Batch Files REG QUERY: How do I set a varable if nothing is returned?

This returns the key containing information on which Windows Service Pack is installed.  If the key does not exist, no service pack has been installed and I need to set Version=0.

EG QUERY "HKLM\Software\Microsoft\Windows NT\CurrentVersion" /v CSDVersion
                                              

1:

This should work for you:

REG QUERY "HKLM\Software\Microsoft\Windows NT\CurrentVersion" /v CDVersion || SET version=0

                                              

1:

Sorry typo mistake in above code:

REG QUERY "HKLM\Software\Microsoft\Windows NT\CurrentVersion" /v CSDVersion || SET version=0

                                              

1:

Can you explain why?  And I still see an error message coming from REG about the key was not found.  How do I fix that?

Please try this:


@echo off
set version=

FOR /F "tokens=3 delims=      " %%A IN ('REG QUERY "HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion" /v CSDVersion') DO SET Version=%%A

if not defined version (
   echo No Service Packs Installed
) else (
   echo Latest Service Pack is: %version%
)

Which is all very well however, if service packs ARE installed then the variable %version% is not set to anything.

What the asker wanted is this:

   REG QUERY
   if no service packs installed then
      do something
   otherwise
      do something else
   end-if

The code I provided above tests the to see if the variable %version% exists after the FOR...REG QUERY command. If it doesn't exist then no service packs are present. If it does exist then it will be set to the value of the service pack version.

Another thing the asker wanted to know is how to suppress the error message should the CSDVersion key not be defined in the registry. This was also exaplined with the redirection of STDERR.

One Last comment before I assign points to this one.


How does this work?

if not defined version (
   echo No Service Packs Installed
) else (
   echo Latest Service Pack is: %version%
)

I've looked online and tried it myself.  That code doesn't seem to work, and I've found no precedence for parrens in batch files.  Was this just pseudo code?

'version' is an environment variable. If a value has been assigned to 'version' then an entry is made in the environment table: Try this in a DOS box:

    SET version

If there is a variable named 'version' which is already set to a value then it will be displayed on the screen. To see all your environment variables in the environment table just enter the following command on it's own:

    SET

To assign a value to a variable named 'version' do this:

    SET version=WinXP

Now enter the SET command on its own again:

   SET

This time it will display the variable name 'version' and it's value ie:

    version=WinXP

To access your environment variable at any time you need to enclose the variable name inside %...% as in the following:

    ECHO %version%

This will merely display the value ie:

    WinXP

To clear the variable from the environment table just reset it to nothing like this:

    SET version=



Now that you know a little about setting variables, displaying them and the fact they reside in the environment table we can now better understand the following code:


    if not defined version (
       echo No Service Packs Installed
    ) else (
       echo Latest Service Pack is: %version%
    )


The first line tests to see if the variable 'version' exists (or is defined) in the environment table (because if it does then it would indicate that the variable is set to a value).

So the line:

    if not defined version (

translates to:

    "IF the environment variable VERSION is NOT DEFINED then do the following ....

Well, clearly, if the environment variable 'version' is not defined (or was assigned an empty value thereby clearing it) then the multiline IF statement displays the message:

    "No Service Packs Installed"

otherwise it displays:

    "Latest Service Pack is: Service Pack 3".

Notice in the code we used '%version%' however, this was substituted for the words "Service Pack 3" (or something similar - it  will be different from one machine to another) as this would have been the current value 'version' is set to.

EXPERIMENT 1

In a DOS box, enter the following command:

    SET MyUserID=Cayman21

Confirm the environment variable 'MyUserID' is set. Enter:

    SET MyUserID

On it's own without the '=' (equal) sign. It should display the following:

    MyUserID=Cayman21

Now enter this command:

    IF DEFINED MyUserID ECHO ok

The ECHO command will display 'ok' on the screen.


Try the reverse. Enter the following command:

    IF NOT DEFINED MyUserID ECHO ok

(Remember this command for later) This time, ECHO doesn't display anything.



EXPERIMENT 2

Now try this. Clear the environment variable from the environment table. Enter the following command:

    SET MyUserID=

Confirm it's gone by entering SET on it's own as in the following:

    SET

(or, to be specific, try this:

    SET MyUserID

This time, DOS displays a message statint the variable 'MyUserID' is not defined.

Now try this command again (from above):

    IF NOT DEFINED MyUserID ECHO ok

This time, DOS diaplays 'ok'

One final point.


   FOR /F "tokens=3 delims= " %%A IN ('REG QUERY "HKEY...etc." /v CSDVersion') DO SET Version=%%A

FOR /F will set the FOR variable (not the same as environment variable) %%A to whatever value is output by the command inside the brackets (the REG QUERY command). The other bits and pieces ie, 'TOKENS=3, DELIMS=, /V, CSDVersion etc. are used to refine the exoected output to the %%A FOR variable.

In this case, if the key CSDVersion exists in the registry file, then whatever it's value is set to is passed into the %%A FOR variable. The 'body' of the FOR command passes the value in %%A to the environemt variable 'version - this is so that we can work with the variable name 'version' rather than %%A.

So, one of three things can result from this FOR command.

    1) The key 'CSDVersion' does not exist in the registry file
    2) The key 'CSDVersion' DOES exist in the registry file however, it has not been assigned a value
    3) The key 'CSDVersion' exists in the registry file and it is assigned a value

So, %%A can either be:

    1) Empty
    2) Empty
    3) Set to the value of the key 'CSDVersion'
 
Now, by assigning the 'value' in %%A to an environment variable (in this case 'version') the variable will be set to one of the corresponding states.

    1) Not defined
    2) Not defined
    3) Set to the value assigned to %%A

To summarise then, under conditions 1) and 2):

    SET version=%%A

would be the same as issuing the command:

    SET version=

In other opwrds, if would UNDEFINE (or clear) the variable 'version' from the environment table whereas, in condition 3):

    SET version=%%A

could be likened to:

    SET version=Service Pack 2

assuming %%A is itself set to "Service Pack 3".

The following IF...ELSE statement then makes the selection based on whether 'version' exists as a variable.

    if not defined version (
       echo No Service Packs Installed
    ) else (
       echo Latest Service Pack is: %version%
    )


The same could have been achieved by just testing %%A as in the following:

    FOR /F "tokens=3 delims= " %%A IN ('REG QUERY "HKEY....etc. /v CSDVersion') DO (
       IF "%%A"="" (
          echo No Service Packs Installed
       ) else (
          echo Latest Service Pack is: %version%
       )
    )


And that's all there is to it. Simple - althoug confusing if you're new to variables and programming in DOS.

The more you experiment, the quicker you'll grasp it.

Have fun!

Apologies for the typing errors. Now, about those points.....