Here is one way of doing it on Windows:

use strict;
use Win32::OLE qw(in);

my $WMI = Win32::OLE->GetObject("winmgmts:")
    or die ("Could not create WMI object.");

my $OS_Col = $WMI->InstancesOf('Win32_OperatingSystem')
    or die ("Could not get OS instances.");

foreach my $OS (in $OS_Col) {
    printf "Free Physical Memory:  %10u kB\n", $OS->{FreePhysicalMemor
+y};
    printf "Free Virtual Memory:   %10u kB\n", $OS->{FreeVirtualMemory
+};
    printf "Total Virtual Memory:  %10u kB\n", $OS->{TotalVirtualMemor
+ySize};
    printf "Total Visible Memory:  %10u kB\n", $OS->{TotalVisibleMemor
+ySize};
}
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