Run command at specified time without at(1).

run-at

#!/bin/sh

EX_USAGE=64
EX_DATAERR=65

WAKEUP_BEFORE_S=10
BUSYLOOP_SLEEP_US=500000

usage_exit() {
  echo "Usage: $0 [-xf] time command args..." 1>&2
  echo "  -x: debug mode" 1>&2
  echo "  -f: force exec" 1>&2
  exit $EX_USAGE
}

exec_cmd() {
  "$SHELL" -c "$*"
}

FORCE_EXEC=0
while getopts "dxfh?" OPT
do
  case $OPT in
    x)
      set -x
      : "Set debug mode."
      ;;
    f)
      : "Set force exec(if specified time is past time)"
      FORCE_EXEC=1
      ;;
    h)  usage_exit
      ;;
    \?) usage_exit
      ;;
  esac
done
shift $((OPTIND - 1))


TIME_STR="$1"
shift

if echo "$TIME_STR" | grep -q '^+[0-9][0-9]*$'; then
  TIME_STR="$(date -d "$TIME_STR minutes" +'%Y/%m/%d %H:%M:00')"
fi

TIME_UT=`date -d "${TIME_STR}" +"%s"`
NOW_UT=`date +"%s"`

TIME_DIFF=`expr "$TIME_UT" - "$NOW_UT"`
if [ "$TIME_DIFF" -lt 0 ]; then
  if [ "$FORCE_EXEC" -ne 1 ]; then
    : "Past time. exiting..."
    exit $EX_DATAERR
  fi
fi

: "Command will execute at `date -d @"$TIME_UT"`"

TIME_SLEEP=`expr "$TIME_DIFF" - "$WAKEUP_BEFORE_S"`
if [ "$TIME_DIFF" -gt 10 ]; then
  sleep "$TIME_SLEEP"
fi

CURRENT_UT=`date +"%s"`
while [ "$CURRENT_UT" -lt "$TIME_UT" ]; do
  usleep "$BUSYLOOP_SLEEP_US"
  CURRENT_UT=`date +"%s"`
done

exec_cmd "$@"