my $record = join q[], @{+shift}; does a whole lot of stuff in one statement, but basically it takes a reference to an array of strings and joins them all into a single string.

It could alternatively be written as:

my $ref_to_list_of_strings = shift @_;
my @list_of_strings        = @{ $ref_to_list_of_strings };
my $empty_string           = q[];
my $record                 = join($empty_string, @list_of_strings);
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... but that sort of coding has been known to cause repetitive strain injuries. Whatsmore, the short way also avoids creating a bunch of temporary variables, so probably runs (ever so slightly) faster.