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sed(stream editor) command in Linux/Unix

Introduction to stream editor

A stream editor is a tool that transforms text, edit a file and replaces file content with the manipulation using the regular expression.

Why I used Stream Editor?

I find this tool handy and more useful when I have to change a word of a file line by line. I faced this issue while updating my Debian operating system from Jessie "Debian 8" to stretch "Debian 9" for that, I have to update my /etc/apt/sources.list file, in which I have to change the each "Jessie" word in that file  to "stretch"
So, I use this command

sudo sed -i 's/jessie/stretch/g' /etc/apt/sources.list

Here the "s" specifies the substitution. The "/" are delimiters.
"jessie" is the search pattern and "stretch" is the replacement pattern.
 for more refer to sed manual page here or prefer manual page in your machine for sed commands.
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