Bitwise string assignment is another option.

Both do the same thing. The second is just a bit more structurally similar to the other cases since it's on one line.

my $str;
$str |.= $_ for @strings;  # more or'ing strings
$longest = length $str; 
print "longest: $longest\n";

$longest = length do {my $s; $s |.= $_ for @strings; $s};  # more or'i
+ng strings
print "longest: $longest\n";
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Edit - fixed typo.