Validate date format in a shell script

Question

I have to create a Shell Script wherein one of the parameters will be the date in the format dd/mm/yyyy. My question is, how can I check if the Date passed as parameter real

Answer 1

I wrote this bash script to validate date. I can accept mont as alphanumeric.

#!/bin/bash

function isDateValid {
    DATE=$1

    if [[ $DATE =~ ^[0-9]{1,2}-[0-9a-zA-Z]{1,3}-[0-9]{4}$ ]]; then
        echo "Date $DATE is a number!"
        day=`echo $DATE | cut -d'-' -f1`
        month=`echo $DATE | cut -d'-' -f2`
        year=`echo $DATE | cut -d'-' -f3`

                if [ "$month" == "01" ] || [ "$month" == "1" ]; then
                        month="Jan"
                elif [ "$month" == "02" ] || [ "$month" == "2" ]; then
                        month="Feb"
                elif [ "$month" == "03" ] || [ "$month" == "3" ]; then
                        month="Mar"
                elif [ "$month" == "04" ] || [ "$month" == "4" ]; then
                        month="Apr"
                elif [ "$month" == "05" ] || [ "$month" == "5" ]; then
                        month="May"
                elif [ "$month" == "06" ] || [ "$month" == "6" ]; then
                        month="Jun"
                elif [ "$month" == "07" ] || [ "$month" == "7" ]; then
                        month="Jul"
                elif [ "$month" == "08" ] || [ "$month" == "8" ]; then
                        month="Aug"
                elif [ "$month" == "09" ] || [ "$month" == "9" ]; then
                        month="Sep"
                elif [ "$month" == "10" ]; then
                        month="Oct"
                elif [ "$month" == "11" ]; then
                        month="Nov"
                elif [ "$month" == "12" ]; then
                        month="Dec"
                fi

        ymd=$year"-"$month"-"$day
        echo "ymd: "$ymd
        dmy=$(echo "$ymd" | awk -F- '{ OFS=FS; print $3,$2,$1 }')
        echo "dmy: "$dmy
        if date --date "$dmy" >/dev/null 2>&1; then
                echo "OK"
            return 0
        else
                echo "NOK"
            return 1
        fi
    else
        echo "Date $DATE is not a number"
        return 1
    fi
}


if isDateValid "15-15-2014"; then
    echo "date is valid =)"
else
    echo "bad format date"
fi
echo "==================="
if isDateValid "15-12-2014"; then
        echo "date is valid =)"
else
        echo "bad format date"
fi
echo "==================="
if isDateValid "15-Dec-2014"; then
        echo "date is valid =)"
else
        echo "bad format date"
fi
echo "==================="
if isDateValid "1-May-2014"; then
        echo "date is valid =)"
else
        echo "bad format date"
fi
echo "==================="
if isDateValid "1-1-2014"; then
        echo "date is valid =)"
else
        echo "bad format date"
fi
echo "==================="
if isDateValid "12-12-2014"; then
        echo "date is valid =)"
else
        echo "bad format date"
fi

Answer 2

How about using awk:

echo "31/12/1999" | awk  -F '/' '{ print ($1 <= 31 && $2 <= 12 && match($3, /^[1-9][1-9][1-9][1-9]$/)) ? "good" : "bad" }'

It prints "good" if its valid date else prints "bad"

Answer 3

Blockquote

DATE = "$*"

[[ "${DATE}" != @(((([123][0]|[012][1-9])|3[1])?([ \/._-])(0[13578]|1[02])?([ \/._-])(19|20)[0-9][0-9])|(([123][0]|[012][1-9])?([ \/._-])\
(0[469]|11)?([ \/._-])(19|20)[0-9][0-9])|(([12][0]|[01][1-9]|2[1-8])?([ \/._-])02?([ \/._-])(19|20)[0-9][0-9])|(29?([ \/._-])02?([ \/._-])\
(19|20(0[48]|[2468][048]|[13579][26])))) ]] && echo error || echo good)

Answer 4

The simplest solution, that still works perfectly, is the following :

if [[ $1 =~ ^[0-9]{4}-[0-9]{2}-[0-9]{2}$ ]] && date -d "$1" >/dev/null 2>&1
   ...

It consists in combining 2 checks :

• the first part checks that $1 is of this format : NNNN-NN-NN
• the second part checks that it is a valid date

You need the two checks because :

• if you don't do the first check, date will exit with code 0 even if your variable is a valid date in another format
• if you don't do the second check, then you can end up with a 0 even for variables such as 2016-13-45

Answer 5

`X="2016-04-21" then check for the below value being 1 or 0.

cal echo $x | cut -c 6-7 echo $x | cut -c 1-4 2>/dev/null | grep -c echo $x | cut -c 9-10

If the value is 1, then it's valid, else it's not valid.

Answer 6

Though the solution (if [[ $1 =~ ^[0-9]{4}-[0-9]{2}-[0-9]{2}$ ]] && date -d "$1" >/dev/null 2>&1) of @https://stackoverflow.com/users/2873507/vic-seedoubleyew is best one at least for linux, but it gives error as we can not directly compare/match regex in if statement. We should put the regex in a variable and then we should compare/match that variable in if statement. Moreover second part of if condition does not return a boolean value so this part will also cause error.

So I have done slight modification in the above formula and this modification can also be customized further for various other formats or combination of them.

DATEVALUE=2019-11-12
REGEX='^[0-9]{4}-[0-9]{2}-[0-9]{2}$'
if [[ $DATEVALUE =~ $REGEX ]] ; then
    date -d $DATEVALUE 
  if [ $? -eq 0 ] ; then
    echo "RIGHT DATE"
   else 
    echo "WRONG DATE"
  fi
else
 echo "WRONG FORMAT"
fi