# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/(Cass\.\s+com\.(?:,\s+(?:avis|QPC))?,\s+(\d{1,2})e?r?(?:\s| )+(\w+\.?)\s+(\d{4}),\s+n(?:°|°|o)s?(?:\s| )+(\d{2}-\d{2})\.?(\d{3}))/<renvoi type="CASS" refid="$5$6" jour="$2" mois="$3" annee="$4">$1<\/renvoi>/gm;t' <<< "Cass. com., 5 janvier 2012, n° 12-45.644"
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