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How to Edit a LISP Routine to Change the Command

Every LISP routine defines its trigger command in one specific line near the top of the file. Renaming it — so RCS becomes something you'll actually remember, or so it doesn't collide with a command you already use — takes about ten seconds once you know what to look for.

Find the defun line

Open the .lsp file in Notepad, VS Code, or any plain text editor (never Word — it can corrupt the file with smart quotes and formatting). Near the top, look for a line starting with (defun c:. The letters right after c: are the command you type in AutoCAD.

For example, our Rotate Reference routine starts like this:

(defun C:RR ()
  (setq ss (ssget))
  ...

That RR is the whole story. Change it to whatever you want:

(defun C:ROT2 ()
  (setq ss (ssget))
  ...

Save the file, reload it (see our guide to loading LISP routines if you need a refresher), and the routine now runs when you type ROT2 instead of RR.

Watch for alias wrappers

Some routines separate the short command from the actual logic — our Roadway Cross-Section Designer is a good example:

(defun c:RCS nil (c:RoadwayCyclePreview))

(defun c:RoadwayCyclePreview ( / *error* ... )
  ...

Here, c:RCS is just a thin alias that calls the real function, c:RoadwayCyclePreview. This is actually the safer file to edit: change the word RCS in that first line and you're done — you never have to touch the actual program logic underneath it.

Avoid command conflicts

Before picking a new name, type it at the AutoCAD command line first. If AutoCAD recognizes it as something else (a built-in command, an alias in your acad.pgp, or another loaded routine), pick a different name. Short one- or two-letter names are the most likely to collide — L is already LINE, M is already MOVE, and so on.

Multiple commands in one file

A single .lsp file can define more than one command. If you see several (defun c:...) lines, each one is a separate trigger word — rename any or all of them independently, as long as each new name is unique within the file and doesn't collide with something else already loaded.