To install sqlcmd on Linux CentOS try to get hold on the following rpm’s :

unixODBC from CentOS: http://mirror.centos.org/centos/7/os/x86_64/Packages/
file: unixODBC-2.3.1-14.el7.x86_64.rpm

msodbcsql from Microsoft: https://packages.microsoft.com/rhel/8/prod/
file: msodbcsql18-18.0.1.1-1.x86_64.rpm

mssql-tools from Microsoft: https://packages.microsoft.com/rhel/7.3/prod/
file: mssql-tools18-18.0.1.1-1.x86_64.rpm

Now run:
sudo yum localinstall unixODBC-2.3.1-14.el7.x86_64.rpm
sudo yum localinstall msodbcsql18-18.0.1.1-1.x86_64.rpm
sudo yum localinstall mssql-tools18-18.0.1.1-1.x86_64.rpm

Accept license when asked and you’re done hopefully . Add to the path (in .bashrc):
export PATH=/opt/mssql-tools18/bin:$PATH

If you’re behind a firewall and your database instance is on port nnnn

sudo iptables -A INPUT -p tcp --dport nnnn -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
sudo iptables -A INPUT -p udp --dport nnnn -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT

Now try:
sqlcmd -S tcp:[hostname],[port] -U [username] -P [password]
or
sqlcmd -C -S tcp:[hostname],[port] -U [username] -P [password]
like
sqlcmd -C -S tcp:some.address.com,50001 -U john -P doe