!include logiclib.nsh

Var tmpInst
ReadRegStr $0 HKLM ${PRODUCT_INST_KEY} "InstallDir"
MessageBox MB_OK "tmpInst 有沒有值: $0"

${If} $0 == ""
MessageBox MB_OK "沒值"
${Else}
MessageBox MB_OK "有值"
${EndIf}