basic

echo 'abcdefj'| sed 's/abc/dd/'

sed -E "s/^(\s+)([^\"]\S+[^'\"])(\s+):(\s+)'(\S+)'/\1\"\2\"\3:\4\"\5\"/" tsed.txt

-i option

replace Inplace

echo "nich to meet you" >> test.txt
sed -i test.txt 's/meet/see/'
cat test.txt