Ragel State Machine Compiler: Ragel compiles executable finite state machines from regular languages. Ragel targets C, C++ and ASM. Ragel state machines can not only recognize byte sequences as regular expression machines do, but can also execute code at arbitrary points in the recognition of a regular language. Code embedding is done using inline operators that do not disrupt the regular language syntax.
安装 epel 源：
yum install epel-release -y yum install http://rpms.remirepo.net/enterprise/remi-release-7.rpm -y
yum install ragel -y
当编译安装 powerdns 时，报错：checking for ragel… no