# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/\[sketchfab\]https:\\/\\/sketchfab.com\\/models\\/([^\[]+)\[\\/sketchfab\]/[MEDIA=sketchfab]$1[\/MEDIA]/g;t' <<< "[sketchfab]https://sketchfab.com/models/ce1b37915f40429ab5567cba35ec549f[/sketchfab]"
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