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Printing Messages

configure scripts need to give users running them several kinds of information. The following macros print messages in ways appropriate for each kind. The arguments to all of them get enclosed in shell double quotes, so the shell performs variable and backquote substitution on them. You can print a message containing a comma by quoting the message with the m4 quote characters:

AC_MSG_RESULT([never mind, I found the BASIC compiler])

These macros are all wrappers around the echo shell command. configure scripts should rarely need to run echo directly to print messages for the user. Using these macros makes it easy to change how and when each kind of message is printed; such changes need only be made to the macro definitions, and all of the callers change automatically.

Macro: AC_MSG_CHECKING (feature-description)
Notify the user that configure is checking for a particular feature. This macro prints a message that starts with `checking ' and ends with `...' and no newline. It must be followed by a call to AC_MSG_RESULT to print the result of the check and the newline. The feature-description should be something like `whether the Fortran compiler accepts C++ comments' or `for c89'.

This macro prints nothing if configure is run with the `--quiet' or `--silent' option.

Macro: AC_MSG_RESULT (result-description)
Notify the user of the results of a check. result-description is almost always the value of the cache variable for the check, typically `yes', `no', or a file name. This macro should follow a call to AC_MSG_CHECKING, and the result-description should be the completion of the message printed by the call to AC_MSG_CHECKING.

This macro prints nothing if configure is run with the `--quiet' or `--silent' option.

Macro: AC_MSG_ERROR (error-description)
Notify the user of an error that prevents configure from completing. This macro prints an error message on the standard error output and exits configure with a nonzero status. error-description should be something like `invalid value $HOME for \$HOME'.

Macro: AC_MSG_WARN (problem-description)
Notify the configure user of a possible problem. This macro prints the message on the standard error output; configure continues running afterward, so macros that call AC_MSG_WARN should provide a default (back-up) behavior for the situations they warn about. problem-description should be something like `ln -s seems to make hard links'.

The following two macros are an obsolete alternative to AC_MSG_CHECKING and AC_MSG_RESULT.

Macro: AC_CHECKING (feature-description)
This macro is similar to AC_MSG_CHECKING, except that it prints a newline after the feature-description. It is useful mainly to print a general description of the overall purpose of a group of feature checks, e.g.,

AC_CHECKING(if stack overflow is detectable)

Macro: AC_VERBOSE (result-description)
This macro is similar to AC_MSG_RESULT, except that it is meant to follow a call to AC_CHECKING instead of AC_MSG_CHECKING; it starts the message it prints with a tab. It is considered obsolete.

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