check_netio: added regex filter for include and exclude

docs/20_Checks/check_netio.md

@@ -13,11 +13,10 @@ This plugin scans `/proc/net/dev` with the regex `eth|en[ops][0-9]*` to show a f
 ## Syntax
 
 ```text
-> ./check_netio -h
 ______________________________________________________________________
 
 CHECK_NETIO
-v1.4
+v1.5
 
 (c) Institute for Medical Education - University of Bern
 Licence: GNU GPL 3
@@ -38,6 +37,10 @@ OPTIONS:
   -h               this help
 
 PARAMETERS:
+
+  -f  REGEX        filter interfaces by given regex.
+  -r  REGEX        remove interfaces by given regex
+
   -i  INTERFACE    show this interface only. Quote multiple interfaces.
                    The check returns unknown if an interface does not
                    exist.
@@ -48,6 +51,16 @@ EXAMPLES:
   check_netio -i "eth0 eth1" 
                    show netio of given interfaces.
 
+  check_netio -f "^eth" 
+                   show netio of interfaces beginning with "eth"
+
+  check_netio -f "^eth" -r "eth2"
+                   show netio of interfaces matching "^eth" but not "eth2"
+
+  check_netio -f "^(enp|wlp)"
+                   Example to include multiple interface names: use brackets
+                   and divide expressions with pipe sign.
+
 ```
 
 ## Examples
@@ -74,10 +87,20 @@ If you enter a wrong interface the check returns with "UNKNOWN".
 `check_netio -i "whatever"`returns
 
 ```txt
-UNKNOWN: Network IO ... IN 0 MB/s >> [host] >> 0 MB/s OUT
+ERROR: the interface [whatever] does not exist.
+```
 
---- whatever:
-UNKNOWN: the interface whatever does not exist.
+### Filter interface list
 
- |rx=0;; tx=0;;
- ```
+The parameter `-f` is followes by pattern that an interface must match.
+The opposite does the regexp behind `-r`: it removes interfaces that match that regex.
+
+You can combine both parameters.
+
+The regexp can be an extended regexp (`grep -E <pattern>`). This allows to use brackets and divide expressions with pipe sign, eg. `check_netio -f "^(enp|wlp)"`
+
+If your filter rules remove all existing interfaces you get an error message:
+
+```txt
+ERROR: No interface was found.
+```