Using ELinks with Lua
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## Using ELinks with Lua

Out of the box, ELinks with Lua will do nothing different from regular ELinks. You need to write some scripts.

### ELinks Lua additions

gets called at a particular point during the execution of ELinks. To make ELinks do what you want, you can add and edit such hooks.

The Lua support also adds an extra dialog box, which you can open while in ELinks with the comma (`,`) key. Here you can enter Lua expressions for evaluation, or override it to do something different.

And finally, you can bind keystrokes to Lua functions. These keystrokes won't let you do any more than is possible with the Lua Console, but they're more convenient.

Note that this document assumes you have some knowledge of programming in Lua. For that, you should refer to the Lua reference manual (http://www.lua.org/docs.html). In fact, the language is relatively trivial, though. You could already do wonders with simply refactoring the example scripts.

### Config file

On startup, ELinks reads in two Lua scripts. Firstly, a system-wide configuration file called `/etc/elinks/hooks.lua`, then a file in your home directory called `~/.elinks/hooks.lua`. From these files, you can include other Lua files with `dofile`, if necessary.

To see what kind of things you should put in here, look at `contrib/lua/hooks.lua`.

### Hooks

The following hooks are available.

goto_url_hook (url, current_url)
  This hook is called when the user enters a string into the "Go to URL" dialog box. It is given the string entered, and the current URL (which may be `nil`). It should return a string, which is the URL that ELinks should follow, or `nil` to cancel the operation.
follow_url_hook (url)
  This hook is passed the URL that Links is about to follow. It should return a string (the URL modified or unmodified), or `nil` to stop ELinks following the URL
pre_format_html_hook (url, html)
  This hook gets called just before the final time an HTML document is formatted, i.e. it only gets called once, after the entire document is downloaded. It will be passed the URL and HTML text as strings, and should return the modified HTML text, or `nil` if there were no modifications.
lua_console_hook (string)

  This hook is passed the string that the user entered into the "Lua Console" dialog box. It should return two values: the type of action to take (`run`, `eval`, `goto-url` or `nil`), and a second argument, which is the shell command to run or the Lua expression to evaluate. Examples:

  - `return "run", "someprogram"` will attempt to run the program `someprogram`.
  - `return "eval", "somefunction(1+2)"` will attempt to call the Lua function `somefunction` with an argument, 3.
  - `return "goto-url", "http://www.bogus.com"` will ask Links to visit the URL "http://www.bogus.com".
  - `return nil` will do nothing.
quit_hook ()
  This hook is run just before ELinks quits. It is useful for cleaning up things, such as temporary files you have created.

### Functions

As well as providing hooks, ELinks provides some functions in addition to the standard Lua functions.

enable_systems_functions ()
  Enable some potentially dangerous functions, as well as some other functions which were unfortunate enough to be lumped in the same group.

The functions are: `openfile`, `closefile`, `readfrom`, `writeto`, `appendto`, `pipe_read`, `remove`, `rename`, `flush`, `seek`, `tmpname`, `read`, `write` `execute`, `exit`, `clock`, `date`, `getenv`, `setlocale`.

Note: `setlocale` is a standard Lua function and will not affect the current ELinks locale. @end deffn

current_url ()
  Returns the URL of the current page being shown (in the ELinks session that invoked the function).
current_link ()
  Returns the URL of the currently selected link, or `nil` if none is selected.
current_title ()
  Returns the title of the current page, or `nil` if none.
current_document ()
  Returns the current document as a string, unformatted.
current_document_formatted ([width])
  Returns the current document, formatted for the specified screen width. If the width is not specified, then the document is formatted for the current screen width (i.e. what you see on screen). Note that this function does not guarantee all lines will be shorter than `width`, just as some lines may be wider than the screen when viewing documents online.
pipe_read (command)
  Executes `command` and reads in all the data from stdout, until there is no more. This is a hack, because for some reason the standard Lua function `read` seems to crash ELinks when used in pipe-reading mode.
execute (string)
  Executes shell commands `string` and returns the exit code. Beware that you must not read or write to stdin and stdout. And unlike the standard Lua function of the same name, the return value is meaningless.
bind_key (keymap, keystroke, function)
  Currently, `keymap` must be the string `"main"`. Keystroke is a keystroke as you would write it in the ELinks config file `~/.elinks/elinks.conf`. The function `function` should take no arguments, and should return the same values as `lua_console_hook`.

### User protocol

There is one more little thing which Links-Lua adds, which will not be described in detail here. It is the fake "user:" protocol, which can be used when writing your own addons. It allows you to generate web pages containing links to "user://blahblah", which can be intercepted by the `follow_url_hook` (among other things) to perform unusual actions. For a concrete example, see the bookmark addon.

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