If I understand correctly, you want something like:

print("\rProcessed line number $ctr.");
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Test code:

for $ctr (1..10) {
   sleep(1);
   print("\rProcessed line number $ctr.");
}
print("\rDone.                      \n");
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Similar to how "\n" (Line Feed) moves the cursor to the begining of the next line, "\r" (Carriage Return) moves the cursor to the begining of the current line.