Docs: Update API and Library Reference chapters

New sub chapters for global functions linked everywhere.
New API examples and clarifications.

fixes #13327
fixes #12449

doc/12-icinga2-api.md

@@ -82,6 +82,10 @@ The output will be sent back as a JSON object:
         ]
     }
 
+Tip: If you are working on the CLI with curl you can also use [jq](https://stedolan.github.io/jq/)
+to format the returned JSON output in a readable manner. The documentation
+prefers `python -m json.tool` as Python is available nearly everywhere.
+
 > **Note**
 >
 > Future versions of Icinga 2 might set additional fields. Your application
@@ -182,6 +186,7 @@ which must return a boolean value.
 
 The following example allows the API user to query all hosts and services which have a
 custom attribute `os` that matches the regular expression `^Linux`.
+The [regex function](18-library-reference.md#global-functions-regex) is available as global function.
 
     permissions = [
       {
@@ -235,6 +240,9 @@ Here are the exact same query parameters as a JSON object:
 
     { "filter": "match(\"example.localdomain*\",host.name)", "attrs": [ "host.name", "host.state" ] }
 
+The [match function](18-library-reference.md#global-functions-match) is available as global function
+in Icinga 2.
+
 ### <a id="icinga2-api-requests-method-override"></a> Request Method Override
 
 `GET` requests do not allow you to send a request body. In case you cannot pass everything as URL parameters (e.g. complex filters or JSON-encoded dictionaries) you can use the `X-HTTP-Method-Override` header. This comes in handy when you are using HTTP proxies disallowing `PUT` or `DELETE` requests too.
@@ -293,7 +301,7 @@ Example matching all services in NOT-OK state:
 
     https://localhost:5665/v1/objects/services?filter=service.state!=ServiceOK
 
-Example matching all hosts by name:
+Example [matching](18-library-reference.md#global-functions-match) all hosts by a name string pattern:
 
     https://localhost:5665/v1/objects/hosts?filter=match("example.localdomain*",host.name)
 
@@ -510,6 +518,35 @@ for downtimes):
 
    https://localhost:5665/v1/objects/comments?joins=host&joins=service
 
+This is another example for listing all service objects which are unhandled problems (state is not OK
+and no downtime or acknowledgement set):
+
+   $ curl -k -s -u root:icinga -H 'X-HTTP-Method-Override: GET' -X POST 'https://127.0.0.1:5665/v1/objects/services' \
+    -d '{ "joins": [ "host.name", "host.address" ], "attrs": [ "name", "state", "downtime_depth", "acknowledgement" ], "filter": "service.state != ServiceOK && service.downtime_depth == 0.0 && service.acknowledgement == 0.0" }' | python -m json.tool
+
+    {
+        "results": [
+            {
+                "attrs": {
+                    "acknowledgement": 0.0,
+                    "downtime_depth": 0.0,
+                    "name": "10807-service",
+                    "state": 3.0
+                },
+                "joins": {
+                    "host": {
+                        "address": "",
+                        "name": "10807-host"
+                    }
+                },
+                "meta": {},
+                "name": "10807-host!10807-service",
+                "type": "Service"
+            }
+        ]
+    }
+
+
 ### <a id="icinga2-api-config-objects-create"></a> Creating Config Objects
 
 New objects must be created by sending a PUT request. The following
@@ -517,7 +554,7 @@ parameters need to be passed inside the JSON body:
 
   Parameters | Type         | Description
   -----------|--------------|--------------------------
-  templates  | string array | **Optional.** Import existing configuration templates for this object type.
+  templates  | string array | **Optional.** Import existing configuration templates for this object type. Note: These templates must either be statically configured or provided in [config packages](12-icinga2-api.md#icinga2-api-config-management)-
   attrs      | dictionary   | **Required.** Set specific object attributes for this [object type](9-object-types.md#object-types).
 
 The object name must be specified as part of the URL path. For objects with composite names (e.g. services)
@@ -586,6 +623,8 @@ In addition to these parameters a [filter](12-icinga2-api.md#icinga2-api-filters
 **Note**: Modified attributes do not trigger a re-evaluation of existing
 static [apply rules](3-monitoring-basics.md#using-apply) and [group assignments](3-monitoring-basics.md#group-assign-intro).
 Delete and re-create the objects if you require such changes.
+Furthermore you cannot modify templates which have already been resolved
+during [object creation](12-icinga2-api.md#icinga2-api-config-objects-create).
 
 
 If attributes are of the Dictionary type, you can also use the indexer format:
@@ -640,6 +679,8 @@ Provides methods to manage configuration templates:
 
 * [querying templates](12-icinga2-api.md#icinga2-api-config-templates-query)
 
+Creation, modification and deletion of templates at runtime is not supported.
+
 ### <a id="icinga2-api-config-templates-query"></a> Querying Templates
 
 You can request information about configuration templates by sending
@@ -653,9 +694,11 @@ A list of all available configuration types is available in the
 [object types](9-object-types.md#object-types) chapter.
 
 A [filter](12-icinga2-api.md#icinga2-api-filters) may be provided for this query type. The
-template object can be accessed in the filter using the `tmpl` variable:
+template object can be accessed in the filter using the `tmpl` variable. In this
+example the [match function](18-library-reference.md#global-functions-match) is used to
+check a wildcard string pattern against `tmpl.name`:
 
-    $ curl -u root:root -k 'https://localhost:5661/v1/templates/hosts' -H "Accept: application/json" -X PUT -H "X-HTTP-Method-Override: GET" \
+    $ curl -k -s -u root:icinga 'https://localhost:5661/v1/templates/hosts' -H "Accept: application/json" -X PUT -H "X-HTTP-Method-Override: GET" \
     -d '{ "filter": "match(\"g*\", tmpl.name)" }'
 
 Instead of using a filter you can optionally specify the template name in the
@@ -1180,7 +1223,8 @@ Example for the `CheckResult` type with the `exit_code` set to `2`:
 
     &types=CheckResult&filter=event.check_result.exit_status==2
 
-Example for the `CheckResult` type with the service matching the string "random":
+Example for the `CheckResult` type with the service [matching](18-library-reference.md#global-functions-match)
+the string pattern "random\*":
 
     &types=CheckResult&filter=match%28%22random*%22,event.service%29
 
@@ -1649,7 +1693,8 @@ The request method is `POST` using `X-HTTP-Method-Override: GET`
 which allows you to send a JSON request body. The examples request
 specific service attributes joined with host attributes. `attrs`
 and `joins` are therefore specified as array.
-The `filter` attribute matches on all services with `ping` in their name.
+The `filter` attribute [matches](18-library-reference.md#global-functions-match)
+on all services with `ping` in their name.
 
 #### <a id="icinga2-api-clients-programmatic-examples-python"></a> Example API Client in Python
 

doc/18-library-reference.md

@@ -2,31 +2,457 @@
 
 ## <a id="global-functions"></a> Global functions
 
-Function                        | Description
+These functions are globally available in [assign/ignore where expressions](3-monitoring-basics.md#using-apply-expressions),
---------------------------------|-----------------------
+[functions](17-language-reference.md#functions), [API filters](12-icinga2-api.md#icinga2-api-filters)
-regex(pattern, text)            | Returns true if the regex pattern matches the text, false otherwise.
+and the [Icinga 2 console](11-cli-commands.md#cli-command-console).
-match(pattern, text)            | Returns true if the wildcard pattern matches the text, false otherwise.
+
-cidr_match(pattern, ip)         | Returns true if the CIDR pattern matches the IP address, false otherwise. IPv4 addresses are converted to IPv4-mapped IPv6 addresses before being matched against the pattern.
+You can use the [Icinga 2 console](11-cli-commands.md#cli-command-console)
-len(value)                      | Returns the length of the value, i.e. the number of elements for an array or dictionary, or the length of the string in bytes.
+as a sandbox to test these functions before implementing
-union(array, array, ...)        | Returns an array containing all unique elements from the specified arrays.
+them in your scenarios.
-intersection(array, array, ...) | Returns an array containing all unique elements which are common to all specified arrays.
+
-keys(dict)                      | Returns an array containing the dictionary's keys.
+### <a id="global-functions-regex"></a> regex
-string(value)                   | Converts the value to a string.
+
-number(value)                   | Converts the value to a number.
+Signature:
-bool(value)                     | Converts the value to a bool.
+
-random()                        | Returns a random value between 0 and RAND_MAX (as defined in stdlib.h).
+    function regex(pattern, text)
-log(value)                      | Writes a message to the log. Non-string values are converted to a JSON string.
+
-log(severity, facility, value)  | Writes a message to the log. `severity` can be one of `LogDebug`, `LogNotice`, `LogInformation`, `LogWarning`, and `LogCritical`. Non-string values are converted to a JSON string.
+Returns true if the regular expression matches the text, false otherwise.
-typeof(value)                   | Returns the [Type](18-library-reference.md#type-type) object for a value.
+**Tip**: In case you are looking for regular expression tests try [regex101](https://regex101.com).
-get_time()                      | Returns the current UNIX timestamp.
+
-parse_performance_data(pd)      | Parses a performance data string and returns an array describing the values.
+Example:
-dirname(path)                   | Returns the directory portion of the specified path.
+
-basename(path)                  | Returns the filename portion of the specified path.
+    $ icinga2 console
-escape\_shell\_arg(text)        | Escapes a string for use as a single shell argument.
+    Icinga 2 (version: v2.6.0)
-escape\_shell\_cmd(text)        | Escapes shell meta characters in a string.
+    <1> => host.vars.os_type = "Linux/Unix"
-escape\_create\_process\_arg(text)| (Windows only) Escapes a string for use as an argument for CreateProcess().
+    null
-exit(integer)                   | Terminates the application.
+    <2> => regex("^Linux", host.vars.os_type)
-sleep(interval)                 | Sleeps for the specified amount of time (in seconds).
+    true
+    <3> => regex("^Linux$", host.vars.os_type)
+    false
+
+### <a id="global-functions-match"></a> match
+
+Signature:
+
+    function match(pattern, text)
+
+Returns true if the wildcard (`\*`) pattern matches the text, false otherwise.
+
+Example:
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => host.display_name = "NUE-DB-PROD-586"
+    null
+    <2> => match("NUE-*", host.display_name)
+    true
+    <3> => match("*NUE-*", host.display_name)
+    true
+    <4> => match("NUE-*-DEV-*", host.display_name)
+    false
+
+### <a id="global-functions-cidr_match"></a> cidr_match
+
+Signature:
+
+    function cidr_match(pattern, ip)
+
+Returns true if the CIDR pattern matches the IP address, false otherwise.
+IPv4 addresses are converted to IPv4-mapped IPv6 addresses before being
+matched against the pattern.
+
+Example:
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => host.address = "192.168.56.101"
+    null
+    <2> => cidr_match("192.168.56.0/24", host.address)
+    true
+    <3> => cidr_match("192.168.56.0/26", host.address)
+    false
+
+### <a id="global-functions-range"></a> range
+
+Signature:
+
+    function range(end)
+    function range(start, end)
+    function range(start, end, increment)
+
+Returns an array of numbers in the specified range.
+If you specify one parameter, the first element starts at `0`.
+The following array numbers are incremented by `1` and stop before
+the specified end.
+If you specify the start and end numbers, the returned array
+number are incremented by `1`. They start at the specified start
+number and stop before the end number.
+Optionally you can specify the incremented step between numbers
+as third parameter.
+
+Example:
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => range(5)
+    [ 0.000000, 1.000000, 2.000000, 3.000000, 4.000000 ]
+    <2> => range(2,4)
+    [ 2.000000, 3.000000 ]
+    <3> => range(2,10,2)
+    [ 2.000000, 4.000000, 6.000000, 8.000000 ]
+
+### <a id="global-functions-len"></a> len
+
+Signature:
+
+    function len(value)
+
+Returns the length of the value, i.e. the number of elements for an array
+or dictionary, or the length of the string in bytes.
+
+**Note**: Instead of using this global function you are advised to use the type's
+prototype method: [Array#len](18-library-reference.md#array-len), [Dictionary#len](18-library-reference.md#dictionary-len) and
+[String#len](18-library-reference.md#string-len).
+
+Example:
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => host.groups = [ "linux-servers", "db-servers" ]
+    null
+    <2> => host.groups.len()
+    2.000000
+    <3> => host.vars.disks["/"] = {}
+    null
+    <4> => host.vars.disks["/var"] = {}
+    null
+    <5> => host.vars.disks.len()
+    2.000000
+    <6> => host.vars.os_type = "Linux/Unix"
+    null
+    <7> => host.vars.os_type.len()
+    10.000000
+
+
+### <a id="global-functions-union"></a> union
+
+Signature:
+
+    function union(array, array, ...)
+
+Returns an array containing all unique elements from the specified arrays.
+
+Example:
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => var dev_notification_groups = [ "devs", "slack" ]
+    null
+    <2> => var host_notification_groups = [ "slack", "noc" ]
+    null
+    <3> => union(dev_notification_groups, host_notification_groups)
+    [ "devs", "noc", "slack" ]
+
+### <a id="global-functions-intersection"></a> intersection
+
+Signature:
+
+    function intersection(array, array, ...)
+
+Returns an array containing all unique elements which are common to all
+specified arrays.
+
+Example:
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => var dev_notification_groups = [ "devs", "slack" ]
+    null
+    <2> => var host_notification_groups = [ "slack", "noc" ]
+    null
+    <3> => intersection(dev_notification_groups, host_notification_groups)
+    [ "slack" ]
+
+### <a id="global-functions-keys"></a> keys
+
+Signature:
+
+    function keys(dict)
+
+Returns an array containing the dictionary's keys.
+
+**Note**: Instead of using this global function you are advised to use the type's
+prototype method: [Dictionary#keys](18-library-reference.md#dictionary-keys).
+
+Example:
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => host.vars.disks["/"] = {}
+    null
+    <2> => host.vars.disks["/var"] = {}
+    null
+    <3> => host.vars.disks.keys()
+    [ "/", "/var" ]
+
+### <a id="global-functions-string"></a> string
+
+Signature:
+
+    function string(value)
+
+Converts the value to a string.
+
+**Note**: Instead of using this global function you are advised to use the type's
+prototype method:
+
+* [Number#to_string](18-library-reference.md#number-to_string)
+* [Boolean#to_string](18-library-reference.md#boolean-to_string)
+* [String#to_string](18-library-reference.md#string-to_string)
+* [Object#to_string](18-library-reference.md#object-to-string) for Array and Dictionary types
+* [DateTime#to_string](18-library-reference.md#datetime-tostring)
+
+Example:
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => 5.to_string()
+    "5"
+    <2> => false.to_string()
+    "false"
+    <3> => "abc".to_string()
+    "abc"
+    <4> => [ "dev", "slack" ].to_string()
+    "[ \"dev\", \"slack\" ]"
+    <5> => { "/" = {}, "/var" = {} }.to_string()
+    "{\n\t\"/\" = {\n\t}\n\t\"/var\" = {\n\t}\n}"
+    <6> => DateTime(2016, 11, 25).to_string()
+    "2016-11-25 00:00:00 +0100"
+
+### <a id="global-functions-number"></a> number
+
+Signature:
+
+    function number(value)
+
+Converts the value to a number.
+
+Example:
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => number(false)
+    0.000000
+    <2> => number("78")
+    78.000000
+
+### <a id="global-functions-bool"></a> bool
+
+Signature:
+
+    function bool(value)
+
+Converts the value to a bool.
+
+Example:
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => bool(1)
+    true
+    <2> => bool(0)
+    false
+
+### <a id="global-functions-random"></a> random
+
+Signature:
+
+    function random()
+
+Returns a random value between 0 and RAND\_MAX (as defined in stdlib.h).
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => random()
+    1263171996.000000
+    <2> => random()
+    108402530.000000
+
+### <a id="global-functions-log"></a> log
+
+Signature:
+
+    function log(value)
+
+Writes a message to the log. Non-string values are converted to a JSON string.
+
+Signature:
+
+    function log(severity, facility, value)
+
+Writes a message to the log. `severity` can be one of `LogDebug`, `LogNotice`,
+`LogInformation`, `LogWarning`, and `LogCritical`.
+
+Non-string values are converted to a JSON string.
+
+Example:
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => log(LogCritical, "Console", "First line")
+    critical/Console: First line
+    null
+    <2> => var groups = [ "devs", "slack" ]
+    null
+    <3> => log(LogCritical, "Console", groups)
+    critical/Console: ["devs","slack"]
+    null
+
+### <a id="global-functions-typeof"></a> typeof
+
+Signature:
+
+    function typeof(value)
+
+Returns the [Type](18-library-reference.md#type-type) object for a value.
+
+Example:
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => typeof(3) == Number
+    true
+    <2> => typeof("str") == String
+    true
+    <3> => typeof(true) == Boolean
+    true
+    <4> => typeof([ 1, 2, 3]) == Array
+    true
+    <5> => typeof({ a = 2, b = 3}) == Dictionary
+
+### <a id="global-functions-get_time"></a> get_time
+
+Signature:
+
+    function get_time()
+
+Returns the current UNIX timestamp as floating point number.
+
+Example:
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => get_time()
+    1480072135.633008
+    <2> => get_time()
+    1480072140.401207
+
+### <a id="global-functions-parse_performance_data"></a> parse_performance_data
+
+Signature:
+
+    function parse_performance_data(pd)
+
+Parses a performance data string and returns an array describing the values.
+
+Example:
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => var pd = "'time'=1480074205.197363;;;"
+    null
+    <2> => parse_performance_data(pd)
+    {
+    	counter = false
+    	crit = null
+    	label = "time"
+    	max = null
+    	min = null
+    	type = "PerfdataValue"
+    	unit = ""
+    	value = 1480074205.197363
+    	warn = null
+    }
+
+### <a id="global-functions-dirname"></a> dirname
+
+Signature:
+
+    function dirname(path)
+
+Returns the directory portion of the specified path.
+
+Example:
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => var path = "/etc/icinga2/scripts/xmpp-notification.pl"
+    null
+    <2> => dirname(path)
+    "/etc/icinga2/scripts"
+
+### <a id="global-functions-basename"></a> basename
+
+Signature:
+
+    function basename(path)
+
+Returns the filename portion of the specified path.
+
+Example:
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => var path = "/etc/icinga2/scripts/xmpp-notification.pl"
+    null
+    <2> => basename(path)
+    "xmpp-notification.pl"
+
+### <a id="global-functions-escape_shell_arg"></a> escape_shell_arg
+
+Signature:
+
+    function escape_shell_arg(text)
+
+Escapes a string for use as a single shell argument.
+
+Example:
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => escape_shell_arg("'$host.name$' '$service.name$'")
+    "''\\''$host.name$'\\'' '\\''$service.name$'\\'''"
+
+### <a id="global-functions-escape_shell_cmd"></a> escape_shell_cmd
+
+Signature:
+
+    function escape_shell_cmd(text)
+
+Escapes shell meta characters in a string.
+
+Example:
+
+    $ icinga2 console
+    Icinga 2 (version: v2.6.0)
+    <1> => escape_shell_cmd("/bin/echo 'shell test' $ENV")
+    "/bin/echo 'shell test' \\$ENV"
+
+### <a id="global-functions-escape_create_process_arg"></a> escape_create_process_arg
+
+Signature:
+
+    function escape_create_process_arg(text)
+
+Escapes a string for use as an argument for CreateProcess(). Windows only.
+
+### <a id="global-functions-sleep"></a> sleep
+
+Signature:
+
+    function sleep(interval)
+
+Sleeps for the specified amount of time (in seconds).
 
 ## <a id="object-accessor-functions"></a> Object Accessor Functions
 

doc/3-monitoring-basics.md

@@ -434,7 +434,7 @@ Before you start using the apply rules keep the following in mind:
 * Define the best match.
     * A set of unique [custom attributes](3-monitoring-basics.md#custom-attributes) for these hosts/services?
     * Or [group](3-monitoring-basics.md#groups) memberships, e.g. a host being a member of a hostgroup, applying services to it?
-    * A generic pattern [match](17-language-reference.md#function-calls) on the host/service name?
+    * A generic pattern [match](18-library-reference.md#global-functions-match) on the host/service name?
     * [Multiple expressions combined](3-monitoring-basics.md#using-apply-expressions) with `&&` or `||` [operators](17-language-reference.md#expression-operators)
 * All expressions must return a boolean value (an empty string is equal to `false` e.g.)
 
@@ -481,7 +481,7 @@ you want to be able to add more than one assign/ignore where expression which ma
 a specific condition. To achieve this you can use the logical `and` and `or` operators.
 
 
-Match all `*mysql*` patterns in the host name and (`&&`) custom attribute `prod_mysql_db`
+[Match](18-library-reference.md#global-functions-match) all `*mysql*` patterns in the host name and (`&&`) custom attribute `prod_mysql_db`
 matches the `db-*` pattern. All hosts with the custom attribute `test_server` set to `true`
 should be ignored, or any host name ending with `*internal` pattern.
 
@@ -494,7 +494,7 @@ should be ignored, or any host name ending with `*internal` pattern.
     }
 
 Similar example for advanced notification apply rule filters: If the service
-attribute `notes` contains the `has gold support 24x7` string `AND` one of the
+attribute `notes` [matches](18-library-reference.md#global-functions-match) the `has gold support 24x7` string `AND` one of the
 two condition passes, either the `customer` host custom attribute is set to `customer-xy`
 `OR` the host custom attribute `always_notify` is set to `true`.
 
@@ -651,8 +651,8 @@ Icinga 2 evaluates the `apply for` rule for all objects with the custom attribut
 `assign/ignore where` expressions. You can access the loop variable
 in these expressions, e.g. for ignoring certain values.
 In this example we'd ignore the `bgp` identifier and avoid generating an unwanted service.
-We could extend the configuration by also matching the `oid` value on certain regex/wildcard
+We could extend the configuration by also matching the `oid` value on certain
-patterns for example.
+[regex](18-library-reference.md#global-functions-regex)/[wildcard match](18-library-reference.md#global-functions-match) patterns for example.
 
 > **Note**
 >
@@ -967,9 +967,9 @@ to a group based on their attributes:
     }
 
 In this example all hosts with the `vars` attribute `mssql_port`
-will be added as members to the host group `mssql`. However, all `\*internal`
+will be added as members to the host group `mssql`. However, all
-hosts or with the `test_server` attribute set to `true` are not added to this
+hosts [matching](18-library-reference.md#global-functions-match) the string `\*internal`
-group.
+or with the `test_server` attribute set to `true` are **not** added to this group.
 
 Details on the `assign where` syntax can be found in the
 [Language Reference](17-language-reference.md#apply).
@@ -1898,8 +1898,8 @@ for the agent daemon responding to your requests, and make all other services
 querying that daemon depend on that health check.
 
 The following configuration defines two nrpe based service checks `nrpe-load`
-and `nrpe-disk` applied to the `nrpe-server`. The health check is defined as
+and `nrpe-disk` applied to the host `nrpe-server` [matched](18-library-reference.md#global-functions-match)
-`nrpe-health` service.
+by its name. The health check is defined as `nrpe-health` service.
 
     apply Service "nrpe-health" {
       import "generic-service"

doc/4-configuring-icinga-2.md

@@ -553,7 +553,7 @@ to previously seen [apply rules](3-monitoring-basics.md#using-apply).
     }
 
 Service groups can be grouped together by similar pattern matches.
-The [match() function](17-language-reference.md#function-calls) expects a wildcard match string
+The [match function](18-library-reference.md#global-functions-match) expects a wildcard match string
 and the attribute string to match with.
 
     object ServiceGroup "ping" {

doc/6-distributed-monitoring.md

@@ -1957,6 +1957,11 @@ execute a local disk check in the `master` on a specific endpoint then.
       assign where host.zone == "master" && match("icinga2-master*", host.name)
     }
 
+The `host.zone` attribute check inside the expression ensures that
+the service object is only created for host objects inside the `master`
+zone. In addition to that the [match](18-library-reference.md#global-functions-match)
+function ensures to only create services for the master nodes.
+
 ### <a id="distributed-monitoring-windows-firewall"></a> Windows Firewall
 
 By default ICMP requests are disabled in the Windows firewall. You can

doc/8-advanced-topics.md

@@ -317,7 +317,7 @@ The other way around you can create objects dynamically using your own global fu
 
 Tips when implementing functions:
 
-* Use [log()](18-library-reference.md#global-functions) to dump variables. You can see the output
+* Use [log()](18-library-reference.md#global-functions-log) to dump variables. You can see the output
 inside the `icinga2.log` file depending in your log severity
 * Use the `icinga2 console` to test basic functionality (e.g. iterating over a dictionary)
 * Build them step-by-step. You can always refactor your code later on.
@@ -490,7 +490,7 @@ writing your own global [functions](17-language-reference.md#functions).
 You can call them inside `assign where` and `ignore where` expressions
 for [apply rules](3-monitoring-basics.md#using-apply-expressions) or
 [group assignments](3-monitoring-basics.md#group-assign-intro) just like
-any other global functions for example [match](18-library-reference.md#global-functions).
+any other global functions for example [match](18-library-reference.md#global-functions-match).
 
 The following example requires the host `myprinter` being added
 to the host group `printers-lexmark` but only if the host uses