How to append a string after a match?
For eg I have a text line "This is not test" where I would like to insert "really" after matching "is"
This is really not test
Similarly you can also append a text after "This" as shown below
This really is not test
How to append a string before a match?
I will append "Really" before my match "this"
Really this is not test
this is not some test
How to do "in place" replacement in a file?
This can be done using "-i" flag with sed command as shown in below example.