sed to replace a word in a file code example

Example 1: ubuntu command line replace word in files

sed -i 's/original/new/g' file.txt

Example 2: sed replace all occurances?

echo dog dog dos | sed -e 's:dog:log:g'

#You can also use the above answer with appropriate slashes like
echo "grepper is a nice grepper" | sed "s/grepper/blow/g"