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I am trying to use this bash code to get the temperature of my Raspberry Pi, convert to Fahrenheit and display both Fahrenheit and Celsius then save as text file:

#!/bin/bash
echo ""
cpu="$(/opt/vc/bin/vcgencmd measure_temp)"
far=$((cpu/1000))
far2=$((far*9))
far3=$((far2/5))
far4=$((far3+32))
echo "CPU => $((cpu/1000))' C or $((far4))' F"
echo ""
echo "Pi temp $far4 degrees F" > /var/www/html/pitemp.txt

However when i run it, the Fahrenheit is ok, but why is the Celsius not shown?

pi@raspberrypi:~ $ nano checkTemp.sh
pi@raspberrypi:~ $ ./checkTemp.sh

./checkTemp.sh: line 3: temp=40.0'C: command not found
CPU => 0' C or 32' F

pi@raspberrypi:~ $ /opt/vc/bin/vcgencmd measure_temp
temp=40.0'C

I checked the value of cpu and far but it seems not to be working. Any advice?[solved]


#!/usr/bin/env bash
echo ""
cpu="$(/opt/vc/bin/vcgencmd measure_temp | sed -E 's/.*=([0-9.]*).*/\1/')"
## convert to Fahrenheit
far=$( echo "$cpu * 9/5 + 32" | bc -l)
## Remove extra decimal digits
printf "CPU => %.2f' C or %.2f' F\n" "$cpu" "$far"
echo ""
printf "Pi temp %.2f degrees F\n" "$cpu" > /var/www/html/pitemp.txt
echo "C:$cpu F:$far"

this new code is working however the Fahrenheit seems has issue becasue the output is:

pi@raspberrypi:~ $ nano checkTemp.sh
pi@raspberrypi:~ $ ./checkTemp.sh

./checkTemp.sh: line 5: bc: command not found
CPU => 43.00' C or 0.00' F

C:43.0 F:
pi@raspberrypi:~ $ /opt/vc/bin/vcgencmd measure_temp
temp=43.0'C
pi@raspberrypi:~ $
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  • Welcome to Unix & Linux! Please don't post images of text. Instead, copy/paste the text into your question and use the formatting tools to format it as code. Commented Oct 11, 2020 at 10:01
  • Also, please show us the output of /opt/vc/bin/vcgencmd measure_temp. Commented Oct 11, 2020 at 10:08
  • I edited it please have a look again. and the temperature is 40~44.0c Now. Commented Oct 11, 2020 at 10:23
  • 1
    Are you sure that is exactly the script you are running? That should give you an invalid arithmetic operator error, not a command not found. Commented Oct 11, 2020 at 10:44
  • I am sure and i am following this instrument:nebulousthinking.wordpress.com/2019/07/27/… his code has multiple error so i was fixing Commented Oct 11, 2020 at 11:04

1 Answer 1

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Your $cpu variable holds temp=40.0'C. That isn't a number, you can't divide that or multiply it, you need to first extract the actual numerical value. So you need to get the 40.0 out. You can do this with:

cpu="$(/opt/vc/bin/vcgencmd measure_temp | sed -E 's/.*=([0-9.]*).*/\1/')"

The next problem is that bash cannot do floating point arithmetic. So it can't deal with non-integer values. You need another tool for that, something like bc:

far=$(echo "$cpu/1000" | bc -l)

Of course, since your CPU temperature will never be higher than (or remotely near) 1000 degrees Celsius, this division cannot be right. The formula for converting Celsius to Fahrenheit seems to be:

T(°F) = T(°C) × 9/5 + 32

You can do this in one step. Putting all this together, this should be a working version of your script:

#!/usr/bin/env bash
echo ""
cpu="$(/opt/vc/bin/vcgencmd measure_temp | sed -E 's/.*=([0-9.]*).*/\1/')"
## convert to Fahrenheit
far=$( echo "$cpu * 9/5 + 32" | bc -l)
## Remove extra decimal digits
printf "CPU => %.2f °C or %.2f °F\n" "$cpu" "$far"
echo ""
printf "Pi temp %.2f degrees F\n" "$far" > /var/www/html/pitemp.txt

If you don't have bc, you can use this:

#!/usr/bin/env bash
echo ""
cpu="$(/opt/vc/bin/vcgencmd measure_temp | sed -E 's/.*=([0-9.]*).*/\1/')"
## convert to Fahrenheit
far=$( perl -le 'print $ARGV[0] * 9/5 + 32' "$cpu")
## Remove extra decimal digits
printf "CPU => %.2f °C or %.2f °F\n" "$cpu" "$far"
echo ""
printf "Pi temp %.2f degrees F\n" "$far" > /var/www/html/pitemp.txt
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