Four of my most-used CLI commands

Scott Reeves lists four of the commands in Linux that he uses most often along with some examples of how he uses them. What are the commands you can't live without?

My main workstation is a Linux laptop, which has a few applications installed that I need to use, such as Libre Office, Lyx, Jabref and g++. I invariably have a terminal window open somewhere on my workspace, which I use for various tasks. There are a few commands that I find myself using most days. This post is a list of four of these commands.


The first command on my list is netstat. There are a few options with netstat; the options I tend to use are -r and -a. The -r option prints out the routing table. This is useful when you want to check the default gateway and subnet mask. But the option I generally use is the -a option, which shows all TCP and UDP connections. It also gives the name of the application (if known) that is using a connection. Finally, it shows the state of TCP connections. See for instance the below output, which is a sample of output from running netstat -a.

Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 *:50450                 *:*                     LISTEN
tcp        0      0 localhost:ipp           *:*                     LISTEN
tcp        0      0 *:17500                 *:*                     LISTEN
tcp       38      0 gudaring.local:33581    v-d-2a.sjc.dropbo:https CLOSE_WAIT
tcp        0      0 gudaring.local:46072    tf-in-f125.1e100.:https ESTABLISHED
tcp        0      0 gudaring.local:49496    r-199-59-148-20.t:https ESTABLISHED
tcp        0      0 gudaring.local:42965    sjc-not15.sjc.dropb:www ESTABLISHED
tcp        0      0 gudaring.local:50959    kwaimuk.canonical:https ESTABLISHED
tcp        0      0 gudaring.local:58176    ESTABLISHED
tcp       38      0 gudaring.local:51187    v-client-1a.sjc.d:https CLOSE_WAIT
tcp        0      0 gudaring.local:54352 ESTABLISHED
tcp       38      0 gudaring.local:35819 CLOSE_WAIT


Another command that I use is awk. I like being able to run a command and pipe the output to awk to view just the fields I want to look at, and use a regular expression to extract the lines I want to view. Going back to netstat, for example, I want to look at only the connections that are established, and of those, I want to look only at the fifth field. I can do this by simply typing in the command string netstat -a | awk ‘/ESTABLISHED/ {print $5}'. This will print out the data I want.


Regular expressions are very handy to know, especially when using awk on the CLI. Going back to the netstat output, you could extract the lines beginning with "tcp" and again print the fifth field of the output.

root@gudaring:/home# netstat -a | awk '/^tcp / {print $5}'


Another command I use is time. What this does in its most basic form is tell you the time it takes to execute a command. As I am at present trying to optimise some code, I use time regularly in order to obtain a measurement of the execution time of a program. The output of time is shown below; it also tells you the time the process spends in system and in user mode.

root@gudaring:/home# time ls
real  0m0.132s
user  0m0.000s
sys   0m0.004s


The final command would likely upset one of my oldest Linux/Unix colleagues if he saw it was last on my list. The command is of course man. My colleague would invariably start any Linux introductory shell programming course stating that man was possibly the most useful command to know on Linux, and that you should, as a start, type in man man.

These are commands that I invariably end up using from day to day. Some, such as netstat, I use daily, whereas others such as time, man and awk are every other day.

What are the commands you can't do without?


Scott Reeves has worked for Hewlett Packard on HP-UX servers and SANs, and has worked in similar areas in the past at IBM. Currently he works as an independent IT consultant, specializing in Wi-Fi networks and SANs.

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