Why Don\'t My Go Program\'s `os.Setenv` Changes Persist in the Current Shell Session?

Setting Environment Variables with Go: Persistence Issue

Introduction

In this programming question, we address a common issue faced by developers when setting environment variables using the "os" package in Go. We will explore the behavior of environment variables in child processes and provide a solution to make the modified variable persistent in the current session.

Question

Consider the following Go code that attempts to set an environment variable:

package main

import (
    "os"
    "fmt"
)

func main() {
    _ = os.Setenv("FOO", "BAR")
    fmt.Println(os.Getenv("FOO"))
}

When running this code, the expected environment variable "FOO" is printed correctly, confirming that the setting was successful. However, when inspecting the environment variable in the current terminal session, it remains empty. This raises the question: why is the set variable not persistent in the session?

Answer

The behavior observed is expected due to the nature of processes in operating systems. When a new process is created (in this case, the Go program), the environment of the parent process (the terminal session) is copied. Any changes to the environment made in the child process (the Go program) are isolated to that process and do not affect the parent process.

Solution

To make the environment variable modification persistent in the current session, one needs to start a new shell process with the modified environment. This can be achieved by using the following approach:

package main

import (
    "os/exec"
    "fmt"
)

func main() {
    // Set the environment variable
    _ = os.Setenv("FOO", "BAR")
    
    // Start a new shell
    cmd := exec.Command("bash")
    cmd.Run()
}

By executing a new shell with the updated environment, the modifications made by the Go program become effective in the current session.

Conclusion

Understanding the behavior of environment variables in child processes is crucial for effective programming. By using the method described in this answer, developers can set and persist environment variables in their Go programs, ensuring that the changes are reflected in the current session.

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