agents: fix lnx_bonding when no bonding interface is configured

When /proc/net/bonding exists but no bonding interface is configured,
head fails with:

  head: *: No such file or directory

Fix this by checking if any interfaces exist before running head

Signed-off-by: Oliver Sedlbauer <os@dev.tdt.de>

Author: osedlbauer

agents/check_mk_agent.linux

@@ -857,7 +857,7 @@ section_bonding_interfaces() {
     (
         cd /proc/net/bonding 2>/dev/null || return
         echo '<<<lnx_bonding:sep(58)>>>'
-        head -v -n 1000 ./*
+        [ -n "$(ls)" ] && head -v -n 1000 ./*
     )
 }
 

agents/check_mk_agent.openwrt

@@ -581,7 +581,7 @@ section_bonding_interfaces() {
     (
         cd /proc/net/bonding 2>/dev/null || return
         echo '<<<lnx_bonding:sep(58)>>>'
-        head -v -n 1000 ./*
+        [ -n "$(ls)" ] && head -v -n 1000 ./*
     )
 }