tar -cvf test.tar /tmp/test/     # Create Verbosely Filename
tar -cvzf test.tar.gz /tmp/test/ # Create Verbosely gzip Filename
# instructs tar to change dir to /tmp/test and start create archive from there
tar --strip-components=1 -cvzf test.tar.gz -C /tmp/test/ .

tar -tvf test.tar.gz             # List Verbosely archive content

tar -xvf test.tar                # Extract Verbosely Archive
tar -xvf test.tar.gz             # Extract Verbosely gzip Archive
# extract a single file from an archive
tar --extract --file=test.tar.gz tmp/test/foo/metasyntactic-vars

$ lsof -i                # show open files in this case TCP/UDP ports (might require root)
$ sudo lsof -i :8080     # find what application is running and listen for connections on port 8080
COMMAND    PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
docker-pr 2282 root    4u  IPv6  53248      0t0  TCP *:http-alt (LISTEN)
$ ps -ef | grep 2282     # find out more about the PID
root        2282    2000  0 Jun23 ?        00:00:01 /usr/bin/docker-proxy -proto tcp -host-ip 0.0.0.0 -host-port 8080 -container-ip 172.17.0.2 -container-port 8080

$ echo "alpha beta gamma delta" | while read A B C D ; do echo $D $C $B $A ; done
delta gamma beta alpha
$ echo "alpha beta gamma delta" | while read first_word rest_of_the_line; do echo $first_word ; done
alpha
$ echo "alpha beta gamma delta" | while read first_word rest_of_the_line; do echo $rest_of_the_line ; done
beta gamma delta

ln                      #
nslookup google.ro      # query Internet name servers
ping                    # ping a remote host, ping uses ICMP type 8 (echo message) and type 0 (echo reply message)
                        # some host block ICMP giving a false-positive of unreachable host

crontab                 #
regex                   #
xargs                   #
eval                    #
trap                    # trap