#!/usr/bin/perl                             
#                                           
# sample_random_lines_from_file.pl  <FName> <NumSamples>     
use 5.10.1;                                 
use strict;                                 
use warnings;                               
use autodie;                                
                                            
my @samples;                                
                                            
my $FName = shift // die "missing: <filename> <numsamples>"; 
my $num = shift // die "missing: <numsamples>";              
                                            
open my $FH, '<', $FName;                   
while (<$FH>) {                             
    if ($num/$. > rand) {                   
        my $i = @samples;                   
        if ($i > $num) { $i = rand @samples; }
        #print "slot $i, size=" . scalar(@samples) . ", line $.\n";
        $samples[$i]=[ $., $_ ];            
    }                                       
}                                           
                                            
print "random samples:\n";                  
print $$_[1] for sort { $$a[0] <=> $$b[0] }  @samples;