Untested: 
my $testvar = "Bob Q Smith bsmith 00001234567 5/1/00 12:00:00";

$testvar =~ s/
              \s           # a whitespace character (space, tab, etc)
              (            # Capture to $1
                \w+        #    one or more word characters (e.g. bsmi
+th)
              )
              \s           # a whitespace character
              (            # Capture to $2
                \d+        #    one or more digits
              )
              \s           # a whitespace character
            /,$1,$2,/x;

[download]
If your data is relatively clean, I think that should work. It relies on you knowing that the first digits you encounter are going to be your serial number and immediately preceding them are some letters. From there, it's pretty straightforward. There are many different ways to write this regex and this may not be the best, but it's fairly clear.

Cheers,
Ovid

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In reply to (Ovid) RE(3): Transpose some spaces to commas in a string by Ovid
in thread Transpose some spaces to commas in a string by cosmicv

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