Send SMS with USB GSM modem when alarm triggered

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My python script needs some work, so I switched back to a bash shell:

/config/send_sms.sh

#!/bin/bash

DEST=$1
MD="/dev/ttyUSB2"

if [ -z "$2" ]
then
read message
else
message="$2"
fi

echo "Sending $message to $DEST"

apk add ppp

stty -F $MD 9600 min 100 time 2 -hupcl brkint ignpar -opost -onlcr -isig -icanon -echo

chat TIMEOUT 10 "" "AT+CMGF=1" "OK" > $MD < $MD
chat TIMEOUT 10 "" "AT+CMGS=\"$DEST\"" "OK" > $MD < $MD
chat TIMEOUT 10 "" "$message^Z" "OK" > $MD < $MD

Also, if you are using a RPI4, I found that you need a udev rule in the config USB stick, for me this config was:

udev\10-gsm-modem.rules

ACTION=="add" \
, ATTRS{idVendor}=="12d1" \
, ATTRS{idProduct}=="14fe" \
, RUN+="/sbin/usb_modeswitch -X -v 12d1 -p 14fe"

You get the vendor id and product id from the output of lsusb