rlauncher: a dmenu_run replacement focused on startup time

Unlike dmenu, which is a mulipurpuse menu utility, rlauncher is an all-in-one program launcher, with a focus on performance and minimising startup time.

Due to differences in command lookup logic, rlauncher is only designed to work on unix-like systems.

Building

rlauncher can be built with nix flakes or directly with cargo.

nix (strongly reccomended for NixOS users): nix build git+https://codeberg.org/binarycat/rlauncher

cargo: cargo install rlauncher

Invocation

rlauncher accepts the following command-line flags:

• -w/--wrapper <WRAPPER_PROGRAM>: specifies a command to use when launching programs.

When a program is launched, rlauncher runs sh -c with the argument ${WRAPPER_PROGRAM} '${selected_program}' & disown.

rlauncher does not accept positional arguments.

Usage

While the rlauncher window is open, there are a few keys that have behviors beyond just text editing:

• Enter: run the selected command (you can also double-click it)
• Escape: close the window (this will suspend rlauncher)
• F5: reload the list of programs in the background (useful if you have installed/uninstalled something, but note this is automatically done whenever a new window is opened)

Optimizations

There are two main strategies employed by rlauncher to minimize its startup time.

Suspend/Resume

The most significant optimization it employs is, rather that exiting after launching a program, it instead hides its window and suspends itself with SIGSTOP. Further invokations of rlauncher will wake the existing instance with SIGCONT instead of creating their own window. This behavior has the nice side effect of making rlaucher mostly idempotent, preventing you from launching multiple instances of it.

rlauncher uses a pidfile to coordinate this behavior. The pidfile's location can be exactly set using the $RLAUNCHER_PIDFILE environment variable.

If $RLAUNCHER_PIDFILE is not set, the path follows the form:

${dir}/rlauncher-${display}.pidfile

${dir} is the first environment variable set in:

• XDG_RUNTIME_DIR
• TEMPDIR
• TEMP
• TMP

or /tmp, if none are set.

${display} is the first environment variable set in:

• WAYLAND_DISPLAY
• DISPLAY

For this reason, when using rlauncher in a multi-user environment, you should make sure one of the following is true:

• RLAUNCHER_PIDFILE is set appropriately in .xinitrc or your compositor config.
• XDG_RUNTIME_DIR is properly set.
• you use a per-user tempdir.

Lazy $PATH reading

$PATH is iterated through in a background thread. This significantly decreases startup latency if you have a complex $PATH or a slow filesystem.