=====
print "(From: $privMsgUser) : $privMsg\n";
pmprint($privMsgUser,$privMsg) ; ＜＝追加

} elsif ($switch eq "0098") {

=====

以下をsub dumpData の上あたりに追加
sub pmprint {
my $privMsgUser = shift;
my $privMsg = shift;
my $dump;
$dump = "(From: $privMsgUser) : $privMsg\n";
open DUMP, ">> pm.txt";
print DUMP $dump;
close DUMP;
}