# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/<div class="wp-caption">([\s\S]*?)<\/div>/<figure>$1<\/figure>/g;t' <<< "
<div class=\"wp-caption\">
<a href=\"https://\">
<img src=\"https://\" alt=\"blabla\">
</a>
</div>"
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