#! perl
use Modern::Perl;

while (<DATA>)
{
    chomp;
    s{\b(\d)\b}{0$1}g;
    say;
}

__DATA__
1,2,3,4
8,9,10,11
7,8,9,10
12,13,14,15

##</code><code>##

16:42 >perl 462_SoPW.pl
01,02,03,04
08,09,10,11
07,08,09,10
12,13,14,15

16:42 >