GNU Info

(m4.info)Diversions

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Diverting and undiverting output
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   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.

Divert

Diverting output

Undivert

Undiverting output

Divnum

Diversion numbers

Cleardiv

Discarding diverted text