How to get "DAYS" between 2 dates in while loop. Getting invalid date error

Question

I'm trying to get DAYS between 2 dates and if certificate expires in 30 days need to send an notification email. EndDate I'm calling from .csv file which is in EST (Thu Aug 18 18:59:59 EST 2022).

File sample3.csv contains:

$ cat sample3.csv
CertName,StartDate,EndDate
sslcertificates,Thu Dec 17 19:00:00 EST 2020,Thu Aug 18 18:59:59 EST 2022

I'm getting error like /bin/date: invalid date. Could anyone please help. I'm new for scripting.

#! /bin/bash
set +x
date=`/bin/date`
TodayDateSec="$(/bin/date "+%s")"
while IFS=, read -r CertName StartDate EndDate;
do
        if [ -z "$EndDate" ]; then
                echo "$EndDate details not exists"
        else
                echo "Name: $Name; StartDate: $StartDate; EndDate: $EndDate";
                date=`/bin/date`
                EndDateSec="$(/bin/date -d "$EndDate" +'%s')";
                DiffDays="$(( ( EndDateSec - TodayDateSec )/86400 ))"
                echo "***********$DiffDays************"
        if [[ "$DiffDays" -lt 30 ]]; then
                echo "Certificate is going to expire in $DiffDays. Please take required action"
    fi
fi

done < sample3.csv

Below is the output:

Name: CertName; StartDate: StartDate; EndDate: EndDate
/bin/date: invalid date ‘EndDate’
***********-19195************
Certificate is going to expire in -19195. Please take required action Name: sslcertificates; StartDate: Thu Dec 17 19:00:00 EST 2020; EndDate: Thu Aug 18 18:59:59 EST 2022
/bin/date: invalid date ‘Thu Aug 18 18:59:59 EST 2022’
***********-19195************
Certificate is going to expire in -19195. Please take required action

Answer 1

Please modify your script to include some (simple) check of data validity. Most probably the date format you are using is not being understood correctly by the command date. This could be caused for a number of reasons. If you could format your date like '2022-08-18T18:59:59' it would be a lot more portable and easier to process by other programs.

#! /bin/bash
set +x
TodayDateSec="$(/bin/date "+%s")"
while IFS=, read -r CertName StartDate EndDate; do
        if [ -z "$EndDate" ]; then
                echo "$EndDate details not exists"
        elif ! /bin/date -d "$EndDate" >/dev/null 2>&1; do
                echo "Invalid date format supplied $EndDate"
        elif 
                EndDateSec="$(/bin/date -d "$EndDate" +'%s')";
                DiffDays="$(( ( EndDateSec - TodayDateSec )/86400 ))"
                echo "*********$DiffDays**********"
                if [[ "$DiffDays" -lt 30 ]]; then
                        echo "Certificate is going to expire in $DiffDays. Please take required action"
                fi
        fi
done < sample3.csv

If the date format you use is not compatible with the date command you have (or the locale you use), you may try to use the date from busybox:

$ busybox date -D '%a %b %d %T %Z %Y' -d 'Thu Aug 18 18:59:59 EST 2022' +'%s'
1660863599

Answer 2

Using a shell loop to process text is an anti-pattern, see Why is using a shell loop to process text considered bad practice?, here's how to do what your script is doing an order of magnitude more efficiently using GNU awk for time functions:

$ cat tst.sh
#!/usr/bin/env bash
awk '
    BEGIN {
        FS=","
        secsInDay = 60 * 60 * 24
        curDate = strftime("%Y %m %d")
        secs = mktime(today " 12 0 0")
        today = int( systime() / secsInDay )
    }
    NR == 1 {
        next
    }
    $3 == "" {
        printf "EndDate details not exists\n"
        next
    }
    {
        printf "Name: %s; StartDate: %s; EndDate: %s\n", $1, $2, $3
        split($3,d," ")
        mthNr = (index("JanFebMarAprMayJunJulAugSepOctNocDec",d[2])+2)/3
        secs = mktime(d[6] " " mthNr " " d[3] " 12 0 0")
        endDay = int( secs / secsInDay )
        diffDays = endDay - today
        printf "*********%d**********\n", diffDays
    }
    diffDays < 30 {
        printf "Certificate is going to expire in %d days. Please take required action\n", diffDays
    }
' "${@:--}"

Though this is a far better way to do what your existing script is doing, a script that produces output like this is not a good starting point for your full task of if certificate expires in 30 days need to send an notification email.. After accepting an answer to this question, ask a new question to get help on how to do THAT.