Perl not printing properly

Question

Ok, so I have some sub routines similar to what you see below, my issue is that the print function is not printing out until the actual command is complete, I want it to print
"Has MySQL, Installing:", and then do the command then print OK. I have already tried using sleep and tried clearing the $ssh_d object. Any advice appreciated. Don't worry about the variables in this particular sub, the issue is happening all over. Thanks guys.

if ($MySQL)
{
    print "Has MySQL, Installing: ";
    $mysqlCmd = "/path/to/script/mysql-install.pl $person > /dev/null 2>&1";
    $ssh_d->cmd("$mysqlCmd");
    print "OK\n";
}

When you run this without the ssh cmd call (I'm assuming that sshd refers to Net::SSH::Perl), does it print out? I'm guessing that the cmd call does something to the stdout handle, somehow. — Horus, May 24 '11 at 01:24
See "Suffering from Buffering" http://perl.plover.com/FAQs/Buffering.html — tadmc, May 24 '11 at 03:56

ysth · Accepted Answer · 2011-05-24T02:04:21.830

13

STDOUT is usually line-buffered, so you won't see your output until you print a newline. You can set $| before printing to force your output to be printed.

To turn on autoflushing after each print, set $| to 1:

$| = 1;
print "Enter a number between 3 and 5: ";
chomp( my $answer = <STDIN> );

(Note that $| isn't actually a single value, it is tracked separately for each filehandle. When you set it, it affects the setting for the currently selected filehandle (see select).

edited May 24 '11 at 02:04

answered May 24 '11 at 01:23

ysth

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Thanks! Can you show me an example of how to use $| I am unfamiliar, this place never fails lol – noledgeispower May 24 '11 at 01:40
@noledgeispower: added an example – ysth May 24 '11 at 02:04
@ysth: Is the autoflush needed here considering that `STDOUT` (in line buffered mode) is flushed automatically when reading from `STDIN`? – sid_com Feb 17 '12 at 15:43
@sid_com: depends. If stdout is going to a file it can make the output more sane. – ysth Feb 26 '12 at 04:30

score 5 · Answer 2 · answered May 24 '11 at 02:06

Thanks! Can you show me an example of how to use $| I am unfamiliar, this place never fails lol –

Will this do?

$| = 1;
print "This is now unbuffered printing. "
sleep 3;
print "You no longer have to wait for the NL character. ";
sleep 3;
print "\n";

Perl not printing properly

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