#!/bin/bash
s='blah
<a href="/torrent/4384536/HorribleSubs-Black-Clover-128-720p-mkv/">[HorribleSubs] Black Clover - 128 [720p].mkv</a>
blah
<a href="/torrent/1111111/AAAAAAAAAAAAAAAAAAAAAA.mkv/">[HorribleSubs] Black Clover - 128 [720p].mkv</a>
blah'
sed -n -E '/.*<a href="(\/torrent\/[^"]*)\/">[^<]*<\/a>.*/{s//\1/p;q}' <<< "$s"