Trojan Horse? (taint mode)

[IraTarball]

I was reading Advanced Perl Programming and came across this little warning about double quote interpolation. 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.

Now for the question.

Isn't a variable only interpolated once? I mean, when I try the following...

perl -swe 'while (<STDIN>) {print "$_"}'

and I type in {system('rm -rf *')} it just prints {system('rm -rf *')} without executing the system call. This is just what I would have expected before reading the quoted material. Am I missing something though?

Along these lines, I'm under the impression that tainted data is mainly a concern if you're going to eval it, or pass it to system or backticks, are there any really sneaky situations that I'm missing?

The reason the above caught my attention was that it implied that every program where I echo user input would need to be run in taint mode. I think that would suck.

What do you think?

Ira,

"So... What do all these little arrows mean?"
~unknown