$re='.*?(@)((?:[a-z][a-z0-9_]*))(\\[)(\\d+)(\\])'; #find arrays e.g: @arry[123]

open(FILE, "+<", "xxxxx.pl");
@code = <FILE>;
close FILE;

$code = join ("",@code);

foreach (@code) {

    if($_ =~ m/$re/) {  #check if this line contains any array

      my $random_number = int(rand(9999));        #create a new index for that array
      $OldVariable = $1.$2.$3.$4.$5;              #store the old array in variable
      $NewVariable = $1.$2.$3.$random_number.$5;  #changing the index in the found array
      $code =~ s/$OldVariable/$NewVariable/g;     #now replace all of that found array with the new one.

    }
}
print $code;
<>;