wait-for-it.sh

#!/usr/bin/env bash
#   Use this script to test if a given TCP host/port are available

cmdname=$(basename $0)

echoerr() { if [[ $QUIET -ne 1 ]]; then echo "$@" 1>&2; fi }

usage()
{
    cat << USAGE >&2
Usage:
    $cmdname host:port [-s] [-t timeout] [-- command args]
    -h HOST | --host=HOST       Host or IP under test
    -p PORT | --port=PORT       TCP port under test
                                Alternatively, you specify the host and port as host:port
    -s | --strict               Only execute subcommand if the test succeeds
    -q | --quiet                Don't output any status messages
    -t TIMEOUT | --timeout=TIMEOUT
                                Timeout in seconds, zero for no timeout
    -- COMMAND ARGS             Execute command with args after the test finishes
USAGE
    exit 1
}

wait_for()
{
    if [[ $TIMEOUT -gt 0 ]]; then
        echoerr "$cmdname: waiting $TIMEOUT seconds for $HOST:$PORT"
    else
        echoerr "$cmdname: waiting for $HOST:$PORT without a timeout"
    fi
    start_ts=$(date +%s)
    while :
    do
        (echo > /dev/tcp/$HOST/$PORT) >/dev/null 2>&1
        result=$?
        if [[ $result -eq 0 ]]; then
            end_ts=$(date +%s)
            echoerr "$cmdname: $HOST:$PORT is available after $((end_ts - start_ts)) seconds"
            break
        fi
        sleep 1
    done
    return $result
}

wait_for_wrapper()
{
    # In order to support SIGINT during timeout: http://unix.stackexchange.com/a/57692
    if [[ $QUIET -eq 1 ]]; then
        timeout $TIMEOUT $0 --quiet --child --host=$HOST --port=$PORT --timeout=$TIMEOUT &
    else
        timeout $TIMEOUT $0 --child --host=$HOST --port=$PORT --timeout=$TIMEOUT &
    fi
    PID=$!
    trap "kill -INT -$PID" INT
    wait $PID
    RESULT=$?
    if [[ $RESULT -ne 0 ]]; then
        echoerr "$cmdname: timeout occurred after waiting $TIMEOUT seconds for $HOST:$PORT"
    fi
    return $RESULT
}

main()
{
  # process arguments
  while [[ $# -gt 0 ]]
  do
      case "$1" in
          *:* )
          hostport=(${1//:/ })
          HOST=${hostport[0]}
          PORT=${hostport[1]}
          shift 1
          ;;
          --child)
          CHILD=1
          shift 1
          ;;
          -q | --quiet)
          QUIET=1
          shift 1
          ;;
          -s | --strict)
          STRICT=1
          shift 1
          ;;
          -h)
          HOST="$2"
          if [[ $HOST == "" ]]; then break; fi
          shift 2
          ;;
          --host=*)
          HOST="${1#*=}"
          shift 1
          ;;
          -p)
          PORT="$2"
          if [[ $PORT == "" ]]; then break; fi
          shift 2
          ;;
          --port=*)
          PORT="${1#*=}"
          shift 1
          ;;
          -t)
          TIMEOUT="$2"
          if [[ $TIMEOUT == "" ]]; then break; fi
          shift 2
          ;;
          --timeout=*)
          TIMEOUT="${1#*=}"
          shift 1
          ;;
          --)
          shift
          CLI="$@"
          break
          ;;
          --help)
          usage
          ;;
          *)
          echoerr "Unknown argument: $1"
          usage
          ;;
      esac
  done

  if [[ "$HOST" == "" || "$PORT" == "" ]]; then
      echoerr "Error: you need to provide a host and port to test."
      usage
  fi

  TIMEOUT=${TIMEOUT:-15}
  STRICT=${STRICT:-0}
  CHILD=${CHILD:-0}
  QUIET=${QUIET:-0}

  if [[ $CHILD -gt 0 ]]; then
      wait_for
      RESULT=$?
      exit $RESULT
  else
      if [[ $TIMEOUT -gt 0 ]]; then
          wait_for_wrapper
          RESULT=$?
      else
          wait_for
          RESULT=$?
      fi
  fi

  if [[ $CLI != "" ]]; then
      if [[ $RESULT -ne 0 && $STRICT -eq 1 ]]; then
          echoerr "$cmdname: strict mode, refusing to execute subprocess"
          exit $RESULT
      fi
      exec $CLI
  else
      exit $RESULT
  fi
}

main $@