How can I log to a specific file in linux using logger command?

Question

I will run the following script:

#!/bin/bash
./myprogram

#get exit code
exitvalue=$?

#log exit code value to /var/log/messages
logger -s \"exit code of my prog         


        

Answer 1

The short "official" answer is that, unfortunately, you can't.

However, in most cases (e.g. on many Linux distros) you may just be lucky enough to have a logger implementation that both supports the --no-act option, and also implements some message formatting on its own (see below), in which case you can use a (moderately ugly) command like this to put a) a properly formatted message, b) to a file, c) not polluting the system logs:

logger --no-act -s "Oh dear..." 2>&1 | sed 's/^<[0-9]\+>//' >> /tmp/my.log

(Shout out to @BasileStarynkevitch, and @Kieveli, who both mentioned parts of it before, just not the whole story.)

Notes:

1) To match the usual log file format, I had to "sed off" the field (PRIVAL = FACILITY * 8 + PRIORITY) that got prepended to the output on my Debian boxes. Your mileage may vary.

2) POSIX itself does not define how exactly the logger command should treat (any of) its options. E.g. the GNU logger does not support --no-act at all. Also, when posting the original version of this answer 2 years ago, -s on my system did not do any formatting to the printed output, it just echoed the raw message alone, rendering it completely useless. (I didn't use Systemd at that time, which might explain the difference, seeing various conditional Systemd-related calls in the logger source code, but this is just vague guesswork.)

3) The most likely reason why the logger command has been so "historically unfriendly" for this trivial use case is that it's just a fairly simple frontend to the system logger. This means that anything you feed to it basically goes right through to syslogd (or systemd-journald etc.), which, in turn, does all sorts of other further processing, and dispatching (to various outlets: files, sockets etc., both local and remote), as well as bridging permission levels (so in your example you could still log to syslog or user.log, for instance, even though you may have no permission to write to those files directly).

For logger to be able to properly log to a file directly, it would either have to (re)implement some of the duties of the system logger, and the syslog() std. library function, or it would be not much more capable than a trivial echo one-liner (less complex, perhaps, even than the above logger invocation! ;) ). Either way, that seems like a bad idea.

A better solution could be if the POSIX interface (logger, syslog()) had a way to specify an ad-hoc outlet/facility parameter (like a filename) along with the message, so one could log to custom files without reconfiguring the system (which normal users have no permission to do anyway).

However, for the lack of anything better, the "canonical" Linux logger implementation actually does seem to duplicate some of the syslog functionality, so most of us can just enjoy that luxury for free. ;)