# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/<a\s[^>]*href="https?:\/\/[^>]*>(.*?)<\/a>/\1/gis;t' <<< "<a href=\"https://site.ru/*****>слово</a>
<a class=\"m\" href=\"https://site.ru/*****>слово</a>
<a href=\"https://site.ru/*****\" class=\"m\" >слово</a>
<a href=\"https://www.site.ru/sistemy-promyshlennogo-konditsionirovaniya/fankoyly/ballu-machine/\" rel=\"nofollow\">слово</a> <br>
<a href=\"https://www.site2.ru/fdescript/1559/?design=1\">слово</a> <br>
<a href=\"https://www.site3.ru/fdescript/997/?design=1\">слово</a> <br>
<a href=\"https://www.site3.ru/fdescript/1003/?design=1\" rel=\"nofollow\">слово</a>
"
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for SED, please visit: https://www.gnu.org/software/sed/manual/html_node/The-_0022s_0022-Command.html