It may be that you want something like:

use strict;
use warnings;

my %dates;

while (<DATA>) {
    next unless /(.)(..)(..)(.{4})/;

    my $date = "$4$3$2";

    if (exists $dates{$date}) {
        print "<TD class=table_font>$date - Hash exists</TD>\n";
        # play with hash
    } else {
        print "<TD class=table_font>$date - Hash doesn't exist</TD>\n"
+;
        # create the hash
        $dates{$date} = undef;
        # play with hash
    }
}

__DATA__
x11112007
y11122007
p11112007
x11132007

[download]

Prints:

<TD class=table_font>20071111 - Hash doesn't exist</TD>
<TD class=table_font>20071211 - Hash doesn't exist</TD>
<TD class=table_font>20071111 - Hash exists</TD>
<TD class=table_font>20071311 - Hash doesn't exist</TD>

[download]

Note that it helps a lot to understand what you are trying to do if you provide a little data and tell us what you expect to see and what you actually see.

DWIM is Perl's answer to Gödel

In reply to Re: Dynamically creating a hash based on a variable by GrandFather
in thread Dynamically creating a hash based on a variable by beethamd

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.