# Module `awful.spawn`

Spawning of programs.

This module provides methods to start programs and supports startup notifications, which allows for callbacks and applying properties to the program after it has been launched. This requires currently that the applicaton supports them.

# Frequently asked questions

Rules of thumb when a shell is needed:

- A shell is required when the commands contain `&&`, `;`, `||`, `&` or any other unix shell language syntax
- When shell variables are defined as part of the command
- When the command is a shell alias

Note that a shell is not a terminal emulator. A terminal emulator is something like XTerm, Gnome-terminal or Konsole. A shell is something like `bash`, `zsh`, `busybox sh` or `Debian ash`.

If you wish to open a process in a terminal window, check that your terminal emulator supports the common -e option. If it does, then something like this should work:

    awful.spawn(terminal.." -e my_command")

Note that some terminals, such as rxvt-unicode (urxvt) support full commands using quotes, while other terminal emulators require to use quoting.

Understanding clients versus PID versus commands versus class:

A process has a PID (process identifier). It can have 0, 1 or many windows.

A command is what is used to start process(es). It has no direct relation with process, client or window. When a command is executed, it will usually start a process which keeps running until it exits. This however is not always the case as some applications use scripts as command and others use various single-instance mechanisms (usually client/server) and merge with an existing process.

A client corresponds to a window. It is owned by a process. It can have both a parent and one or many children. A client has a class, an instance, a role, and a type. See client.class, client.instance, client.role and client.type for more information about these properties.

Understanding blocking versus asynchronous execution:

Awesome is single threaded, it means only one thing is executed at any time. But Awesome isn't doomed to be slow. It may not have multiple threads, but it has something called coroutine and also has callbacks. This means things that take time to execute can still do so in the background (using C threads or external process + sockets). When they are done, they can notify the Awesome thread. This works perfectly and avoid blocking Awesome.

If you want to update the text of a wibox.widget.textbox with the output of a shell command, you should use the awful.spawn.easy_async_with_shell command. It is strongly recommanded not to use io.popen is explained in the "Getting a command's output" section. Asynchronous execution is at first a bit tricky to understand if you never used that before. The example below should demonstrate how it works.

If we do (but really, don't do that):

    -- **NEVER, EVER, DO THIS**: your computer will freeze
    os.execute("sleep 1; echo foo > /tmp/foo.txt")
    mylabel.text = io.popen("cat /tmp/foo.txt"):read("*all")

The label will display `foo`. But If we do:

    -- Don't do this, it wont work.
    -- Assumes /tmp/foo.txt does not exist
    awful.spawn.with_shell("sleep 1; echo foo > /tmp/foo.txt")
    mylabel.text = io.popen("cat /tmp/foo.txt"):read("*all")

Then the label will be empty. awful.spawn and awful.spawn.with_shell will not block and thus the io.popen will be executed before `sleep 1` finishes. This is why we have async functions to execute shell commands. There are many variants with difference characteristics and complexity. awful.spawn.easy_async is the most common as it is good enough for the general "I want to execute a command and do something with the output when it finishes".

    -- This is the correct way
    local command = "sleep 1; echo foo > /tmp/foo.txt"

    awful.spawn.easy_async_with_shell(command, function()
        awful.spawn.easy_async_with_shell("cat /tmp/foo.txt", function(out)
            mylabel.text = out
        end)
    end)

In this variant, Awesome will not block. Again, like other spawn, you cannot add code outside of the callback function to use the result of the command. The code will be executed before the command is finished so the result wont yet be available.

Getting a command's output:

First, do not use io.popen ever. It is synchronous. Synchronous functions block everything until they are done. All visual applications lock (as Awesome no longer responds), you will probably lose some keyboard and mouse events and will have higher latency when playing games. This is also true when reading files synchronously, but this is another topic.

Awesome provides a few ways to get output from commands. One is to use the `Gio` libraries directly. This is usually very complicated, but gives a lot of control on the command execution.

This modules provides with_line_callback and easy_async for convenience. First, lets add this bash command to rc.lua:

    local noisy = [[bash -c '
      for I in $(seq 1 5); do
        date
        echo err >&2
        sleep 2
      done
    ']]

It prints a bunch of junk on the standard output (stdout) and error (stderr) streams. This command would block Awesome for 10 seconds if it were executed synchronously, but will not block it at all using the asynchronous functions.

with_line_callback will execute the callbacks every time a new line is printed by the command:

    awful.spawn.with_line_callback(noisy, {
        stdout = function(line)
            naughty.notify { text = "LINE:"..line }
        end,
        stderr = function(line)
            naughty.notify { text = "ERR:"..line}
        end,
    })

If only the full output is needed, then easy_async is the right choice:

    awful.spawn.easy_async(noisy, function(stdout, stderr, reason, exit_code)
        naughty.notify { text = stdout }
    end)

Default applications:

If the intent is to open a file/document, then it is recommended to use the following standard command. The default application will be selected according to the Shared MIME-info Database specification. The `xdg-utils` package provided by most distributions includes the `xdg-open` command:

    awful.spawn({"xdg-open", "/path/to/file"})

Awesome does not manage, modify or otherwise influence the database for default applications. For information about how to do this, consult the ARCH Linux Wiki.

If you wish to change how the default applications behave, then consult the Desktop Entry specification.

# Spawning applications with specific properties

The startup notification protocol:

The startup notification protocol is an optional specification implemented by X11 applications to bridge the chain of knowledge between the moment a program is launched to the moment its window (client) is shown. It can be found on the FreeDesktop.org website.

Awesome has support for the various events that are part of the protocol, but the most useful is the identifier, usually identified by its `SNID` acronym in the documentation. It isn't usually necessary to even know it exists, as it is all done automatically. However, if more control is required, the identifier can be specified by an environment variable called `DESKTOP_STARTUP_ID`. For example, let us consider execution of the following command:

    DESKTOP_STARTUP_ID="something_TIME$(date '+%s')" my_command

This should (if the program correctly implements the protocol) result in `c.startup_id` to at least match `something`. This identifier can then be used in awful.rules to configure the client.

Awesome can automatically set the `DESKTOP_STARTUP_ID` variable. This is used by awful.spawn to specify additional rules for the startup. For example:

    awful.spawn("urxvt -e maxima -name CALCULATOR", {
        floating  = true,
        tag       = mouse.screen.selected_tag,
        placement = awful.placement.bottom_right,
    })

This can also be used from the command line:

    awesome-client 'awful=require("awful");
      awful.spawn("urxvt -e maxima -name CALCULATOR", {
        floating  = true,
        tag       = mouse.screen.selected_tag,
        placement = awful.placement.bottom_right,
      })'

This table contains the client properties that are valid when used the `sn_rules` or `prop` function argument. They are the same as in awful.rules.

Name | Description
--- | ---
placement | The client default placement on the screen
honor\_padding | When applying the placement, honor the screen padding
honor\_workarea | When applying the placement, honor the screen work area
tag | The client default tag
tags | The client default tags
new\_tag | Create a new tag for this client
switch\_to\_tags | Unselect the current tags and select this client tags
focus | Define if the client should grab focus by default
titlebars\_enabled | Should this client have a titlebar by default
callback | A function to call when this client is ready
marked | If a client is marked or not
is\_fixed | Return if a client has a fixed size or not
immobilized | Is the client immobilized horizontally?
immobilized | Is the client immobilized vertically?
floating | The client floating state
x | The x coordinates
y | The y coordinates
width | The width of the client
height | The height of the client
dockable | If the client is dockable
requests\_no\_titlebar | If the client requests not to be decorated with a titlebar
shape | Set the client shape
window | The X window id
name | The client title
skip\_taskbar | True if the client does not want to be in taskbar
type | The window type
class | The client class
instance | The client instance
pid | The client PID, if available
role | The window role, if available
machine | The machine client is running on
icon\_name | The client name when iconified
icon | The client icon as a surface
icon\_sizes | The available sizes of client icons
screen | Client screen
hidden | Define if the client must be hidden, i
minimized | Define it the client must be iconify, i
size\_hints\_honor | Honor size hints, e
border\_width | The client border width
border\_color | The client border color
urgent | The client urgent state
content | A cairo surface for the client window content
opacity | The client opacity
ontop | The client is on top of every other windows
above | The client is above normal windows
below | The client is below normal windows
fullscreen | The client is fullscreen or not
maximized | The client is maximized (horizontally and vertically) or not
maximized\_horizontal | The client is maximized horizontally or not
maximized\_vertical | The client is maximized vertically or not
transient\_for | The client the window is transient for
group\_window | Window identification unique to a group of windows
leader\_window | Identification unique to windows spawned by the same command
size\_hints | A table with size hints of the client
motif\_wm\_hints | The motif WM hints of the client
sticky | Set the client sticky, i
modal | Indicate if the client is modal
focusable | True if the client can receive the input focus
shape\_bounding | The client's bounding shape as set by awesome as a (native) cairo surface
shape\_clip | The client's clip shape as set by awesome as a (native) cairo surface
shape\_input | The client's input shape as set by awesome as a (native) cairo surface
client\_shape\_bounding | The client's bounding shape as set by the program as a (native) cairo surface
client\_shape\_clip | The client's clip shape as set by the program as a (native) cairo surface
startup\_id | The FreeDesktop StartId
valid | If the client that this object refers to is still managed by awesome
first\_tag | The first tag of the client

### Info:

- Copyright: 2008 Julien Danjou,2014 Emmanuel Lepage Vallee
- Author: Julien Danjou <julien@danjou.info>,Emmanuel Lepage Vallee <elv1313@gmail.com>

## Functions

spawn (cmd[, sn_rules=true[, callback]]) | Spawn a program, and optionally apply properties and/or run a callback.
with_shell (cmd) | Spawn a program using the shell.
with_line_callback (cmd, callbacks) | Spawn a program and asynchronously capture its output line by line.
easy_async (cmd, callback) | Asynchronously spawn a program and capture its output.
easy_async_with_shell (cmd, callback) | Call spawn.easy_async with a shell.
read_lines (input_stream, line_callback[, done_callback[, close=false]]) | Read lines from a Gio input stream
once (cmd, rules[, matcher[, unique_id[, callback]]]) | Spawn a command if it has not been spawned before.
single_instance (cmd, rules[, matcher[, unique_id[, callback]]]) | Spawn a command if an instance is not already running.
raise_or_spawn (cmd, rules[, matcher[, unique_id[, callback]]]) | Raise a client if it exists or spawn a new one then raise it.

## Functions

Methods

spawn (cmd[, sn_rules=true[, callback]])
  Spawn a program, and optionally apply properties and/or run a callback.

  Applying properties or running a callback requires the program/client to support startup notifications.

  See awful.rules.execute for more details about the format of `sn_rules`.

  - cmd string or table The command.
  - sn_rules table or boolean A table of properties to be applied after startup; `false` to disable startup notifications. (default true)
  - callback function A callback function to be run after startup. (optional)

  ### Returns:

  1. integer The forked PID.
  2. optional string The startup notification ID, if `sn` is not false, or a `callback` is provided.

  ### Or

  string Error message.
with_shell (cmd)
  Spawn a program using the shell. This calls `cmd` with `$SHELL -c` (via awful.util.shell).
  - cmd string The command.
with_line_callback (cmd, callbacks)
  Spawn a program and asynchronously capture its output line by line.
  - cmd string or table The command.
  - callbacks Table containing callbacks that should be invoked on various conditions.
    - stdout function Function that is called with each line of output on stdout, e.g. `stdout(line)`. (optional)
    - stderr function Function that is called with each line of output on stderr, e.g. `stderr(line)`. (optional)
    - output_done function Function to call when no more output is produced. (optional)
    - exit function Function to call when the spawned process exits. This function gets the exit reason and code as its arguments. The reason can be "exit" or "signal". For "exit", the second argument is the exit code. For "signal", the second argument is the signal causing process termination. (optional)

  ### Returns:

  Integer the PID of the forked process.

  ### Or

  string Error message.
easy_async (cmd, callback)
  Asynchronously spawn a program and capture its output. (wraps spawn.with_line_callback).
  - cmd string or table The command.
  - callback Function with the following arguments
    - stdout string Output on stdout.
    - stderr string Output on stderr.
    - exitreason string Exit reason ("exit" or "signal").
    - exitcode integer

      Exit code (exit code or signal number,

           depending on "exitreason").

  ### Returns:

  Integer the PID of the forked process.

  ### Or

  string Error message.

  ### See also:

  spawn.with_line_callback
easy_async_with_shell (cmd, callback)
  Call spawn.easy_async with a shell. This calls `cmd` with `$SHELL -c` (via awful.util.shell).
  - cmd string The command.
  - callback Function with the following arguments
    - stdout string Output on stdout.
    - stderr string Output on stderr.
    - exitreason string Exit reason ("exit" or "signal").
    - exitcode integer

      Exit code (exit code or signal number,

           depending on "exitreason").

  ### Returns:

  Integer the PID of the forked process.

  ### Or

  string Error message.

  ### See also:

  spawn.with_line_callback
read_lines (input_stream, line_callback[, done_callback[, close=false]])
  Read lines from a Gio input stream
  - input_stream Gio.InputStream The input stream to read from.
  - line_callback function Function that is called with each line read, e.g. `line_callback(line_from_stream)`.
  - done_callback function Function that is called when the operation finishes (e.g. due to end of file). (optional)
  - close boolean Should the stream be closed after end-of-file? (default false)
once (cmd, rules[, matcher[, unique_id[, callback]]])
  Spawn a command if it has not been spawned before.

  This function tries its best to preserve the state across `awesome.restart()`.

  By default, when no `unique_id` is specified, this function will generate one by hashing the command and its rules. If you have multiple instance of the same command and rules, you need to specify an UID or only the first one will be executed.

  The rules are standard awful.rules.

  This function depends on the startup notification protocol to be correctly implemented by the command. See client.startup_id for more information. Note that this also wont work with shell or terminal commands.

  - cmd string or table The command.
  - rules table The properties that need to be applied to the client.
  - matcher function A matching function to find the instance among running clients. (optional)
  - unique_id string A string to identify the client so it isn't executed multiple time. (optional)
  - callback function A callback function when the client is created. (optional)

  ### See also:

  awful.rules
single_instance (cmd, rules[, matcher[, unique_id[, callback]]])
  Spawn a command if an instance is not already running.

  This is like awful.spawn.once, but will spawn new instances if the previous has finished.

  The rules are standard awful.rules.

  This function depends on the startup notification protocol to be correctly implemented by the command. See client.startup_id for more information. Note that this also wont work with shell or terminal commands.

  Note that multiple instances can still be spawned if the command is called faster than the client has time to start.

  - cmd string or table The command.
  - rules table The properties that need to be applied to the client.
  - matcher function A matching function to find the instance among running clients. (optional)
  - unique_id string A string to identify the client so it isn't executed multiple time. (optional)
  - callback function A callback function when the client is created. (optional)

  ### See also:

  awful.rules
raise_or_spawn (cmd, rules[, matcher[, unique_id[, callback]]])
  Raise a client if it exists or spawn a new one then raise it.

  This function depends on the startup notification protocol to be correctly implemented by the command. See client.startup_id for more information. Note that this also wont work with shell or terminal commands.

  - cmd string or table The command.
  - rules table The properties that need to be applied to the client.
  - matcher function A matching function to find the instance among running clients. (optional)
  - unique_id string A string to identify the client so it isn't executed multiple time. (optional)
  - callback function A callback function when the client is created. (optional)

  ### Returns:

  client The client if it already exists.

  ### See also:

  awful.rules

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