I'm assuming you don't know the final count of operations? If you do, check out Term::ProgressBar, which will even give you an ETA. ;-)

Otherwise:

## calculate Fibonacci sequence, only print status
my @fib = (0,1);
my $rpt_freq = 1000; # how many elements until I print a mark?
while (@fib < 50000) { # only do first 50k numbers
    push @fib, $fib[-1]+$fib[-2];
}
continue {
    print '...'.scalar(@fib) if ( @fib % $rpt_freq == 0 );
}
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