HACKTUX notes from the trenches

You can connect to a socket using Bash by using exec and redirecting to and from the pseudo-path /dev/tcp/<hostname>/<port> or /dev/udp/<hostname>/<port>. For instance, to connect to your localhost SSH port using TCP:

exec 3<>/dev/tcp/localhost/22

Then, use cat and echo to read or write to the socket. Here is an example read:

cat <&3
SSH-2.0-OpenSSH_5.6

Notice that there is no such file as /dev/tcp or /dev/udp. Bash interprets the pseudo-path.

ls -l /dev/tcp
ls: cannot access /dev/tcp: No such file or directory
 
ls -l /dev/udp
ls: cannot access /dev/udp: No such file or directory

As another example, maybe you want to download a webpage:

exec 3<>/dev/tcp/www.fedora.org/80
echo -e "GET /\n" >&3
cat <&3

Finally, let's say you wanted to connect to an IRC server. Here is an example:

#!/bin/bash
 
##########################################################
# Config
 
NICK="mynick"
SERVER="irc.freenode.net"
PORT=6667
CHANNEL="#bashirc"
 
##########################################################
# Main
 
exec 3<>/dev/tcp/${SERVER}/${PORT}
echo "NICK ${NICK}" >&3
echo "USER ${NICK} 8 * : ${NICK}" >&3
echo "JOIN ${CHANNEL}" >&3
cat <&3
 
exit $?

Sources

tldp.org: Advanced Bash-Scripting Guide - Chapter 29
thesmithfam.org: Bash socket programming with /dev/tcp

Internet Relay Chat (IRC), a form of Internet chat was created by Jarkko Oikarinen in 1988. Here is a list of Linux clients that will get you connected to IRC Networks. For an extensive list of IRC clients and their features, see the Wikipedia Comparison of Internet Relay Chat clients page.

• Irssi
  Irssi is the self proclaimed client of the future and my favorite IRC client. Irssi is a terminal based, feature-rich, highly configurable, themed environment with support for Perl scripts. The project website hosts a large variety of themes and scripts that can be used with Irssi.
  • Screenshots
  • Documentation
• BitchX
  BitchX is a feature-rich and highly configurable, terminal based IRC client based on ircII. BitchX supports custom scripts, which can be written in TCL.
  • Screenshots
  • FAQ
• ChatZilla
  ChatZilla is a cross platform, graphical IRC client written entirely in JavaScript and XUL. ChatZilla is a mozilla.org project and can be installed as a Firefox plugin.
  • Screenshots
  • FAQ
• Konversation
  Konversation is a graphical IRC client for the KDE that supports multiple identities and theme support for nick icons.
  • Screenshots
  • Handbook
• Pidgin
  Pidgin is a Gnome based, multi-protocol Instant Messaging client with support for IRC.. With Pidgin, you can manage your instant messaging accounts and IRC connections with one, graphical client.
  • Screenshots and About
  • Developer FAQ
• CenterIM
  CenterIM is a terminal based, multi-protocol Instant Messaging client with support for IRC. If you want the functionality of Pidgin in a text-based console, then CenterIM is for you.
  • Screenshots
  • FAQ