The author warns that a string like "$a" does variable interpolation. No surprise there. Then he say's "But you now know that "a" can be replaced ba a block as long as it returns a reference to a scalar..." and so we should be worried about someone filling a variable with {system('/bin/rm -rf /*')} and maybe doing 'bad things' to us.

In my humble opinion, by his statement, "a" can be replaced, the original author may be discussing literally replacing the letter 'a' in the expression, "$a", with an actual (curly brace-delimited) block of code; in other words, changing the expression (quotes and all), "$a" to the different other expression, "${system('/bin/rm -rf /*')}", not necessarily assigning such a string as "{system('/bin/rm -rf /*')}", to the variable, $a and interpolating that.

I by no means intend, by posting this reply, to minimize the importance of the interpolation discussions. Nor is it my purpose to cast a pall on any of the extemely pertinant, valid points made in any of those threads.

However, the questions being discussed do not seem to me to be addressing the behavior described (as I read it) by the original author (not that it was especially well written). Perhaps all is right with the world and interpolation is, in fact, predictable.

dmm

You can give a man a fish and feed him for a day ...
Or, you can teach him to fish and feed him for a lifetime