Output is diverted using
The current diversion is changed to number. If number is left out or empty, it is assumed to be zero. If number cannot be parsed, the diversion is unchanged.
The expansion of
When all the
m4 input will have been processed, all existing
diversions are automatically undiverted, in numerical order.
divert(`1') This text is diverted. divert ⇒ This text is not diverted. ⇒This text is not diverted. ^D ⇒ ⇒This text is diverted.
Several calls of
divert with the same argument do not overwrite
the previous diverted text, but append to it. Diversions are printed
after any wrapped text is expanded.
define(`text', `TEXT') ⇒ divert(`1')`diverted text.' divert ⇒ m4wrap(`Wrapped text precedes ') ⇒ ^D ⇒Wrapped TEXT precedes diverted text.
If output is diverted to a negative diversion, it is simply discarded.
This can be used to suppress unwanted output. A common example of
unwanted output is the trailing newlines after macro definitions. Here
is a common programming idiom in
m4 for avoiding them.
divert(`-1') define(`foo', `Macro `foo'.') define(`bar', `Macro `bar'.') divert ⇒
Traditional implementations only supported ten diversions. But as a GNU extension, diversion numbers can be as large as positive integers will allow, rather than treating a multi-digit diversion number as a request to discard text.
divert(eval(`1<<28'))world divert(`2')hello ^D ⇒hello ⇒world
divert is an English word, but also an active macro
without arguments. When processing plain text, the word might appear in
normal text and be unintentionally swallowed as a macro invocation. One
way to avoid this is to use the -P option to rename all
builtins (see Invoking m4). Another is to write
a wrapper that requires a parameter to be recognized.
We decided to divert the stream for irrigation. ⇒We decided to the stream for irrigation. define(`divert', `ifelse(`$#', `0', ``$0'', `builtin(`$0', $@)')') ⇒ divert(`-1') Ignored text. divert(`0') ⇒ We decided to divert the stream for irrigation. ⇒We decided to divert the stream for irrigation.