use Fctl qw(:flock);

my $fh = new IO::File("file1","r");
flock($fh,LOCK_EX) or die "can't get lock";
my $fh2 = new IO::File("file2","w");
# read fh and write fh2 (ie do a filter)
# move fh2 over fh
# rename("file2","file1"); doesn't work
# File::Copy's move($fh2,$fh1); doens't work
flock($fh,LOCK_UN);

##</code><code>##

#!/usr/bin/perl

use IO::File;
use Fcntl qw(:DEFAULT :flock);

print "opening file1\n";
  my $fh1 = new IO::File("file1",O_RDONLY | O_CREAT);
print "locking file1\n";
  flock($fh1,LOCK_EX) or die "failed to lock file1";
print "opening file2\n";
  my $fh2 = new IO::File("file2",O_WRONLY | O_CREAT);
print "writing to file2\n";
  print $fh2 "file2";
  close($fh2);
print "renaming file2 over file1\n";
  rename("file2","file1") or die "failed to rename file2 over file1";
print "unlocking file1\n";
 #flock($fh1,LOCK_UN);#probably not needed as close does it
                                 #(might cause issues with buffering?)
 close($fh1);

##</code><code>##

#!/usr/bin/perl
use IO::File;
use File::Copy;
use Fcntl qw(:DEFAULT :flock);

print "opening and locking file~\n";
  my $fh_lock = new IO::File("file~",O_RDWR | O_CREAT);
  flock($fh_lock,LOCK_EX) or die "failed to lock file1";
print "opening file1\n";
  my $fh1 = new IO::File("file1",O_RDWR | O_CREAT);
print "opening file2\n";
  my $fh2 = new IO::File("file2",O_WRONLY | O_CREAT);
print "reading from file1\n";
  seek($fh1,0,2);
  close($fh1);
print "writing to file2\n";
  print $fh2 "file2";
  close($fh2);
print "renaming file2 over file1\n";
  rename("file2","file1")
    or print "failed to rename file2 over file1, $!\n";
print "unlocking file~\n";
  #flock($fh_lock,LOCK_UN);	#bad with older flock implementations
  close($fh_lock);
  unlink("file~")
    or print "couldn't remove lock - someone else must have it";