I start a bash shell script via a oneshot unit. I output standard messages currently with
echo $message
echo $message >> $logfile.txt
With this I have output on screen and additionally in a logfile. I don’t know if there is a better way to do that.
This works for standard infos fine. Additionally there must be a way to output also error messages and warnings, since when I look into other services, I see red messages for errors and yellow/orange colored messages for warnings.
How can I do such things with my bash script and output other levels like warnings in yellow and errors in red?
AFAIK the general approach to logging with systemd is that the application simply writes to stdout/stderr and systemd takes care of passing the output to whatever logging target/s you configured.
As for signaling log levels with bash, you can write functions that prepend any timestamps, markers or wrap the string in any color codes you want.