Why undefine failed in m4?

Question

define(foo,0000)
foo
0000
undefine('foo')
foo
0000

---

thanks.
jcyang.

Answer 1

You have to quote foo with a backtick in front and a single-quote after in order to undefine it. Otherwise, it winds up substituted and you undefine 0000. So:

undefine(`foo')