cron-test.sh: tests if a date/time (or the current time if no time) matches a cron specifier. Only the *standard* special characters are supported:

check-cron.sh

#!/bin/bash

target=$1
datetime=$2

if [ -z "$target" ] ; then
  >&2 echo 'No target is specified.'
  >&2 echo "Usage: $0 <cron-specification> [<date-time>]"
  >&2 echo "  e.g. $0 '* 16,17 * * *'"
  >&2 echo "  e.g. $0 '* 16,17 * * *' '2014-01-01 17:32'"
  >&2 echo "Crontab syntax:  Minute  Hour  DayOfMonth  Month  DayOfWeek"
  >&2 echo "Only the basic syntax is supported. This includes multiple values (16,17),"
  >&2 echo "  ranges (13-17) and predefined schedules (@daily,...)"
  >&2 echo "All other things (like multiple values combined with ranges) are NOT"
  >&2 echo "  supported."
  exit 2
fi

if [ -z "$datetime" ] ; then
  components=$(date +"%M %H %d %m %w")
else
  components=$(date --date "$datetime" +"%M %H %d %m %w")
fi

case $target in
  @yearly )
    target='0 0 1 1 *' ;;
  @annually )
    target='0 0 1 1 *' ;;
  @monthly )
    target='0 0 1 * *' ;;
  @weekly )
    target='0 0 * * 0' ;;
  @daily )
    target='0 0 * * *' ;;
  @midnight )
    target='0 0 * * *' ;;
  @hourly )
    target='0 * * * *' ;;
esac

if [ $(echo "$target" | wc -w) -ne "5" ]
then
  >&2 echo "Invalid target specification: $target"
  exit 2
fi
if [ $(echo "$components" | wc -w) -ne "5" ]
then
  >&2 echo "Invalid component list: $component"
  exit 2
fi

for i in 1 2 3 4 5
do
  t=$(echo "$target" | awk -v N=$i '{print $N}')
  c=$(echo "$components" | awk -v N=$i '{print $N}')

  #>&2 echo "Checking $t - $c"

  # star match
  if [ "$t" = '*' ] ; then
    #>&2 echo "Checking $t - $c ==> STAR MATCH"
    continue
  fi

  # interval match
  if [[ "$t" =~ ^([^-]+)-([^-]+)$ ]] ; then
    from="${BASH_REMATCH[1]}"
    to="${BASH_REMATCH[2]}"
    if [ $from -le $c -a $c -le $to ] ; then
      #>&2 echo "Checking $t - $c ==> INTERVAL [$from,$to] MATCH"
      continue
    else
      #>&2 echo "Checking $t - $c ==> INTERVAL [$from,$to] NO MATCH"
      exit 1
    fi
  fi

  # comma separated list
  if [[ "$t" =~ , ]] ; then
    IFS=","
    found=0
    for i in $t
    do
      if [ "$c" = "$i" ] ; then
        found=1
        break
      fi
    done
    if [ $found -eq 1 ] ; then
      #>&2 echo "Checking $t - $c ==> LIST [$t] MATCH"
      continue
    else
      #>&2 echo "Checking $t - $c ==> LIST [$t] NO MATCH"
      exit 1
    fi
  fi

  # exact match
  if [ "$c" = "$t" ] ; then
    #>&2 echo "Checking $t - $c ==> EXACT MATCH"
    continue
  fi

  #>&2 echo "Checking $t - $c ==> NO MATCH"
  exit 1
done

exit 0