Perl Print function does not work properly when Sleep() is used

Question

I have the following code to print a "." each second to simulate a progress bar.

$num = 15;
while($num--){
    sleep(1);
    print ".";
}

The problem I'm having now is the "." character is not printed after each loop. Instead, all 15 "." are printed at once after the loop exits. However if I print ".\n", it works fine. But the "." will be printed on a new line every time which is not what I want.

It seems quite weird and could not figure out why. Could anyone provide some help? Thank you.

Regards, Allen

Answer 1

That's probably because I/O is being buffered. Try disabling buffering (autoflush):

$| = 1;

before your loop.

For a more complete explanation, refer to How do I flush/unbuffer an output filehandle? Why must I do this?