Linux.Desktop.Hacks [Electronic resources] نسخه متنی

Hack 26. Never Miss Another Reminder

Flash your reminders on your desktop on top of
any applications you are running.

Did you know you can display pop-up messages on
top of X Windows, even if you're using multiple
virtual desktops? This trick can come in handy when a pop-up dialog
box or messages in a terminal window simply aren't
sufficient to get your attention. And it can be fun, too. This hack
explores the power of X11 On-Screen Display (XOSD), and then uses it
to set reminders that will pop up on-screen at the preset time.

XOSD allows you to print messages, symbols, and even progress bars
directly on-screen, on top of anything else you have displayed on
your desktop. Think of it as the equivalent of the volume control
meter that pops up on many televisions when you adjust the volume.

Use your distribution's preferred installation
method to install XOSD. The package name usually includes the term
XOSD. If you have yum set
up properly, you can log in as root and install it on Fedora Core
(and some other RPM-based Linux distributions) with this command:

# yum install xosd

On Debian or RPM-based distributions that support
apt-get, install it with this command:

# apt-get install xosd-bin

On Gentoo, install it with this:

# emerge xosd

The distinct advantage of using XOSD is that it is often more likely
to get your attention than any other alert technique.
That's because the message appears on every virtual
desktop, and it appears on top of any applications you are using. You
can try out the XOSD program, osd_cat, with a
simple command, such as the following:

$ echo "Hello there, this is osd_cat speaking." | osd_cat

You should see the message appear in tiny red text in the upper-left
corner of the screen. It's so tiny, in fact, that
it's hardly useful. Don't worry;
you can do something about that. As long as you see the text (or
something red that looks like text) you know
osd_cat is working.

4.6.1. The Way You Like It

You can add several customization switches to tune how the
osd_cat command presents text on the screen. The
first thing you want to do is increase the text size. Use the
-f switch followed by a font
definition to make osd_cat use the
font you prefer.

Font definitions, such as the ones used by
osd_cat, can appear intimidating because they
contain so much information littered with dashes and asterisks. Each
part of the definition says something about the type of font, the
point size, whether the font is bold, etc. It's
probably safe to stick with the definitions listed here, but if you
want to play with various font definitions, run the program
xfontsel. This program lets you play with the
various parameters that make up a font definition while showing the
results in the window. When you come up with a combination you like,
you can click the Select button, which will copy the full definition
onto the clipboard and let you paste it into your script or program.

If you want a big eye-catching font, you'll probably
want to use the following font definition, which is available in
almost every Linux distribution:

-adobe-helvetica-bold-r-normal-*-*-240-*-*-p-*-*-*

If you have the Microsoft TrueType fonts installed [Hack #25], you can get a much broader
range of font sizes at the cost of speed. The larger you make the
font, the longer it takes for osd_cat to render
the message. Here's one example:

"-microsoft-comic sans ms-*-*-*-*-48-*-*-*-*-*-*-*"

You can get some fonts to display text larger than 48 points, but it
might take several seconds before you see the text on your screen.

Make sure you enclose font descriptions in quotes if the font name includes spaces. Otherwise, the spaces in the font description will confuse the osd_cat program.

Let's try the osd_cat test
again, this time with a font definition:

$ echo "Hello there, this is osd_cat speaking." |
osd_cat -f "-adobe-helvetica-bold-r-normal-*-*-240-*-*-p-*-*-*"

If everything works properly, you should see the message in much
larger text.

You can use the -c switch to change the color of
the text. You can use any color name defined in the
/usr/X11R6/lib/X11/rgb.txt file, but unless
you're really picky, it's safe to
stick with basic color names, such as blue, green, yellow, cyan,
white, black, and magenta. If you really want to branch out into
colors, such as PapayaWhip, however, be my guest.

Green is typical of television on-screen displays, so see if it looks
good for XOSD:

$ echo "Hello there, this is osd_cat speaking." |
osd_cat_-c green -f "-adobe-helvetica-bold-r-normal-*-*-240-*-*-p-*-*-*"

If you want to get fancy, present the text with a bit of a shadow. Of
course, if the message displays on a dark background, you probably
won't see the shadow. Add the -s
2 switch to create a 2-pixel shadow for the message:

$ echo "Hello there, this is osd_cat speaking." |
osd_cat -c green -s 2 -f "-adobe-helvetica-bold-r-normal-*-*-240-*-*-p-*-*-*"

Now position the text in the middle of the screen with the
-p middle switch (you can choose
top or bottom, if you prefer).
You might see the message appear at the top of the screen for a
moment, after which it shifts to the middle of the screen. This is an
occasional idiosyncrasy of osd_cat that will
probably be fixed as it matures. Finally, you can make the message
display on the screen for longer than the default 5 seconds. Add the
-d 60 switch to tell osd_cat
to leave the message on the screen for 60 seconds:

$ echo "Hello there, this is osd_cat speaking." |
osd_cat -c green -s 2 -p middle -d 60
-f "-*-helvetica-*-*-*-*-34-*-*-*-*-*-*-*"

A number of other switches are also available, such as a switch to
indent the text. Browse the manpage for osd_cat
for a list of the available customization switches.

4.6.2. Scripting the Attention-Getting Reminder

Now that you know what XOSD can do, you can put it to work by writing a
script that will cause reminders to flash on the screen at the
appointed time. In addition to osd_cat, you also
need the at program installed for this script to
work, and you must have the atd daemon running.
Many Linux distributions install at and
atd, and run the daemon by default. If yours
does not, you have to follow the procedure for your particular
distribution to install at and
atd, and make sure atd
starts when you boot the computer.

Now, on to the script itself. Log in as root or use
sudo to fire up your favorite editor, create the
file /usr/local/bin/remindme, and type in the
bash script from Example 4-1 or fetch the script
from O'Reilly's Examples web site
for this book.

Example 4-1. remindme bash script

#!/bin/bash
# figure out which display we're currently using
HOST="$(xrdb -symbols | grep SERVERHOST | cut -d= -f2)"
DISPLAYNUM="$(xrdb -symbols | grep DISPLAY_NUM | cut -d= -f2)"
THISDISPLAY=$HOST:$DISPLAYNUM.0
# check to see if the reminders directory exists in the home directory
# if not, then create the directory
if [ ! -e ~/reminders ] ; then
mkdir ~/reminders
fi
unique=`date +%F-%H-%M-%S`
reminder="reminders/reminder-"$unique
# Now output the reminder script
echo '#!/bin/bash' > ~/$reminder
echo -n 'export DISPLAY=' >> ~/$reminder
echo $THISDISPLAY >> ~/$reminder
echo "echo \"$2 today\" | osd_cat -s 2 -c green -p middle -f -adobe-helvetica-bold-r-normal-*-*-240-*-*-p-*-*-* -d 60" >> ~/$reminder
# Make the reminder script executable
chmod +x ~/$reminder
# Schedule it to run
at $1 -f ~/$reminder

Save your work, and change the file to be executable with this
command:

$ sudo chmod +x /usr/local/bin/remindme

Do you need to set a quick reminder to call your boss at 2:00 p.m.?
Simply type the following command:

$ remindme 2:00pm "Call your boss now." 

From this command the bash script creates a separate reminder script
and schedules it to run at 2:00 p.m. The script it creates will put
the message on the screen using on-screen display. That means you
won't be able to miss the message, because it will
appear on every virtual desktop at the same time.

Here's how it works. The first part of the script
determines which X Windows display you are using. Then it adds a line
to the reminder file that exports the discovered display setting. The
osd_cat program does not get that information
from the environment, so it must be specified in the script. You
can't depend on the user always being on the default
display of :0.0, which is why the script has to
determine the current display by querying the system with the
xrdb command.

Some versions of osd_cat are cranky about how the DISPLAY variable is set, and they won't work if you specify the hostname in front of the <:0.0>. Keep that in mind when trying to get this working on your system.

The next part of the bash script creates a unique filename based on
the current time. Then it creates the first line of the bash script
(#!/bin/bash) and writes it to the reminder file
that will run at the proper time.

Next, it adds the on-screen display command, which substitutes
"Call your boss now" for the second
argument, $2. It makes the reminder script
executable, and finally, it schedules the computer to run your
reminder program with the at command, which uses
the time at which you typed the command as your first argument. The
time argument is flexible, by the way. You can type the time as
2:00PM, 2pm, or even 14:00. The script adds today
for you, although if you are ambitious, you can rewrite the script to
let you create reminders for specific dates in the future.

If you look carefully at the script, you can see that it stores files
as something such as
~/reminders/reminder-2004-10-04-05-07-39. Note
that the symbol ~ refers to your home directory,
so it is storing all the reminders in the
reminders subdirectory just below your home
directory. If you like this script and use it often, this directory
will fill up with those temporary reminder script files. They
don't take up much space, so that
shouldn't be much of a concern. But if you want to
clean out old reminders, you can do so by checking the filenames to
see how old they are. Each reminder script includes the year, month,
day, hour, minute, and second as part of the filename. This makes it
easy to identify expired reminders and delete them.

Note that the year, month, day, hour, minute, and second in the filename represent the time you created the reminder script file, not the time it is scheduled to run. If you create a reminder at 1:00 p.m. that is supposed to run at 3:00 p.m., don't delete the file because it's older than the current time if the current time is sometime before 3:00 p.m. It expires after it was scheduled to runat 3:00 p.m.not after the time it was created.