AutoCAD (and its vertical applications Map 3D, Plant 3D, Civil 3D, Architecture, etc.) is a venerable and complicated program. It was first released in December of 1982! And the amazing thing is that many of the original commands still run to this day.
Over the years, the program has grown significantly in functionality and complexity. As new functions are added, new potential workflows are introduced. To accommodate different workflows, variables can be set to control the behavior of AutoCAD. The more you understand how to set and control these system variables, the more proficient you will be.
This is the first of three blogs explaining how to manage these variables:
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This one explains the concept of system variables and how to change their values.
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Simple LISP and Loading demonstrates a simple LISP program to change variables and how to load these programs into AutoCAD.
Examples of system variables
There are close to 900 system variables! They essentially control the behavior of AutoCAD. For example, the FILEDIA variable controls if the Select File dialog box is invoked when opening or saving a drawing (Save As).
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It can be on (variable set to 1) or off (variable set to 0).
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This value is stored in the registry, which means it is set for the program.
Some values are stored in the drawing and can differ from drawing to drawing. Other values are not stored at all, like ACADPREFIX, which is the prefix of the drawing; in other words, the path where the drawing resides.
Some values are read-only and cannot be changed within the system (like the ACADPREFIX).
To change a system variable, you simply type in the name of the variable and then the desired value to change it to. This can be done at the command line. But of course, that only works when you know what the variable is (of the close to 900 of them!) that you want to change.
Accessing the system variables
A convenient way to see all the system variables is found in the Tools panel on the Express Tools tab, as shown below. The command is sysvdlg, which you can type in at the command line.
The System Variables dialog box lists all the variables along the left panel. You can type in a search to find a variable and use wildcards to simplify the search. For example, CMD* will list all the variables starting with CMD, as shown above.
The System Variables dialog box lists the following:
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New Value: What you are changing the variable to (it is greyed out if it is read-only).
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Current Value: What the variable is currently set to (before you opened the dialog box).
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Initial Value: What the default setting is for the variable.
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Saved In: Where the system variable is saved. The options are:
a. Registry: The variable is the same for all drawings.
b. Drawing: The variable may be different for different drawings.
c. Not saved: The variable cannot be changed (and the New Value is set to read-only).
5. Type: The variable can be one of the following types:
a. Integer
b. String
c. Real number
d. Switch
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The description panel gives a detailed description of the system variable along with the options and how these options effect AutoCAD. THIS IS INVALUABLE!
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You can save the variable settings to an external file.
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You can read variable settings from an external file.
Conclusion
AutoCAD is a complicated program. It has many settings controlled by system variables. Once these variables are better understood, they can be useful in your mastery of the program.
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