unlinker,

"...I just want to split the binary string into two parts. I was using 'substr' until I read that unpack is faster and more efficient."

First off, I luv 'pack/unpack', but it may not always be the most efficient. There are several way to determine performance, but an excellent tool to use is 'NYTprof'. I had a Perl script that I couldn't improve the performance no matter what I did. I profiled it and found that my problem was calling 'pack/unpack' too often. On a run of 50,000 records, the script was calling 'pack/unpack' over 5,000,000 times. The 'pack/unpack' was in a tight loop, working on 32 byte substrings of a 4K string.

What came to the rescue was 'substr'. Using the 4 parameter as

      my $val = substr( $data, 0, 32, "" );      # $data already defin
+ed
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In this situation, 'substr' just moves the pointer to the new beginning of the string, and was more efficient. I then used the 3 parameter non-destructive 'substr' to see it this was the substring I wanted, and then call 'pack/unpack'. Immediately, I saw a 300% improvement in performance and 'pack/unpack' was now called about 150,000 times.

Perl has lots of powerful tools!

Good Luck!