my @array = qw(A B C D E);
join('|', @array) =~ /\A(\|?ABCDE\|?)+\z/g or warn "Validation failure
+\n";
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Untested, as always. You'll have to choose the seperator char carefuly, of course. Note that the quantifier ? after each \| is important to handle the case of the start and end of the string.

Update: Added /g modifier.

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Invent a rounder wheel.