Here:

use strict;
use warnings;

use Log::Log4perl qw(:easy);

my $conf = <<EOT;
log4perl.category                  = TRACE, Screen

    # Regular Screen Appender
log4perl.appender.Screen           = Log::Log4perl::Appender::Screen
log4perl.appender.Screen.stdout    = 1
log4perl.appender.Screen.layout    = PatternLayout
log4perl.appender.Screen.Threshold = TRACE
log4perl.appender.Screen.layout.ConversionPattern = %m%n

    # File appender
log4perl.rootLogger = DEBUG, Log1
log4perl.appender.Log1 = Log::Log4perl::Appender::File
log4perl.appender.Log1.mode = append
log4perl.appender.Log1.autoflush = 0
log4perl.appender.Log1.layout = Log::Log4perl::Layout::SimpleLayout
log4perl.appender.Log1.filename = test.log
log4perl.appender.Log1.Threshold = INFO
EOT

Log::Log4perl->init(\$conf);

TRACE("message #1 (screen only)");
INFO("message #2");
INFO("message #3");
sleep(10);
ERROR("message #4");
[download]

In my play around, I found that buffering only reliably works when buffering to screen (which makes sense, given that switching off autoflush effectively buffers file output).