Windows – Easiest way to update a Registry value

command lineregeditwindowswindows-registry

While using Linux I've grown accustomed to one-liners when I search online to fix annoying defaults. I know that these one liners could be very dangerous so I always make sure I know what they are doing before running them.

At the same time, I hate having to update windows registry keys because I need to open up regedit and navigate The Tree.

Is there an easy way to edit a specific registry value?

Something like:

regupdate path type newvalue

Best Answer

As of the time of writing this, the accepted answer to this by David Marshall answers the question, but doesn't provide any detail beyond the link itself. In the interest of writing an answer that is both easily readable and invulnerable to potential link rot, I decided to write my own answer to the question.

How do I update the Windows Registry using the command line?

The reg command, made available from as far back as Windows Server 2000, is used for this exact purpose, and the syntax is fairly simple to use.

To add a key

Run the following in a command line window:

reg add HKLM\Software\Classes\MyKey

...where HKLM\Software\Classes\MyKey is the registry key that you want to create.

To add registry values and data along with keys, parameters are required. The /v parameter specifies the name of the value to be added, the /t parameter specifies the value type, and the /d parameter specifies the data to be contained within the value.

To add the key HKLM\Software\Classes\MyKey with a DWORD value named LegacyDisable that contains data of 000:

reg add HKLM\Software\Classes\MyKey /v LegacyDisable /t reg_dword /d 000

To delete a key

reg delete HKLM\Software\Classes\MyKey

Parameters include /v, for deleting a particular value within a key instead of the key itself; /ve, to delete a key only if it contains no values; and /f, which overrides the command's default behaviour of waiting for user confirmation and forces the deletion.

To delete a value within a key:

reg delete HKLM\Software\Classes\MyKey /v LegacyDisable

To compare two keys

The reg command's compare also allows you to compare two registry keys, listing the differences between the two by default:

reg compare HKCR\.doc HKCR\.docx

To change the default behaviour of listing differences, and instead list both the differences and similarities between two different keys, use the /oa parameter.

When adding or modifying a registry key that contains spaces, make sure to wrap the key in quotes to avoid a bad syntax error.
When referring to any of the registry hives in a key path - HKEY_LOCAL_MACHINE, HKEY_CLASSES_ROOT, HKEY_CURRENT_USER, HKEY_USERS and HKEY_CURRENT_CONFIG - the reg command allows referencing them using their abbreviated versions - HKLM, HKCR, HKCU, HKU, and HKCC respectively - as demonstrated in the examples above.
When a command is about to overwrite a currently-existing value, CMD defaults to prompting for confirmation. To bypass this confirmation, use the /f parameter to force the overwrite.
The linked Microsoft documentation for the reg command doesn't list any supported operating systems after Windows 7, so it's currently unclear as to whether this command runs successfuly on either Windows 8 or 10. Input from anyone with these operating systems would be appreciated here.

Related Solutions

Windows – How to modify the data of an existing registry key value name from cmd

Use REG ADD with the "/f" parameter to force overwrite.

REG ADD /? explains the parameters.

REG ADD KeyName [/v ValueName | /ve] [/t type] [/s Separator] [/d Data] [/f]

KeyName     [\\Machine\]FullKey

Machine     Name of remote machine - omitting defaults to the current machine 
            Only HKLM and HKU are available on remote machines
FullKey     ROOTKEY\SubKey ROOTKEY [ HKLM | HKCU | HKCR | HKU | HKCC ] SubKey 
            The full name of a registry key under the selected ROOTKEY
/v          The value name, under the selected Key, to add
/ve         adds an empty value name <no name> for the key
/t          RegKey data types
            [ REG_SZ | REG_MULTI_SZ | REG_DWORD_BIG_ENDIAN | REG_DWORD | 
              REG_BINARY | REG_DWORD_LITTLE_ENDIAN | REG_NONE | REG_EXPAND_SZ ]
            If omitted, REG_SZ is assumed
/s          Specify one character that you use as the separator in your data 
            string for REG_MULTI_SZ. If omitted, use "\0" as the separator
/d          The data to assign to the registry ValueName being added
/f          Force overwriting the existing registry entry without prompt

To insert a new value or toggle a string value from "false" to "true", use a command like this:

reg add HKCU\Software\Citrix\Receiver /t REG_SZ /v UpgradeDone /d true /f

Example which reads an existing value and appends some string before writing it back:

set append=XXXXXX
set key=HKCU\Software\myTest
set value=myValue
set oldVal=

for /F "skip=2 tokens=3" %%r in ('reg query %key% /v %value%') do set oldVal=%%r
echo previous=%oldVal%

set newVal=%oldVal%%append% 

reg add %key% /v %value% /d %newVal% /f

Note: This sample assumes that the old value and the new value have no blanks. Otherwise one has to add quotes and change the "tokens" parameter. Extra error checking omitted for brevity. However, all registry manipulating code definitely must do adequate error checking.

Windows XP PRO SP3- stop changes to security software registry key(s) set by unknown program

I found this in a cached post on wugnet.com

BIG WARNING Do not go to the original wugnet domain. The Google search I performed and that led me there is a contaminated link leading through another URL to a third displaying an AdultFriendFinder advertisement

-Quote-

It's a namespace subdirectory created by the NT Object Manager during the boot process. The named objects in this subdirectory are symbolic links to Object Manager resources accessible by the Win32 API. For example, C: might be a symbolic link to \Device\HardiskVolume1, when a Win32 call is made for a file on C: the Win32 subsystem converts it to \??\C: and the the Object Manager locates the symbolic link in the \?? subdirectory and finds the device object where the file is located.

You can get a better idea of how the Object namespaces are organized with SysInternals' WinObj utility:
http://technet.microsoft.com/en-us/sysinternals/bb896657.aspx

My guess is that the full path to the Object Manager's \?? subdirectory is used in the registry values because when those registry entries are processed during the boot process the Win32 subsystem may not yet be fully initialized and as such without the \?? portion of the path the boot process would not be able to resolve the paths referenced in those registry values. Most of these \?? paths are in the HKEY_LOCAL_MACHINE\SYSTEM key and without the full path the machine would probably not boot, or if it did it would boot in a severely crippled state.

-end quote-

If this is true, your statement "This in effect disables..." is dubious. Did you actually observe that the software related to those registry keys does not function correctly?
If not, you should change your question title to something like Mysterious double question marks preceeding file paths in registry keys?

Additional remark 1
Wugnet is a strange site anyway, that page appears to be scraped from pcreview.co.uk

Additional remark 2
This issue is not to be confused with another floating around the web about single question marks replacing colons in paths. I'm including this, although it does not seem related (but I may be wrong). Here's a user who got strange C?\ values in his registry keys which might have been a MS bug, and after manually fixing them the issue was gone (long thread, several pages). The post mentions importing/exporting the keys to get them fixed quickly (but that would not be required in your case, because there's nothing wrong there). The OP writes there: New "corrupted" registry keys continue to be created when new apps are installed, but the corrected registry keys seem to remain unchanged.