PolettiX:~# dd if=/dev/zero of=testfile bs=1024 count=1024
1024+0 records in
1024+0 records out
1048576 bytes transferred in 0.019164 seconds (54715967 bytes/sec)
PolettiX:~# 
PolettiX:~# 
PolettiX:~# mkfs.ext2 testfile
mke2fs 1.37 (21-Mar-2005)
testfile is not a block special device.
Proceed anyway? (y,n) y
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
128 inodes, 1024 blocks
51 blocks (4.98%) reserved for the super user
First data block=1
1 block group
8192 blocks per group, 8192 fragments per group
128 inodes per group

Writing inode tables: done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 27 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.
PolettiX:~# 
PolettiX:~# 
PolettiX:~# mount testfile -o loop /mnt
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Now you have a filesystem that will be easy to fill up:

#!/usr/bin/perl
use strict;
use warnings;
use Fatal qw( open close );

chdir '/mnt';
{
   open my $fh, '>', 'prova.dat';
   print {$fh} "ciao\n" for 1 .. 1000000;
   # close $fh;
}

print {*STDERR} "should be closed here!\n";
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In my system, the final string on STDERR gets printed when the close above is commented; uncommenting the close triggers the fatal error:

Can't close(GLOB(0x814cd4c)): No space left on device at (eval 2) line
+ 3
        main::__ANON__('GLOB(0x814cd4c)') called at ./prova.pl line 13
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