It appears blazar has the best approach. I added data validation to, and bencmarked, the two main solutions (regexes and unpack), as well as doing the same thing with sprintf (just for fun). 

@my_array = <DATA>;

use Benchmark ':all';


sub regex_method {
    my  $array = [@_];
    for (@$array) {
        next unless /^\d{6}\s*$/;  ## validate data
        s:(\d{2})(?!$):$1/:g;
    }
}

sub sprint_method {
    my $array = [@_];
    for (@$array) {
       next unless /^\d{6}\s*$/;  ## validate data
       $_ = sprintf "%d%d/%d%d/%d%d", split('',$_);
    }
}

sub unpack_method {
    my $array = [@_];
    for (@$array) {
        next unless /^\d{6}\s*$/;  ## validate data
        $_=join '/', unpack 'A2' x 3, $_ for @arr;
    }
}

cmpthese( 50000, {
    'regex'   => sub { regex_method(@my_array) },
    'sprintf' => sub { sprint_method(@my_array) },
    'unpack'  => sub { unpack_method(@my_array) },
});

__DATA__
010203
020304
012398
122399

[download]

With these results (representative of many runs): 

           Rate sprintf   regex  unpack
sprintf 20383/s      --    -23%    -79%
regex   26441/s     30%      --    -73%
unpack  96899/s    375%    266%      --

[download]
<-radiant.matrix->
Larry Wall is Yoda: there is no try{} (ok, except in Perl6; way to ruin a joke, Larry! ;P)
The Code that can be seen is not the true Code
"In any sufficiently large group of people, most are idiots" - Kaa's Law

In reply to Re: modify the contents of an array by radiantmatrix
in thread modify the contents of an array by s_gaurav1091

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.