start_comm_daemon.sh
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start_comm_daemon.sh
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	#!/usr/bin/env bash

	service_command="$1" # The command used to start the service (e.g. mariadbd)
	service_name="$2" # The official name of service (e.g. MariaDB)
	entrypoint="$3" # Command or script used to initiate service
	pidfile="$4" # Location of PID file

	# Check if service was already started
	set +e # allow for pgrep to not find matches
	# BSD pgrep doesn't have a "count" feature, use wc then trim whitespace
	service_count=$(pgrep "$service_command" \| wc -l \| xargs echo)
	set -euo pipefail

	if [[ "$service_count" -eq "0" ]]; then
	echo "Starting $service_name"
	# No service present, start our own
	# Launch in subshell so if the original terminal is closed, the process
	# will be inherited instead of also being forced closed
	mkdir -p "$(dirname "${pidfile}")"
	($entrypoint &
	echo "$!" > "$pidfile")

	elif [[ "$service_count" -eq "1" ]]; then

	# Check if it was started by this script
	running_pid="$(pgrep "$service_command")"
	if [[ ! -f "$pidfile" ]] \|\| \
	[[ "$(cat "$pidfile")" != "$running_pid" ]]; then
	echo "Existing $service_name instance found outside of nix environment" >&2
	echo "Please stop existing services and attempt 'nix develop' again" >&2
	exit 1
	fi

	else
	echo "Many $service_name instances found outside of nix environment" >&2
	echo "Please stop existing services and attempt 'nix develop' again" >&2
	exit 1

	fi