"That is perfect, ..."

Well, not quite! :-)

I saw your meditation after I read, and responded to, your OP in this thread. I now see where the Chinese characters come from; although, I still think they're superflous in the context of this specific question.

The focus of my answer was the 'r' modifier (in response to your "possible ... in one step?"). I probably should have paid more attention to your regex (/^\s+|\s+$/), rather than just copying it verbatim. With the Chinese issue out of the way, and having spent some time looking more closely at what I wrote, here's some clarifications and corrections.

The substitution example with the Chinese characters should have included a 'g' modifier. I'm now reasonably certain that wasn't what you wanted; however, it should have been written like this:

$ perl -Mutf8 -C -E 'say join " ", split //, " 北亰 " =~ s/^\s+|\s+$//gr'
北 亰

I was correct in not using the 'g' modifier in the other two substitution examples; however, I should have also removed the alternation. As the two examples splitting "1234" clearly demonstrate, there's no trailing whitespace: you only need to remove the leading whitespace. For those examples, these would have been better:

$ perl -E 'say join(" ", split /(..)/, "e58c97e4bab0") =~ s/^\s+//r'
e5  8c  97  e4  ba  b0

$ perl -E 'say join(" ", split /(..)/, "e58c97e4bab0") =~ s/^\s+//r =~
+ y/ / /rs'
e5 8c 97 e4 ba b0
[download]

Now, hopefully, it's "perfect". :-)