use IO::Handle;   #for flush method

my $rtlamr = "/home/jj/go/bin/rtlamr -msgtype=scm+ --format=json -filterid=1 +01419821,101419999 -unique=false";
open my $fh, '-|', $rtlamr or die "unable to start rtlamr program $!";

my $disk_file = "somepath";
open my $disk_fh, '>>', $disk_file or die "unable to open disk history file! $!";

while (<$fh>)  # this is a "blocking" read of radio receiver
{
   print $disk_fh $_;
   $disk_fh-> flush;  # update disk file immediately
}
__END__
That's it.
The analysis program of the disk file, "somepath" is a 
   separate program.