Shell Programming and Scripting

I have seen versions of cal which print three months by default. The above scripts fail in that case.

Code:

_days_in_month() ## USAGE: _days_in_month [month [year]]
{
    case ${1#0} in
        9|4|6|11) _DAYS_IN_MONTH=30 ;; ## 30 days hath September...
        1|3|5|7|8|10|12) _DAYS_IN_MONTH=31 ;;
        2) is_leap_year ${2:-`date +%Y`} && _DAYS_IN_MONTH=29 || _DAYS_IN_MONTH=28 ;;
        *) return 5 ;;
    esac
}

is_leap_year() { ## USAGE: is_leap_year [year]
    ily_year=${1:-`date +%Y`}
    case $ily_year in
        *0[48] |\
        *[2468][048] |\
        *[13579][26] |\
        *[13579][26]0|\
        *[02468][048]00 |\
        *[13579][26]00 ) _IS_LEAP_YEAR=1
                         return 0 ;;
        *) _IS_LEAP_YEAR=0
           return 1 ;;
    esac
}

eval "$(date "+monthname=%B month=%m year=%Y")"
_days_in_month "$month" "$year"
printf "%s has %d days\n" "$monthname" "$_DAYS_IN_MONTH"

I use a library of date functions which can be found in my first book; see 8: The Dating Game