Configure a light-weight status bar for XMonad: Xmobar

The status bar Xmobar works out of the box on the top edge of your screen and shows useful system info. However, if you want to make it look nice and change what information to show, you can customize it with a tiny bit of Haskell.

You can customize Xmobar by creating a file named .xmobarrc in your home folder with

gedit ~/.xmobarrc

and copy-paste the following example content

Config
{ bgColor =      "white"
, fgColor =      "black"
, border =       BottomB
, borderColor = "black"
, commands = -- what information to show
  -- network activity monitor (dynamic interface resolution)
  [ Run DynNetwork [] 10 -- network traffic
  , Run Memory ["-t" ,"RAM: <usedratio>%"] 10 -- RAM usage
  , Run Battery [] 10 -- battery time
  , Run Volume "default" "Master" [] 10
  , Run Date "%d %b %T" "mydate" 10
  , Run StdinReader -- text coming from xmonad
  ]
-- where to show command information
, template = "%StdinReader% }{ %memory% | %default:Master% | %dynnetwork% | %battery% | %mydate% |"
}

which you should modify to your liking. It uses a single Haskell (record) datastructure called Config where each field/option like bfColor or border is optional: If you don’t set a field, a default field value is used.
[How to create a Haskell datastructure?]

xmobar <path to xmobar.hs>

xmobar ~/.xmobarrc

The options that you surely want to tweak but may be difficult to understand are commands and template:
First, you define what information to show within commands. It’s a list of small apps (called “commands” or System Monitor Plugins) which run with a certain frequency to retrieve and summarize (system) information into a small piece of text. Each command defines a “template identifier” or “alias” like %mydate% or %memory%. Some commands define them automatically but for others you have to define them manually. For example, the Memory command defines the identifier %memory% automatically, while the Date command forces you to define an identifier like %mydate% yourself.
[How to write commands?]
[How to write lists in Haskell?]

Second, you define where to show the information of a command along the Xmobar statusbar with the template string. This is a string like

"%StdinReader% }{ %memory% | %default:Master% | %dynnetwork% | %battery% | %mydate% |"

which is printed literally into the statusbar after the “template identifiers” (like %mydate%) have been replaced by the piece of text from the corresponding command in commands. For example, the XMonad status text from the StdinReader command, which corresponds to %StdinReader%, will be printed on the left of the statusbar while the text from the Date command, which corresponds to %mydate%, will be printed on the far right.

Note that you can display a piece of text with color by wrapping it with “font color” HTML tags like

text <fc=#FF0000>red text</fc> other text

where the color is given in RGB hex notation.

Also note that the }{ symbol in template will separate everything on its left as far away as possible from everything on its right. If you like, you can configure/change this symbol (and the % symbol within the “template identifiers”) with:

Config
{ -- ...
, sepChar =  "%"   -- symbol to recognize template identfiers/aliases
, alignSep = "}{"  -- symbol to separate between left-center-right alignment
-- ...
}

How to write commands

Every command roughly follow this pattern:

Run <command name> [<options>] <refreshrate>

• A command is named after its use, e.g. Wireless or Volume.
• Every command has an “id”, “template identifier” or “alias” that is used in the template string to define where on in the bar the command’s output should be shown.
• Every command has a list of options. If you leave the list empty, some default options are used. Possibly the most important option is "-t" (for “template”) to further tweak what and how information is actually shown. Take a look at the documentation of a command to find out what options are available.
  [How to write lists in Haskell?]
• Every command has a refreshrate, which defines how frequently the command’s app is run. The unit for the refreshrate is a 10th of a second so that the default recommended refreshrate value of 10 updates your command every 1 second (divide the refreshrate value by 10 to get the number of seconds).

Run Date "<date formating>" "<template identifier>" <refreshrate>

Run Date "%d %b %T" "mydate" 10

11 Oct 14:20:34

template = ".... %mydate% .... "

Run Wireless "<wifi device name>" [<options>] <refreshrate>

Run Wireless "wlp3s0" ["-t", "Wifi: [<qualitybar>] <essid>"] 10

lo        no wireless extensions.

wlp3s0    IEEE 802.11  ESSID:"TP-LINK"... <-- contains your wifi device name

enp2s0    no wireless extensions.

Wifi: [####::::::] TP-LINK

template = ".... %wlp3s0wi% .... "

Run Volume "<soundcard" "<channel>" [<options>] <refreshrate>

Run Volume "default" "Master" ["-t", "Vol: [<volumebar>] <status>"] 10

Vol: [####::::::] [on]

template = ".... %default:Master% .... "

Run Com ".xmonad/get-volume.sh" [] "myvolume" 10

template = ".... %myvolume% .... "

Run Brightness [<options>] <refreshrate>

Run Brightness ["-t", "Brightness: [<bar>]"] 10

Brightness: [####::::::]

template = ".... %bright% .... "

/sys/class/backlight/

Run Brightness ["-t", "Screen: [<bar>]", "--", "-D", "intel_backlight"] 10

Run Brightness ["-t", "Screen: [<bar>]", "--", "-D", "amdgpu_bl0"] 10

cd /sys/class/backlight/ && ls

Run Com "<terminal app/script>" [<app arguments>] <template identifier> <refreshrate>

Run Com "whoami" [] "myuser" 0

Run Com "uname" ["-r"] "mykernel" 0

template = ".... %myuser% .... %mykernel% ..."