# this should be read from the last line to the top one
my @sorted= map  { substr( $_, 8) }                  # [3]: remove the date
            sort                                     # [2]: sort aplphabetically on the date
            map  { $_= @{[split(/\s/, $_)]}[3] . $_} # [1]: get the date and add it at the beginning of the string
           <DATA>;
print join "\n", @sorted;
__DATA__
<b><a href="url">text</a></b> 20000407 text
<b><a href="url">text</a></b> 20000409 text
<b><a href="url">text</a></b> 20000408 text
<b><a href="url">text</a></b> 20000507 text