logger(1) is your friend!

Here is how to use logger(1) to generate custom syslog messages, possibly for use in testing your log analysis tools.

What is logger?
Logger is a unix command apparently first appearing in 4.3 BSD back in 1993. The manpage also says "The logger command is expected to be IEEE Std 1003.2 (``POSIX.2'') compatible."

Logger writes messages to the system log via syslog. Therefore, it is useful for adding custom messages to your system logs. This can be useful in either testing or monitoring type situations.

I've found logger to be available on most any reasonable *NIX type system (My Mac OS 10 box has it in /usr/bin/!). Not only that, but I've found the version under OS X, FreeBSD, and Linux to be the same! (wha-hoo compatability!)

Logger usage:

logger [-is] [-f file] [-p pri] [-t tag] [message ...]

Examples:
To add the message "this is a test" to the system log:

$ logger this is a test

Which leaves this line in the system log:

Sep 20 06:44:13 localhost dl: this is a test

Notice that in that example, the "service" listed was my username, "dl". Often, this is not what we want. You could specify the service using the '-t' option like this:

$ logger -t test-service this is a test

Which leaves this line in the system log:

Sep 20 06:46:56 localhost test-service: this is a test

Now, we have specified the name of the "service" that is logged. Often, an actual syslog message will contain the PID of the service logging the message. This can be accomplished by also passing the '-i' option to logger like this:

$ logger -i -t test-service this is a test

Which leaves this line in the system log:

Sep 20 06:50:11 localhost test-service[2615]: this is a test

What if we want several messages to all originate from the same service with the same PID? That can be accomplished by writing all of the messages to a file and specifying that file with the '-f' option to logger like this:

$ cat /tmp/testlog 
first test message
second test message
third test message

$ logger -i -t test-service -f /tmp/testlog

would leave the following 3 lines in the system log:

Sep 20 06:53:17 localhost test-service[2629]: first test message 
Sep 20 06:53:17 localhost test-service[2629]: second test message 
Sep 20 06:53:17 localhost test-service[2629]: third test message

Finally, if we have syslogd configured to log messages of different priorities to different places, we may specify the priority we would like with the '-p' option, like this:

$ logger -i -p local3.info -t test-service this is a test

Which would leave the following line in the system log where local3.info messages are sent:

Sep 20 07:15:32 localhost test-service[2647]: this is a test