The Mac OS X Finder (file manager) annoyingly doesn't merge a source directory into a pre-existant target directory but replaces the latter with
the former.  The following script helps out, though not very well.

And now I would like to have my ones and zeroes back.

 #!/usr/local/bin/scsh \
 -e main -s

 USAGE
 movedirfiles FROM-DIR TO-DIR

 SYNOPSIS:  Moves visible (not dotted) files from FROM-DIR into TO-DIR,
 preserving relative paths --provided they don't clash with a namesake.

 This isn't carefully wrought comfort code.  It's digidirt good enough
 for my purpose.  In particular, it relies on the nonstandard "mv -n"
 option of the OS X / BSD variant of "mv".  (Edited after use.)
 !#

 ;; simplify and remove trailing "/." (forgetting about symlinks)
 (define (simplerify-file-name fn)
   (let ((sn (simplify-file-name fn)))
     (cond ((string-suffix? "/." sn)
            (string-drop-right sn 2))
           ((string= sn ".") "")
           (else sn))))

 (define (file-name-sans-directory path)
   (last (split-file-name path)))

 (define (file-name-dotted? fname)
   (and (not (file-name-directory? fname))
        (string-any #\. (file-name-sans-directory fname))
        (string-null? (file-name-extension fname))))


 ;; Return quasirelative paths of subdirectories, each dir before its subdirs
 (define (find-directories dirname)
   (with-cwd dirname
     (run/strings  (find "." -type d))))

 (define (find-visible-files dirname)
   (remove! (lambda (fname) (file-name-dotted? fname))
            (run/strings (find ,dirname -type f))))


 (define (copy-directory-skeleton orig-dir clone-dir)
   (for-each (lambda (path0)
               (let ((path1 (path-list->file-name (list path0) clone-dir)))
                 (if (file-not-exists? path1)
                     (create-directory (simplerify-file-name path1)))))
             (find-directories orig-dir)))


 ;; ... but don't overwrite an existing file ("mv -n", a nonstandard switch)
 ;; (RENAME-FILE wouldn't move files onto another device.)
 (define (move-file from-fname to-filordirname)
   (format #t "(-> \"~a\" \"~a\")~%" from-fname to-filordirname)
   (run (mv -n ,from-fname ,to-filordirname)))

 (define (move-directory-files from-dir to-dir)
   (copy-directory-skeleton from-dir to-dir)
   (for-each (lambda (fname)
               (move-file (path-list->file-name (list fname) from-dir)
                          (path-list->file-name (list fname) to-dir)))
             (with-cwd from-dir
               (find-visible-files "."))))


 (define (main args)
   (let ((from-dir (second args))
         (to-dir (third args)))
     (move-directory-files from-dir to-dir)))