# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/\btest1="[^"\s]*\K[^"]+//gm;t' <<< "hi test1=\"12c4 ab3d\" blablabla test1=\"5678 sdfg\"
hi test1=\"12c4 ab3d\" blablabla test1=\"abcd 3456 sdfs 2435\""
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