Apple Logger

This is an open-source command-line tool to write to Apple's Unified Logging interface. It's very small and simple and easy to read. It's shorter than this README.

It takes logs from stdin and writes them to the platform's logging interface using the subsystem ID of your choice.

It is not endorsed by or written by Apple. It is named because of the Apple-created interface it logs to.

Usage

For example, to log a single message from a shell script:

echo "This is a log message" | ./apple-logger com.myappname

Or if you want to stream many logs from an app:

my_app | ./apple-logger com.myappname

In these examples, com.myappname is an arbitrary subsystem ID. You can use this to look up your logs later using Apple's built-in tools:

log show --info --style=compact \
    --predicate 'subsystem=="com.myappname"' \
    --last 1d

All logs are written at "info" severity level, and by default, the "category" is set to the word "default". You can change that category with a second argument to the logger:

echo "This is a log message" | ./apple-logger com.myappname mycategory

You can filter on categories with something like:

log show --info --style=compact \
    --predicate 'subsystem=="com.myappname" AND category=="mycategory"' \
    --last 1d

Compilation

swiftc apple-logger.swift

Alternatives

I really couldn't find a single command-line utility for this in late 2023. I may have overlooked some. 🤷

With Apple having introduced these APIs in 2016 from what I can tell, I was shocked not to find a "unixy" utility for this. So I wrote this one.

One alternative that's built-in is to use the standard unixy command line utility logger, however, this doesn't let you set a subsystem ID. You can really only filter based on the process name, which would be logger, and you would have to set appropriate prefixes on all your log lines. I found this cluttered the logs and was hard to use for filtering and logging of multiple services.