Update a configuration file where \<expr\> is a dot-separated human-readable [path expression](#ii-path-expressions) and \<content\> is a string or a file. If a string is given, it will <u>override/add the field</u> ; if a file is given the configuration file will be <u>replaced</u> by it.
| `alt` | Alternative file if there is more than one for a package. If **omitted** it will default to the _main_ configuration file. | `httpd@main`, `http@ports` |
| `field` | Field is a dot-separated chain of strings that match with a configuration field. If **omitted**, the \<value\> will just be added at the end of the configuration file. In the same way if the field does not point to a raw field but a parent or group containing fields, the \<value\> will be added at the end. | `sshd.AllowGroups`, `nginx.http.gzip` |
----
## Example
_myserver.build_
```
sys name ubuntu #
sys version 18.4 # required to choose which package-manager to use