How can I print text immediately without waiting for a newline in Perl?

Question

I have a computationally expensive task in perl, and would like to inform the user that computation is ongoing by printing out a period after each portion of the computation is completed. Unfortunately, until I print a "\n", none of my periods are printed. How can I address this?

Answer 1

set $|=1 before you start printing. Eg.

perl -e ' $|=1; foreach (1..10) { print "$_ "; sleep(1); }'

Answer 2

You need to set autoflush for STDOUT. Example:

use IO::Handle;
STDOUT->autoflush(1);
foreach (1..20) {
  print '.';
  sleep(1);
}

Answer 3

See the FAQ How do I flush/unbuffer an output filehandle? Why must I do this? and note:

Besides the $| special variable, you can use binmode to give your filehandle a :unix layer, which is unbuffered ...

For the general problem, you might want to look at Time::Progress:

%b

%B

progress bar which looks like:

##############......................

Answer 4

An excellent article you should read: Suffering from Buffering?

Answer 5

What worked for me was to put the line

STDOUT->autoflush(1);

before my line

print ".";

inside my existing loop. Didn't use the sleep for fear of slowing the things down even more.