From 54f5a8037d09da9c129a7941a6bc0c80f6107b35 Mon Sep 17 00:00:00 2001 From: Vsevolod Stakhov Date: Sun, 5 Jan 2014 01:16:47 +0000 Subject: Add UCL language documentation. --- doc/markdown/configuration/ucl.md | 296 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 296 insertions(+) create mode 100644 doc/markdown/configuration/ucl.md (limited to 'doc/markdown') diff --git a/doc/markdown/configuration/ucl.md b/doc/markdown/configuration/ucl.md new file mode 100644 index 000000000..15fda9369 --- /dev/null +++ b/doc/markdown/configuration/ucl.md @@ -0,0 +1,296 @@ +## Introduction + +This document describes the main features and principles of the configuration +language called `UCL` - universal configuration language. + +## Basic structure + +UCL is heavily infused by `nginx` configuration as the example of a convenient configuration +system. However, UCL is fully compatible with `JSON` format and is able to parse json files. +For example, you can write the same configuration in the following ways: + +* in nginx like: + +```nginx +param = value; +section { + param = value; + param1 = value1; + flag = true; + number = 10k; + time = 0.2s; + string = "something"; + subsection { + host = { + host = "hostname"; + port = 900; + } + host = { + host = "hostname"; + port = 901; + } + } +} +``` + +* or in JSON: + +```json +{ + "param": "value", + "param1": "value1", + "flag": true, + "subsection": { + "host": [ + { + "host": "hostname", + "port": 900 + }, + { + "host": "hostname", + "port": 901 + } + ] + } +} +``` + +## Improvements to the json notation. + +There are various things that make ucl configuration more convenient for editing than strict json: + +### General syntax sugar + +* Braces are not necessary to enclose a top object: it is automatically treated as an object: + +```json +"key": "value" +``` +is equal to: +```json +{"key": "value"} +``` + +* There is no requirement of quotes for strings and keys, moreover, `:` may be replaced `=` or even be skipped for objects: + +```nginx +key = value; +section { + key = value; +} +``` +is equal to: +```json +{ + "key": "value", + "section": { + "key": "value" + } +} +``` + +* No commas mess: you can safely place a comma or semicolon for the last element in an array or an object: + +```json +{ + "key1": "value", + "key2": "value", +} +``` +### Automatic arrays creation + +* Non-unique keys in an object are allowed and are automatically converted to the arrays internally: + +```json +{ + "key": "value1", + "key": "value2" +} +``` +is converted to: +```json +{ + "key": ["value1", "value2"] +} +``` + +### Named keys hierarchy + +UCL accepts named keys and organize them into objects hierarchy internally. Here is an example of this process: +```nginx +section "blah" { + key = value; +} +section foo { + key = value; +} +``` + +is converted to the following object: + +```nginx +section { + blah { + key = value; + } + foo { + key = value; + } +} +``` + +Plain definitions may be more complex and contain more than a single level of nested objects: + +```nginx +section "blah" "foo" { + key = value; +} +``` + +is presented as: + +```nginx +section { + blah { + foo { + key = value; + } + } +} +``` + +### Convenient numbers and booleans + +* Numbers can have suffixes to specify standard multipliers: + + `[kKmMgG]` - standard 10 base multipliers (so `1k` is translated to 1000) + + `[kKmMgG]b` - 2 power multipliers (so `1kb` is translated to 1024) + + `[s|min|d|w|y]` - time multipliers, all time values are translated to float number of seconds, for example `10min` is translated to 600.0 and `10ms` is translated to 0.01 +* Booleans can be specified as `true` or `yes` or `on` and `false` or `no` or `off`. +* It is still possible to treat numbers and booleans as strings by enclosing them in double quotes. + +## General improvements + +### Commments + +UCL supports different style of comments: + +* single line: `#` +* multiline: `/* ... */` + +Multiline comments may be nested: +```c +# Sample single line comment +/* + some comment + /* nested comment */ + end of comment +*/ +``` + +### Macros support + +UCL supports external macros both multiline and single line ones: +```nginx +.macro "sometext"; +.macro { + Some long text + .... +}; +``` +There are two internal macros provided by UCL: + +* `include` - read a file `/path/to/file` or an url `http://example.com/file` and include it to the current place of +UCL configuration; +* `includes` - read a file or an url like the previous macro, but fetch and check the signature file (which is obtained +by `.sig` suffix appending). + +Public keys which are used for the last command are specified by the concrete UCL user. + +### Variables support + +UCL supports variables in input. Variables are registered by a user of the UCL parser and can be presented in the following forms: + +* `${VARIABLE}` +* `$VARIABLE` + +UCL currently does not support nested variables. To escape variables one could use double dollar signs: + +* `$${VARIABLE}` is converted to `${VARIABLE}` +* `$$VARIABLE` is converted to `$VARIABLE` + +However, if no valid variables are found in a string, no expansion will be performed (and `$$` thus remains unchanged). This may be a subject +to change in future libucl releases. + +### Multiline strings + +UCL can handle multiline strings as well as single line ones. It uses shell/perl like notation for such objects: +``` +key = <