patch is invoked like this:
The full format for invoking
patch options… [origfile [patchfile]]
You can also specify where to read the patch from with the -i
patchfile or --input=patchfile option.
If you do not specify patchfile, or if patchfile is
patch reads the patch (that is, the
from the standard input.
If you do not specify an input file on the command line,
tries to intuit from the leading text (any text in the patch
that comes before the
diff output) which file to edit.
See Multiple Patches in a File.
patch replaces the original input file with the
patched version, possibly after renaming the original file into a
backup file (see Backup File Names, for a description of how
patch names backup files). You can also specify where to
put the output with the -o file or
--output=file option; however, do not use this option
if file is one of the input files.