# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/(const uint[138][26]?_t)(\s?\S+\s*) (\s*[0-9]*[xXa-fA-F0-9]*)$/\1\2 = \3;/;t' <<< "const uint8_t T_SYN_3 23"
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