The following macros define file descriptors used to output messages (or input values) from configure scripts. For example:
echo "$wombats found" >&AS_MESSAGE_LOG_FD echo 'Enter desired kangaroo count:' >&AS_MESSAGE_FD read kangaroos <&AS_ORIGINAL_STDIN_FD`
However doing so is seldom needed, because Autoconf provides higher level macros as described below.
The file descriptor for ‘checking for...’ messages and results.
AS_INIT sets this to ‘1’ for standalone M4sh
AC_INIT shuffles things around to another file
descriptor, in order to allow the -q option of
configure to choose whether messages should go to the script’s
standard output or be discarded.
If you want to display some messages, consider using one of the printing macros (see Printing Messages) instead. Copies of messages output via these macros are also recorded in config.log.
This must either be empty, or expand to a file descriptor for log
messages. By default,
AS_INIT sets this macro to the empty
string for standalone M4sh clients, thus disabling logging. However,
AC_INIT shuffles things around so that both
config.status use config.log for log messages.
Macros that run tools, like
AC_COMPILE_IFELSE (see Running the Compiler), redirect all output to this descriptor. You may want to do
so if you develop such a low-level macro.
This must expand to a file descriptor for the original standard input.
AS_INIT sets this macro to ‘0’ for standalone
M4sh clients. However,
AC_INIT shuffles things around for
configure runs, it may accidentally execute an
interactive command that has the same name as the non-interactive meant
to be used or checked. If the standard input was the terminal, such
interactive programs would cause
configure to stop, pending
some user input. Therefore
configure redirects its standard
input from /dev/null during its initialization. This is not
normally a problem, since
configure normally does not need
In the extreme case where your configure script really needs to
obtain some values from the original standard input, you can read them