Newbie -- conditionally setting Registry key

Newbie question here -- I want to make some Registry keys during my install, but if the keys already exist -- I don't want to overwrite the existing value. I've checked through the docs that come with the installer -- but I can't seem to find the right answer.

Re: Newbie -- conditionally setting Registry key

from bigtest.nsi example

ClearErrors

ReadRegStr $1 HKCR "software\microsoft" shit

IfErrors 0 NoError

  MessageBox MB_OK "could not read from HKCR\software\microsoft\shit"

  Goto ErrorYay

NoError:

  MessageBox MB_OK "read '$1' from HKCR\software\microsoft\shit"

ErrorYay:

SectionEnd

this should work:

Section "Registry check"

ClearErrors

ReadRegStr $1 HKCU "software\microsoft" shit

IfErrors 0 NoError

  WriteRegStr HKCU software\microsoft "shit" "0"

  Goto ErrorYay

NoError:

  MessageBox MB_OK "read '$1' from HKCU\software\microsoft\shit"

ErrorYay:

SectionEnd

without MessageBox:

Section "Registry check"

ClearErrors

ReadRegStr $1 HKCU "software\microsoft" shit

IfErrors 0 NoError

  WriteRegStr HKCU software\microsoft "shit" "0"

NoError:

  SectionEnd