Documentation minor update

Signed-off-by: Denys Fedoryshchenko <denys.f@collabora.com>

PPPOE_misc_tricks.md

@@ -79,3 +79,25 @@ If you see accel-pppd process you can start it with:
 /usr/sbin/accel-pppd -c /etc/accel-ppp.conf -p /var/run/accel-ppp.pid -d
 ```
 
+## Shell tricks
+
+For example i want to filter all lines that begin with "fadi" in users list:
+```
+accel-cmd show sessions username|grep "^ fadi"
+```
+What does it mean and how it works?
+
+* accel-cmd show sessions username - will show all sessions, but username field will be shown only
+* | - pipe, it will pass output of previous command to next command
+* grep "^ fadi" - will filter only lines that begin with " fadi", symbol ^ means beginning of line, space is needed to filter accel-specific output (it has space before username)
+
+Now, for example i want to save this list and disconnect all users that begin with "fadi":
+```
+accel-cmd show sessions username|grep "^ fadi"|awk '{print $1}'|xargs -I {} accel-cmd terminate username {}
+```
+
+What does it mean and how it works?
+
+* awk '{print $1}' - will print first field of each line, which is username, it will remove leading space
+* xargs -I {} - will pass each line to next command, {} is placeholder for line(variable)
+* accel-cmd terminate username {} - will disconnect user by username