Working with patch files

CREATING patch file

    diff -Naur oldpath newpath > file.patch

    Where the path items may be single files or directories.  Both
    the old ad new items should have the same number of directory levels.

    N.b.:  Beware the "a" switch.  Says to treat all files as ASCII.
    Why not let diff decide whether the files are ASCII?

APPLYING a patch file

    Take a look at the patch file to see where it expects the source
    and directory elements to be relative to.

    cd somewhere  # based on findings above
    patch -pX < file.patch

    The number X is the number of levels to strip off of the paths
    in the patch file.

    If you specify no -p at all, ALL directories are stripped off.

    If patch is created well, and you restore from the right location, you
    normally want to give "-p0".

SIMPLE USE SPECIFYING INDIVIDUAL FILES

    To patch one or more files in a single directory, just get old and
    new files in two peer directories at the same level.  Name one of
    the directories to indicate that it contains the older or newer
    files.  It's fine if either directories contain other files not
    used for the patch.  Go to the parent directory and run

    diff -Naur olddir/file1 newfile/file1 > file.patch
    diff -Naur olddir/file2 newfile/file2 >> file.patch
    ...
    [N.b.:  The "r" switch should not be necessary]

    Note that the element may not exist in olddir or in newdir, in
    which case the patch file will instruct to add or remove the file.

    To apply, just cd to an olddir and run

    patch < file.patch