use strict;
use warnings;

use Fcntl      qw( SEEK_SET );
use IO::Handle qw( );

my $qfn = 'test_eagi.tmp';

open(my $fh, '+>', $qfn)
    or die("Can't create \"$qfn\": $!\n");

$fh->autoflush(1);

( my $pos = tell($fh) ) >= 0
    or die("tell: $!\n");

$fh->write('abcde')
    or die("write: $!\n");

seek($fh, $pos, SEEK_SET)
    or die("seek: $!\n");

my $buf = '';
while (!$fh->eof) {
    $fh->read($buf, 4096, length($buf))
        or die("read: $!\n");
}

print "$buf\n";