The SvREFCNT macro (perlguts) returns this number. I am sure this is already somewhere on cpan, but a simple XS routine could look like this: 
/* generated by h2xs -c Scalar::RefCount */
#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"

#include "ppport.h"



MODULE = Scalar::RefCount       PACKAGE = Scalar::RefCount

int
refcount(s)
    SV* s
PROTOTYPE: $
CODE:
    RETVAL = SvREFCNT(s);
OUTPUT:
    RETVAL

[download]
use Test::More tests => 6;
BEGIN { use_ok('Scalar::RefCount') };

#########################

my $a;

is(Scalar::RefCount::refcount($a),1, 'return 1');

my $b = \$a;
is(Scalar::RefCount::refcount($a),2, 'return 2');

my $c = \$a;
is(Scalar::RefCount::refcount($a),3, 'return 3');

{
my $d = \$a;
is(Scalar::RefCount::refcount($a),4, 'return 4');
}
is(Scalar::RefCount::refcount($a),3, 'return 3');

[download]
Update: Ah, thanks cdarke.

In reply to Re: The number of references to a variable by lima1
in thread The number of references to a variable 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.