今儿个讲得是判断输入的日期是否正确，有利用到我们之前03这个例子中的函数
下面是代码

#!/bin/sh# valid-date -- Validates a date, taking into account leap year rules.exceedsDaysInMonth(){ case $(echo $1|tr '[:upper:]' '[:lower:]') in jan* ) days=31 ;; feb* ) days=28 ;; mar* ) days=31 ;; apr* ) days=30 ;; may* ) days=31 ;; jun* ) days=30 ;; jul* ) days=31 ;; aug* ) days=31 ;; sep* ) days=30 ;; oct* ) days=31 ;; nov* ) days=30 ;; dec* ) days=31 ;; * ) echo "$0: Unknown month name $1" >&2; exit 1 esac if [ $2 -lt 1 -o $2 -gt $days ] ; then return 1 else return 0 # the day number is valid fi}isLeapYear(){ year=$1 if [ "$((year % 4))" -ne 0 ] ; then return 1 # nope, not a leap year elif [ "$((year % 400))" -eq 0 ] ; then return 0 # yes, it's a leap year elif [ "$((year % 100))" -eq 0 ] ; then return 1 else return 0 fi}## Begin main scriptif [ $# -ne 3 ] ; then echo "Usage: $0 month day year" >&2 echo "Typical input formats are 8 3 2002" >&2 exit 1fi# Normalize date and split back out returned valuesif [ $? -eq 1 ] ; then exit 1 # error condition already reported by normdatefimonthnoToName(){ # Sets the variable 'month' to the appropriate value case $1 in 01|1 ) monthd="Jan" ;; 02|2 ) monthd="Feb" ;; 03|3 ) monthd="Mar" ;; 04|4 ) monthd="Apr" ;; 05|5 ) monthd="May" ;; 06|6 ) monthd="Jun" ;; 07|7 ) monthd="Jul" ;; 08|8 ) monthd="Aug" ;; 09|9 ) monthd="Sep" ;; 10) monthd="Oct" ;; 11) monthd="Nov" ;; 12) monthd="Dec" ;; * ) echo "$0: Unknown numeric month value $1" >&2; exit 1 esac return 0}monthnoToName $1month="$monthd" day="$2" year="$3" if ! exceedsDaysInMonth $month "$2" ; then if [ "$month" = "Feb" -a "$2" -eq "29" ] ; then if ! isLeapYear $3 ; then echo "$0: $3 is not a leap year, so Feb doesn't have 29 days" >&2 exit 1 fi else echo "$0: bad day value: $month doesn't have $2 days" >&2 exit 1 fifiecho "Valid date: $newdate"exit 0

分析：
1）首先判断用户输入的参数个数是否正确，接着case $1 in 语句判断月份是否合理。
2）monthnoToName 函数之前出现在我们之前的第03个脚本案例中，用来转换输入的数字日期为字符串。
3） exceedsDaysInMonth 用来判断天数是否超过对应月的最大天数，紧跟着 if [ "$month" = "Feb" -a "$2" -eq "29" ] ; then if ! isLeapYear $3 ; then 用来判断闰年2月的特殊情况
4）总体的感觉是脚本还是很紧凑的，特别是在判断闰年与2月的关系的那段代码，有点意思。