What is the scope of Perl's $| (OUTPUT_AUTOFLUSH) setting?

Question

I have a Perl script running on an old CentOS 5.6 server which has Perl 5.8.8 installed. Unfortunately I can't upgrade either the OS or the version of Perl that's running on this server.

When I'm running this script from the command prompt, despite there being a $| = 1; statement at the top of the script (in the global scope), it still seems to buffer output to the console (over a ssh session).

Writes to both a log file and STDOUT are carried out by a function, for example:

#!/usr/bin/perl
$| = 1;

&writelog("Started...");

# Do work with lots of writelog'ing

&writelog("...Done.");

exit(0);

sub writelog {

    # This is greatly simplified for the purpose of this question

    my ($logentry) = @_;
    my $logfile = "/var/log/thelog.log";
    my $logline = "$logentry\n";
    print $logline;
    open (LOGFILE, ">>$logfile");
    print LOGFILE, "$logline";
    close (LOGFILE);
}

Does the value of $| only affect output in the current scope, i.e. in this case the script's global scope? Or should it, in the example above, also cause immediate flushing to STDOUT/LOGFILE by the print statements in writelog?

Answer 1

$| affects only the currently selected default output filehandle.

You can explicitly set it for a filehandle like:

LOGFILE->autoflush(1);

See http://perldoc.perl.org/perlvar.html#Variables-related-to-filehandles