sed command example

sed - stands for stream editor.

So, you wish to replace a string in a file.

Example:

sed -ie 's/few/asd/g' hello.txt

Here, 

-i in place

-e expresssion - here for making use of s/ which is search

g - global , to change in the whole line.

source:

http://unix.stackexchange.com/questions/159367/using-sed-to-find-and-replace