```
#!/usr/bin/env bash

PIPE=pipe
mkfifo $PIPE

# both journal and file
if false; then
  systemd-cat -t test-for-nixos < $PIPE &
  exec 3>$PIPE
  exec &> >(tee -a $PIPE log)
  exec 2>&1
# journal only
elif false; then
  systemd-cat -t test-for-nixos < $PIPE &
  exec &>$PIPE
  exec 2>&1
# file only
else
  exec 3>&-
  exec >>log
  exec 2>&1
fi

echo this is stdout >> /dev/stdout
echo this is stderr >> /dev/stderr

exec 3>&-
```