# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/(<p>|<div .*>)(\s*)(<a .*>)?(\s*)(<img .* \\/>)(\s*)(<\\/a>)?(\s*)(<p .*>.*<\\/p>)?(\s*)(<\\/p>|<\\/div>)/$3$5$7$9/;t' <<< "<div id=\"attachment_3340\" style=\"width: 865px\" class=\"wp-caption alignnone\">
<img class=\"size-full wp-image-3340\" alt=\"Testbild\" src=\"https://beispiel.de/images/Testbild.jpg\" width=\"855\" height=\"631\" />
<p class=\"wp-caption-text\">© Copyright</p>
</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