UNIX for Dummies Questions & Answers

My project is to get a temperature reading from a refridgerator every 2 minutes and check to see if the door has been left open.

I don't yet have the mastery of Linux, being a complete noob, but I reckon I need a text file with the latest temperature reading in it. This I've managed to do by getting cron to call up a script called fridgedoor every 2 minutes and outputting the result from Digitemp (serial temperature reader) to fridgedoor.txt.

So every 2 minutes fridgedoor.txt is overwritten with the current temperature. The file just has a number in it e.g "3.06"

So I've got line 1 of my script done and dusted.

My next job is to get it to play a .wav if the temperature is greater than 5.00

Aaaah! My knowledge of commands was pretty well used up on line 1.

I know I start with if and end with fi. It's just the teensy weensy bits in the middle I'm clueless about.

Anybody want to help a knackered old sop like me out with the middle bit?

I await in eager anticipation...

Happy New Year by the way...

Code:

while true
do
    [  $(( $(<fridgedoor.txt)  > 5.00 ))  ]  && echo ok || echo 'not ok'
    sleep 120
done

Place a command after the || part (ie remove the second echo statement) that plays a tone on your box.

Oooh! It's so close!

Thanks for the quick reply
Hit a bit of a snag though...

The script is:

Code:

#!/bin/bash
/usr/bin/digitemp_DS9097 -a -q -o"%.2C" -c /etc/digitemp.conf > /home/brafferton/Downloads/fridgedoor.txt

while true
do
  [ $(( $(</home/brafferton/Downloads/fridgedoor.txt) > 5.00 )) ] && echo ok || echo 'not ok'
done

I've left out the sleep 120 as cron does that.
Q: Is while do a never ending loop?

Anyway!
Typing in the command line:

brafferton@cameras:~/Downloads$ fridgedoor

gets:

/usr/bin/fridgedoor: line 6: 2.88 > 5.00 : syntax error: invalid arithmetic operator (error token is ".88 > 5.00 ")

---------- Post updated at 11:04 PM ---------- Previous update was at 08:45 PM ----------

I've been doing a lot of trawling and I think that either the CR at the end of the line, (and I presume there is one) is cocking up everything OR that bash won't do decimals, or both
If it's not the CR thingy then how would I strip the decimals off fridgedoor.txt i.e. if 6 > 5 then sound the alarm?

---------- Post updated 28-01-11 at 08:49 AM ---------- Previous update was 27-01-11 at 11:04 PM ----------

More trawling overnight and I've managed:

Code:

REAL=$(/usr/bin/digitemp_DS9097 -a -q -o"%.0C" -c /etc/digitemp.conf)
echo "${REAL} C"
if [ "${REAL}" -ge 5 ] ;then
echo door closed    
else
echo door open
fi

No Errors!
Seems to work...