Small DateValidation bash script

[Garrett85]

Below is a program I'M trying to write that will take an 8 digit date and validate whether or not it's a valid date. I'M very new to shell scripting so I really a have no idea what I'M going. Could you take a look and let me know what all I'M doing wrong here? Thanks.

#! /bin/bash -x

# This is the calender array for the DateValidation program
CALENDER=(31 28 31 30 31 30 31 31 30 31 30 31)

read -p "Enter a date for validation: " DATE

# establish the varible LEN to hold the number of characters in Date, 8 is the only valid number
LEN=$(echo ${#DATE})

if [ $LEN -eq 8 ]; then #{
 
	# set date dariables MM, DD, & YY
	export MM=${DATE:0:2}
	export DD=${DATE:2:2}
	export YY=${DATE:4:4}

	if [ ${YY} -gt 0 ]; then #{
		if [ ${MM} -gt 0 & < 13 ]; then #{
			if [ ${MM} -eq 2 ]; then #{
				if [ is_leap_year ${YY} == 1 ]; then #{
					if [ ${DD} -gt 0 & -le 29 ]; then #{
			elif [ ${DATE} -gt 0 & -le ${CALENDER[${MM}]}] #}}}}}}

	echo "${DATE} is a valid date"
else
	"${DATE} is an invalid date"
fi #}

#############################
### FUNCTION-is_leap_year ###
#############################

is_leap_year() {

if [ 0 -eg ${YY} % 4 & 0 -ne {YY} % 100 or 0 -eq ${YY} % 400 ]; then #{

	return true #}
else #{
	return false #}

exit
#END

[watael]

hi,

function should be declared before it's used.

LEN=$(echo ${#DATE}) # echo is useless, so is command substitution
export MM=${DATE:0:2} # exports are useless
if [ ${MM} -gt 0 & < 13 ]; then # a single & puts the process in background, you need 2 to be an AND, but it doesn't work inside test [ ]
# < is redirection from file, 13 is not a file
#  if [ $MM -gt 0 ] && [ $MM -lt 13 ]
if [ is_leap_year ${YY} == 1 ]; then # you need command substitution : if [ "$(is_leap_year "$YY")" -eq 1 ]; then

[drl]

Hi.

Perhaps this skeleton will help:

 11 if [ ... ; then
 18   if [ ... ; then
 19     if [ ... ; then
 20       if [ ... ; then
 21         if [ ... ; then
 22           if [ ... ; then
 23           elif [
 24           elif [
 Expected then, but got at line 24: 
 26         else
 36           if [ ... ; then
 39           else
 Unbalanced: (if - fi) count: 7

Best wishes ... cheers, drl

[Garrett85]

Thanks guys. Still don't have my script working but what you gave me was some much needed info. Thanks again.

[alf55]

remember that arrays are referenced from 0 and not 1.

[pgmer6809]

1. I presume you have a reason for using the shell, rather than some more powerful scripting language such as perl or python?
2. Once you get your script working, may I suggest a bit of human engineering?
a) validate the input. i.e. months 1-12, etc.
b) allow user to enter dates with / or - as in mm-dd-yyyy
c) allow user to enter dates with yy
d) It always annoys me (as a non USA resident) when programs assume the date is mm-dd-yyyy. This seems to me to be a very illogical format. It is neither ascending order (dd-mm-yyyy) nor descending order. It is not that difficult to allow yyyy/mm/dd or yyyy-mm-dd which AFAIK is the international ISO standard way of doing dates, (as well as mm-dd-yyyy which is what your USA users will probably assume.).

Just my two cents worth.......
pgmer6809