gomruby

// create new VM instance and load context
mruby := gomruby.New()
defer mruby.Delete()
context := mruby.NewLoadContext("select.rb")
defer context.Delete()

// this is user-supplied code
userCode := `
		message.include? "500"
	`

// define method
code := fmt.Sprintf(`
		def select(message)
			%s
		end`, userCode)
_, err := context.Load(code)
if err != nil {
	panic(err)
}

// iterate over messages and select interesting
for _, message := range []string{
	`1.2.3.1 - - [04/Jun/2013:18:02:01 +0000] host "GET /foo HTTP/1.0" 200`,
	`1.2.3.2 - - [04/Jun/2013:18:02:02 +0000] host "GET /bar HTTP/1.0" 300`,
	`1.2.3.3 - - [04/Jun/2013:18:02:03 +0000] host "GET /baz HTTP/1.0" 400`,
	`1.2.3.4 - - [04/Jun/2013:18:02:04 +0000] host "GET /bzr HTTP/1.0" 500`,
} {
	code := fmt.Sprintf("select(%q)", message)
	res, err := context.Load(code)
	if err != nil {
		panic(err)
	}
	fmt.Println(res.(bool))
}

Output:

false
false
false
true