// Aus "autoexec.bat" wird "autoexec.old" 
procedure TForm1.Button1Click(Sender: TObject); 
begin 
  Label1.Caption := 'c:\autoexec.bat'; 
  Label2.Caption := changefileext(label1.caption, '.old'); 
end; 
 
// Umbennen einer Datei 
procedure TForm1.Button1Click(Sender: TObject); 
var f: file; 
  p: pchar; 
begin 
  p := 'c:\test.bmp'; 
  assignfile(f, p); 
  rename(f, changefileext(p, '.jpg')); 
end;