add biastee (#9)

* Add BiasTee option

* Add Biastee to read

* Update aiscatcher - linter

README.md

@@ -184,6 +184,7 @@ You can use `rtl_test` to see which devices and device serials are connected to
 | `RTLSDR_DEVICE_GAIN` | SDR device gain. Can also be set to `auto` | `33` |
 | `RTLSDR_DEVICE_PPM`| PPM deviation of your RTLSDR device | Empty |
 | `RTLSDR_DEVICE_BANDWIDTH` | Channel bandwitdh of the receiver | `192K` |
+| `RTLSDR_DEVICE_BIASTEE` | If set to `on`, `1`, `enabled`, or `yes`, the bias-tee function of the RTLSDR device will be switched on | Empty |
 | `AISCATCHER_CHANNELS` | Channels flag for `ais-catcher`. Set to `AB` (receive on channel AB, default value if omitted), `CD` (receive on channel CD), or `CD AB` (receive on channel CD but forward this data to aggregators saying it's channel AB; this can be used to send channels CD data to aggregators that can't handle CD data) | Empty (`AB`) |
 | `AISCATCHER_DECODER_MODEL` | Decoder model number for `ais-catcher` | `2` |
 | `AISCATCHER_DECODER_AFC_WIDE` | `-go AFC_WIDE` flag for `ais-catcher`. Recommended to set to `on` | `on` |

rootfs/etc/s6-overlay/scripts/aiscatcher

@@ -1,9 +1,7 @@
 #!/command/with-contenv bash
-# shellcheck shell=bash disable=SC1091,SC2016,SC2068,SC2076,SC2086,SC2015
+# shellcheck shell=bash disable=SC1091,SC2016,SC2068,SC2076,SC2086,SC2015,SC2154
 
 source /scripts/common
-APPNAME="aiscatcher"
-s6wrap=(s6wrap --quiet --timestamps --prepend="${APPNAME}")
 
 #---------------------------------------------------------------------------------------------
 # Copyright (C) 2022-2024, Ramon F. Kolb (kx1t)
@@ -204,6 +202,9 @@ if [[ -n "${RTLSDR_DEVICE_SERIAL}" ]]; then
     #AISCATCHER_EXTRA_OPTIONS="$(sed -E 's/-c\s+[a-dA-D ]+//g' <<< "$AISCATCHER_EXTRA_OPTIONS")"   # remove any -c items from param to avoid duplication
     aiscatcher_command+=("-d ${RTLSDR_DEVICE_SERIAL}")
     aiscatcher_command+=("-gr tuner ${RTLSDR_DEVICE_GAIN} rtlagc ON")
+    if chk_enabled "${RTLSDR_DEVICE_BIASTEE}"; then
+        aiscatcher_command+=("BIASTEE on")
+    fi
     if [[ -n "${RTLSDR_DEVICE_PPM}" ]]; then
         aiscatcher_command+=("-p ${RTLSDR_DEVICE_PPM}")
         #AISCATCHER_EXTRA_OPTIONS="$(sed -E 's/-p\s+[0-9]+\s*//g'<<< "$AISCATCHER_EXTRA_OPTIONS")"   # remove any -p items from param to avoid duplication