batches: make `-f` optional
Created by: LawnGnome
New behaviour (assuming COMMAND is any command that accepted -f, including apply, preview, repos, or validate):
-
src batch COMMANDon a TTY: will wait for 250ms in case there's input on stdin; otherwise errors -
src batch COMMANDwith a file redirected in: waits indefinitely for input -
src batch COMMAND -f -: waits indefinitely for input -
src batch COMMAND FILE: reads fromFILE; equivalent tosrc batch COMMAND -f FILE -
src batch COMMAND -f FILE: works as before
In summary, this shouldn't break backward compatibility in any case except for the user slowly typing in a batch spec on stdin.
Fixes #680.