macOS equivalent of `cmdtool` I recently saw someone on a Unix system run the command

cmdtool &lt;some_log_file.log&gt;

and the terminal showed a logging window that live-updated as text was entered into the log file. (I'm probably missing some arguments there.)

Is there a Mac OS equivalent to get this behavior?

See cmdtool on Ubuntu man pages.
You can use the tail command to see live output of a textual log file:

tail -f &lt;some_log_file.log


tail does not open a new Terminal.app window, but this could be achieved with AppleScript or Automator.