BTW, You can use diagnostics; in your code to get long-form explanations for such error messages:

Use of uninitialized value in length at cpg8.pl line 4 (#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.
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In order to say more, it'd be useful to see just what line 4 of your script actually says.