How to list all TCP ports in Linux ?

In this post, we will check how to list all TCP ports in Linux.

Lets us quickly check the command and output:

[root@nglinux ~]# cat /etc/services  | grep -Po '^\w+.*\d{1,5}/tcp' | head
tcpmux          1/tcp
rje             5/tcp
echo            7/tcp
discard         9/tcp
systat          11/tcp
daytime         13/tcp
qotd            17/tcp
msp             18/tcp
chargen         19/tcp
ftp-data        20/tcp

[root@nglinux ~]# cat /etc/services  | grep -Po '^\w+.*\d{1,5}/tcp' | wc -l
5374

Command Description
The command greps:
a. the exact matching output(-o)
b. using the text searched by perl command(-P)
c. ‘^\w+.*\d{1,5}/tcp’ is the perl command to grep a word(\w) followed by digits(\d) and /tcp.

In case your system has different file than /etc/services, you can use wildcards to get all files matching the pattern.

[root@nglinux ~]# cat /e*/s*s | grep -Po "^\w+.*\d{1,5}/tcp" | head
tcpmux          1/tcp
rje             5/tcp
echo            7/tcp
discard         9/tcp
systat          11/tcp

I hope you liked the post. Please do comment below in case of any suggestions/queries.