. / sed

# grep for string
sed -n '/string/p'

# double space a file
cat file.txt | sed G

# delete trailing whitespace (spaces and tabs)
cat file.txt | sed 's/[ \t]*$//'  

# put bar in quotes
echo "foo bar baz" | sed 's/bar/"&"/'

# replace spaces with tabs
sed 's/ /\t/g'

# replace foo with bar
sed -i -e 's/foo/bar/' ~/file.txt

# delete lines matching a pattern
sed -i -e '/kern/d' /etc/syslog.conf

# comment out a line (should anchor)
sed -i -e '/^Something.*/#&/g' /tmp/file.txt