# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/<td([^>]*)>\s*((?:.(?!<\/td>))+\s*)\s*<\?php audioButton\("([^"]*)\/.+?",".*?"\);.*?\?>.*?<\/td>/<td$1>$2<?php audioButton("$3\/cat", "cat");?><\/td>/g;t' <<< "<td class=\"danish\">kat
<?php audioButton(\"../../audio/words/dog\",\"dog\");?></td>
<td class=\"danish\">kat
<?php audioButton(\"../../audio/words/dog\",\"dog\");?></td>
<td class=\"danish\">kat</td>
<td><?php audioButton(\"../../audio/words/dog\",\"dog\");?></td>
<td class=\"danish\">kat
<?php audioButton(\"../../audio/words/dog\",\"dog\");?></td>"
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