Symantec Endpoint Protection (SEP) for Linux definitions can be installed using Intelligent Updater through the following one-liner, which produces no output:

Red Hat-based distributions

yum -y -q install sharutils ncompress curl > /dev/null 2>&1 && curl -Os `curl -s https://www.symantec.com/security_response/definitions/download/detail.jsp?gid=sep#secTab3 | grep -Eo 'http://.*/defs/[0-9]+-...-core15unix.sh'` && chmod +x *core15unix.sh && ./*core15unix.sh > /dev/null 2>&1 && rm -f *core15unix.sh

Debian-based distributions

apt-get -y -qq install sharutils ncompress curl > /dev/null 2>&1 && curl -Os `curl -s https://www.symantec.com/security_response/definitions/download/detail.jsp?gid=sep#secTab3 | grep -Eo 'http://.*/defs/[0-9]+-...-core15unix.sh'` && chmod +x *core15unix.sh && ./*core15unix.sh > /dev/null 2>&1 && rm -f *core15unix.sh

SuSE-based distributions

zypper -q install sharutils curl > /dev/null 2>&1 && curl -Os `curl -s https://www.symantec.com/security_response/definitions/download/detail.jsp?gid=sep#secTab3 | grep -Eo 'http://.*/defs/[0-9]+-...-core15unix.sh'` && chmod +x *core15unix.sh && ./*core15unix.sh > /dev/null 2>&1 && rm -f *core15unix.sh

This will:

1. Install Intelligent Updater prerequisites sharutils and ncompress, as well as curl (if not installed already).
2. Download the source of the Symantec Security Response web site that provides HTTP and FTP links to the latest Intelligent Updaters for Unix-based systems, parse it to obtain the HTTP URL and feed that URL to curl, which downloads the file and saves it with the same name.
3. Make executable, run and delete the latest Intelligent Updater file.

As part of running the Intelligent Updater file, log output will be added to /var/log/iu-install.log:

BEGIN Log of Intelligent Updater installation on ####.####.###
Fri Jun 28 06:39:26 PDT 2019
Validating available tools...
Decoding Intelligent Updater package...
Checking distribution integrity...
Extracting distribution files...
Installing virus defintions to /opt/Symantec/virusdefs/incoming/
Copying definition files...
Removing temporary files...

Virus definitions installed successfully.
Fri Jun 28 06:39:45 PDT 2019
END Log of Intelligent Updater installation on ####.####.###

If definitions were not successfully installed before, then restart the services using /etc/init.d/smcd restart && /etc/init.d/autoprotect restart. The successful update of the virus definitions can be verified using /opt/Symantec/symantec_antivirus/sav info -d. 

Notes:

• Supported Red Hat-based distributions include Amazon Linux, the Community Enterprise Operating System (CentOS), Fedora, Oracle Linux (OL) and Red Hat Enterprise Linux (RHEL).
• Supported Debian-based distributions include Debian GNU/Linux and Ubuntu.
• Supported SuSE-based distributions include SuSE Linux Enterprise Server and SuSE Linux Enterprise Desktop. OpenSuSE additionally requires the ncompress package to be installed.
• To allow for the installation of sharutils in RHEL, ensure the Optional repository is enabled, using subscription-manager repos --enable=rhel-`rpm -qf /etc/redhat-release | sed 's/.*el\([0-9]\).*/\1/'`-server-optional-rpms. The command in-between backticks will result in 6 for RHEL 6.x-based systems, 7 for RHEL 7.x-based systems, 8 for RHEL 8.x-based systems, etc.