shouted down.
