Unpack Bin file problem

mark4444az has asked for the wisdom of the Perl Monks concerning the following question:

I'm novice level and in a little over my head on this one. I have some code (run from cygwin)where I unpack a bin file to a text file:

open (OUTFILE, ">bin.txt") or die "Can't open new text file! \n" , &cl
+ean_up;      # Make temp text file to unpack the bin file
    
    open (INFILE, "$bin_file_name") or die "Can't open nvm file! \n" ,
+ &clean_up;      # Open nvm binary file
    #### This unpacks the binary file and puts it in a text file bin.t
+xt ####
    my @lines = unpack ("W*", <INFILE>);
    my $line;
    foreach $line (@lines)
     {
      print OUTFILE sprintf("%02X", $line);
     }
    close (OUTFILE);
    close (INFILE);
[download]

The &clean_up sub just removes files and that works fine. The problem I have is when I unpacked a bin file it stopped printing on 0x0A, which is an ascii line feed. I changed it to an 0x0B and it worked fine. This makes me think that my printout is content sensitive, which would be BAD. I further suspect that the W* may be the wrong way to go on this. Any suggestions?

Comment on Unpack Bin file problem Download Code

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Re: Unpack Bin file problem by bart (Canon) on Mar 01, 2013 at 21:38 UTC
Your problem is in `my @lines = unpack ("W*", <INFILE>);` [download] and you haven't touched `$/`, so this will just read one line, until the first "\n". Do `local $/;` [download] just before you read the file, for example in a bare block, and oh, don't forget to binmode the filehandle if this has to work on something other than Linux, and it'll work fine. It sets this special variable to `undef`, in case you were wondering, so now you'll read the whole file.	[reply] [d/l] [select]
Re^2: Unpack Bin file problem by mark4444az (Sexton) on Mar 01, 2013 at 22:36 UTC
OK, That worked. Your comment, "It sets the special variable to undef", is not yet clear to me. I will have to research this. I greatly appreciate you help. I understand the concept of $_, just not how local $/ modifies it.	[reply]
Re^3: Unpack Bin file problem by bart (Canon) on Mar 01, 2013 at 23:37 UTC
It doesn't modify the behavior of `$_`, but of `<INFILE>` (for any handle). Perl has a bunch of special variables that change the behavior of perl. `$/` Is one of them, it changes what string readline, and thus `<INFILE>`, searches for as a line terminator, to read a whole line at once. When `undef`, it'll just make it slurp in the rest of the file.	[reply] [d/l] [select]
Re^3: Unpack Bin file problem by mark4444az (Sexton) on Mar 04, 2013 at 15:58 UTC
OK, that makes sense now. Thanks again.	[reply]