#Complete code!
#(Almost . . .)
# @lines contains the *PIN lines . . .

foreach $PIN (@lines) {
    foreach $ground_var (split /,/, $runset{GROUND-NODE}) {
        $PIN =~ s/$ground_var:./$ground_var:G/g;
    }
    foreach $power_var (split /,/, $runset{POWER-NODE}) {
        $PIN =~ s/$power_var:./$power_var:P/g
}