See:
https://news.ycombinator.com/item?id=37528558
by llimllib
Specifically:
curl -o /tmp/euro.zip -z /tmp/euro.zip
"Request a file that has been modified later than the given time and date, or one that has been modified before that time."
And:
https://news.ycombinator.com/item?id=37529690
by sltkr:
"the server doesn't support that header, but since the response does include a Last-Modified header, curl helpfully aborts the transfer if the Last-Modified date is the same as the mtime of the previously downloaded file."
See:
https://news.ycombinator.com/item?id=37528558
by llimllib
Specifically:
Option o is output, option z says"Request a file that has been modified later than the given time and date, or one that has been modified before that time."
And:
https://news.ycombinator.com/item?id=37529690
by sltkr:
"the server doesn't support that header, but since the response does include a Last-Modified header, curl helpfully aborts the transfer if the Last-Modified date is the same as the mtime of the previously downloaded file."