if ($line =~ /DOWN/) {
        # ...
    } elsif ($line =~ /PROBLEM/) {
        # ...
    }

##</code><code>##

my $error = "DOWN";
my $warn  = "PROBLEM";

# ... and later ...

    if ($line =~ /$error/) {
        # ...
    } elsif ($line =~ /$warn/) {
        # ...
    }

##</code><code>##

    my $error = "Server ... DOWN";
    if ($line =~ /$error/) {
        # conditional clause
    }