Use of uninitialized value $cells in pattern match (m//) at
        yahoogroups_files.pl line 244, line 2 (#1)
    (W uninitialized) An undefined value was used as if it were alread
+y
    defined.  It was interpreted as a "" or a 0, but maybe it was a mi
+stake.
    To suppress this warning assign a defined value to your variables.

    To help you figure out what was undefined, perl will try to tell y
+ou the
    name of the variable (if any) that was undefined. In some cases it
+ cannot
    do this, so it also tells you what operation you used the undefine
+d value
    in.  Note, however, that perl optimizes your program and the opera
+tion
    displayed in the warning may not necessarily appear literally in y
+our
    program.  For example, "that $foo" is usually optimized into "that
+ "
    . $foo, and the warning will refer to the concatenation (.) operat
+or,
    even though there is no . in your program.
[download]

The actual part of the code that causes problems looks like this:

my ($cells) = $content =~ /<!-- start content include -->\s+(.+?)\s+<!
+-- end content include -->/s;
        
while ($cells =~ /<tr>.+?<span class="title">\s+<a href="(.+?)">(.+?)<
+\/a>\s+<\/span>.+?<\/tr>/sg)
[download]

The $cells variable gets in the while loop unintialized.

Why does this happen? The $content variable contains the HTML Yahoo login page(I've checked it by outputting its contents to a html file).

Also, what does this mean?

"/<!-- start content include -->\s+(.+?)\s+<!-- end content include -->/s"

I can understand only simple m// patterns, so I can't figure what's the string that it searches for.

Please help.

$cells is unititialized because the "find stuff between these to comments" match is failing.

The pattern's looking for the shortest string it can find between the start and end comments for the content include, throwing away any leading spaces. Here's how it breaks down:

    \s+       # one or more spaces - don't capture these
     (        # start capturing
        .+?   # one or more anythings, shortest match to what follows
     )        # end capture
[download]

Check the text of the page in $content; my guess is that the Groups folks have reformatted their pages, and the comments that this match is looking for have changed.