freebsd-dev/contrib/libucl/doc/lua_api.md

Module ucl

This lua module allows to parse objects from strings and to store data into ucl objects. It uses libucl C library to parse and manipulate with ucl objects.

Example:

local ucl = require("ucl")

local parser = ucl.parser()
local res,err = parser:parse_string('{key=value}')

if not res then
	print('parser error: ' .. err)
else
	local obj = parser:get_object()
	local got = ucl.to_format(obj, 'json')
end

local table = {
  str = 'value',
  num = 100500,
  null = ucl.null,
  func = function ()
    return 'huh'
  end
}


print(ucl.to_format(table, 'ucl'))
-- Output:
--[[
num = 100500;
str = "value";
null = null;
func = "huh";
--]]

###Brief content:

Functions:

ucl_object_push_lua(L, obj, allow_array)

ucl.to_format(var, format)

Methods:

parser:parse_file(name)

parser:parse_string(input)

parser:get_object()

Functions

The module ucl defines the following functions.

Function ucl_object_push_lua(L, obj, allow_array)

This is a C function to push UCL object as lua variable. This function converts obj to lua representation using the following conversions:

• scalar values are directly presented by lua objects
• userdata values are converted to lua function objects using LUA_REGISTRYINDEX, this can be used to pass functions from lua to c and vice-versa
• arrays are converted to lua tables with numeric indicies suitable for ipairs iterations
• objects are converted to lua tables with string indicies

Parameters:

• L {lua_State}: lua state pointer
• obj {ucl_object_t}: object to push
• allow_array {bool}: expand implicit arrays (should be true for all but partial arrays)

Returns:

• {int}: 1 if an object is pushed to lua

Back to module description.

Function ucl.to_format(var, format)

Converts lua variable var to the specified format. Formats supported are:

• json - fine printed json
• json-compact - compacted json
• config - fine printed configuration
• ucl - same as config
• yaml - embedded yaml

If var contains function, they are called during output formatting and if they return string value, then this value is used for ouptut.

Parameters:

• var {variant}: any sort of lua variable (if userdata then metafield __to_ucl is searched for output)
• format {string}: any available format

Returns:

• {string}: string representation of var in the specific format.

Example:

local table = {
  str = 'value',
  num = 100500,
  null = ucl.null,
  func = function ()
    return 'huh'
  end
}


print(ucl.to_format(table, 'ucl'))
-- Output:
--[[
num = 100500;
str = "value";
null = null;
func = "huh";
--]]

Back to module description.

Methods

The module ucl defines the following methods.

Method parser:parse_file(name)

Parse UCL object from file.

Parameters:

• name {string}: filename to parse

Returns:

• {bool[, string]}: if res is true then file has been parsed successfully, otherwise an error string is also returned

Example:

local parser = ucl.parser()
local res,err = parser:parse_file('/some/file.conf')

if not res then
	print('parser error: ' .. err)
else
	-- Do something with object
end

Back to module description.

Method parser:parse_string(input)

Parse UCL object from file.

Parameters:

• input {string}: string to parse

Returns:

• {bool[, string]}: if res is true then file has been parsed successfully, otherwise an error string is also returned

Back to module description.

Method parser:get_object()

Get top object from parser and export it to lua representation.

Parameters:

nothing

Returns:

• {variant or nil}: ucl object as lua native variable

Back to module description.

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