If the default organization of program and support files does not suit your needs,
you can change it. However, some applications look for certain files in specific locations,
and you should verify that modifications do not conflict with the requirements of
those applications. Without the full path, including drive and folder, the program
can locate only those files that are found in its library search paths.

The program references the user profile of the operating system to identify where
local and roamable customizable files should be stored. The locations of the local
and roamable folders can be accessed using the following system variables:

• LOCALROOTPREFIX – Stores the full path to the root folder where local customizable files were installed.
• ROAMABLEROOTPREFIX – Stores the full path to the root folder where roamable customizable files were
  installed.

Beginning with AutoCAD 2013 SP1 on Windows and AutoCAD 2014 for Mac, the reserved
acad<release_number.lsp and acad<release_numberdoc.lsp files and their successors are loaded only from the product’s default installation
folders. Depending on the setting of the SECURELOAD system variable, the TRUSTEDPATHS
system variable specifies the folders from where AutoCAD-based products can load and
execute other files that contain code. In addition, the LEGACYCODESEARCH system variable
controls whether the Start In folder will be searched for executable files.

The following AutoLISP sample code defines the CUSTFILES command, and opens Windowsآ®
Explorer or File Explorer to the location where roamable customizable files were installed.

(defun c:custfiles ()
  (command "shell" 
    (strcat "explorer "" (getvar "roamablerootprefix") """)
  )
 (princ)
)

Library Search Path

The library search path specifies where the program searches for files when you do
not specify a full path name, as follows:

• Start In folder. This folder is determined either by the Start In attribute of the
  desktop shortcut icon, or by the folder in which a file is double-clicked. (STARTINFOLDER
  system variable)
• Folder that contains the current drawing file. (DWGPREFIX system variable)
• Folder of the project name for an external reference file, such as an image, xref,
  or underlay. (PROJECTNAME system variable)
• Folders listed in the program’s Support File Search paths. (ACADPREFIX system variable)
• Folder that contains the installed files for the program.

Depending on the current environment, two or more folders may be the same.

If a file is not in this search path, you must specify its full or its relative path
name and file name before the program can find it. For example, if you want to insert
the part5.dwg file into your current drawing and it is not in the library search path, you must
specify its full path name or a relative path name based on a valid path in the library
search path. A relative path name is shown here:

Command: -insert

Enter block name or [?]: /files2/olddwgs/part5

Folder Structure

The program uses tree-structured folders and subfolders. It is recommended that you
keep supplemental files, such as AutoLISP applications (not in AutoCAD LT), customization
files, or third-party applications, separate from the installed program and support
files. This makes it easier to track possible conflicts and to upgrade each application
without affecting the others.

The default location for the program is in the Program Files folder on Windows and Applications on Mac OS. You can create a new folder on the same level (for example, /AcadApps) and store custom programs, customization files, and other third-party applications
in subfolders on the next level. If you want to maintain multiple drawing folders
(for separate job files), you can create a folder such as /AcadJobs with subfolders for each job.

Command Search Procedure

When you enter a command, the application 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 (or acadlt.pgp in AutoCAD LT) file
• An AutoCorrect entry for a command in the autoCorrectUserDB.pgp file
• A synonym entry for a command in the acadSynonymsGlobalDB.pgp file
• A user-defined AutoLISP command
• A user-defined command by an ObjectARX or Managed .NET application
• A device driver command

You can enter a command at the Command prompt or start it from the user interface.
Commands can also be started from a script file or by an AutoLISP, ObjectARX, or Managed
.NET application.

The following list describes the search order to validate a command name.

1. If the input is a null response (Spacebar or Enter), the program uses the name of
   the last command issued. HELP is the default.
2. The command is checked against the list of built-in commands. If the command is in
   the list and is not preceded by a period (.), the program 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. The command is checked against the names of commands defined by a device driver, and
   then by those defined by the display driver.
4. The command is checked against the external commands defined in the program parameters
   file. If the command name corresponds to a defined external command, that command
   runs, and the search is complete.
5. The command is checked against the list of commands defined by AutoLISP, ObjectARX,
   and Managed .NET applications. At this point, an autoloaded command is loaded. (Not
   available in AutoCAD LT)
6. The program checks the command name against the list of system variables. If the command
   name is in the list, the SETVAR command is executed, using the input as the variable
   name.
7. If the command name corresponds to a command alias, AutoCorrect name, or synonym defined
   in their associated program parameters files, the expanded command name is used and
   the search process starts over with the list of built-in commands.
8. If all the preceding steps fail, the search terminates with a warning message about
   illegal command names.