Linux / UNIX: Sed Replace Newline

How do I replace newline (\n) with sed under UNIX / Linux operating systems?

You can use the following sed command:

sed '{:q;N;s/\n//g;t q}' /path/to/data.txt

You can replace newline (\n) with * character or word 'FOO':

sed '{:q;N;s/\n/*/g;t q}' /path/to/data.txt

OR

sed '{:q;N;s/\n/FOO/g;t q}' /path/to/data.txt

OR replace it with tab (\t):

sed '{:q;N;s/\n/\t/g;t q}' /path/to/data.txt

To update file use -i option:

sed -i '{:q;N;s/\n/\t/g;t q}' /path/to/data.txt