[Pdx-pm] bit wise comparison

[Michael R. Wolf]

On Feb 11, 2010, at 1:35 PM, Eric Wilhelm wrote:

> # from Tom Keller
> # on Thursday 11 February 2010 12:22:
>
>> $in = 'ACCTCCTCCTCGAGTATGTG';
>> $tgt = 'TATCTTGCGCCGGAGATAAT';
>> $mask = pack("A*",$in)^pack("A*",$tgt);
>> $matches = $mask =~ tr/"\x0"/"\x0"/;
>
> I get warnings from the quotes (") in the tr//.  You *did* enable
> warnings, right?  :-D

tr's args are weird.

As written, the first arg has 3 characters: double-quote, NUL, double- 
quote.
So does the second arg.

Effectively, it's setting up this mapping
  "   =>   "
\x0 =>  \x0
"   =>  "

Maybe it's more obvious if you see it this way, another 3-arg to 3-arg  
transliteration:
   tr/abc/ABC/

The original is best written as a 1-arg to 1-arg:
tr/\x0/\x0/
  or
tr#\x0#\x0#
  or
tr{\x0}{\x0}


-- 
Michael R. Wolf
     All mammals learn by playing!
         MichaelRWolf at att.net