It is a good use for carriage return and select to get a sub 1 sec sleep. A variation on this is wget style progress bar if that is more approptriate to the task at hand ie you know how far you are through the task.

while( $waiting or 1 ) {
    spin();
}

{
    my $c=0;  # closure to remember spin state
    sub spin {
        local $| = 1;
        print "\r", qw( | / - \ )[$c++%4];
        select undef, undef, undef, 0.25;  # sleep 250 msec
    }
}
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Unbuffered output as per beebles note.