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# hololink::module::env_hololink_ip

> Get the IP address of a device from the HOLOLINK_IPS environment variable.

```cpp showLineNumbers={false}
inline std::string hololink::module::env_hololink_ip(
    std::size_t index,
    const std::string &fallback
)
```

Get the IP address of a device from the `HOLOLINK_IPS` environment variable.

`HOLOLINK_IPS` holds a comma-separated list of device addresses, for example `192.168.0.2,192.168.0.3`. This returns the entry at position `index`, counting from zero. It lets a test harness (for example `ctest`, or pytest through its `--channel-ips` option) choose the devices a program uses, without each program needing its own command-line option; programs normally pass the result as the default for such an option.

The entry is returned exactly as written: whitespace is not removed and the text is not checked to be a valid address.

**Returns:** The selected address, or `fallback`.

**Parameters**

**`index`** `std::size_t`

Zero-based position in the list.

---

**`fallback`** `const std::string &`

Value to return when no address is available for `index`: the variable is unset or empty, the list has `index` or fewer entries, or the entry at `index` is empty (as in `a,,b`).

---