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https://github.com/raphink/narcissus

Map configuration files to Go structures using Augeas
https://github.com/raphink/narcissus

augeas configuration configuration-management golang golang-library parser parsing

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Map configuration files to Go structures using Augeas

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Narcissus: edit configuration files as go structs
=================================================

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This go package aims to provide reflection for the [Augeas](http://augeas.net) library.

This allows to turn Augeas lenses into Go structs for easy parsing and
modification of configuration files.

## Example

```go
import (
"log"

"honnef.co/go/augeas"
"github.com/raphink/narcissus"
)

func main() {
aug, err := augeas.New("/", "", augeas.None)
if err != nil {
log.Fatal("Failed to create Augeas handler")
}
n := narcissus.New(&aug)

user := n.NewPasswdUser("raphink")
if err != nil {
log.Fatalf("Failed to retrieve user: %v" err)
}

log.Printf("UID=%v", user.UID)

// Modify UID
user.UID = 42

err = n.Write(user)
if err != nil {
log.Fatalf("Failed to save user: %v", err)
}
}
```

## Available types

### Fstab

* [`Fstab`](https://godoc.org/github.com/raphink/narcissus#Fstab) maps a whole `/etc/fstab` file
* [`FstabEntry`](https://godoc.org/github.com/raphink/narcissus#FstabEntry) maps a single `/etc/fstab` entry

### Hosts

* [`Hosts`](https://godoc.org/github.com/raphink/narcissus#Hosts) maps a whole `/etc/hosts` file
* [`Host`](https://godoc.org/github.com/raphink/narcissus#Host) maps a single `/etc/hosts` entry

### Passwd

* [`Passwd`](https://godoc.org/github.com/raphink/narcissus#Passwd) maps a whole `/etc/passwd` file
* [`PasswdUser`](https://godoc.org/github.com/raphink/narcissus#PasswdUser) maps a single `/etc/passwd` entry

### Services

* [`Services`](https://godoc.org/github.com/raphink/narcissus#Services) maps a whole `/etc/services` file
* [`Service`](https://godoc.org/github.com/raphink/narcissus#Service) maps a single `/etc/services` entry

## Mapping your own structures

```go
import (
"log"

"honnef.co/go/augeas"
"github.com/raphink/narcissus"
)

type group struct {
augeasPath string
Name string `narcissus:".,value-from-label"`
Password string `narcissus:"password"`
GID int `narcissus:"gid"`
Users []string `narcissus:"user"`
}

func main() {
aug, err := augeas.New("/", "", augeas.None)
if err != nil {
log.Fatal("Failed to create Augeas handler")
}
n := narcissus.New(&aug)

group := &group{
augeasPath: "/files/etc/group/docker",
}
err = n.Parse(group)
if err != nil {
log.Fatalf("Failed to retrieve group: %v", err)
}

log.Printf("GID=%v", group.GID)
log.Printf("Users=%v", strings.Join(group.Users, ","))
}
```

## Tag values

The `narcissus` tag accepts multiple comma separated values. The first value in
the list is the relative path where the field is mapped in the Augeas tree.

Other possible (optional) values are:

* `value-from-label`: get field value from the node label instead of its value;
* `seq` (slice field only): will treat field as a seq entry in the Augeas tree;
* `key-from-value` (map field only): get the key from the node label instead
of its value;
* `purge` (map field only): purge all unknown keys in the map.

## Fields

Described structures have special fields to specify parameters for Augeas.

* `augeasPath` (mandatory): the path to the structure in the Augeas tree;
* `augeasFile` (optional): let Augeas load only this file. If `augeasLens` is
not specified, Augeas will use the default lens for the file if available;
* `augeasLens` (optional): if `augeasFile` is set (ignored otherwise),
specifies which lens to use to parse the file. This is required when parsing
a file at a non-standard location.

Each of these fields can be specified in one of two ways:

* by using the `default` tag with a default value for the field, e.g.

```go
type group struct {
augeasPath string `default:"/files/etc/group/root"`
}
```

* by specifying a value for the instance in the structure field, e.g.

```go
myGroup := group {
augeasPath: "/files/etc/group/docker",
}
```