$ perl -Mstrict -Mwarnings -E '
    my $host = q{a.b.c};
    my $re = qr{([a-zA-Z][-a-zA-Z0-9]*\.[a-zA-Z]+)$};
    my $base = ($host =~ $re)[0];       # How I might have written it
    say $base;
    $base = ($host =~ m{($re)}) [0];    # How you wrote it
    say $base;
    $base = ($host =~ m{($re)}) [1];    # Fodder for another SoPW
    say $base;
'
b.c
b.c
b.c