Actually in a sense $bytesread should be doing something though... I should be ensuring that it is undef on each iteration of the loop... I think I now see the light. I should rewrite this as:

{
 # read() returns the number of bytes read or undef on error
 $bytesread = read($raw_file,$buffer,1024);

 # let's exit with an error if read() returned undef
 die "error with file read: $!" if !defined($bytesread);

 # let's exit with an error if print() did not return true
 unless (print O $buffer) die "error with print: $!";

 # let's redo the loop if we read > 0 chars on the last read
 redo unless !$bytesread
}
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And many thanks for one of the very first posts ever from the all-great merlyn which showed me the merits of a naked do block.