Erm.. 
for my $i (0..20) {
    vec( $bitstring, $offset++, 4 ) = $i ;
}

[download]
That sets consecutive nybbles (half-bytes) to 0,1,2,3 .. etc. 

my $bits = unpack("A4*", $bitstring);

[download]
This "unpacks" an ascii string of 4 bytes (the * at the end doesn't do anything since you didn't give a format letter). In other words, it just returns the first 4 bytes of $bitstring without converting them in any way.

I don't think there's an unpack template for nybbles. If you want to see what you put in $bitstring, you might want to use the bit string template: "b*": 

print unpack("b*",$bitstring);

[download]
output (broken up for readability): 
0000100001001100001010
1001101110000110010101
1101001110110111111100
0010000100110000100000

[download]
or hex: 
print unpack("h*",$bitstring);

[download]
output: 
0123456789abcdef012340

[download]
"What should it profit a man, if he should win a flame war, yet lose his cool?"

In reply to Re: HowTo unpack a vec (bitstring) by Joost
in thread HowTo unpack a vec (bitstring) by jeanluca

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.