See perlre (Capture buffers).

use warnings;
use strict;

while (<DATA>) {
    if (/ ^ (\d+) [.] (\d+) [.] (\d+) $ /x) {
        print "$1 $2 $3\n";
    }
}

__DATA__
7.55.3
12.0.2
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Prints:

7 55 3
12 0 2
[download]

Update: I noticed your update, and maybe you want to restrict it to 1- or 2-digit only:

    if (/ ^ (\d{1,2}) [.] (\d{1,2}) [.] (\d{1,2}) $ /x) {
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