4.4)  How can an executing program determine its own pathname?

      Your program can look at argv[0]; if it begins with a "/", it is
      probably the absolute pathname to your program, otherwise your
      program can look at every directory named in the environment
      variable PATH and try to find the first one that contains an
      executable file whose name matches your program's argv[0] (which
      by convention is the name of the file being executed).  By
      concatenating that directory and the value of argv[0] you'd
      probably have the right name.

      You can't really be sure though, since it is quite legal for one
      program to exec() another with any value of argv[0] it desires.
      It is merely a convention that new programs are exec'd with the
      executable file name in argv[0].

      For instance, purely a hypothetical example:
        
        #include <stdio.h>
        main()
        {
            execl("/usr/games/rogue", "vi Thesis", (char *)NULL);
        }

      The executed program thinks its name (its argv[0] value) is
      "vi Thesis".   (Certain other programs might also think that
      the name of the program you're currently running is "vi Thesis",
      but of course this is just a hypothetical example, don't
      try it yourself :-)