# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/^app[0-9]+\s=\s\x22([0-9]+)\x22$/\1/gm;t' <<< "app1 = \"0123456789\"
app2 = \"1234567890\"
app3 = \"2345678901\"
app4 = \"3456789012\"
app5 = \"4567890123\""
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