use strict;
use warnings;

my $filename = 'logfile.txt';
my $backupfile = 'logfile.backup';

open(my $handle, '>>', $filename) or die;
link $filename, $backupfile;
unlink($filename);
print $handle "First line\n";
syswrite($handle, "Second line\n");
close($handle);
rename $backupfile,$filename; # ok to fail if $filename still exists
unlink $backupfile;