Write Inno Setup environmental variable (srcexe) to a file

I would like to write the srcexe (Should return c:\setup.exe) to a file in my application folder.

Here is what I have tried. However the file gets created but it is empty.

Maybe im running in the wrong procedure or I'm calling incorrectly.

[Code]
procedure DeinitializeSetup();
var Path : string;
begin
  Path := GetEnv('srcexe');
  SaveStringToFile('C:\appname\filename.txt',Path, False);
end;