PERL Miscellaneous - Output to file is not flushing immediately

Author

Output to file is not flushing immediately

void.no.spam.com@gmail.com

2008-03-25, 7:19 pm

I have a perl script that writes stuff to a text file. While the
script is running, I do a "tail -f" on the text file to see the
output. But I can tell that the output isn't being flushed
immediately, because the script writes something to the file
immediately before sleeping for 60 seconds, but I don't see that
output show up in the "tail -f" until after it comes back from
sleeping.

I thought that putting a "\n" at the end of a print would do a flush,
but that's obviously not the case.

I also read that if you put "$| = 1" at the beginning of your script,
then it would do a flush after every print or write command. I tried
that, and it still does not flush.

xhoster@gmail.com

2008-03-25, 7:19 pm

"void.no.spam.com@gmail.com" <void.no.spam.com@gmail.com> wrote:
> I have a perl script that writes stuff to a text file. While the
> script is running, I do a "tail -f" on the text file to see the
> output. But I can tell that the output isn't being flushed
> immediately, because the script writes something to the file
> immediately before sleeping for 60 seconds, but I don't see that
> output show up in the "tail -f" until after it comes back from
> sleeping.
>
> I thought that putting a "\n" at the end of a print would do a flush,
> but that's obviously not the case.

use IO::Handle;
#...
$fh->autoflush();

>
> I also read that if you put "$| = 1" at the beginning of your script,
> then it would do a flush after every print or write command. I tried
> that, and it still does not flush.

That will only turn autoflush on for the STDOUT (or whatever the currently
selected filed handle is).

Read all about it here:
perldoc -q flush

Xho

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