# From /etc/security/limits:
#   Sizes are in multiples of 512 byte blocks
#   fsize      - soft file size in blocks
# To test this program, I set block size via:
#   ulimit -f 900

use strict;
use warnings;
$| = 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': $!";
my $niter = 1000;
my $size = 0;
my $block = 'a' x $bsize;
for my $i (0..$niter) {
   $size += $bsize;
   print "$i: $size bytes written\n" if $i % 100 == 0;
   print $fh $block or die "$i: error in print: $!";
}
close $fh or die "error: close: $!";

##</code><code>##

ulimit -f 900

##</code><code>##

% perl f.pl
ulimit=900 blocks (block size=512)
0: 512 bytes written
100: 51712 bytes written
200: 102912 bytes written
300: 154112 bytes written
400: 205312 bytes written
500: 256512 bytes written
600: 307712 bytes written
700: 358912 bytes written
800: 410112 bytes written
900: 461312 bytes written
904: error in print: A file cannot be larger than the value set by ulimit. at f.pl line 22.

##</code><code>##

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: $!";

##</code><code>##

ulimit=900 blocks (block size=512)
0: 0 bytes written
100: 51200 bytes written
200: 102400 bytes written
300: 153600 bytes written
400: 204800 bytes written
500: 256000 bytes written
600: 307200 bytes written
700: 358400 bytes written
800: 409600 bytes written
900: 460800 bytes written
900: error in print: A file cannot be larger than the value set by ulimit. at f.pl line 23.

##</code><code>##

% type ulimit
ulimit is a shell builtin.
% ulimit -f 900
% ulimit -f
900
% ksh -c 'ulimit -f'
900
% bash -c 'ulimit -f'
450