At the time of this writing, smarty.net is not working.
Anyway, how to replace line breaks with space in smarty variable? Is it something like this {$var|regex_replace:'[\\r\\n]':'\s'}? I tried, but it did not work.
{$var|regex_replace:'[\\r\\n]':'\s'}
Try it if it works:
{$var|regex_replace:"/[\r\n]/" : " "}