英文:
Can I pass to build command flag and read inside code?
问题
我想在init函数中执行以下两行代码之一：
func init() {
log.SetPrefix(">>>>>>>>>> ")
log.SetOutput(ioutil.Discard)
}
如何实现类似于C语言中的宏定义和makefile中的宏定义？我使用go build my_project来构建Go程序，没有自定义的makefile。我可以在构建命令中传递标志，并在代码中读取吗？
英文:
I want in init function to execute one of those two lines
func init() {
log.SetPrefix(">>>>>>>>>>>>> ")
log.SetOutput(ioutil.Discard)
}
How to achieve something similiar to C and macro definition in make file ?
I build go program like go build my_project and I don't have any custom make file. Can I pass to build command flag and read inside code ?
答案1
得分: 6
创建一个字符串变量，你可以进行测试。然后使用传递给链接器的-X参数设置该字符串变量。例如：
package main
var MODE string
func main() {
if MODE == "PROD" {
println("I'm in prod mode")
} else {
println("I'm NOT in prod mode")
}
}
现在，如果你只使用go build进行构建，MODE将是""。但你也可以这样构建：
go build -ldflags "-X main.MODE PROD"
现在，MODE将是"PROD"。你可以根据构建设置修改逻辑。我通常使用这种技术在二进制文件中设置版本号，但它也可以用于各种构建时配置。请注意，它只能设置字符串。因此，你不能将MODE设置为布尔值或整数。
你还可以使用标签来实现这一点，这需要设置稍微复杂一些，但更加强大。创建三个文件：
main.go
package main
func main() {
doThing()
}
main_prod.go
// +build prod
package main
func doThing() {
println("I'm in prod mode")
}
main_devel.go
// +build !prod
package main
func doThing() {
println("I'm NOT in prod mode")
}
现在，当你使用go build进行构建时，你将得到main_devel.go版本（文件名无关紧要，只要顶部的// +build !prod行）。但是，你可以通过使用go build -tags prod进行构建来获得生产版本。
请参阅build文档中有关构建约束的部分。
英文:
Create a string variable that you can test. Then set that string variable using -X passed to the linker. For example:
package main
var MODE string
func main() {
if MODE == "PROD" {
println("I'm in prod mode")
} else {
println("I'm NOT in prod mode")
}
}
Now, if you build this with just go build, MODE will be "". But you can also build it this way:
go build -ldflags "-X main.MODE PROD"
And now MODE will be "PROD". You can use that to modify your logic based on build settings. I generally use this technique to set version numbers in the binary; but it can be used for all kinds of build-time configuration. Note that it can only set strings. So you couldn't make MODE a bool or integer.
You can also achieve this with tags, which are slightly more complicated to set up, but much more powerful. Create three files:
main.go
package main
func main() {
doThing()
}
main_prod.go
// +build prod
package main
func doThing() {
println("I'm in prod mode")
}
main_devel.go
// +build !prod
package main
func doThing() {
println("I'm NOT in prod mode")
}
Now when you build with go build, you'll get your main_devel.go version (the filename doesn't matter; just the // +build !prod line at the top). But you can get a production build by building with go build -tags prod.
See the section on Build Constraints in the build documentation.
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