Golang : Setting variable value with ldflags

This short tutorial will demonstrate how to initialize a variable value during runtime at the stage of compilation/linking. Go linker has an option to set the value of an uninitialised string variable:

-X symbol value

Set the value of an otherwise uninitialized string variable.

The symbol name should be of the form importpath.name,

as displayed in the symbol table printed by "go tool nm".

For example :

 package main

 import "fmt"

 var str string

 func main() {
 fmt.Println(str)
 }

and execute the program with -ldflags to initialize the str variable value

$ go run -ldflags "-X main.str abc" main.go

or if you prefer, build it first into executable binary :

$ go build -ldflags "-X main.str 'abc'" main.go && ./main

Output :

abc

Reference :

http://golang.org/cmd/ld/