If you use backticks in scalar context, like you do, you'll get the whole output in one string. If you use them in list context, you'll get the lines of output as a list.
So what you need is: 
my $num = () = qx{/usr/bin/lpstat -h $server -W not-completed};

[download]
which puts the number of lines output by the command into $num.
This syntax puts qx{...} into list context and returns the number of elements in the list rather than the list itself.

Besides, why are you using Data::Dumper? This is nice for structured variables, but for plain strings it's more straightforward to write: 

print "number is: $num\n";

[download]

In reply to Re^3: Number of lines from a system call by betterworld
in thread Number of lines from a system call by tcf03

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.