wait_for.sh

#!/bin/sh

if [ -z "$1" ]; then
  cat <<-END_OF_HELP
wait_for

Usage:
  wait_for  FILE

Checks for existance of file repeatedly until it succeeds then it exits. File
can also be a couple of predefined commands (spring and bundler), TCP port or
http/https URL.
END_OF_HELP
exit 1
fi

action=$1
attempts=1
case $action in
  spring)
    set -- "bin/spring status 2>/dev/null | grep -q 'Spring is running'"
    ;;
  bundler)
    set -- "bin/bundle check"
    ;;
  http://* | https://*)
    set -- wget --spider "$@"
    ;;
  *:*)
    host=$(echo "$@" | cut -d: -f1)
    port=$(echo "$@" | cut -d: -f2)
    set -- nc -z "$host" "$port"
    ;;
  *)
    if which "$1" >/dev/null 2>&1; then
      set -- "$@"
    else
      set -- test -f "$1"
    fi
    ;;
esac

printf "\nWaiting for %s\n" "$action"
while ! "$@" > /dev/null 2>&1; do
  if [ $attempts = "${WAIT_FOR_ATTEMPTS:-0}" ]; then
    echo " Failed after $attempts attempts!"
    exit 1
  fi

  attempts=$((attempts + 1))
  printf "."
  sleep "${WAIT_FOR_TIME:-1}"
done
printf " Succeded after %s attempts!\n" "$attempts"