prefer $() over backquotes

diff --git a/exec/vif_down b/exec/vif_down
index af4be16..b36f1d6 100755 (executable)
--- a/exec/vif_down
+++ b/exec/vif_down
@@ -38,7 +38,7 @@ if re.match(r'(tun|tap)%d-\d+' % sliceid, vif ) is None:
 public_src = os.popen("ifconfig | grep $(ip route | grep default | awk '{print $3}' | awk -F. '{print $1\"[.]\"$2}') | head -1 | awk '{print $2}' | awk -F : '{print $2}'").read().rstrip()
 cmd_iptables_del_in = "/sbin/iptables -D INPUT -i %s -m mark ! --mark %d -j DROP 2>/dev/null" % (vif, sliceid)
 cmd_iptables_del_out = "/sbin/iptables -D OUTPUT -o %s -m mark ! --mark %d -j DROP 2>/dev/null" % (vif, sliceid)
-cmd_iptables_del_pr = "/sbin/iptables -t nat -D POSTROUTING -s `ip ro | grep 'dev %s' | head -1 | awk '{print $1}'` -j SNAT --to-source %s --random" % (vif, public_src,)
+cmd_iptables_del_pr = "/sbin/iptables -t nat -D POSTROUTING -s $(ip ro | grep 'dev %s' | head -1 | awk '{print $1}') -j SNAT --to-source %s --random" % (vif, public_src,)
 
 os.system(cmd_iptables_del_in)
 os.system(cmd_iptables_del_out)