use strict;
my $size = shift @ARGV || 3; # sample size
my @sample;


my $taken = 0; # for making sure we get the first $size lines

while( my $line =  <> ) {
    chomp $line;

    if ( rand(1) < ($size/$.) ){
        my $position;
        do{
            $position = int rand($size);
        }
        while( $taken < $size && $sample[$position] );
        $sample[$position] = $line;
        $taken++;
    }
}

for( my $i = 0; $i < @sample; $i++ ){
    print "[$i] '$sample[$i]'\n";
}
print "\n";