I don't have time at the moment to do full justice to this, but an (untested!) snippet might look like this:

open(my $FH, "cleartool find /vobs/41Rational_Val/. -all -print|")
    or die "Something went wrong\n";

print STDERR "Reading cleartool command, line ";
while (<$FH>) {
    do_something_here;
    unless ($. % 200) { # every 200 lines
        print STDERR "$. ";
  }
}
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However, there is no way to know the percent complete progress of the cleartool command.