Quick and dirty explanation of interpolation for ya:
my $this = 'hello';
my $thisvar = 'goodbye';
# prints 'hello' of course
# single quotes mean no interpolation occurs, prints '$this'
# double quotes invoke interpolation, prints 'hello'
# perl does 'greedy' interpolation (don't know if that's the
# right term) so this prints 'goodbye'
# this makes it explicit that we only want $this, so this
# line prints 'hellovar'
I'm sure the faq has a more detailed explanation that covers
list interpolation as well...