basename, dirname —
return filename or directory portion of pathname
basename deletes any prefix ending with the last slash
  ‘/’ character present in
  string, and a suffix, if given.
  The resulting filename is written to the standard output. A non-existent
  suffix is ignored.
dirname deletes the filename portion,
    beginning with the last slash ‘/’
    character to the end of string, and writes the result
    to the standard output.
Both the basename and dirname
  utilities exit 0 on success, and >0 if an error occurs.
The following line sets the shell variable FOO to
  /usr/bin.
FOO=`dirname
  /usr/bin/trail`
The basename and dirname
  utilities conform to IEEE Std 1003.2-1992
  (“POSIX.2”).