How do I get both STDOUT and STDERR to go to the terminal and a log file?

I have a script which will be run interactively by non-technical users. The script writes status updates to STDOUT so that the user can be sure that the script is running OK.

I want both STDOUT and STDERR redirected to the terminal (so that the user can see that the script is working as well as see if there was a problem). I also want both streams redirected to a log file.

I've seen a bunch of solutions on the net. Some don't work and others are horribly complicated. I've developed a workable solution (which I'll enter as an answer), but it's kludgy.

The perfect solution would be a single line of code that could be incorporated into the beginning of any script that sends both streams to both the terminal and a log file.

EDIT: Redirecting STDERR to STDOUT and piping the result to tee works, but it depends on the users remembering to redirect and pipe the output. I want the logging to be fool-proof and automatic (which is why I'd like to be able to embed the solution into the script itself.)

Use "tee" to redirect to a file and the screen. Depending on the shell you use, you first have to redirect stderr to stdout using

./a.out 2>&1 | tee output

or

./a.out |& tee output

In csh, there is a built-in command called "script" that will capture everything that goes to the screen to a file. You start it by typing "script", then doing whatever it is you want to capture, then hit control-D to close the script file. I don't know of an equivalent for sh/bash/ksh.

Also, since you have indicated that these are your own sh scripts that you can modify, you can do the redirection internally by surrounding the whole script with braces or brackets, like

  #!/bin/sh
  {
    ... whatever you had in your script before
  } 2>&1 | tee output.file

Approaching half a decade later...

I believe this is the "perfect solution" sought by the OP.

Here's a one liner you can add to the top of your Bash script:

exec > >(tee -a $HOME/logfile) 2>&1

Here's a small script demonstrating its use:

#!/usr/bin/env bash

exec > >(tee -a $HOME/logfile) 2>&1

# Test redirection of STDOUT
echo test_stdout

# Test redirection of STDERR
ls test_stderr___this_file_does_not_exist

(Note: This only works with Bash. It will not work with /bin/sh.)

Adapted from here; the original did not, from what I can tell, catch STDERR in the logfile. Fixed with a note from here.