CODE EXAMPLE FOR SHELL

replace a newline using sed linux bash

sed ':a;N;$!ba;s/
/ /g' file

:a create a label 'a'
N append the next line to the pattern space
$! if not the last line, ba branch (go to) label 'a'
s substitute, /
/ regex for new line, / / by a space, /g global match (as many times as it can)