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Variable Substitution

Configuring all these variables in configure.in is one thing. But they have to passed to the Makefile ultimately.

This is done using AC_SUBST. 

HTML_DIR=/tmp/html

AC_SUBST(HMTL_DIR)

This fragment will replace all occurences of @HTML_DIR@ in any Makefile.am with the value of the HTML_DIR variable that is computed in the configure script.

Note

If a variable's contents are empty when it is substituted, the empty string will be used as the value. This can be used to effect conditional compilation, amongst other things.

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