REGEDIT

Import, export or delete registry settings from a text (.REG) file

syntax
      Export the Registry (all HKLM plus current user)
      REGEDIT /E pathname

      Export part of the Registry
      REGEDIT /E pathname "RegPath"

      Import a reg script
      REGEDIT pathname

      Silent import
      REGEDIT /S pathname

      Start the regedit GUI
      REGEDIT 

key
   /E : Export 

   /S : Silent Import

How to add keys and values from the registry:

Create a text file like this:

REGEDIT4
[HKEY_CURRENT_USER\SomeKey]
"SomeStringValue"="Hello" 

When double clicking this .reg file the key and value will be added.
Alternatively run REGEDIT MYKEY.REG from the command line.

How to delete keys and values from the registry:

Create a reg file like this, notice the hyphen inside the first bracket

REGEDIT4
[-HKEY_CURRENT_USER\SomeKey]  

When double clicking this .reg file the key "SomeKey" will be deleted along with all string, binary or Dword values in that key.

If you want to just delete values leaving the key in place, set the value you want to delete = to a hyphen
e.g.

REGEDIT4
[HKEY_CURRENT_USER\SomeKey]
"SomeStringValue"=-

Again double clicking this .reg file will delete the values specified - or you can use REGEDIT /s MyDeleteScript.REG.

Windows XP Registry files.
Under Windows NT all registry scripts start with:
REGEDIT4

Under 2K and XP this first line changes to:
Windows Registry Editor Version 5.00

To be sure that a .REG script will run under any version of Windows use the earlier syntax: REGEDIT4.

Compare the Registry of two machines

Windiff is your friend, this simple GUI utility from the resource kit will list all the differences.

Comments
Within a registry file, comments can be preceded by "; "
e.g.
;
; Turn the NUMLOCK on at login
;
[HKEY_CURRENT_USER\Control Panel\Keyboard]
"InitialKeyboardIndicators"="2"

Related commands:

REGEDT32.EXE - Edit the registry including Security and Auditing Options (NT 4)
REG - Read, Set or Delete registry keys and values
SET - Display, set, or remove Windows NT environment variables
SETX - Set environment variables permanently
Dureg - Registry Size Estimator. (Win 2K ResKit)

Equivalent Linux BASH commands:

none