This is pulling out all the digits. The OP is just asking for the "digits between the spaces".

my $x = "a1aa11 b2bb22bbb222 c3cc33";
my @nums = $x =~ /\d+/g;
print join(" ", @nums) . "\n";

Output:
1 11 2 22 222 3 33
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Ikegami's answer is pulling out the numbers between the spaces.