List::Util::reduce()

my @array = ('3','4','71','1', '-598', '-100203');

print reduce{ $a = $b if $array[$b] >=0 and $array[$b] < $array[$a]; $
+a } 0 .. $#array;;
3
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Or more simply:

print reduce{ $array[$b] >=0 && $array[$b] < $array[$a] ? $b : $a } 0 
+.. $#array;
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Bad data -- ie. empty array, or all negatives -- returns undef. Doesn't check values are integer.