found a way :
// open pipe to generated file.
$fpop=popen("pico $gen_filename","w");
// Delete the first line read
fputs($fpop,chr(27));
fputs($fpop,chr(27));
fputs($fpop,"k");
// Undo the delete
fputs($fpop,chr(27));
fputs($fpop,chr(27));
fputs($fpop,"u");
// Send file quit command
fputs($fpop,chr(27));
fputs($fpop,chr(27));
fputs($fpop,"x");
// Yes to save
fputs($fpop,"y");
// Enter
fputs($fpop,"\r");
// Close pipe.
pclose($fpop);
Regards,
-m.