You Cannot Get Ye Telnet

Debugging a mail setup at work (on Windows :(), I tried unsuccessfully to find a program to just open up a TCP connection to a random host and port. But, we do have git installed, which means a full copy of bash. And that means that /dev/tcp and /dev/udp are available, despite /dev not existing.

So, I wrote telnet in bash (extra lines added by... chrome?blogger):

#!/bin/bash

HOST=$1
PORT=${2-23}

exec 3<>"/dev/tcp/$HOST/$PORT" || exit 1

while read line ; do
        echo $line
done >&3 &

while read line ; do
        echo -en "$line\r\n" >&3
done

It's not a perfect drop-in replacement, but now I can at least test email:

$ ./telnet.bash alt1.aspmx.l.google.com 25
220 mx.google.com ESMTP c64si6457617yhj.60
HELO localhost.localdomain
250 mx.google.com at your service
MAIL From:<aaron@xxxxx>
250 2.1.0 OK c64si6457617yhj.60
RCPT To:<aaron@xxxxx>
250 2.1.5 OK c64si6457617yhj.60
DATA
354 Go ahead c64si6457617yhj.60
Subject: test
Date: Mon, 08 Aug 2011 16:16:29 -0700
From: "Aaron Fellin" <aaron@xxxxx>
To: "Aaron Fellin" <aaron@xxxxx>

This is a test email.

I <3 bash
.
250 2.0.0 OK 1312845535 c64si6457617yhj.60
QUIT
221 2.0.0 closing connection c64si6457617yhj.60
^D

:wq