13.3 Exiting from `m4'
If you need to exit from `m4' before the entire input has been read,
you can use `m4exit':
-- Builtin: m4exit ([CODE = `0'])
Causes `m4' to exit, with exit status CODE. If CODE is left out,
the exit status is zero. If CODE cannot be parsed, or is outside
the range of 0 to 255, the exit status is one. No further input
is read, and all wrapped and diverted text is discarded.
A common use of this is to abort processing:
-- Composite: fatal_error (MESSAGE)
Abort processing with an error message and non-zero status. Prefix
MESSAGE with details about where the error occurred, and print the
resulting string to standard error.
`errprint(__program__:__file__:__line__`: fatal error: $*
fatal_error(`this is a BAD one, buster')
error-->m4:stdin:4: fatal error: this is a BAD one, buster
After this macro call, `m4' will exit with exit status 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
( M4wrap) is not reread. (This macro has a subtle bug, when
invoked from wrapped text. You should try to see if you can find it and
correct it. Answers)
m4wrap(`This text is lost to `m4exit'.')
divert(`1') And so is this.
Note that it is still possible for the exit status to be different
than what was requested by `m4exit'. If `m4' detects some other error,
such as a write error on standard out, the exit status will be non-zero
even if `m4exit' requested zero.
If standard input is seekable, then the file will be positioned at
the next unread character. If it is a pipe or other non-seekable file,
then there are no guarantees how much data `m4' might have read into
buffers, and thus discarded.
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