Bash script global redirection with exec and write to screen

Question

I have a large bash script and I want to globally redirect all stdout/stderr to a file, except some progress indicators such specific echo messages. For example, consider the following script

#!/bin/bash

# all stdout and stderr go to out.log
exec &> out.log

special_echo "starting"

# many other commands go here
# which output both the stdout and stderr
# also some special_echo commands in here,
# for example
echo "msg1"
special_echo "middle"
echo "msg2" >&2

special_echo "finished"

When it is run the output should be

$ ./script
starting
middle
finished
$

But, out.log should contain

msg1
msg2

How to implement special_echo functionality? I've tried using a file descriptor and echoing to that but can't get it to display on the screen.

Is there a way to achieve this without appending redirection to every line or doing something like in this answer?

Answer 1

Yes, using another file descriptor is the way to go:

#!/bin/bash

exec 3>&1
special_echo () {
    echo "$@" >&3
}

exec &> out.log

special_echo "starting"
echo "msg1"
special_echo "middle"
echo "msg2" >&2
special_echo "finished"

Answer 2

Redirect to /dev/tty, which is the controlling terminal. Works also for input.