### 14.1 Printing error messages ¶

You can print error messages using `errprint`:

Builtin: errprint(message, …) ¶

  Prints message and the rest of the arguments to standard error, separated by spaces. Standard error is used, regardless of the `--debugfile` option (see Invoking m4).

  The expansion of `errprint` is void. The macro `errprint` is recognized only with parameters.

    errprint(`Invalid arguments to forloop
    ')
    error→Invalid arguments to forloop
    ⇒
    errprint(`1')errprint(`2',`3
    ')
    error→12 3
    ⇒

A trailing newline is not printed automatically, so it should be supplied as part of the argument, as in the example. Unfortunately, the exact output of `errprint` is not very portable to other `m4` implementations: POSIX requires that all arguments be printed, but some implementations of `m4` only print the first. Furthermore, some BSD implementations always append a newline for each `errprint` call, regardless of whether the last argument already had one, and POSIX is silent on whether this is acceptable.