my $stuff = [ 'a', 'b', 'c', 'd' ];

sub cycle
{
   push @{$_[0]}, shift @{$_[0]};
   return $_[0]->[-1];
}

print cycle $stuff for 1..30;

# result: 
# $ perl cycle.pl
# abcdabcdabcdabcdabcdabcdabcdab