sure , what ever match if matching value store is $&, before matching word $`

That doesn't make sense.

Consider your questions how to do replace more then one matches? and how to do get digit numbers like -,.?

And consider the respective answers Re: how to do replace more then one matches? and Re: how to do get digit numbers like -,.?

Neither of the answers above use $&

The examples in perlintro don't use $&

You're using $& in how to get numbers only from n numbers or more digit numbers? but its not doing what you want -- its not working for you -- why keep using $& when it doesn't help you?