You can pack a null-padded ASCII string using the Z pack template: 
$str = 'Hello, world!';
$len = length $str;

$packed_str = pack 'N', $len;

$len += 4 - (($len % 4) || 4);       # next multiple of 4

$packed_str .= pack "Z$len", $str;

# for testing:
($test_str = $packed_str) =~ s/([^\x20-\x7E])/sprintf '\\x%02x', ord $
+1/ge;
print "$test_str\n";

__END__

[download]
And the testing section prints the expected: \x00\x00\x00\x0dHello, world!\x00\x00\x00 Since you're packing the unpadded length in the first four bytes, you'll have to make it the next multiple of 4 before unpacking the string as well.

In reply to Re: How to use pack/unpack data over a network by chipmunk
in thread How to use pack/unpack data over a network by Anonymous Monk

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.