I am working on Net::OpenSSH::Gateway, a Net::OpenSSH extension that allows this module to cross through proxies and SSH gateways.

As part of it, I have written a Perl one-liner that is a netcat clone, but this one-liner is bigger than I wish, so I would like to get your help in order to reduce its length.

You can improve on the current version or rewrite it from scratch, I don't mind as long as it is able to run an SSH session on top of it (using ProxyCommand, see ssh_config) and exit when any side of the connection closes. It should only use core modules and be able to run on older Perls.

Here is the current one-liner:

perl -MFcntl=F_SETFL,F_GETFL,O_NONBLOCK -MSocket '-e$0=perl;socket($c,
+AF_INET,SOCK_STREAM,0)&&connect($c,sockaddr_in$ARGV[1],inet_aton$ARGV
+[0])||die$!;fcntl$_,F_SETFL,O_NONBLOCK|fcntl$_,F_GETFL,0 for@d=(*STDI
+N,$c),@e=($c,*STDOUT);L:for(0,1){sysread($d[$_],$f,8**5)||exit and$f[
+$_].=$f if vec$g,$_*($h=fileno$c),1;substr$f[$_],0,syswrite($e[$_],$f
+[$_],8**5),"";vec($g,$_*$h,1)=($i=length$f[$_]<8**5);vec($j,$_||$h,1)
+=!!$i}select$g,$j,$k,5;goto L' perlmonks.org 80
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It is automatically generated from this more readable version:

$0=perl;
socket($socket, AF_INET, SOCK_STREAM, 0) &&
connect($socket,  sockaddr_in PORT, inet_aton "SERVER") || die $!;
fcntl $_, F_SETFL, O_NONBLOCK|fcntl $_, F_GETFL, 0 for @in = (*STDIN, 
+$socket), @out = ($socket, *STDOUT);

L:
for (0, 1) {
    sysread ($in[$_], $buffer, 8**5) || exit and $buffer[$_] .= $buffe
+r
        if vec $iv, $_ * ($socket_fileno = fileno $socket), 1;
    substr $buffer[$_], 0, syswrite($out[$_], $buffer[$_], 8**5), "";
    vec($iv, $_ * $socket_fileno, 1) = ($l = length $buffer[$_] < 8**5
+);
    vec($ov, $_ || $socket_fileno, 1) = !!$l;
}
select $iv, $ov, $u, 5;
goto L
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