Mmv moves (or copies, appends, or links, as specified) each source file matching
a from pattern to the target name specified by the to pattern. This multiple
action is performed safely, i.e. without any unexpected deletion of files due to
collisions of target names with existing filenames or with other target names.
Furthermore, before doing anything, mmv attempts to detect any errors that would
result from the entire set of actions specified and gives the user the choice of
either proceeding by avoiding the offending parts or aborting.