Q . How to Find and Replace text of any file using command line in linux.

I have a file named test.txt.

I want to replace all abc text to xyz using command line in ubuntu.

sed -i 's/original/new/g' file.txt

Explanation:

sed = Stream EDitor
-i = in-place (i.e. save back to the original file)
The command string:
- 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