added elem

README.md

@@ -8,4 +8,5 @@ For POSIX shell compatible scripts, see the [sh-goodies](https://codeberg.org/lu
 
 * [YouStore](./ys): a way to securely store any set of files/directories inside a video
 * [1DLife](./1dlife): Jon Millen's 1D Game of Life in pure Bash
+* [Elem](./elem): Stephen Wolfram's elementary cellular automatons in pure Bash
 * [bmux](./bmux): a simple, dmux-like session manager in Bash on top of just dtach

elem

@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+# Elementary cellular automatons (rule X) in pure Bash (zero dependencies)
+# Usage: echo 'state' | elem rule# [iterations]
+# Created by Luxferre in 2026, released into public domain
+
+D2B=({0..1}{0..1}{0..1}{0..1}{0..1}{0..1}{0..1}{0..1})
+RULENO="$1"
+if ((RULENO > 255 || RULENO < 0)); then
+  echo "Invalid rule number!"
+  exit 1
+fi
+rule="${D2B[RULENO]}"
+
+ITERS="$2"
+if [[ -z "$ITERS" ]]; then # get the iteration count dynamically
+  shopt -s checkwinsize # enable checking the terminal size
+  :|: # trigger the WINCH signal to get the size
+  ITERS=$((LINES - 1)) # the row count is now in LINES
+fi
+[[ -z "$RENDER_CHAR" ]] && RENDER_CHAR='#'
+
+# read and process the state
+IFS= read -r state
+state="${state//[[:space:]]/0}"
+state="${state//[^0]/1}"
+slen=$((${#state} - 1)) # length + 4 (temporary padding) - 5
+
+for ((i=0; i<ITERS; ++i)); do
+  state="0${state}0" # pad the current state from both sides
+  newstate=''
+  for ((k=0; k<slen; ++k)); do
+    vidx=$((2#${state:k:3}))
+    newstate="${newstate}${rule:$vidx:1}"    
+  done
+  state="$newstate"
+  newstate="${newstate//0/ }"
+  printf '%s\n' "${newstate//1/$RENDER_CHAR}"
+done