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How to import a *.reg file into the registry
Revised and expanded 22 Mar 2005
Topics in this article:
 Reg file
 Reg file format
1. Reg file
A *.reg file is a plain text file that is associated with the Windows registry editor. The registry editor in Windows XP, regedit.exe is an updated version and combines the features of the old regedit.exe and regedt32.exe in Windows 2000.
You can make one in any text editor such as Notepad and save as reg (File, save as, all files) or export it directly from an existing registry key in the registry editor in: File > Export, reg. To reduce errors, export a key and edit it.
Windows XP exports reg files with the Windows Registry Editor version 5.0 heading; this uses unicode. Older versions uses Regedit 4 and uses ANSI. Windows XP supports both formats but version 5 is not supported in older versions of Windows. Reg files can add, change or delete registry keys and can be used in scripts. To find out about the format, export some keys and look inside with Notepad.
It is important to note that merging a reg file does not delete those keys which are not referred to in the file and some keys in use by the system cannot be altered. Therefore it is not a foolproof method of backing up the registry. For this purpose, export the registry as a registry hive file instead or use other methods such as system restore.
If you did not make the reg file, before you import it, it is prudent to open it first in Notepad (R click, Edit) and examine its content carefully. If you are not sure what it does, do not import it.
You can open the Registry editor to import the file directly. Go to File > Import and select the reg file.
You can double-click a reg file directly from its directory. When you double-click a *.reg file a Registry Editor window pops up and ask if you want to go ahead unless you have deliberately changed the file association as a security measure (fig. 1).
Fig. 1. Registry Editor prompt
Click Yes. Another window pops up to confirm that the file has been merged: click OK to finish (Fig. 2). There is no cancel or go back button so be careful in the previous step.
Fig. 2. Registry Editor confirmation message
Sometimes editing the registry takes effect immediately: this commonly happens with HKCU keys. Other times you need to reboot, or re-logon to your account or reopen explorer.exe in Windows Task Manager and this commonly happens with HKLM but there are exceptions.
There is one important limitation with this method: in Windows XP you cannot use this method to unlock the registry if it has been disabled. This has been covered in detail in this article.
Some have been covered in other tutorials and the rest I hope to cover in due course.
Honeycutt, Jerry, Microsoft Windows XP Registry Guide (Redmond: Microsoft Press, 2003)
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Last updated 22 Mar 2005