my @varnames = qw(
    Var1
    Var2
    Var3
);

my %params;
@params{@varnames} = map { $cgi->param($_) } @varnames;

if (grep { !defined $params{$_} || $params{$_} eq '' } @varnames)
{
    &complain;
}

# Now, at this point, you have read in all your parameters
# and verified that each is defined as well as not the
# empty string.

# Do other stuff here.