sed is a stream editor. It takes input from a file, processes it, and outputs to STDOUT:
Substitutions:
sed -e 's/Andrew/Andy/' -e 's/McDonough/Donut/' file
Read somefile and substitute all occurrences of somexpession with a replacement
cat somefile.file | sed s/someexpression/replacement/
Find all words ending in the letters de in the word list, remove the de and print to the screen.
grep -ri ".*de$" /usr/share/dict/linux.words | sed s/..$//