When I use gnuplot I use its special file handle '-' and inline the data.

Would it be better to use a tempfile? and if so what are the advantages?

I'd write your code like this :-

use v5.12; use warnings; use autodie;
use IO::Handle;

open my $out,'|-','gnuplot';
say $out 'unset key';
say $out "plot '-' with lines lw 3";

for my $t (100..500) {
  say $out $t*sin($t*0.1),' ',$t*cos($t*0.1);
}
say $out 'e';

flush $out;
<STDIN>;
close $out;
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