# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/\[(quote)\]?\s*(?:author)?=?(\S+)*/[$1=$2]/gm;t' <<< "[quote author=username link=1150111054/0#7 date=1150151926][/quote]
[quote] username link=1142890417/0#43 date=1156429613]This is a very simple test sentence.[/quote]
[quote=user name pid=123456]
Test.[/quote]
[quote] user name link=1142890417/0#43 date=1156429613][quote] username link=1142890417/0#43 date=1156429613]This is a very simple test sentence.[/quote]
This is a very simple test sentence.[/quote]
"
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