This is similar to $ ($POSTMATCH ) except that it does not incur the performance penalty associated with that variable, and is only guaranteed to return a defined value when the pattern was compiled or executed with the /p modifier.
The output record separator for the print operator. If defined, this value is printed after the last of prints arguments. Default is undef. (Mnemonic: you set $ instead of adding " " at the end of the print. Also, its just like $/ , but its what you get "back" from Perl.)