use strict;
use warnings;
use IO::Handle;    # <-- Added this line for autoflush
$| = 1;
my $bsize = 512;
my $ulimit = `ulimit -f`;
chomp $ulimit;
print "ulimit=$ulimit blocks (block size=$bsize)\n";
my $fname = 'f.tmp';
open my $fh, '>', $fname or die "error: open '$fname': $!";
$fh->autoflush();    # <-- Added this line to make print autoflush
my $niter = 1000;
my $size = 0;
my $block = 'a' x $bsize;
for my $i (0..$niter) {
   print "$i: $size bytes written\n" if $i % 100 == 0;
   print $fh $block or die "$i: error in print: $!";
   $size += $bsize;    # <-- Moved this line to after successful print
}
close $fh or die "error: close: $!";