New commands can be defined with the defun function and by prefixing a function name with c:.
Functions prefixed with c: can be accessed directly from the AutoCAD Command prompt and used to redefine an AutoCAD command.
Functions that are defined as commands should not accept arguments directly, instead input for a command should be obtained using one of the getXXX functions.
The following defines a function named HELLO. This function displays a simple message.
(defun HELLO () (princ "\nHello world.") (princ)) HELLO
Functions can be issued from the AutoCAD Command prompt or an AutoLISP program. The HELLO function can be called from the AutoCAD Command prompt by entering the following:
Command: (hello)
Hello world.
The HELLO function must be wrapped in parentheses since it is not defined as a command. Entering HELLO without the parentheses at the AutoCAD Command prompt, returns the following error message:
Unknown command "HELLO". Press F1 for help.
Adding c: to the front of the HELLO function name results in the function being declared as a command, and can then be entered at the AutoCAD Command prompt without being wrapped with parentheses. For example:
(defun C:HELLO () (princ "\nHello world.") (princ)) C:HELLO
While HELLO is declared as a command, it is also an AutoLISP function as well. The command can now be entered at the AutoCAD Command prompt, as follows:
Command: hello
Hello world.
The HELLO command can also be used transparently because it does not make a call the command function. At the AutoCAD Command prompt, you could do the following:
Command: line
From point: 'hello
Hello world.
From point:
If an AutoLISP function is declared as a command, you can call the command from an AutoLISP program by wrapping the whole function name with parentheses. For example:
(c:hello)
You cannot usually use an AutoLISP statement to respond to prompts from an AutoLISP-implemented command. However, if your AutoLISP routine makes use of the initget function, you can use arbitrary keyboard input with certain functions. This allows an AutoLISP-implemented command to accept an AutoLISP statement as a response. Also, the values returned by a DIESEL expression can perform some evaluation of the current drawing and return these values to AutoLISP.