14

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?

brian d foy
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shino
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5 Answers5

17

You need to set autoflush for STDOUT. Example:

use IO::Handle;
STDOUT->autoflush(1);
foreach (1..20) {
  print '.';
  sleep(1);
}
Alexandr Ciornii
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7

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

perl -e ' $|=1; foreach (1..10) { print "$_ "; sleep(1); }'
Sinan Ünür
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Martin
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  • @ar, `STDOUT->autoflush(1)` is the same thing as `$|=1` except `$|=1`, is global and `STDOUT->autoflush(1)` is specific to one handle. – Evan Carroll Mar 12 '10 at 17:18
  • Except you have to do a `use IO::Handle`. Not that `IO::Handle` hasn't been a standard module for eons, but ... yeah. :(` – Robert P Mar 12 '10 at 17:37
4

An excellent article you should read: Suffering from Buffering?

ysth
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2

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:

##############......................
Community
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Sinan Ünür
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0

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.

John Conde
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ekemmler
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