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9. Diverting and undiverting output

Diversions are a way of temporarily saving output. The output of m4 can at any time be diverted to a temporary file, and be reinserted into the output stream, undiverted, again at a later time.

Numbered diversions are counted from 0 upwards, diversion number 0 being the normal output stream. The number of simultaneous diversions is limited mainly by the memory used to describe them, because GNU m4 tries to keep diversions in memory. However, there is a limit to the overall memory usable by all diversions taken altogether (512K, currently). When this maximum is about to be exceeded, a temporary file is opened to receive the contents of the biggest diversion still in memory, freeing this memory for other diversions. So, it is theoretically possible that the number of diversions be limited by the number of available file descriptors.

9.1 Diverting output  
9.2 Undiverting output  
9.3 Diversion numbers  
9.4 Discarding diverted text  


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