The LaTeX Input Method

As someone who has frequent online conversations about math, I often find myself needing to use mathematical or technical symbols like the right arrow (→), the set intersection symbol (∩), and various Greek letters (π, Σ, ϵ, δ, Δ). In an online discussion, frequently the best way to use these symbols is as Unicode characters¹. Inserting these characters from a standard American English keyboard is nontrivial; on Linux, some symbols (like arrows, ≠, super- and subscript numerals, °, and accented characters like ô) can be inserted using the Compose key; a key is pre-designated as the Compose key, and then pressing the Compose key followed by two or three characters that roughly represent the desired character will insert that character. Compose oo yields °, Compose o^ yields ô, Compose -> yields →, Compose >= yields ≥, and so on. But there is no Compose key support for Greek letters or many math symbols; the Compose key, in fact, was developed more for inserting accented letters than specialized symbols. And many Linux users do not have a Compose key configured.

On my computer, pressing Super+Tab opens a menu into which one can type the \(\LaTeX\) code for a symbol (and other things, which will be explained later). The menu gives completions, which one can accept by pressing Enter. Pressing Shift+Enter accepts the input as entered. The program then looks up the code in a dictionary and uses XDoTool to insert that symbol into whichever dialog is currently focused. XDoTool can sometimes be flaky², so a facility is provided to insert the previously-selected character again quickly by pressing Super+Tab and then Enter (or entering !last at the prompt).

This program is written in ZSH, and stores the code-character mapping in a ZSH associative array. A Julia program pulls Julia's code-character mappings and outputs them as a shell script that adds each into that associative array. User-defined symbols can be added to the array in the first few lines of the source code file. I've also defined ways of entering some emoji, box-drawing characters, and commonly-used blackboard bold characters; these are shown in the tables below. Entering Uxxxxxxxx or Uxxxx at the prompt inserts the Unicode character with hex code U+xxxxxxxx or U+xxxx, respectively. Pressing Super+Shift+Tab invokes the \(\LaTeX\) input method but copies the selected character to the clipboard instead of inserting it using XDoTool—handy for when XDoTool is misbehaving.

The program uses dmenu to get user input and present a list of possible completions to the user, XDoTool to insert characters, and xclip to copy characters. I have the i3 window manager configured to run dmenu_latexinput.zsh whenever Super+Tab is pressed and dmenu_latexinput.zsh -c whenever Super+Shift+Tab is pressed. The -c command line option copies the selected character to the clipboard instead of inserting it, -p does the same but to the X11 PRIMARY selection, and -r outputs the selected character to stdout.