If it helps, this is how I have changed the PATH env. var. using some other weird obscure language (OK, C++). Sorry it is not in Perl, I hope this is enough for you to get the gist: 
#define ENVNAME "Path"
#define MAXLEN  1024

static void UpdatePath (char *szDir)
{
   char szPath [MAXLEN]={0};
   DWORD dwReturnValue;

   // Get previous value 
   if ( !GetEnvironmentVariable (ENVNAME, szPath, MAX_PATH) )
      ReportError ("GetEnvironmentVariable", GetLastError());

   // Update path 
   strcat (szPath, ";");
   strcat (szPath, szDir);

   // On W2K we need OSVERSIONINFOEX
   OSVERSIONINFO OsVer;
   OsVer.dwOSVersionInfoSize = sizeof (OsVer);
   GetVersionEx (&OsVer);

   if ( OsVer.dwPlatformId == VER_PLATFORM_WIN32_NT )
   {
      // Write to the user environment variables - 
      // only exists on WNT/W2K!

      HKEY hEnv;
      dwReturnValue = RegOpenKeyEx (HKEY_CURRENT_USER, 
                                    "Environment", 0, 
                                    KEY_SET_VALUE, 
                                    &hEnv) ;
      if ( dwReturnValue != ERROR_SUCCESS )
         ReportError ("RegOpenKeyEx", dwReturnValue);

      dwReturnValue = RegSetValueEx (hEnv, ENVNAME, 0, 
                                     REG_SZ, (BYTE*)szPath, 
                                     strlen(szPath)+1);

      if ( dwReturnValue != ERROR_SUCCESS )
         ReportError ("RegSetValueEx", dwReturnValue);

      RegFlushKey (hEnv);

      if ( hEnv ) RegCloseKey(hEnv);
   }
   
   // Tell the rest of the world (cmd line)

   if ( !SendMessageTimeout(HWND_BROADCAST, WM_SETTINGCHANGE, 0,
                     (LPARAM) "Environment", SMTO_ABORTIFHUNG,
                     5000, &dwReturnValue) )
   {
      ReportError ("SendMessageTimeout", GetLastError());
   }

   // Tell our children 

   if ( !SetEnvironmentVariable (ENVNAME, szPath) )
      ReportError ("SetEnvironmentVariable", GetLastError());

}  // UpdEnv

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In reply to Re^2: Changing parent process environment variable by cdarke
in thread Changing parent process environment variable by tcf22

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