I want users send data by formmail but when they send nothing or call it from web site they will see error. codes in PHP like this: if (isset($HTTP_POST_VARS)){ .......... } else{ echo ("error lalalalal") } How it will look in perl?

In php it will be like 
if (isset($HTTP_POST_VARS)){
....
}
In perl, tried this.
if ($ENV{'REQUEST_METHOD'} eq 'POST'){
.....
}