bartender is a tool to manage the I/O needed to make your bar, such as lemonbar, work in an efficient fashion. Much like a real bartender it handles synchronous and asynchronous events, while seamlessly updating the data it manages.

Many standalone bars expect input from stdin and format it according to a simple set of rules. Updates are done by sending a new line with the changed data. When a user wants to include the output of both synchronous events, such as a clock updating every minute, and events that need to be received asynchronously, he/she is forced to write a shellscript to collect all necessary data, format it and pipe that to the bar. Most such solutions are very ad-hoc and often waste lots of resources. bartender addresses this problem by providing a simple way to push all the heavy lifting related to I/O on a single binary, so that the user can focus on implementing the logic he/she needs.

bartender reads a simple configuration file from ~/.bartenderrc or a custom path passed as a command line parameter, and spawns threads to perform the actions necessary (namely, either spawn a script each n seconds or read linewise from a FIFO in the filesystem). These two facilities allow for both synchronous (timers) and asynchronous (lines coming from a FIFO) input that gets passed to a simple formatting object and printed to stdout on updates.

Sure. Here is a ~/.bartenderrc, which is in TOML format and uses mustache templates for the output format:

# our format string
format = """
{{! our format string }}
{{{ clock }}}
 {{{ calendar }}}
 {{{ fifo_entry }}}
{{^ fifo_entry }} {{! a way of implementing default values in-template }}
some value
{{/ fifo_entry }}
 - and some static stuff
"""

[timers.clock]
# you can use `seconds`, `minutes`, `hours` or any combination therof to
# specify the timer interval
seconds = 5
command = "date +%H:%M:%S.%N" # run this command at each interval

[timers.calendar]
hours = 24
command = "date +%F"

[fifos.fifo_entry]
fifo_path = "~/tmp/entry_b_fifo"
default = "some default string" # another way of specifying defaults

Let's split it up and look how it functions. The config file has to define a mustache template in a string of name format. The variables are filled from the timers and FIFOs, as evident above.

Now, to actually run bartender, I have this snippet in my ~/.xinitrc:

  bartender | lemonbar -p -g 1366x20+0+0 > /dev/null &
  RUST_LOG=debug exec gabelstaplerwm 2> ~/wm_log > ~/tmp/tagset_fifo

Granted, this is a pretty minimal configuration, but it serves pretty well for demonstration purposes.