NSIS finds out whether the file exists and sets the installation path

Var GIT
Function .onInit
  !insertmacro MUI_LANGDLL_DISPLAY
  
  StrCpy $GIT "false"
  MessageBox MB_OK $9
  IfFileExists "C:\Program Files\Git\git-cmd.exe" 0 +4
               MessageBox MB_OK "Git already installed "
               StrCpy $INSTDIR "C:\Program Files\Git"
               StrCpy $GIT "true"
  IfFileExists "D:\Program Files\Git\git-cmd.exe" 0 +4
               MessageBox MB_OK "Git already installed "
               StrCpy $INSTDIR "D:\Program Files\Git"
               StrCpy $GIT "true"
  ${If} $GIT == "false"
               MessageBox MB_OK "Git No installation , Exit setup ！"
               Abort
  ${EndIf}
FunctionEnd