The venerable 'logger' command has been around so long it's part of the Single Unix Specification (really, logger — log messages ). Although syslog(3) is in 4.2 BSD (along with syslog(8) , the daemon), it doesn't seem to have been until 4.3 BSD that we got logger(1) , with more or less the same arguments as the POSIX version. Unfortunately, if you want to do more than throw messages into your syslog and actually create well-formed, useful syslog messages , ' logger ' has some annoyances and flaws.

The flaw is front and center in the manual page and the POSIX specification , if you read the description of the -i option carefully:

-i : Log the process ID of the logger process with each message.

(Emphasis mine.)

In shell scripts where you want to report the script's activities to syslog, it's not unusual to want to report more than one thing. In well-formed syslog messages , these would all have the same PID, so that you can tell that they all came from the same invocation of your script. Logger doesn't support this; if you run logger several times over the course of your script and use '-i', every log message will have a different PID. In some environments (such as FreeBSD and Linux with systemd), logger usually puts in its own PID whether you like it or not.

(The traditional fake for this was to not use '-i' and then embed your script's PID into your syslog identifier (FreeBSD even recommends this in their logger(1) manual page). This worked okay when syslog identifiers were nothing more than what got stuck on the front of the message in your log files, but these days it's not necessarily ideal even if your 'logger' environment doesn't add a PID itself. If you're sending syslog to a log aggregation system, the identifier can be meaningful and important and you want it to be a constant for a given message source so you can search on it.)

Since it's a front end to syslog, logger inherits the traditional syslog issues that you have to select a meaningful syslog facility, priority, and identifier (traditionally, the basename of your script). On the positive side, you can easily vary these from message to message; on the not so great side, you have to supply them for every logger invocation and it's on you to make sure all of your uses of logger use the same ones. Logger doesn't insist that you provide these and it doesn't have any mechanism (such as a set of environment variables) for you to provide defaults. This was a bigger issue in the days before shell functions, since these days you can write a 'logit' function for your shell script that invokes logger correctly (for your environment). This function is also a good place to automatically embed your script's PID in the logged message (perhaps as 'pid=... <supplied message>').

Out of the three of these, the syslog identifier is the easiest to do a good job of (since you should be picking a meaningful name for your script anyway) but the traditional syslog environment makes the identifier relatively meaningless.

It's possible to send all of the output of your script to syslog, or with a bunch of work you can send just standard error to syslog (and perhaps repeat it again). But doing either of these requires wrapping the body of your script up and feeding all of it to logger :

(
... script stuff ...
) 2>&1 | logger -i -t "$(basename "$0")" -pX.Y

(Everything will have the same facility and priority, but if it's really important to log things at a different priority you can put in direct 'logger' invocations in the body of the script.)

I suspect that people who used logger a lot probably wrote a wrapper script (you could call it 'stderr-to-syslog') and ran all of the real scripts under it.

All of this adds up to a collection of small annoyances. It's not impossible to use logger in scripts to push things into syslog, but generally it has to be relatively important to capture the information. There's nothing off the shelf that makes it easy. And if you want to have portable logging for your scripts, this basic logger use is all you get.

(Linux with systemd has an entire separate system for this and the standard Linux logger has additional options even for syslog logging. But OpenBSD logger(1) is quite minimal and FreeBSD logger(1) is in between, with its own additional features that don't overlap with the Linux version.)