If you undefine line separator (undef $/;) than whole file will be red as one line ($bookfile_contents = <FILE>;)

If you want to read from file line by line than use

if(-f "$bookfile"){
  open(FILE, "+<$bookfile") 
   || &debug("Oops, I cannot read the bookfile $bookfile: $!");
  if($opsys eq "unix"){flock(FILE, 2);}
  else{binmode(FILE);}
  while (my $line = <FILE>) {
    # do something with one line
  }
}
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What does mean $/ = "tr/\n /";? Your line will end with following text? I don't think so.

tr/
 /
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