It's likely to mean exactly what it says. From perldiag:

       Use of uninitialized value%s
           (W uninitialized) An undefined value was used as if it were already
           defined.  It was interpreted as a "" or a 0, but maybe it was a
           mistake.  To suppress this warning assign a defined value to your
           variables.

           To help you figure out what was undefined, perl tells you what
           operation you used the undefined value in.  Note, however, that
           perl optimizes your program and the operation displayed in the
           warning may not necessarily appear literally in your program.  For
           example, "that $foo" is usually optimized into ""that " . $foo",
           and the warning will refer to the "concatenation (.)" operator,
           even though there is no "." in your program.

If you add "use diagnostics" to your code, then Perl will tell you _exactly_ what it means.

A 'string' is a variable with some text in it.
But yours doesn't have anything in it, it's empty.
It's empty because you haven't put anything in it.
On whatever line the error's coming up, Perl is expecting that there should be something in it.
Perl is warning you that you could have made a mistake.

Here's an example that produces the same error:

use warnings; 
my $foo; 
if ($foo eq "hey!") {
    print "yes"
}
[download]

Hope that helps.

andye

(by the way: sorry if any of this sounds patronising: your question was pretty short so I couldn't tell what you already knew, so I thought it better to start from first principles as much as I could. Hope that's OK).

$ perl -e '
> use strict;
> use warnings;
> my $string;
> print qq{>$string<\n};'
Use of uninitialized value in concatenation (.) or string at -e line 5
+.
><
$ perl -e '
> use strict;
> use warnings;
> my $string = q{};
> print qq{>$string<\n};'
><
$
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I hope this illustrates the difference.

Cheers,

JohnGG

It would help us to answer if you'd show us the code in question (for example: Uninitialized Value Question).

$item = "$code[0]" . "."."$code[1]" . ".". "$code[2]";
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Erm . . . ouch.

• The quotes around "$code[0]" are superfluous, to start
• You could have just written it as "$code[0].$code[1].$code[2]" in one swell foop
• Of course that locks you in to a fixed number of elements; if you want to join an arbitrary number of items in @code then just use join: $item = join( ".", @code );

If want a specific subset of elements, then you can use a slice:

my $item = join( ".", @code[0..2] );
my $not_item = join( ".", @code[9,7,0,3] );
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TGI says moo

Fletch, agreed that it's untidy as it is, but  $code[0].$code[1].$code[2] ne join( ".", @code ).

Best,

andye

Update: Anno is right, I did overlook a pair of quotes. Ignore me. :)

One or more of ($code[0], $code[1], $code[2]) has nothing in it.

Best,

andye