2012

The default location for AutoCAD is in the Program Files folder. You can create
a new directory on the same level (for example, /AcadApps) and store your
custom AutoLISP and VBA macros, customization files, and other third-party
applications in subdirectories on the next level. If you want to maintain
multiple drawing directories (for separate job files), you can create a directory
such as /AcadJobs with subdirectories for each job.
Command Search Procedure
When you enter a command, AutoCAD goes through a series of steps to
evaluate the validity of the command name. A command can be a built-in
command or system variable, an external command or alias defined in the
acad.pgp file, or a user-defined AutoLISP command. Commands can also be
defined by ObjectARX applications or a device driver command. You can enter
a command on the command prompt or choose a command from the
appropriate menu. Commands can also be entered from a script file or by an
AutoLISP or ObjectARX application.
The following list describes the search order AutoCAD uses to validate a
command name.
1 If the input is a null response (Spacebar or Enter), AutoCAD uses the
name of the last command issued.
HELP is the default.
2 AutoCAD checks the command name against the list of built-in
commands. If the command is in the list and is not preceded by a period
(.), AutoCAD then checks the command against a list of undefined
commands. If the command is undefined, the search continues.
Otherwise, the command is run, unless another reason prevents it from
doing so. Running it transparently or in Perspective mode might be
impossible.
3 AutoCAD checks the command name against the names of commands
defined by a device driver, and then by those defined by the display
driver.
4 AutoCAD checks the command name against the external commands
defined in the program parameters file (acad.pgp). If the command name
corresponds to a defined external command, that command runs, and
the search is complete.
5 AutoCAD checks the command name against the list of commands
defined by AutoLISP or ObjectARX applications. At this point, an
autoloaded command is loaded.
6 | Chapter 1 Basic Customization