I need to convert a date into a day number and I can use
date +%s --date "10 March 1990"
To get the second number. Then I divide that number to the number of seconds in a day - 86400
date +%s --date "10 March 1990" / 86400
But it doesn't work for dates before 1 January 1970
and I need to use for dates between 1950 and 2020
Is there any fix for that? Maybe there is some date binary that allows to redefine epoch time to a different date than 1/1/1970 ?