Normally patch is invoked like this:
The full format for invoking patch is:
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 diff output) from the standard input.
If you do not specify an input file on the command line, patch 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.
By default, patch replaces the original input file with the patched version, possibly after renaming the original file into a backup file (see Backup 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.