Linux.com - https://www.linux.com/news/how-use-logger-linux
The logger command provides an easy way to add log files to /var/log/syslog — from the command line, from scripts, or from other files. In today’s post, we’ll take a look at how it works.
How easy is easy?
This easy. Just type logger <message> on the command line and your message will be added to the end of the /var/log/syslog file.