$ sed -i 's/ugly/beautiful/g' /home/bruno/old-friends/sue.txt

http://www.brunolinux.com/02-The_Terminal/Find_and%20Replace_with_Sed.html

From the referenced website:
Well, that command speaks for itself "sed" edits "-i in place ( on the spot ) and replaces the word "ugly with "beautiful" in the file "/home/bruno/old-friends/sue.txt"

Find and replace with sed

replace, find

Bash