You have a scope issue. You can see this if you change your array declaration from my @binarysearcharray=... to our @binarysearcharray=.... The eval for the benchmark occurs in Benchmark package, and variables declared with my are not visible outside your current scope, in contrast to our. For a little more description of scope, see Private Variables via my().

Please note that if you include output in a benchmarking run, the i/o is likely to invalidate your conclusions.