#! perl
use strict;
use warnings;
use Fcntl ':seek';

my $file = 'aaa.txt';

if (!-e $file || -z $file)
{
#   print "File '$file' is empty\n";
    open(my $fh1, '>', $file)
        or die "Cannot open file '$file' for writing: $!";
    print $fh1 "The quick brown fox jumped over the unfortunate dog.\n";
    close $fh1
        or die "Cannot close file '$file': $!";
}

open(my $fh2, '+>>', $file)
    or die "Cannot open file '$file' for appending and reading: $!";
print $fh2 "We have nothing to fear but fear itself.\n";
seek $fh2, 0, SEEK_SET;
print while <$fh2>;
close $fh2
    or die "Cannot close file '$file': $!";