30:  How do I make Emacs display the current line (or column) number?
  
  To find out what line of the buffer you are on right now, do "M-x
  what-line".  Use "M-x goto-line" to go to a specific line.  To find the
  current column number, type "M-ESC (current-column)".
  
  Typing "C-x l" will also tell you what line you are on, provided the
  buffer isn't separated into "pages" with C-l characters.  In that case, it
  will only tell you what line of the current "page" you are on.  WARNING:
  "C-x l" gives the wrong value when point is at the beginning of a line.
  
  There is no "correct" way to constantly display the current (or total)     +
  line (or column) number on the mode line in Emacs 18, or to display the
  line numbers next to the lines like vi can.  Emacs is not a line-oriented
  editor, and really has no idea what "lines" of the buffer are displayed in
  the window.  It would require a lot of work at the C code level to make
  Emacs keep track of this.  It would not be that hard to get the column
  number, but it would still require changes at the C code level.
  
  None of the vi emulation modes provide the `set number' capability of vi   !
  (as far as I know).
  
  Emacs 19 will probably be able to show the line number on the mode-line,
  but probably very inefficiently.
  
  People have written various kludges to display line numbers.  One is       +
  `display-line-numbers' by Wayne Mesard <wmesard@tofu.oracle.com,           +
  Mesard@bbn.com>.  Look in the Lisp Code Directory.  (See question          +
  90.)