use strict;
use warnings;

my $val1 = '5234';

$val1 = append($val1,'_');

unless($val1)
{
    print "return undef\n";
}

print "$val1\n";

sub append
{
    my $val2 = shift;
    my $character = shift;
    if($val2 =~ /\d\d\d\d/)
    {
        $val2 =~ s/(\d)(\d)(\d\d)/$1$character$2$character$3$4/g;
    }
    elsif($val2 =~ /\d\d\d/)
    {
        $val2 =~ s/(\d)(\d)(\d)/$1$character$2$character$3/g;
    }
    elsif($val2 =~ /\d\d/)
    {
        $val2 =~ s/(\d)(\d)/$1$character$2/g;
    }
    else
    {
        return;
    }
    return $val2;
}
Cheers!
<br>
Marshall, 
<br>
First of all thank for reply But if there is 4 digit(5234) I want it to be(5_2_34)!<br>
where as for 3(523) I want it (5_2_3)<br> 
and for 2(52) is want it to be (5_2)<br><br>
Thanks any way!!!<br>