Depending on the size of the file, you may exhaust the machine's memory allocated to disk buffering, which means that if you use File::Copy you will physically reread the same disk sectors over and over again. If this is true, the most effecient method of writing to multiple files would be to read a line, and write it out to all the output files. Something like:

my %fd = (
  'file1'         => 'fd1',
  '/tmp/foo       => 'fd2',
  '/home/me/file' => 'fd3',
);

my $in = shift || die "No file specified.\n";
open IN. $in or die "Cannot open $in for input: $!\n";
foreach( keys %fd ) {
  open $fd{$_}, ">$_" or die "Cannot open $_ for output: $!\n";
}
while( <IN> ) {
  foreach my $fd( keys %fd ) {
    print $fd $_;
  }
}
foreach( keys %fd ) {
  close $fd{$_};
}
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