Try 'compgen' - an interesting command

'compgen' is a handy Bash built-in command to list all the Commands, Aliases and Bash Built-ins functions available for a logged-in user.
To list all the commands     :  compgen -c
To list all the Aliases          :   compgen -a
To list all the Bash Built-ins :  compgen -b

How to check when a patch was last installed or upgraded ?

Syntax: rpm -qa --last | grep <package name>

Example:  Suppose you want to know when the MySql packages was last installed or upgraded.

The syntax should be:  
[root@Hostxyz ~]# rpm -qa --last | grep -i mysql
MySQL-client-5.6.5_m8-1.rhel5                 Fri 13 Jul 2012 02:35:01 AM PDT
MySQL-server-5.6.5_m8-1.rhel5                Fri 13 Jul 2012 02:34:44 AM PDT
php54-mysql-5.4.0-1.el5                           Fri 13 Jul 2012 01:17:21 AM PDT
[root@Hostxyz ~]#

To list the entire package list, just execute # rpm -qa --last

Complex Arithmetic using Linux Binary calculator

Lets say you want to execute the below arithmetic expression using Binary calculator (bc):
((10*10)+100)/4. The expected value for this arithmetic expression is 50.

The syntax using 'bc' would be :
# echo "10*10;.+100;./4" | bc
100
200
50

#

Please note the semicolon(;) and period (.) used in-between.

Other version using 'last' keyword:

# echo "10*10;last+100;last/4" | bc

100

200

50

#

The period (.) or 'last' keyword denotes result of previous execution.

Rsync command syntax

Below given is the recommended Rsync syntax which can be used to sync 2 file-systems. However appropriate options can be chosen based on the requirement:
 Source machine# nohup rsync -atlrzvuop --progress /<source folder>/  <Destination IP/Hostname>:/<Dest folder>/  &
-a  :  Archive mode
-t  :   Preserve modification time
-l  :   Preserve symbolic links
-r :   Copy recursively
-v :   Verbose
-z  :  Zip the files before transfer
-u :  Skips files which exist on the destination and have a modified time newer than the source file.
-p :  Preserve permissions
-o :  Preserve owner
--bwlimit=<kpbs> : To control the I/O bandwidth if you are syncing across WAN (e.g. --bwlimit= 30000  - to sync at 30 Mbps)
--delete  :   Delete all the extra files on Destination which aren’t present in the Source.
--exclude=<pattern>  :   Exclude files from syncing whose filenames matching the PATTERN  (e.g. --exclude=.zip )

Automated Rsync script:
http://smart-scripts-for-sysadmins.blogspot.com/2012/03/sample-rsync-script.html