How to replace strings with sed
**Q. How can I replace a word with another without "opening" file on the fly with sed?
A. Sed is a wonder and powerful stream *editor, and with it you can make modifications to files from the command line.
Replace with sed
sed 's/old/new/g' file.txt
That will output the file to the screen with all occurences of old changed to new, if you want to replace and save the file in one step.
sed -i '' 's/old/new/g' file.txt
This last one will open the file, replace and save the file again.