Works for me, that is, I am able to play with conditions and see what happens as I experiment.

  DB<1> $s=qq(1a2a3a4a5a); if ($s=~/(\d+)/){print $1};
1
  DB<2> $s=qq(1a2a3a4a5a); while ($s=~/(\d+)/g){print $1};
12345
  DB<3> $s=q(1a22b333c4567d89);

  DB<4> $re=qr~(\d+)~;

  DB<5> print $1 while $s =~ /$re/g;
122333456789
  DB<6> $re=qr~(\d{3,})~;

  DB<7> print $1 while $s =~ /$re/g;
3334567

Just keep playing with inputs and patterns until you understand what is going on   (or until you get something that works and then put 'study' on your to-do list ;-)

And strangely enough, shortly before/after your question, in another thread antirice offered a suggestion to use a tool to try explaining what a RE means - see Re: Pattern Matching Question.   Hey, that became next on my todo list!