SolidworksHow-ToBeginner · 4 min read

How to Automate AutoCAD Using Lisp: Simple Guide

You can automate AutoCAD by writing Lisp scripts that run commands and manipulate drawings automatically. Use defun to define functions and command to execute AutoCAD commands inside Lisp. Load your Lisp file in AutoCAD and run your custom functions to automate tasks.

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Syntax

In AutoCAD Lisp, automation scripts are written as functions using defun. The command function runs AutoCAD commands. Variables store data, and princ outputs messages.

(defun functionName () ... ): Defines a new function.
(command "COMMAND" args): Runs an AutoCAD command.
princ: Prints text to the command line.

lisp

(defun c:hello ()
  (princ "Hello, AutoCAD!")
  (princ)
)

Output

Hello, AutoCAD!

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Example

This example creates a simple Lisp function that draws a line between two points automatically when run in AutoCAD.

lisp

(defun c:drawline ()
  (command "LINE" '(0 0) '(100 100) "")
  (princ "\nLine drawn from (0,0) to (100,100).")
  (princ)
)

Output

Line drawn from (0,0) to (100,100).

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Common Pitfalls

Common mistakes include forgetting to end commands with an empty string "", which causes AutoCAD to wait for more input. Also, not using princ at the end of functions can clutter the command line. Avoid naming conflicts by prefixing custom functions with c:.

lisp

(defun c:badline ()
  (command "LINE" '(0 0) '(50 50)) ; Missing "" ends command
  (princ "This will cause AutoCAD to wait for input.")
  (princ)
)

(defun c:goodline ()
  (command "LINE" '(0 0) '(50 50) "") ; Properly ends command
  (princ "Line drawn correctly.")
  (princ)
)

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Quick Reference

Here is a quick cheat sheet for common Lisp automation commands in AutoCAD:

Command	Description
defun	Defines a new Lisp function
command	Executes AutoCAD commands
princ	Prints text to command line
c:	Prefix for user commands callable in AutoCAD
(list x y)	Defines a point coordinate

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Key Takeaways

Use defun to create reusable automation functions in AutoCAD Lisp.

Always end command sequences with an empty string "" to finish commands properly.

Prefix custom functions with c: to make them callable from AutoCAD command line.

Use princ to print messages and keep the command line clean.

Test Lisp scripts in a safe drawing to avoid unintended changes.