Reverse words with tac

Imagine you’re writing a shell script and try to reverse the order of words in a variable. For example,

a="abc 123 ABC"
b=... # Do something here
echo $b # This should print "ABC 123 abc"

Although there are many ways to do this with lots of tools, I like this one using tac.

b=$(for x in $a; do echo $x; done | tac)

Or

b=$(echo $a | tac -s ' ')

The latter one is a little tricky because the output of echo $a | tac -s ' ' is

ABC
123 abc

because tac doesn’t treat a new line as a separator. Even so, when you put it into a variable, you can get what you want.