Doing it in a single regexp is possible, although it won't be what you're looking at:

s{.*}
{              xx
             xxxx
            xxxxxx
           xxxxxxxx
          xxxxxxxxxx
         xxxxxxxxxxxx
        xxxxxxxxxxxxxx
       xxxxxxxxxxxxxxxx
      xxxxxxxxxxxxxxxxxx
     xxxxxxxxxxxxxxxxxxxx
    xxxxxxxxxxxxxxxxxxxxxx
   xxxxxxxxxxxxxxxxxxxxxxxx
  xxxxxxxxxxxxxxxxxxxxxxxxxx
 xxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
              xx
              xx}s;
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