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Hack 27. Make Applications Trigger On-Screen Alerts

Many applications can run a program when an
event occurs. Use XOSD to make these alerts really grab your
attention.

Many of the applications you use daily might give you the option of
executing a program when an event occurs. The KMail email client,
Jpilot personal information manager, and Swatch log-monitor program
are three examples. Each hack in this section takes advantage of XOSD
[Hack #26] .

4.7.1. KMail

If you use the KDE KMail
email client, you can have KMail execute a
program when new mail arrives. Here's how you can
have KMail display the on-screen new-mail notification
"You've got mail!"
with XOSD.

First, you need to create a script that displays the on-screen alert
"You've got
mail!". KMail doesn't allow you to
insert the entire echo and
osd_cat command line, but it will execute a script
that displays the message. Fire up your favorite editor, and enter
this script into a file called ~/youhavemail.
(This script executes from your home directory, so you
don't need any special privileges for it to work.)

#!/bin/bash
# figure out which display we're currently using
# then export the DISPLAY environment variable
HOST="$(xrdb -symbols | grep SERVERHOST | cut -d= -f2)"
DISPLAYNUM="$(xrdb -symbols | grep DISPLAY_NUM | cut -d= -f2)"
THISDISPLAY=$HOST:$DISPLAYNUM.0
export DISPLAY=$THISDISPLAY
echo "You've got mail"'!' | osd_cat -s 2 -c yellow -p middle -f -adobe-helvetica-bold-r-normal-*-*-240-*-*-p-*-*-* -d 30

The placement of various quotes in the text for the echo command looks a bit odd, doesn't it? Here's why. The bash shell interpreter will allow you to embed only a single quote in a string that is enclosed by double quotes. If the string "You've" wasn't isolated within double quotes, the echo command would report an error. In addition, the exclamation point (!) has a special meaning in bash. It refers to the command history (a recording of your most recent commands). In this case, you can display the exclamation point only if you surround it with single quotes. This creates a dilemma in the first part of our message because it requires double quotes, yet we have to surround the exclamation point with single quotes. The answer is simple. Break up the message into two parts, the main part surrounded by double quotes followed by the single exclamation point surrounded by single quotes. The echo command handles both strings as part of a single message.

Save your work and change the script to be executable:

$ chmod +x ~/youhavemail

Now follow these steps to configure KMail to execute the script when
new mail arrives:

Start up KMail and then click SettingsConfigure KMail.

Click the button entitled Other Actions at the bottom of the dialog,
located right below the Detailed New Mail Notification box, which
should be checked by default.

Click the More Options button at the bottom of the next dialog box
that appears.

Check the "Execute a program" box.

Enter ~/youhavemail in the edit field for this
selection.

Click the Apply and/or OK buttons until you are back to the KMail
interface.

4.7.2. Jpilot

You can configure the Jpilot
personal information manager (PIM) to run a script that displays an
on-screen message when a scheduled event occurs. Fire up your
favorite editor, and enter this script into a file called
~/jpilotalert. (This script executes from your
home directory, so you don't need any special
privileges for it to work.)

#!/bin/bash
# figure out which display we're currently using
# then export the DISPLAY environment variable
HOST="$(xrdb -symbols | grep SERVERHOST | cut -d= -f2)"
DISPLAYNUM="$(xrdb -symbols | grep DISPLAY_NUM | cut -d= -f2)"
THISDISPLAY=$HOST:$DISPLAYNUM.0
export DISPLAY=$THISDISPLAY
echo "You have an appointment scheduled for $1 $2"'!' | osd_cat -s 2 -c yellow 
-p middle -f -adobe-helvetica-bold-r-normal-*-*-240-*-*-p-*-*-* -d 30

Here is how to set up Jpilot to execute this script and enter the
date and time as part of the alert:

Select FilePreferences from the menu, or press Ctrl-E to
get to the Preferences dialog.

Click the Alarms tab.

Check the box labeled "Execute this
command."

Enter the following string of text into the Alarm Command text field:
~/jpilotalert "%d"
"%t".

4.7.3. Swatch

Swatch is a program that monitors your system
logs to watch for certain important keywords in one or more log
files. If Swatch finds a keyword, perhaps a word or pattern that
indicates someone might be trying to guess passwords and break into
your network, Swatch will do whatever you tell it to do to issue the
alert.

Normally, when Swatch issues an alert, it simply prints it to the
screen where Swatch is running. Swatch can also send you an email
alert, but if Swatch detected an attempted break-in, your network
could be compromised by the time you check your email. This hack
exploits the power of XOSD to give Swatch a better chance of grabbing
your attention when something potentially serious is afoot.

Here is an example of how to set up Swatch to tell you when someone
tries to log in, but fails (a possible indication that someone is
trying to guess a password). Assume that the Swatch configuration
file you are using is /root/.swatchrc, and the
log file to be monitored is /var/log/auth.log,
which, for some Linux distributions, is the file that records all
login attempts. Here is just one section of a larger file called
/root/.swatchrc, which looks for the word
"failure" in
/var/log/auth.log:

# Bad login attempts
watchfor  /failure/
pipe "osd_cat -c magenta -p middle -f \"-*-arial black-*-*-*-*-48-*-*-*-*-*-*-*\" -d 60"

When Swatch finds a new log entry with the word
"failure" in
/var/log/auth.log, it prints the suspicious log
entry on-screen by piping it through osd_cat,
which makes the event almost impossible to miss if
you're working at the computer. Note that
we're using a smaller font than we used for the
previous hacks. That's because Swatch messages can
sometimes be lengthy, and you don't want to have the
most important information hidden off-screen.