Nifty feature to change text inside large file over Linux commandline
sed -i 's/original/new/g' file.txt
sed = Stream EDitor
-i = in-place (i.e. save back to the original file)
s = the substitute command
original = a regular expression describing the word to replace (or just the word itself)
new = the text to replace it with
g = global (i.e. replace all and not just the first occurrence)
file.txt = the file name
Letsencrypt on Ubuntu 16.04 LAMP howto commandline How to change Linux files/folders permissions under same directory recursively 644/755
