Filesys::DiskSpace will do what you want. It doesn't use df or du. It uses a sub that uses syscall.

#!/usr/bin/perl

use strict;
use warnings;
use Filesys::DiskSpace;
use Data::Dumper::Concise;

my $dir = '/';
print Dumper(
my($fs_type, $fs_desc, $used, $avail, $fused, $favail) = df $dir);
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