You can convert TODAY() to a string with a calculated field: STR(TODAY()).
Then make a calculated field to append that new string field to the end of your url as described here:
Your calculated field would end up as something like...
If you want to see how this might work, I appended a viz URL from Tableau Public with a date filter:
(the part I added is ?Date=2008-08-01)
If you don't want to filter by date and instead want to show everything up to today for instance, you can do something like what is described in the comment here:
I tried this and it works when you create a calculated field and then also create a URL action which includes the date.
What i am looking at is something different.
I want today's date in the URL which i am going to share with users and they will open the dashboard using that URL.
so when a dashboard is opened for the first time (without clicking on any action within dashboard) the calculated field does not work, because there is no way the url know what it means and what its value is. I am looking for a html tag or something similar to populate date from the computer when a URL is run
That date will ultimately be passed to a parameter in the dashboard which will be opened for the first time.
I see - I'm not sure how you would accomplish that.