[SOLVED] Can't get the hang of while do

Fitch · 04-02-2011, 06:47 AM

This code is meant to retrieve ascii from a temperature sensor in the fridge, check that it is not the error code (85 degrees) and append it to a csv file.

If the reading is 85 degrees, then either my fridge is on fire or the sensor cocked up, in which case it is meant to try again.

It's the last bit that I can't get to work.

Code:

#!/bin/bash
COUNT=4
while [ $COUNT -gt 0 ]; do
  /usr/bin/digitemp_DS9097 -a -q -o"%d/%b/%g %H:%M%t%.2C" -c /etc/digitemp.conf > /home/brafferton/Downloads/check.txt
  CHECK=$(tail -c 6 /home/brafferton/Downloads/check.txt)
     if [ "${CHECK}" = 85.00 ];then
#        echo bad result
        COUNT=$((COUNT - 1))
     else
        COUNT=0 
        cat /home/brafferton/Downloads/check.txt >> /home/brafferton/Downloads/$(date +%G-%b).csv
#        echo good result
     fi
done

Check.txt is empty if the reading is bad, and nothing is appended to the log.
This check is done every 4 hours, day and night. But as you can see from below, a few results are missing.

the results (so far) from 2011-Apr.csv

01/Apr/11 00:30 4.19
01/Apr/11 04:30 3.69
01/Apr/11 20:31 3.88
02/Apr/11 00:30 5.12
02/Apr/11 04:30 4.06
02/Apr/11 08:31 3.62

Can somebody tell me what I'm doing wrong?

I use Ubuntu 10.04 (Lucid), if that's any help...

catkin · 04-02-2011, 07:19 AM

If "Check.txt is empty if the reading is bad" then the "bad" test will never be passed ...

If /home/brafferton/Downloads/check.txt is empty when the reading is bad then CHECK=$(tail -c 6 /home/brafferton/Downloads/check.txt) sets CHECK to an empty string and if [ "${CHECK}" = 85.00 ] fails, COUNT is set to zero, an empty string is appended to /home/brafferton/Downloads/$(date +%G-%b).csv and the while loop ends.

Would it be more robust to check that /home/brafferton/Downloads/check.txt contains a valid value rather than sentinel value of 85.00? Or to test for it being empty as you say it is when the reading is bad?

jlinkels · 04-02-2011, 07:46 AM

I am not good in re-playing code in my mind, so I let the code run and look at the output.

I would run the code with sh -x /path/to/your/script 2>&1 >> logfile

Next, I don't quite trust

Code:

[ "${CHECK}" = 85.00 ]

. Can you change that to:

Code:

[ "${CHECK}" == "85.00" ]

although the '==' is not really required, '= ' should work as well.

jlinkels

Fitch · 04-02-2011, 08:15 AM

I am eager to put in a check for a blank check.txt, but my knowledge of the code doesn't quite stretch that far. (this is my very first attempt at scripting)

I am now getting endless "good results", which is great, but doesn't really tell me if I've fixed it...

I bolded the line that is worrying below:

brafferton@cameras:~$ sh -x /usr/bin/fridgeexp 2>&1 >> /home/brafferton/Downloads/log.txt
+ COUNT=4
+ [ 4 -gt 0 ]
+ /usr/bin/digitemp_DS9097 -a -q -o%d/%b/%g %H:%M%t%.2C -c /etc/digitemp.conf
+ tail -c 6 /home/brafferton/Downloads/check.txt
+ CHECK= 3.81
+ [ 3.81 == 85.00 ]
[: 1: 3.81: unexpected operator
+ COUNT=0
+ date +%G-%b
+ cat /home/brafferton/Downloads/check.txt
+ echo good result
+ [ 0 -gt 0 ]

Fitch · 04-02-2011, 11:51 AM

Using a single equals sign stopped the unexpected operator. And I've read up on the -o and -a functions.

I am hoping this works.. It will take a day or two to find out.
Meanwhile, is there anything glaringly obviously wrong?

Code:

#!/bin/bash
COUNT=4
while [ $COUNT -gt 0 ]; do
  /usr/bin/digitemp_DS9097 -a -q -o"%d/%b/%g %H:%M%t%.2C" -c /etc/digitemp.conf > /home/brafferton/Downloads/check.txt
  CHECK=$(tail -c 6 /home/brafferton/Downloads/check.txt)
     if [ "${CHECK}" = "85.00" -o "${CHECK}" = "" ]
	then     
	COUNT=$((COUNT - 1))
#	echo bad result
else
        COUNT=0 
        cat /home/brafferton/Downloads/check.txt >> /home/brafferton/Downloads/$(date +%G-%b).csv
#        echo good result
	fi     
done

The output is as follows, which seems to do the right thing:

brafferton@cameras:~$ sh -x /usr/bin/fridge 2>&1 >> /home/brafferton/Downloads/log.txt
+ COUNT=4
+ [ 4 -gt 0 ]
+ /usr/bin/digitemp_DS9097 -a -q -o%d/%b/%g %H:%M%t%.2C -c /etc/digitemp.conf
+ tail -c 6 /home/brafferton/Downloads/check.txt
+ CHECK= 3.25
+ [ 3.25 = 85.00 -o 3.25 = ]
+ COUNT=0
+ date +%G-%b
+ cat /home/brafferton/Downloads/check.txt
+ [ 0 -gt 0 ]

Fitch · 04-02-2011, 02:42 PM

Didn't have to wait too long...

+ COUNT=4
+ [ 4 -gt 0 ]
+ /usr/bin/digitemp_DS9097 -a -q -o%d/%b/%g %H:%M%t%.2C -c /etc/digitemp.conf
+ tail -c 6 /home/brafferton/Downloads/check.txt
+ CHECK=
+ [ = 85.00 -o = ]
+ COUNT=3
+ [ 3 -gt 0 ]
+ /usr/bin/digitemp_DS9097 -a -q -o%d/%b/%g %H:%M%t%.2C -c /etc/digitemp.conf
+ tail -c 6 /home/brafferton/Downloads/check.txt
+ CHECK= 3.38
+ [ 3.38 = 85.00 -o 3.38 = ]
+ COUNT=0
+ date +%G-%b
+ cat /home/brafferton/Downloads/check.txt
+ [ 0 -gt 0 ]

So the null bit worked.
Thing is....
If I type it on the command line, I get perfect results every time.
It's when cron does it that the errors come.

My crontab:

MAILTO=""
# m h dom mon dow command
# Check fridge door every 3 minutes during the day
*/3 8-22 * * * fridgedoor >/dev/null 2>&1
# Get temperature readings from fridge and save to monthly file in Downloads
# 30 */4 * * * fridge >/dev/null 2>&1
30 */4 * * * sh -x /usr/bin/fridge -l 2>&1 | tee /home/brafferton/Downloads/log.txt
# Send report via email on the last day of the month
0 1 1 * * /usr/bin/sendfridge

jlinkels · 04-02-2011, 05:00 PM

What goes wrong? What is the output of the job when it is run by cron?

jlinkels

Fitch · 04-03-2011, 05:47 AM

The logs don't show any errors for cron.
The log of sh -x /usr/bin/fridge -l 2>&1 | tee -a /home/brafferton/Downloads/log.txt
does show a crc error on the reading from digitemp - which, funnily enough, gives a null output.

My theory (whistling in the dark now) is that cron calls digitemp faster than I can do it on the keyboard, and digitemp sometimes can't handle it.

Now however, the new checks allow digitemp to re-read, and hey presto! it gets it right second time around. Good enough!

Thanks Jlinklels and catkin for your help. Much appreciated.