To check for socks, use Net::Proxy::Type.

#!/usr/bin/perl

use strict;
use warnings;
use Net::Proxy::Type ':types';

my $proxytype = Net::Proxy::Type->new();
my $proxy = 'remotehost';

if ($proxytype->is_socks4($proxy)) {
              warn "$proxy is  a socks4 proxy", "\n";
}
elsif ($proxytype->is_socks5($proxy)) {
              warn "$proxy is a socks5 proxy", "\n";
}
else {
              warn "$proxy is unknown", "\n";
}
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