Why Don\'t Environment Variable Changes Using `os.Setenv` Persist in My Terminal Session?

Environment Variable Persistence in Terminal Sessions

In an attempt to set an environment variable using the "os" package, you encountered an unexpected result where the variable was not persistent in your terminal session. To understand this behavior, let's dive into the underlying mechanisms.

Process Isolation

When a new process is created, it inherits an isolated copy of its parent process's environment. This means that any changes made to the environment within a child process do not propagate back to the parent process and vice versa.

Impact on Environment Variables

When you call os.Setenv("FOO", "BAR"), the "FOO" environment variable is set within your Go program's process space. However, it remains confined to that process. If you subsequently launch a shell or other commands from within your program, they will not inherit the modified environment.

Solution: Shell Invocation

To make the environment variable persistent in your session, you must instruct your program to launch a shell with the updated environment. This can be achieved using the following code:

// Launch a shell with the modified environment.
cmd := exec.Command("sh", "-c", "echo $FOO")
cmd.Env = append(os.Environ(), "FOO=BAR")
cmd.Run()

The above code:

1. Creates a new shell process (sh) with the modified environment (where "FOO=BAR").
2. Calls the echo $FOO command within that shell, effectively printing the environment variable.

By taking this approach, you essentially set the environment variable and immediately launch a new shell that inherits the modified environment, ensuring its persistence.

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