Perl not printing properly

问题

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";
}

回答1:

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).

回答2:

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";

来源：https://stackoverflow.com/questions/6104811/perl-not-printing-properly