Update command line output

Say

$| = 1

somewhere early in your program to turn autoflushing on for the output buffer.

Also consider using "\r" to move the cursor back to the beginning of the line, rather than trying to explicitly count how many spaces you need to move back.

Like you said, don't print out a newline while your progress counter is running or else you will print out your progress on a separate line instead of overwriting the old line.

Use autoflush with STDOUT:

local $| = 1; # Or use IO::Handle; STDOUT->autoflush;

print 'Progress: ';
my $progressString;
while ...
{
  # remove prev progress
  print "\b" x length($progressString) if defined $progressString;
  # do lots of processing, update $counter
  $progressString = "$counter / $total"; # No more newline
  print $progressString; # Will print, because auto-flush is on
  # end of processing
}
print "\n"; # Don't forget the trailing newline