# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/^\s*\[(?P<id>\d+)\]\s*:\s*(?P<link>[^\n]+)$/[\1]: \2/gm;t' <<< "This is a sample doucument that would have inline links.
[Example 0][0], [Example 1][1], [Example 2][2] , [Example 3][3] , [Example 4][4]
[0]: http://example.com
[1]: http://example.com/1
[2] : http://example.com/2
[3]: http://example.com/3
[4] : http://example.com/4"
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