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#!/bin/sh
# setup
set -e
die() { echo "usage: $0 [-r relay] [-s state] [-ght] [device]" && exit $1 ; }
getstate() {
tty=$1
relay=${2:-1}
# write 0xFF for status
printf '\377' > $tty
# read status response for selected relay
while read r; do case "$r" in "CH${relay}: "*) echo "$r" && return ;; esac; done < $tty
}
genbytes() {
# the relay is controled by a fixed 4 byte command as follows:
start=160 # always 0xA0
relay=$1 # relay id (counts from 1)
state=$2 # whether to energize 1 or 0
checksum=$(( start + relay + state )) # checksum is just a sum
# generate the octal sequence with printf, then convert to bytes with printf again
printf "$(printf '\\%03o\\%03o\\%03o\\%03o' $start $relay $state $checksum)"
}
# args
relay=1
state=1
while getopts 'r:s:ght' opt; do
case "$opt" in
r) relay="$OPTARG" ;;
s) state="$OPTARG" ;;
g) get=1 ;;
t) get=1 && toggle=1 ;;
h) die 0 ;;
\?) die 1 ;;
esac
done
shift $((OPTIND - 1)) # shift to final arg
tty="${1:-/dev/stdout}" # output to stdout as fallback
# validate
case $relay in [1-9]|[1-9][0-9]*) ;; *) die 1 ;; esac
case $state in [01]) ;; *) die 1 ;; esac
[ -n "$get" ] && [ "$tty" = "/dev/stdout" ] && die 1
# handle get commands
if [ -n "$get" ]; then
s=$(getstate "$tty" $relay) || die 1
if [ -z "$toggle" ]; then
echo "$s" && exit 0 # exit when no toggle
else
case "$s" in
*ON) state=0 ;;
*OFF) state=1 ;;
esac
fi
fi
# go
genbytes $relay $state > "$tty"
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