sed is a linux command that can replace characters and words in a file very easy!

Syntax:

sed -i 's/word/newword/g' file.txt

It means:

replace all “word” with “newword” in the file called “file.txt”. Be aware! The option -i means that you will manipulate the file file.txt on-the-fly!
If you are not sure, skip the -i option.