PCRE_OBJ="" AC_SUBST(PCRE_OBJ) AC_SUBST(PCRE_LIBS) AC_SUBST(PCRE_CFLAGS) PKG_CHECK_MODULES(PCRE, libpcre) PKG_CHECK_EXISTS(libpcre >= 7, [AC_MSG_NOTICE([PCRE version is 7 or higher])], [AC_MSG_NOTICE([PCRE version is below 7]) AC_DEFINE([HAVE_LIBPCRE_LESSER_THAN_7], 1, [Define if libpcre version is less than 7])]) AC_CHECK_HEADERS(pcre.h) AC_CHECK_LIB(pcre, pcre_compile, [ PCRE_LIBS="-lpcre" ], [AC_MSG_ERROR([PCRE is required])])