$line = "kernel: hda error 22";
$pat = "kernel: (.*?) error";
$re = /$pat/;

if ( $line =~ $re ) {
        print "A: \$1 = $1\n";
        if ( $line =~ /$pat/ ) {
                print "B: \$1 = $1\n";
        }
}
[download]

output:

infinity(77)>./test.pl 
A: $1 = 
B: $1 = hda