[NTLUG:Discuss] More shell scripting madness

[. Daniel]

>. Daniel wrote:
> > I know it's hard to see, but I'm actually starting to learn this stuff
> > little by little.
> >
> > Here's the purpose:
> >
> > I upgraded the processor and video in my laptop.  Now it gets warmer 
than I
> > like, especially during game play, which slows down when the processor 
and
> > video heat up.  While I intend to improve the actual heatsink materials
> > (Copper is surprisingly hard to get in the form I need it... and 
EXPENSIVE)
> > I would like to keep the processor fans running.
> >
> > As it turns out, the system is controlling the fans by itself based on
> > certain criteria.  But there is also a handy little utility to simply 
turn
> > on the fan!  It's called "i8kfan."  Run i8kfan without parameters and 
it
> > will simply return with two numbers indicating the mode of the fans at 
that
> > moment.  The values are 0, 1 and 2.  So if both fans are off, it will
> > return "0 0" and if both are on high speed it will return "2 2".
> >
> > So I wrote a loop that checks the fan status every two seconds and if 
it's
> > not "2 2" it will set the fans to "2 2" and go back to sleep.  I then 
set
> > up an icon on my panel to start the process when I want to play a game 
so I
> > can prolong my "cool time."
> >
> > Here's the problem though:  Gnome shortcuts no longer seem to want to
> > launch processes in terminal.  In earlier versions, there was a check 
box
> > to select this option.  It was a good option to use when you were 
debugging
> > because you could see error messages streaming by or whatever.  Now 
it's
> > gone and I can't run the script in a terminal window expect by hand...
> > which, of course, I don't wanna do.
> >
> > So here's the script as simple as it is:
> >
> > "i8kfanloop.sh"
> > -----
> > #!/bin/bash
> >
> > loop=1
> >
> > while [ loop ]
> > do
> >   status=`i8kfan`
> >   if [ "$status" != "2 2" ]
> >   then
> >      i8kfan 2 2
> >   fi
> >   sleep 2
> > done
> > -----
> >
> > That's some pretty simple bash code right?
> >
> > Here's what I'd like to add to it.  I'd like to add some code that will
> > detect if a previous instance of this script is currently running and 
if it
> > is, kill it and exit.  If it's not running, just go into the loop.  So 
the
> > result would be, if I click the icon once, it runs the loop.  If I 
click
> > the icon again, it will stop the loop.
> >
> > I imagine some code that will get the shell script's process ID number 
and
> > stores it somewhere, say "/tmp/$username_i8kfanloop.pid" or something 
like
> > that.  Then at the beginning of the script, it will look for said file 
and
> > compare the process ID recorded in the file with the process listing to 
see
> > if the process ID is there and actually the same script.
> >
> > If the filename doesn't exist, create the PID file and enter the loop.
> > If the filename exists but the process doesn't, it should erase the 
file,
> > create a new PID file and enter the loop.
> > If the filename exists and the process exists but the PID doesn't match 
up
> > with the script name, then erase the file, create a new PID file and 
enter
> > the loop.
> >
> > I feel confident that if I messed with this for a few hours, I'd be 
able to
> > cobble up something that works.  But before I spend my work day on my
> > personal stuff, I'm willing to bet someone already has or knows about 
some
> > shell code out there that does this already.  And I'm hoping that 
someone
> > will be kind and generous enough to paste their code into a reply so 
that I
> > could learn and adapt my skills further. :)
> >
>
>Consider a front end script called mydaemon-start.sh:
>
>#!/bin/sh
>if pid=$(pgrep mydaemon.sh); then
>         kill -9 $pid
>fi
>
>exec /usr/local/bin/mydaemon.sh &
>
>Where your script is what is inside of mydaemon.sh
>
>You can always add a mydaemon-kill.sh that just does
>the first part, or make the frontend understand
>parameters so you can use the same script to 'start'
>and 'stop' mydaemon.sh

!!!! PGREP !!!!

I didn't know that existed.  That's *the* simple answer to this.  Set up 
the script with an "if-then-else" and inside the "then" set up to kill the 
process and in the "else" start the process.  

By far that is the most simple solution.  I was sort of hacking my way 
through using various expressions and the like, but that process control 
structure wins hands-down.

But while hacking around, I came up with a question I haven't yet figured 
out.

How can I set up an expression that tests if one string is found within 
another.  Let's say, for example, A="ABCDEFGHIJK" and B="CDEF".  Obviously 
$B can be found within $A.  But how to set up an expression where the 
result is true or false and can run a conditional off of the result?

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