How to replace the third occurrence of the string in the file using sed command.

Example:

Change only the third occurrence of is to us in the file.

My input file contains:

hai this is linux.
hai this is unix.
hai this is mac.
hai this is unchanged.

The expected output is:

hai this is linux.
hai thus is unix.
hai this us mac.
hai this is unchanged.

How can I replace the Nth (for example, the third) occurrence of a string (or pattern) in a file using the sed command?  I do mean the Nth occurrence in the file, not the Nth occurrence in a line or the first occurrence in the Nth matching line.  There may be multiple occurrences in a line, and an occurrence (a match) might be a partial word.

Example:

Change only the third occurrence of is to us in the file.

My input file contains:

hai this is linux.
hai this is unix.
hai this is mac.
hai this is unchanged.

The expected output is:

hai this is linux.
hai thus is unix.
hai this is mac.
hai this is unchanged.

Note that “this” has been replaced by “thus” in the second line.

How to replace the third occurrence of the string in the file using sed command.

Example:

Change only the third occurrence of is to us in the file.

My input file contains:

hai this is linux.
hai this is unix.
hai this is mac.
hai this is unchanged.

I am expecting output is:

hai this is linux.
hai thus is unix.
hai this is mac.
hai this is unchanged.

How to replace the third occurrence of the string in the file using sed command.

Example:

Change only the third occurrence of is to us in the file.

My input file contains:

hai this is linux.
hai this is unix.
hai this is mac.
hai this is unchanged.

The expected output is:

hai this is linux.
hai thus is unix.
hai this us mac.
hai this is unchanged.