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9.4 Discarding diverted text

Often it is not known, when output is diverted, whether the diverted text is actually needed. Since all non-empty diversion are brought back on the main output stream when the end of input is seen, a method of discarding a diversion is needed. If all diversions should be discarded, the easiest is to end the input to m4 with `divert(-1)' followed by an explicit `undivert':

divert(1) Diversion one: divnum divert(2) Diversion two: divnum divert(-1) undivert ^D

No output is produced at all.

Clearing selected diversions can be done with the following macro:

define(`cleardivert', `pushdef(`_num', divnum)divert(-1)undivert($@)divert(_num)popdef(`_num')') =>

It is called just like undivert, but the effect is to clear the diversions, given by the arguments. (This macro has a nasty bug! You should try to see if you can find it and correct it.)