NSIS - check if registry key value exists

Question

I need to check, if a registry value exists. How can I do that?

My first approach:

ReadRegStr $0 HKLM "SOFTWARE\Microsoft\Windows NT\CurrentVersion\Ports" "NUL:"
        ${IF} $0 == ""
              MESSAGEBOX MB_OK "NUL exists"
        ${ELSE}
               WriteRegStr HKLM "SOFTWARE\Microsoft\Windows NT\CurrentVersion\Ports" "NUL:" ""
        ${ENDIF}

But this also works, when the value doesn’t exist. I guess, because "doesn’t exist" and empty string are handled the same way.

With Registry.nsh I did it like this:

${registry::Read} "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Ports" "NUL:" $var1 $var2

        ${IF} $var2 == "REG_SZ"

But I get an error, because the Pop ${_STRING} in the registry.nsh doesn’t work.

Help and suggestions welcome!

Answer 1

You should check the error flag after reading:

ClearErrors
ReadRegStr $0 HKLM "SOFTWARE\Microsoft\Windows NT\CurrentVersion\Ports" "NUL:"
${If} ${Errors}
  MessageBox MB_OK "Value not found"
${Else}
  ${IF} $0 == ""
              MESSAGEBOX MB_OK "NUL exists and it's empty"
        ${ELSE}
               WriteRegStr HKLM "SOFTWARE\Microsoft\Windows NT\CurrentVersion\Ports" "NUL:" ""
        ${ENDIF}
${EndIf}

Also, you may be interested in EnumRegValue before trying to read it.