How to log output in bash and see it in the terminal at the same time?

Question

I have some scripts where I need to see the output and log the result to a file, with the simplest example being:

$ update-client > my.log

I want to be able to see the output of the command while it's running, but also have it logged to the file. I also log stderr, so I would want to be able to log the error stream while seeing it as well.

Answer 1

update-client 2>&1 | tee my.log

2>&1 redirects standard error to standard output, and tee sends its standard input to standard output and the file.

Answer 2

Just use tail to watch the file as it's updated. Background your original process by adding & after your above command After you execute the command above just use

$ tail -f my.log

It will continuously update. (note it won't tell you when the file has finished running so you can output something to the log to tell you it finished. Ctrl-c to exit tail)