Change ip segment so that the tests can be executed on OSX as well

Change regular expressions to a more compatible format.

powerlevel9k.zsh-theme

@@ -1088,18 +1088,20 @@ prompt_ip() {
   else
     if defined POWERLEVEL9K_IP_INTERFACE; then
       # Get the IP address of the specified interface.
-      ip=$(ip -4 a show "$POWERLEVEL9K_IP_INTERFACE" | grep -o "inet\s*[0-9.]*" | grep -o "[0-9.]*")
+      ip=$(ip -4 a show "$POWERLEVEL9K_IP_INTERFACE" | grep -o "inet\s*[0-9.]*" | grep -o -E "[0-9.]+")
     else
       local interfaces callback
       # Get all network interface names that are up
-      interfaces=$(ip link ls up | grep -o -E ":\s+[a-z0-9]+:" | grep -v "lo" | grep -o "[a-z0-9]*")
-      callback='ip -4 a show $item | grep -o "inet\s*[0-9.]*" | grep -o "[0-9.]*"'
+      interfaces=$(ip link ls up | grep -o -E ":\s+[a-z0-9]+:" | grep -v "lo" | grep -o -E "[a-z0-9]+")
+      callback='ip -4 a show $item | grep -o "inet\s*[0-9.]*" | grep -o -E "[0-9.]+"'
 
       ip=$(getRelevantItem "$interfaces" "$callback")
     fi
   fi
 
+  if [[ -n "$ip" ]]; then
     "$1_prompt_segment" "$0" "$2" "cyan" "$DEFAULT_COLOR" "$ip" 'NETWORK_ICON'
+  fi
 }
 
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