Writing outputs to log file and console

I tried joonty's answer, but I also got the

exec: 1: not found

error. This is what works best for me (confirmed to work in zsh also):

#!/bin/bash
LOG_FILE=/tmp/both.log
exec > >(tee ${LOG_FILE}) 2>&1
echo "this is stdout"
chmmm 77 /makeError

The file /tmp/both.log afterwards contains

this is stdout
chmmm command not found 

The /tmp/both.log is appended unless you remove the -a from tee.

Hint: >(...) is a process substitution. It lets the exec to the tee command as if it were a file.

exec 3>&1 1>>${LOG_FILE} 2>&1

would send stdout and stderr output into the log file, but would also leave you with fd 3 connected to the console, so you can do

echo "Some console message" 1>&3

to write a message just to the console, or

echo "Some console and log file message" | tee /dev/fd/3

to write a message to both the console and the log file - tee sends its output to both its own fd 1 (which here is the LOG_FILE) and the file you told it to write to (which here is fd 3, i.e. the console).

Example:

exec 3>&1 1>>${LOG_FILE} 2>&1

echo "This is stdout"
echo "This is stderr" 1>&2
echo "This is the console (fd 3)" 1>&3
echo "This is both the log and the console" | tee /dev/fd/3

would print

This is the console (fd 3)
This is both the log and the console

on the console and put

This is stdout
This is stderr
This is both the log and the console

into the log file.