$_ = "a"; s/(.(.*))/($2ne'')?$2:$1/e; print

That gives "a". I'd expect nothing to get printed - if I remove the first character of a one-character string,
I should be left with the empty string, not with the same string.

As stated - "First, but not last" which means in plain English - the 1-st symbol is not the last one and if so - it is cut.