pushd [ arg ]
     pushd old new
     pushd +-n
          Change the current directory, and push the old  current
          directory onto the directory stack.  In the first form,
          change the current directory to arg.   If  arg  is  not
          specified,  change to the second directory on the stack
          (that is, exchange the top two entries), or  change  to
          the value of HOME if the PUSHD_TO_HOME option is set or
          if there is only one entry on the stack.  If arg is  -,
          change  to the value of OLDPWD, the previous directory.
          If a directory named arg is not found  in  the  current
          directory and arg does not contain a slash, search each
          component of the shell parameter cdpath.  If the option
          CDABLEVARS  is  set,  and  a parameter named arg exists
          whose value begins with a slash, treat its value as the
          directory.   If the option PUSHD_SILENT is not set, the
          directory stack will be printed after a pushd  is  per-
          formed.

          The second form of pushd substitutes the string new for
          the  string  old  in the name of the current directory,
          and tries to change to this new directory.

          The third form of pushd is equivalent to popd.