You need to read data from the file before you try to operate on it. eval operates on $_ in lieu of arguments, so you need to put something into $_ first:

open(FILE, "< filename") or die "filename: $!";
{
  local $/;
  $_ = <FILE>;
}
close(FILE);
eval;
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Or you could just use Perl's do function:

do "filename" or die "filename: $! ($@)";
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