Bash script that waits for SQL server to accept logins

wait-for-sql-server

#! /usr/bin/env bash

wfss__help() {

	printf '%s\n'\
		'wait-for-sql-server - Tries to connect to sql server otherwise fails            ' \
		'                                                                                ' \
		'Usage:                                                                          ' \
		'  wait-for-sql-server [options] -- <sqlcmd options>                             ' \
		'  wait-for-sql-server <sqlcmd options>                                          ' \
		'                                                                                ' \
		'sqlcmd options:                                                                 ' \
		'  Options passed to sqlcmd see `sqlcmd -?` for more information. You might want ' \
		'  to consider setting `[-l login timeout]`, the default value here is 8 seconds.' \
		'                                                                                ' \
		'Options:                                                                        ' \
		'  -a, --attempts <attemps>  Number of attempts to connect to sql server before  ' \
		'                            exiting with a failure. Default value 8             ' \
		'                                                                                ' \
		'  -?, --help             Shows this help message                                ' \
		'                                                                                ' \
		'Examples:                                                                       ' \
		'  wait-for-sql-server --attempts 1 -- -U sa -P "P455word!!!" -S "localhost,1433"' \
		'  wait-for-sql-server -U sa -P "P455word!!!" -S "localhost,1433"                ' \
		'                                                                                ' \

	exit

}

wfss__wait_for_sql_server() {

	#
	# Check if we can actually sqlcmd executable
	#
	which sqlcmd > /dev/null 2>&1 || {
		echo "[ wait-for-sql-server ] sqlcmd not found"
		exit 1
	}

	#
	# Parse the arguments, first sieve the arguments to check if we have arguments of
	# our own. If we don't easy-peasy continue building the sqlcmd arguments and try
	# to connect to sql server, otherwise process our options and then go on with the
	# connecting to sqlserver business.
	#
	local attempts=8;
	
	local parsed_options=();
	local sqlcmd_options=();

	while (( $# )); do

		case $1 in
			"-?" | --help) wfss__help ;;
			--) shift ; sqlcmd_options=( "$@" ); break 2 ;;
			*)  parsed_options+=( "$1" ) ; shift ;;
		esac

	done

	if [[ -z "${sqlcmd_options[*]}" ]]; then
		
		sqlcmd_options=( "${parsed_options[@]}" )

	else

		for (( i = 0; i < ${#parsed_options[@]}; i++ )); do

			case ${parsed_options[ $i ]} in
				-a | --attempts) attempts=${parsed_options[ 1 + $i ]}; (( i++ )) ;;
				*) {
					echo "[ wait-for-sql-server ] Unknown option [ ${parsed_options[ $i ]} ]"
					exit 1
				}
			esac

		done

	fi

	local connection_command="sqlcmd ${sqlcmd_options[@]} <<-SQL
		:quit
	SQL"
	
	for (( attempt = 1; attempt < attempts + 1; attempt++ )); do

		echo "[ wait-for-sql-server ] Connection attempt [ ${attempt} / ${attempts} ]" >&2

		if bash -c "${connection_command}" > /dev/null 2>&1; then
			echo "[ wait-for-sql-server ] Successfully connected to sql server"
			exit 0
		fi

	done

	echo "[ wait-for-sql-server ] Failed to connect to sql server"
	exit 1

}

(return 0 2>/dev/null) || wfss__wait_for_sql_server "$@"