CODEWITHSUNDEEP
perl
Allen Qin
Allen Qin

Reputation: 19947

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

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

Upvotes: 5

Views: 5306

Answers (3)

aschepler
aschepler

Reputation: 72401

You need to disable buffering on STDOUT. See $| in perlfaq

Upvotes: 4

Mat
Mat

Reputation: 206727

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?

Upvotes: 21

Philip
Philip

Reputation: 5917

The standard output stream is usually buffered. Try flushing the output stream after each print statement. See the Perl Cookbook, §7.13 for a detailed explanation and solution.

Upvotes: 1

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