my $rx = qr"^DMSC0022\s+\S+\s+(\w+)$";
my $fmt = "Logfile_Connection_Lost Hostname: %s";

$_="DMSC0022 X10 oswald";
if(my @match = /$rx) {
    printf "$fmt\n", @match;
}

##</code><code>##

my $rx = qr"^DMSC0022\s+\S+\s+(\w+)$";
my $fmt = "Logfile_Connection_Lost Hostname: %1";

$_="DMSC0022 X10 oswald";
if(my @match = /$rx/) {
    (my $msg = $fmt) =~ s/%\d+/$match[$1]/e;
    print "$msg\n";
}