# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/\bF150\b.*/$0\nG1 F1000/gm;t' <<< "G1 X277.8072 Y212.6482 Z-2.5000
G1 X277.3935 Y212.6617 Z-2.5000
G1 X276.9809 Y212.6737 Z-2.5000
G1 F150 Z-4.0000
G1 X276.9809 Y212.6738 Z-4.0000
G1 X276.5705 Y212.6846 Z-4.0000 "
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