my @array = ("12.found","1.found","2.found", "4.found", "5.found", "8.found", "100.found");
my @e = sort {$a<=>$b} map {m/^(\d+)/ && $1}@array;
my %hash;
@hash{@e}= (@array);
for ($e[0]..$e[-1]) {defined ($hash{$_})or$hash{$_} ="$_.missing"}
print join " ", sort {$a<=>$b} values %hash;