Hmmmm, no he probably doesn't want that.

$a and $b are special variables and even in sample code should be avoided. In fact more effort should go into making sample code clean and clear than even production code because you are providing example code for other people. You could write your sample like:

while (<$fh>) {
    my ($value, $truth) = split /,/;
    push @groups, [$value, $truth];
}
[download]

which hints at using lexical file handles, avoids special variables, uses correctly scoped sensibly named lexical variables and uses consistent white space.

Update: replaced ) with ] - thanks Laurent_R