$ sample 10 somelongfile.txt  ## to get 10 random lines

$ some long command | sample 50 > mysample.txt

##</code><code>##

my $wanted = shift || 10;
my @got;

die "Invalid number of lines!\n" if $wanted < 1;

while (<>) {
  if (@got < $wanted) {
      push @got, $_;
  } elsif (rand($.) < $wanted) {
      splice @got, rand(@got), 1;
      push @got, $_;
  }
}

die "Not enough lines!\n" if @got < $wanted;
print @got;