my $ipconfig = `ipconfig /renew`;
my $ipcfg_success = $?;

if ($ipcfg_success == 0) {
    do something;
} else {
    do something;
}

##</code><code>##

my $ipconfig = `ipconfig /renew`;
my $ipcfg_success = $?;

die "command failed: $?" unless $ipcfg_success == 0;