How can I redirect the output of multiple commands at once?

Redirecting the standard output of a single command is as easy as 

    date > file

To redirect standard error: 

    date 2> file

To redirect both: 

    date > file 2>&1

In a loop or other larger code structure: 

    for i in $list; do
        echo "Now processing $i"
        # more stuff here...
    done > file 2>&1

However, this can become tedious if the output of many programs should be redirected. If all output of a script should go into a file (e.g. a log file), the exec command can be used: 

    # redirect both standard output and standard error to "log.txt"
    exec > log.txt 2>&1
    # all output including stderr now goes into "log.txt"

Otherwise command grouping helps: 

    {
        date
        # some other command
        echo done
    } > messages.log 2>&1

In this example, the output of all commands within the curly braces is redirected to the file messages.log.