Perl's join() function is used to connect all the elements of a specific list or array into a single string with the JOINER expression. The list is concatenated into one string with the element contained in the JOINER variable in between each item.
$STRING = join(JOINER, @LIST);
Think of the @myNames array as a row of numbered boxes, each with a name in it. The join() function would take all of the content in those boxes in the @myNames array and connect them together with a comma and a space. The value of @someNames then becomes "Jacob, Michael, Joshua, Matthew". The list of names is concatenated, or joined, by commas.
@myNames = ('Jacob', 'Michael', 'Joshua', 'Matthew'); $someNames = join(', ', @myNames);