I'm not really up to speed with this, but I think you might want something like:

use Math::GSL::Histogram qw/:all/;
use Math::GSL qw/:all/;

$file = "blah.txt";
$mode = 'w';

$h = gsl_histogram_alloc(3);
gsl_histogram_set_ranges($h, [0, 41, 61, 100], 4);
gsl_histogram_increment ($h, 0);
gsl_histogram_increment ($h, 41);
gsl_histogram_increment ($h, 61);
gsl_histogram_increment ($h, 100);
$stream = gsl_fopen $file, $mode;
gsl_histogram_fprintf($stream, $h, '%f', '%f');
[download]

At least that runs without error. On my Windows Vista box, I need to view 'blah.txt' in something like wordpad. For me, notepad ignores the newlines.

It might be worth your while to download the Math::GSL source from CPAN, as the test files (in the 't' folder) provide useful examples of correct usage.

Cheers,
Rob