debian - Comparing 2 dates in bash

Question

So I am trying to compare 2 dates in bash , but my dates contains characters like Jan or Monday . Can I compare them directly or do i need to format them like this "20201607"(and how do i do this plz) and them numerically compare them? Thank you For example:

today=$(date)
day='21 Jan 2021'

if [ $today < $day ]
   echo "$day"

basically my function will just return the dates who does not happened atm.

question from:https://stackoverflow.com/questions/65902239/comparing-2-dates-in-bash

Answer 1

Use the date to seconds since the epoch (1970-01-01 UTC) through specifying %s with date and so:

day='21 Jan 2021'
if [[ "$(date +%s)" -lt "$(date -d "$day" +%s)" ]];
then 
    echo "$day";
fi