e.g.

my @numbers = ('1', '2', '2', '3', '3');
my @strings = ('hello', 'green', 'grass', 'rainbow', 'pretty');
my @new_strings;

##</code><code>##

hello
greengrass
rainbowpretty

##</code><code>##

for ( 0 .. $#numbers ) {
  push @{$h{$numbers[$_]}}, $strings[$_];
}
for ( sort { $a <=> $b } keys %h ) {
  push @new_strings, join('', @{$h{$_}}), ">>\n";
}
                                                                                                            
my $v = join ('', @new_strings);
@new_strings = split (/>>/, $v);                                                                                                                                             
my @final_strings;
                                                                                                                                             
for (my $k=0; $k<@new_strings; $k++)     {
             $new_strings[$k] =~ s/\n+//g;
             $new_strings[$k] =~ s/\s+//g;

              if ($new_strings[$k] =~ /\w+/)   {
                       push @final_strings, "$new_strings[$k]";
              }
}

##</code><code>##

@check = ('1','2','3','4');

# desired output:
#-----------------
hello
greengrass
rainbowpretty
xxxxxxxx   	# THE 4TH ELEMENT NOW CONTAINS 'xxxxxxxx' as there isn't a '4' in @numbers