IRC Hacks [Electronic resources] نسخه متنی

Hack 92 Use IRC Within screen

If you're regularly on the
move, you need a way to keep track of IRC while away from your
computer. Run a console-based IRC client in screen as a simple yet
powerful solution.

If
you're running a text mode (console) IRC client on a
remote system, it can be annoying having to reconnect if your
connection drops or if you have to move to another machine. When you
reconnect, you will no longer see the messages that were sent when
you were last connected.

GNU screen
provides a neat solution to this problem. It allows you to disconnect
from a terminal session without quitting your running programs. You
can then log in and resume the screen session at
a later time, giving the appearance that you never disconnected.

screen is provided as a package on most
Unix-based systems. If it isn't already installed,
install the screen package or download and
install it from source at http://www.gnu.org/software/screen/screenl.

Starting screen is amazingly simple, yet many
people overlook the usefulness of it. At a shell prompt, simply type:

% screen

If you get a startup message, just press Enter. You should then see a
shell prompt. This is just like any other shell, but with one
differenceevery time you press Ctrl-A, it will be intercepted
by screen. All of
screen's commands are accessed
by typing a different letter after this key.
screen provides a short summary of the commands
if you press Ctrl-A followed by the ? key. These combinations are
often abbreviated to the form ^A ?.

Probably the most useful command is the one that lets you
"detach" from a
screen session. Typing ^A
d will detach your session, leaving the programs running
inside the screen just as they were. To reattach
to the session, just type:

% screen -r

You should now see the screen as you left it. You can also log out
completely, and later log back in and reattach. By default,
screen will also detach sessions when the
terminal is closed, so screen sessions survive
network connections dying and closing the terminal window. If for
some reason your connection dies and the screen
isn't detached, screen -r is not
enough to reattach. You will need to run the command screen
-r -d to detach and then reattach. Also,
if you are running more than one screen, you
need to give the pid (process ID) or name of the
screen process that you want to reattach to
after the -r parameter.

If you are using the BitchX IRC client, detaching is even easier. Simply type /detach to detach your client, then run the scr-bx command to bring your session back again. However, this feature is nowhere near as powerful as screen and won't detach automatically.

screen's other great strength
is that it lets you run more than one program inside one terminal
window. This makes it easy to leave several programs running and
access all of them from another location, even if you are restricted
to a very slow connection. This is achieved by supporting virtual
windows inside the screen session. You can
create a new window by pressing ^A c. Once you
have more than one window, you can use ^A n or
^A <space> to go to the next window, and
^A p to go to the previous window. This
feature is made even more flexible because
screen allows windows to be split. This means
you can see more than one window on the screen at a time. To split
the screen, type ^A S. This one is case
sensitive, so you will need to hold down the Shift key as well. This
splits the window into two, and you should see a new blank window in
the bottom half of the screen. Pressing ^A
<tab> will change to this new window, and you can
either change to another existing window by pressing ^A
n, or you can create a new window. If you want to get rid
of the split windows, ^A Q will hide all the
inactive windows.

The screenshot in Figure 14-8 shows
screen with a split window, displaying
irssi in a channel where system logs are sent to
IRC, and the screen manual page in the bottom
half.

Figure 14-8. Screen with a split window

If you have played with the split-window feature, you may have
noticed you can have a window visible in several split windows at the
same time. This is actually a very useful feature because
screen allows you to attach to a
screen session more than once. This is called
multiple display mode, and you can use it to display the same window
on multiple terminals, or you can display a different window on
different terminals. To use it, simply add the -x
option to the reattach command, so it becomes:

% screen -r -x

screen also has support for copy and paste from
one window to another. Type ^A [ to start the
copy, move the cursor with the arrow keys, and press Enter to start
copying; then move the cursor to the end of the text you want to copy
and press Enter again. The text that you have copied will be stored
in memory until you use ^A ] to paste it. When
you are selecting the text, there are some other keys that you can
use. For example, pressing / will allow you to
search within the text buffer, and Page Up and Page Down will scroll
a full screen.

More relevant to IRC is a script that checks that your IRC client is
running so you don't even have to manually restart
if it crashes or if the system you're running it on
is rebooted.

This makes use of the cron facility found on most
Unix systems, along with a little bit of Bourne shell scripting.

To edit your user's crontab, run this command:

% crontab -e

You can then create a new line in your crontab:

*/5 * * * * IRC=`screen -ls | grep -v Dead | grep "\\.irc"`;
if [ "x$IRC" = "x" ]; then screen -dmS irc irssi;fi

This causes the script to be run every five minutes. When it runs, it
checks the output of screen -ls for a session
called irc. If it doesn't find
it, it starts screen in detached mode (with the
options -dm) and names the session
irc (option -S).
screen will run the command irssi once it has
started. If you want to use a different IRC client, you could replace
the irssi with whatever you use to start your IRC
client.

screen also has a command line as well as key
shortcuts. You can access the command line via ^A
:. For example, to change the title of a window (this is
useful when you're using split screens), you would
type ^A :title
new-title.

If you are paranoid about security, you can password-protect
reattaching to your screen by running the password
command on the screen command line. You can do
this by typing ^A
:password and following the
prompts. If you want to make this permanent after setting the
password, edit the file ~/.screenrc (create it
if it doesn't exist) and type
password followed by ^A
] (this pastes the contents of the paste buffer). Your
line should look something like password
NSQuRKGNxIEbw. Whenever someone runs
screen -r from now on, they
will be prompted for the password. The security provided by this is
in addition to that provided by your login password, but it
won't deter someone who is determined to get past if
they have access to your system account.

There isn't enough room to cover all of
screen's features here;
however, screen has a very good manual page so
man screen will tell you lots more, such as
how to remap keys to suit your tastes and how to allow multiple users
to share a screen session. With
screen, it's easy to run
multiple IRC clients and access them from anywhere in the world.

Quick key reference:

^A c

Create window.

^A d

Detach.

^A n or ^A <space>

Next window.

^A p or ^A <backspace>

Previous window.

^A <number key>

Change to that window number.

^A [ or ^A <escape>

Start a copy.

^A ]

Paste copy buffer.

^A S

Split window.

^A Q

Hide inactive windows.

^A :

Enter a screen command.

To get a quick list of all of
screen's key bindings, press
^A? at any time.

David Leadbeater