## Configuration Syntax

### Object Definition

Icinga 2 features an object-based configuration format. In order to
define objects the `object` keyword is used:

    object Host "host1.example.org" {
      display_name = "host1",

      macros = {
        address = "192.168.0.1"
      }
    }

> **Note**
>
> The Icinga 2 configuration format is agnostic to white space characters and
> new-lines.

> **Note**
>
> Colons (:) are not permitted in object names.

Each object is uniquely identified by its type (`Host`) and name
(`host1.example.org`). Objects can contain a comma-separated list of
property declarations. The following data types are available for
property values:

#### Numeric Literals

A floating-point number.

Example:

    -27.3

#### Duration Literals

Similar to floating-point numbers except for the fact that they support
suffixes to help with specifying time durations.

Example:

    2.5m

Supported suffixes include ms (milliseconds), s (seconds), m (minutes),
h (hours) and d (days).

#### String Literals

A string.

Example:

    "Hello World!"

Certain characters need to be escaped. The following escape sequences
are supported:

  Character                           |Escape sequence
  ------------------------------------|------------------------------------
  "                                   |\\"
  \\                                  |\\\\
  \<TAB\>                             |\\t
  \<CARRIAGE-RETURN\>                 |\\r
  \<LINE-FEED\>                       |\\n
  \<BEL\>                             |\\b
  \<FORM-FEED\>                       |\\f

In addition to these pre-defined escape sequences you can specify
arbitrary ASCII characters using the backslash character (\\) followed
by an ASCII character in octal encoding.

#### Multi-line String Literals

Strings spanning multiple lines can be specified by enclosing them in
{{{ and }}}.

Example.

    {{{This
    is
    a multi-line
    string.}}}

> **Note**
>
> Unlike in ordinary strings special characters to not have to be escaped
> in multi-line string literals.

#### Boolean Literals

The keywords `true` and `false` are equivalent to 1 and 0 respectively.

#### Null Value

The `null` keyword can be used to specify an empty value.

#### Dictionary

An unordered list of key-value pairs. Keys must be unique and are
compared in a case-insensitive manner.

Individual key-value pairs must be separated from each other with a
comma. The comma after the last key-value pair is optional.

Example:

    {
      address = "192.168.0.1",
      port = 443
    }

> **Note**
>
> Identifiers may not contain certain characters (e.g. space) or start
> with certain characters (e.g. digits). If you want to use a dictionary
> key that is not a valid identifier you can put the key in double
> quotes.

> **Note**
>
> Setting a dictionary key to null causes the key and its value to be
> removed from the dictionary.

#### Array

An ordered list of values.

Individual array elements must be separated from each other with a
comma. The comma after the last element is optional.

Example:

    [ "hello", 42 ]

> **Note**
>
> An array may simultaneously contain values of different types, such as
> strings and numbers.

### Operators

In addition to the `=` operator shown above a number of other operators
to manipulate configuration objects are supported. Here's a list of all
available operators:

#### Operator =

Sets a dictionary element to the specified value.

Example:

    {
      a = 5,
      a = 7
    }

In this example a has the value 7 after both instructions are executed.

#### Operator +=

Modifies a dictionary or array by adding new elements to it.

Example:

    {
      a = [ "hello" ],
      a += [ "world" ]
    }

In this example a contains both `"hello"` and `"world"`. This currently
only works for dictionaries and arrays.

<!--

#### Operator -=

Removes elements from a dictionary.

Example:

    {
      a = { "hello", "world" },
      a -= [ "world" ]
    }

In this example a contains `"hello"`. Trying to remove an item that does
not exist is not an error. Not implemented yet.

#### Operator \*=

Multiplies an existing dictionary element with the specified number. If
the dictionary element does not already exist 0 is used as its value.

Example:

    {
      a = 60,
      a *= 5
    }

In this example a is 300. This only works for numbers. Not implemented
yet.

#### Operator /=

Divides an existing dictionary element by the specified number. If the
dictionary element does not already exist 0 is used as its value.

Example:

    {
      a = 300,
      a /= 5
    }

In this example a is 60. This only works for numbers. Not implemented
yet.

-->

### Indexer

The indexer syntax provides a convenient way to set dictionary elements.

Example:

    {
      hello["key"] = "world"
    }

This is equivalent to writing:

    {
      hello += {
        key = "world"
      }
    }

### Inheritance

Objects can inherit attributes from other objects.

Example:

    template Host "default-host" {
      macros["color"] = "red"
    }

    template Host "test-host" inherits "default-host" {
      macros["color"] = "blue"
    }

    object Host "localhost" inherits "test-host" {
      macros["address"] = "127.0.0.1",
      macros["address6"] = "::1"
    }

The `default-host` and `test-host` objects are marked as templates
using the `template` keyword. Unlike ordinary objects templates are not
instantiated at run-time. Parent objects do not necessarily have to be
templates though in general they are.

> **Note**
>
> The final macros dictionary contains all 3 macros and the macro
> `color` has the value `"blue"`.

Parent objects are resolved in the order they're specified using the
`inherits` keyword.

### Variables

Global variables can be set using the `set` keyword:

    set VarName = "some value"

The value can be a string, number, array or a dictionary.

### Constant Expressions

Simple calculations can be performed using the constant expression syntax:

    {
      check_interval = (15 * 60)
    }

Valid operators include +, -, * and /. The default precedence rules can be
overridden by grouping expressions using parentheses:

    {
      check_interval ((15 * 60) / 2)
    }

Global variables may be used in constant expressions.

    set MyCheckInterval = 10m

    ...

    {
      check_interval = (MyCheckInterval / 2.5)
    }

> **Note**
>
> Constant expressions are evaluated as soon as they're encountered in
> the configuration file.

### <a id="comments"></a> Comments

The Icinga 2 configuration format supports C/C++-style comments.

Example:

    /*
     This is a comment.
     */
    object Host "localhost" {
      check_interval = 30, // this is also a comment.
      retry_interval = 15
    }

### Includes

Other configuration files can be included using the `include` directive.
Paths must be relative to the configuration file that contains the
`include` directive.

Example:

    include "some/other/file.conf"
    include "conf.d/*.conf"

> **Note**
>
> Wildcard includes are not recursive.

Icinga also supports include search paths similar to how they work in a
C/C++ compiler:

    include <itl/itl.conf>

Note the use of angle brackets instead of double quotes. This causes the
config compiler to search the include search paths for the specified
file. By default $PREFIX/icinga2 is included in the list of search
paths. Additional include search paths can be added using
[command-line options](#cmdline).

Wildcards are not permitted when using angle brackets.

### <a id="library"></a> Library directive

The `library` directive can be used to manually load additional
libraries. Libraries can be used to provide additional object types and
methods.

Example:

    library "snmphelper"

> **Note**
>
> The `icinga` library is automatically loaded at startup. You don't need
> to load it manually.

<!--

### Type Definition

By default Icinga has no way of semantically verifying its configuration
objects. This is where type definitions come in. Using type definitions
you can specify which attributes are allowed in an object definition.

Example:

    type Pizza {
            %require "radius",
            %attribute number "radius",

            %attribute dictionary "ingredients" {
                    %validator "ValidateIngredients",

                    %attribute string "*",

                    %attribute dictionary "*" {
                            %attribute number "quantity",
                            %attribute string "name"
                    }
            },

            %attribute any "custom::*"
    }

The Pizza definition provides the following validation rules:

-   Pizza objects must contain an attribute `radius` which has to be a
    number.

-   Pizza objects may contain an attribute `ingredients` which has to be
    a dictionary.

-   Elements in the ingredients dictionary can be either a string or a
    dictionary.

-   If they're a dictionary they may contain attributes `quantity` (of
    type number) and `name` (of type string).

-   The script function `ValidateIngredients` is run to perform further
    validation of the ingredients dictionary.

-   Pizza objects may contain attribute matching the pattern
    `custom::*` of any type.

Valid types for type rules include:

* any
* number
* string
* scalar (an alias for string)
* dictionary

-->