use List::Util 'shuffle';

my @fileData = shuffle map { "$_\n" } 1 .. 20, (1) x 5;

my $linenumber=1;
foreach my $line(@fileData) {
   $linenumber=$linenumber+1;
   if ($line =~ m/^1$/) {
       print "$linenumber\n";
   }
}