The code uses an old API. Graph has changed significantly since the old versions. It keeps some compatibility API, but it does not seem to help here. Maybe this is what you needed?

#!/usr/bin/perl
use warnings;
use strict;

use Graph;
use Graph::Directed;

my $g = 'Graph::Directed'->new;

$g->add_weighted_path(qw(a 1 b 4 c 1 d));
$g->add_weighted_path(qw(a 3 f 1 e 2 d));
$g->add_weighted_edges(qw(a  c 2  a  d 4  b  e 2  f  d  2 ));
 
my $APSP = $g->APSP_Floyd_Warshall;

print "     ";
foreach my $v ($APSP->vertices ) { 
    printf "%-9s ", "$v";
}
print "\n";

foreach my $u ($APSP-> vertices ) {
    print "$u: ";
    foreach my $v ( $APSP->vertices ) {
        my $w = $APSP->path_length($u, $v);

        if ($w) {
            my @p = $APSP->path_vertices($u, $v);
            printf "(%-5s)=%d ", "@p", $w;

        } else {
            printf "%-9s ", "-"
        }
    }
    print "\n"
}
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