What causes "environment variable '{key}' must be set" in nautechsystems/nautilus_trader?

Export the environment variable before running: export KEY=value

environment variable '{key}' must be set

Error message

environment variable '{key}' must be set

What it means

`get_env_var` reads an environment variable and returns a descriptive error when it is not set at all (std::env::VarError::NotPresent). The library throws it because a required configuration value can only come from the environment and proceeding without it would be undefined.

Source

Thrown at crates/core/src/env.rs:30

//  See the License for the specific language governing permissions and
//  limitations under the License.
// -------------------------------------------------------------------------------------------------

//! Cross-platform environment variable utilities.
//!
//! This module provides functions for safely accessing environment variables
//! with proper error handling.

/// Returns the value of the environment variable for the given `key`.
///
/// # Errors
///
/// Returns an error if the environment variable is not set or is not valid Unicode.
pub fn get_env_var(key: &str) -> anyhow::Result<String> {
    match std::env::var(key) {
        Ok(var) => Ok(var),
        Err(std::env::VarError::NotPresent) => {
            anyhow::bail!("environment variable '{key}' must be set")
        }
        Err(std::env::VarError::NotUnicode(_)) => {
            anyhow::bail!("environment variable '{key}' is not valid Unicode")
        }
    }
}

/// Returns the provided `value` if `Some`, otherwise falls back to reading
/// the environment variable for the given `key`.
///
/// Only attempts to read the environment variable when `value` is `None`,
/// avoiding unnecessary environment variable lookups and errors.
///
/// # Errors
///
/// Returns an error if `value` is `None` and the environment variable is not set.
pub fn get_or_env_var(value: Option<String>, key: &str) -> anyhow::Result<String> {
    match value {

View on GitHub (pinned to 18893faf8b)

Solutions

Export the environment variable before running: export KEY=value
Add it to your .env file / shell profile / CI secrets so it is always present
Check for typos in the variable name shown in the error message
Use `get_or_env_var` with a default if the value is genuinely optional

Example fix

// before
let path = get_env_var("NAUTILUS_PATH")?; // panics-free error if unset
// after
let path = get_or_env_var("NAUTILUS_PATH", "/tmp/nautilus")?; // or ensure: export NAUTILUS_PATH=...

Defensive patterns

Strategy: validation

Validate before calling

let val = std::env::var("MY_KEY");
if val.is_err() {
    eprintln!("MY_KEY must be set; see deployment docs");
    std::process::exit(1);
}

Type guard

fn env_var_set(key: &str) -> bool {
    std::env::var_os(key).is_some()
}

Try / catch

match get_env_var("MY_KEY") {
    Ok(v) => configure(v),
    Err(e) => anyhow::bail!("startup config incomplete: {e}"), // fail fast with context
}

Prevention

Maintain a .env.example listing every required variable
Validate all env vars at startup, before doing any work
Use get_or_env_var with defaults for genuinely optional values
Check CI/deployment secrets match the variable names in code

When it happens

Trigger: Calling `get_env_var("KEY")` (directly, or via `from_env`/`main` config loading) when `KEY` was never exported in the process environment.

Common situations: Running the app without a .env file loaded; forgetting to export a variable in the shell or CI; typo in the variable name (e.g. NAUTILUS_PATH vs NAUTILUSPATH); variable defined in one environment (prod) but not another (local dev container).

Understand the failure class

Background: "environment variable is not set" and "Missing keys in environment" errors: what missing required env var messages mean and how to fix them — this error's family across 28 libraries.

Related errors

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/d9e1876234d1da02. Report an issue: GitHub.