Try this, then:

use strict;
use warnings;

open(my $fh, "/path/to/file") or die $!;
while(<$fh>) {
   last if $_ eq "#### end_ascii_header\n";
}
#$fh is now positioned at the beginning of the binary data; do what yo
+u will
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Update:Fixed a typo in the code (missing 'if')