1. `perldoc CGI`
2. See if $ENV{QUERY_STRING} is defined or ne "".
3. 
use CGI;
use strict;
my $cgi = new CGI;
my $param1 = "";
$param1 = $cgi->param('textboxonform');
if ($param1 ne "") {
    #There was data passed from Post/Get
}

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4. If you are going to use the CGI parameters for anything...do not manually parse the QUERY_STRING. I put that option (#2 above) JIC you only want to know, "Was this script loaded from a Post/Get?"
UPDATE:
5. And if you really want to know which method of parameter passing was used...see fireartist's post above that reads, "my $method = $q->request_method();"

In reply to Re: Detecting a post via cgi by cbro
in thread Detecting a post via cgi by jcpunk

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