autogain1090 not cleanly handling commented lines in config

[f3sty]

I ran into an issue with a commented-out RECEIVER_OPTIONS line in /etc/default/readsb from an SDR swap, e.g.

 # RECEIVER_OPTIONS="--device 0 --device-type rtlsdr --gain 48.0 --ppm 50"  
RECEIVER_OPTIONS="--device 0 --device-type rtlsdr --gain 44.5 --ppm 25"

autogain1090 was throwing awk errors, not selecting an appropriate new gain value, and writing the new (incorrect) value to both config lines, not just the uncommented line.

Below is an excerpt from a autogain1090 run - oldgain is being set to 48.0\n44.5 which is breaking all the math:

+ '[' -f /boot/adsb-config.txt ']'
++ grep -P -e 'gain \K[0-9-.]*' -o /etc/default/readsb
+ oldgain='48.0
44.5'
+ [[ 48.0
44.5 == '' ]]
+ gain_index=28
+ for i in "${!ga[@]}"
+ awk 'BEGIN{ exit  (48.0
44.5 <= 0.0) }'
awk: line 1: missing ) near end of line
awk: line 2: extra ')'
+ gain_index=0
+ break
+ awk 'BEGIN{ exit  (48.0
44.5 > 49.6) }'
awk: line 1: missing ) near end of line
awk: line 2: extra ')'
+ gain_index=28
+ [[ 48.0
44.5 == \-\1\0 ]]
+ awk 'BEGIN{ exit (0.000 > 0.5) }'
+ awk 'BEGIN{ exit (0.000 < 0.5) }'
+ [[ 28 == 29 ]]
+ awk 'BEGIN{ exit (0.000 < 0.5) }'
+ gain_index=29
+ action=Increasing
+ awk 'BEGIN{ exit (0.000 > 7.0) }'
+ awk 'BEGIN{ exit (0.000 > 7.0) }'
+ gain=-10
+ [[ -10 == '' ]]
+ '[' -f /boot/piaware-config.txt ']'
+ '[' -f /boot/adsb-config.txt ']'
+ grep gain /etc/default/readsb
+ sed --follow-symlinks -i -E -e 's/--gain -?[0-9]*\.?[0-9]*/--gain -10/' /etc/default/readsb
+ systemctl restart readsb
+ echo 0
+ echo 0
+ echo 'Increasing gain to -10 (0.000% messages >-3dB)'
Increasing gain to -10 (0.000% messages >-3dB)

Resulting /etc/default/readsb with both lines modified and incorrect gain step:

# RECEIVER_OPTIONS="--device 0 --device-type rtlsdr --gain -10 --ppm 50"
RECEIVER_OPTIONS="--device 0 --device-type rtlsdr --gain -10 --ppm 25"

I'll submit a PR for this shortly.

[wiedehopf]

Really use --gain auto anyhow :)

[f3sty]

readsb-gain also modifies commented lines in /etc/default/readsb, PR#49 updated with a fix for this too.