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007-valid-date.sh
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007-valid-date.sh
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#!/bin/sh
# valid-date - validate date, taking into account leap year rules
normdate="./003-normdate.sh" # hack #3 for normalizing month name
exceedsDaysInMonth()
{
# given a month name, return 0 if the specified day value is
# less than or equal to the max days in the month, 1 otherwise
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 # all is well
fi
}
isLeapYear()
{
# this function returns 0 if a leap year, 1 otherwise
# The formula for checking whether a year is a leap year is:
# 1. years divisible by four are leap years, unless..
# 2. years also divisible by 100 are not leap years, except...
# 3. years divisible by 400 are leap years
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 script
if [ $# -ne 3 ] ; then
echo "Usage: $0 month day year" >&2
echo "Typical input formats are August 3 1962 and 8 3 2002" >&2
exit 1
fi
# normalize date and split back out returned values
newdate="$($normdate "$@")"
if [ $? -eq 1 ] ; then
exit 1 # error condition already reported by normdate
fi
month="$(echo $newdate | cut -d\ -f1)"
day="$(echo $newdate | cut -d\ -f2)"
year="$(echo $newdate | cut -d\ -f3)"
# Now that we have a normalized date, let's check to see if the
# day value is logical
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
fi
fi
echo "Valid date: $newdate"
exit 0