とりあえず送れればいい人向け
perl
use LWP::UserAgent;
use HTTP::Request::Common;
use JSON;
my $url = "https://hooks.slack.com/services/......"; #webhook url
my $post = {
"channel" => "#hoge",
"username" => "perl bot",
"text" => "fuga"
};
my $request = POST( $url, Content_Type => 'application/json', Content => encode_json($post));
my $ua = LWP::UserAgent->new;
$ua->request($request);