Thank you for the reply jeroenes.
(BTW, the first block in my question has a mistake, saying "$_" where it should say "$next".)
You said
I wouldn't use and with substitution, though. Just:

   s/test/somestuff/;
   print;
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does the job cleaner: only one print.

You're right about that. Would the following be a better illustration of the advantage I perceive?

s/^(\d+)/("0"x(8-length).$1)/xe and print or
       s/^(\w)/("\x20"x(8-length).$1)/xe and print for @ARGV;
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Suppose that @ARGV is a combination of digits and words, all digits get zero-padding and all words are padded by space. Anything that fails both matches should be discarded.

Update:
Very well then, jeroenes - I will follow the tradition
And thanks again for the replies :-) mkmcconn