This chapter describes various builtins, that do not really belong in any of the previous chapters.
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 =>
m4
If you need to exit from m4 before the entire input has been
read, you can use m4exit:
m4exit(opt code)
which causes m4 to exit, with exit code code. If
code is left out, the exit code is zero.
define(`fatal_error', `errprint(`m4: '__file__: __line__`: fatal error: $* ')m4exit(1)') => fatal_error(`This is a BAD one, buster') error-->m4: 57.m4exit: 5: fatal error: This is a BAD one, buster
After this macro call, m4 will exit with exit code 1. This macro
is only intended for error exits, since the normal exit procedures are
not followed, e.g., diverted text is not undiverted, and saved text
(see section Saving input) is not reread.
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