SHELL

sed add word to beginning of line

$ sed 's/^/#/' file.txt
#add
#character
#at the
#beginning of
#each line

sed add word to end of line

sed 's/.*/&:80/'  abcd.txt >abcde.txt

add string at end of line sed

# Save suffixed file into a new file
sed -e 's/$/suffix/' file > file.new

# Edit file and overwrite with suffixed text
sed -i -e 's/$/suffix/' file