return success code on "end of month" and "leap year"

end-of-month.sh

#!/bin/bash
# Usage:
#   # crontab: need to run some-command at end-of-month.
#   0 15 28-31 * * end-of-month.sh && some-command

set -o errexit

arg=$1
if [ $(date +%m -d "$arg tomorrow" ) != $(date +%m -d "$arg" ) ] ; then
    exit 0;
else
    exit 1;
fi

leap-year.sh

#!/bin/bash
# Usage:
#   # crontab: need to run some-command at leap-year or not it.
#   5 18  1 3 * * leap-year.sh || some-command
#   5 18 29 2 * * some-command

set -o errexit

arg=$1
if [ "$arg" ] ; then
    year=$arg
else
    year=$( date +%Y )
fi

if [ $(( $year % 4 )) = 0 ] ; then
    if [ $(( $year % 100 )) = 0 ] ; then
	if [ $(( $year % 400 )) = 0 ] ; then
	    exit 0
	else
	    exit 1
	fi
    else
	exit 0
    fi
else
    exit 1
fi