@stuff=($0.5,$0.5,$0.5)
You're concatenating the value of the special variable $0
with 5. For the example you gave, this would fill @stuff
with ('-e5', '-e5', '-e5').
Watch out for variable interpolation.
perl -e "@stuff=('$0.5', '$0.5', '$0.5');my $x=0;foreach (@stuff){s/\$//; $x+=$_}; print $x"
or
perl -e "@stuff=qw($0.5 $0.5 $0.5);my $x=0;foreach (@stuff){s/\$//; $x+=$_}; print $x"