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sector-f
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Description

Executes multiple programs concurrently to generate output for bars

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Admiral

Executes multiple programs concurrently to generate output for bars

Table of Contents

Introduction

If you just want to get Admiral running, skip to the next section.

Programs like lemonbar and i3bar have become popular in recent years, and with good reason. For those of you who are unfamiliar with them, these programs read from standard input and then output what they receive on a bar. For the most part, their output is identical to their input, but they accept some format strings which allow the user to specify things like colors, justification, and clickable areas.

The advantage of this system is that it is very powerful. The disadvantage is that it can be rather difficult to configure.

A typical bar script looks something like this: a shell script, probably bash, is used to collect and format the output of various commands. This is done in an infinite loop, probably ending with

sleep 0.1
or something similar. The output of this script is then piped into the bar program, which receives a new line (which may be identical to its previous line) ten times per second.

The main problem with this method is that it's rather difficult to handle timing correctly. A counter showing the number of outdated programs on the system can be updated less frequently than a clock.

Actually, a previous bar script I had contained both of the aforementioned items. One day, I noticed the clock on my bar had stopped working. The cause? The internet had died. This prevented the package counter command (

checkupdates | wc -l
) from ever finishing, which caused the entire bar to stop working.

Another major problem is that shell scripts of these types are bug-prone and tend to become very bloated. Admiral has a declarative style which allows you to configure your bar with ease and avoid pesky bugs.

What Admiral Does

Admiral runs programs specified by the user and prints their output. It allows for a clear separation of different sections, which simplifies configuration.

The best part? Each program is run in its own thread. This means that each section is updated independently of the other sections. It also means that if something fails, it fails independently of the other sections. That example where the clock stopped? This would never happen with Admiral. Sure,

checkupdates
would still hang indefinitely and prevent that number from changing. But the clock (and the rest of the bar) would be unaffected.

Admiral also limits its output. Whenever one of its programs updates, it checks to see if anything has actually changed since it last printed a message. If nothing has changed, Admiral prints nothing—this limits the amount of refreshing that your bar program has to do.

Getting Started

Prerequisites

  • rustc
    — the Rust compiler
  • cargo
    — the Rust package manager
  • git
    (optional but recommended)

These can probably be installed via your distribution's package manager. If the Rust compiler and Cargo are not packaged for your distro, you can download them here.

Installation

  1. Clone this repository with
    git clone https://github.com/sector-f/admiral.git
    • Alternatively, a .zip file of the master branch can be downloaded here
  2. cd
    into the newly-created
    admiral/
    directory
  3. Run
    cargo build --release

This will create an

admiral
excutable in the
./target/release/
directory. You may want to copy this to somewhere in your
$PATH
, like
/usr/local/bin/
or
~/.local/bin/

You may then copy the provided

admiral.d/
directory to
~/.config/
(or your
$XDG_CONFIG_HOME
directory, if you have that environment variable set).

Configuration

Configuration is done with an

admiral.toml
file. This file is looked for in
~/.config/admiral.d/
(Or
$XDG_CONFIG_HOME/admiral.d/
, if that environment variable is set). Alternatively, a configuration file may be specified with the
-c
flag, e.g.
admiral -c /path/to/file.toml
.

An example

admiral.d/
(complete with the
admiral.toml
) is included in this repository.

[admiral]

[admiral]
is the section where Admiral's output is configured. It has one required entry:
items
. Here is an example
[admiral]
section:
[admiral]
items = ["music", "workspaces", "clock"]

Each entry in the

items
table specifies a section of the config file that will be run. Note that the order specified here is the order that Admiral will use for the scripts' output.

Sections of the admiral.toml

Each section of the

admiral.toml
contains a command that produces some output; you can use shell scripts, python scripts, executable binaries, etc.

Here is an example script section:

[clock]
path = "date '+%I:%M %p'"
reload = 1

path

path
is the only required entry for a script. The specified command is executed by a shell running in the same directory as the
admiral.toml
. So,
path = "./mpd.sh"
will run the
mpd.sh
in the same directory as the
admiral.toml
, and
path = "echo 'Hello, world!'"
will output "Hello, world!" using your shell. Note that the shell is determined via the
$SHELL
environment variable.

shell

shell
is an optional variable that specifies an alternate shell to execute commands with. The default shell is your
$SHELL
environment variable. Using an alternate shell may be useful if you wish to leverage features of a specific shell for a certain command. An example use is
shell = "/usr/bin/fish"
.

reload

The

reload
value is the optional duration in seconds between each execution of the script. It may be either an integer such as
10
or a float such as
0.5
.

If no

reload
value is specified, and
static
is not set to
true
, this indicates that the script should never exit. It will be run, and each line it outputs will be used separately. This is for commands such as
xtitle -s
, which handle polling themselves and output new information on a new line. If the process is killed, it will automatically be restarted.

static

static
is an optional boolean variable. It is set to false by default. It is for scripts that only need to be run once. Here is an example:
[center]
path = "echo '%{c}'"
static = true

This script is used to add a format sequence for

lemonbar
. It only needs to be run once, and its output will never change.

Newlines

Bars expect newline characters to be used only at the end of each full line of input; Admiral tries to respect this by trimming newline characters from the output of scripts. Users should be aware of how this is handled:

  • Both

    \r
    and
    \n
    characters are removed from the start and end of a script's output
  • If no

    reload
    value is specified and
    static
    is false, Admiral uses each line produced by the script. This means that each line meant to be displayed must end in either
    \n
    or
    \r\n
    . However, these characters will still be stripped from Admiral's output so as to keep its complete output on a single line.

Example

An example

admiral.d/
directory is included with admiral. The example is designed for use with bspwm, and also relies on xtitle to get the window title. Its output is designed to be piped to
lemonbar
. The command
admiral | lemonbar -g x30 | sh
should work for a demonstration, although a greater number of clickable areas may need to be specified with
lemonbar -a
if you have more than 8 desktops.

The example bar has three sections: BSPWM workspace information, the current window title, and the current time. The workspace section uses the letters

f
,
o
, and
u
to represent free (empty), occupied, and urgent desktops, respectively. Lowercase letters represent unfocused desktops, and an uppercase letter represents the focused desktop.

This workspace section is clickable. Left-clicking on a letter will switch to the corresponding desktop. Scrolling up with the mouse wheel while the cursor is over the workspace section will switch to the previous desktop, and scrolling down with the mouse wheel will switch to the next desktop.

This directory contains two files: an

admiral.toml
file and
bspwm_workspaces.sh
. Let's look at the example
admiral.toml
:

[admiral]

This is the provided

[admiral]
section:
[admiral]
items = ["left", "workspaces",
         "center", "title",
         "right", "clock"]

Six scripts are listed. Three are used to provide information, and the other three are used for formatting the output.

Scripts

These are the first three scripts listed in the example

admiral.toml
file:
[workspaces]
path = "./bspwm_workspaces.sh"

[title] path = "xtitle -s -t 100"

[clock] path = "date '+%-I:%M %p '" reload = 1

bspwm_workspaces.sh
is a Bash script that parses the output of
bspc subscribe report
and converts it into a clickable, human-readable format for
lemonbar
. Because
bspc subscribe report
(and therefore
bspwm_workspaces.sh
) never exits, no reload value is specified.

Formatting

These are the last three scripts:

[left]
path = "echo '%{l}'"
static = true

[center] path = "echo '%{c}'" static = true

[right] path = "echo '%{r}'" static = true

These output format strings to be interpreted by

lemonbar
. As their output only needs to be captured once,
static
is set to
true
. Remember that
admiral
removes trailing newline characters; this means that using
echo
rather than
echo -n
will still work here.

Keeping the format strings outside of the main scripts allows for quicker, easier formatting.

Bugs

  • Specifying a toml file in the current directory as
    admiral -c admiral.toml
    causes scripts with relative paths to fail.
    • Workaround: Give the "directory name" as well, i.e.
      admiral -c ./admiral.toml

Any bugs that are found should be reported here.

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