# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/^.*?(rcp\d+).*(_mon\d+).*/\1\2/gm;t' <<< "diff_pr_EUR-44_cordex_rcp45_mon_ave_2048-2060_minus_2005-2017_mon10_ave1_withsd.nc
"
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