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13.1 Printing error messages

You can print error messages using errprint:

 
errprint(message, ...)
which simply prints message and the rest of the arguments on the standard error output.

The expansion of errprint is void.

 
errprint(`Illegal arguments to forloop
')
error-->Illegal arguments to forloop
=>

A trailing newline is not printed automatically, so it must be supplied as part of the argument, as in the example. (BSD flavored m4's do append a trailing newline on each errprint call).

To make it possible to specify the location of the error, two utility builtins exist:

 
__file__
__line__
which expands to the quoted name of the current input file, and the current input line number in that file.

 
errprint(`m4:'__file__:__line__: `Input error
')
error-->m4:56.errprint:2: Input error
=>


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