I really don't like BASH or SH so I try to find ways not to use it.
This is what I came up to for use instead of [< file > -lt < file2 >] compare
This is to describe how you can find and replace a text in many many files at once. It might take some time .. but it will do the job.
Observe that paths or text with a / in them need the / to be escaped(\) for sed to accept it as a / and not end of statement.
Rsync is one of those utilities that doesn't come nativity normally. Some flavors do install it during installation of the operating system while others demand you to install it.
You don't have to install it but it is good if you need to do some special tasks.
It's meant as a utility to synchronize two directories which in turn can be done in various ways. It can do it between two servers/computers or between two local directories or even as a server for others to synchronize with your local package.