Understanding environment variable precedence in Windows XP

by Greg Shultz | Mar 23, 2005 8:00:00 AM

Tags: Microsoft Windows, Greg Shultz, Autoexec.bat, Autoexec.bat file, Environment Variables, environment variable, Environment Variables dialog box, System Variables, dialog box, Microsoft Windows XP

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Takeaway: Have you ever set an environment variable in the Autoexec.bat file and then discovered that the variable has a different value than the one you specified? This is because the variable was probably overridden by the same setting in the Environment Variables dialog box. Discover how to avoid such problems.

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Many IT pros still use the Autoexec.bat file to set environment variables, which is fine in most cases. However, if you set an environment variable in the Autoexec.bat file and then discover that the variable has a different value than the one you specified, the variable was probably overridden by the same setting in the Environment Variables dialog box.

This is because during the startup procedure Windows XP searches the startup files and processes the environment variable settings in the following order:

Autoexec.bat files
System Variables
User Variables

Therefore, if you set the same environment variable in the Autoexec.bat file and in the System Variables section, the value assigned in the System Variables section will override the value assigned in the Autoexec.bat file.

To avoid these types of problems, you might want to get into the habit of setting environment variables in the Environment Variables dialog box. Here's how:

Right-click My Computer and select Properties to open the System Properties dialog box.
Select the Advanced tab and press the Environment Variables button.

From the Environment Variables dialog box, you can set user-specific variables or system-specific variables by pressing the New or Edit buttons and then selecting OK.

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