Why undefine failed in m4?

define(foo,0000)

foo

0000

undefine('foo')

foo

0000

开发者_StackOverflow社区

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thanks.

jcyang.

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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')