1272: bash script; simple gcd example (#2421)

docs/lang-bash.md

@@ -1,3 +1,42 @@
 # Using WebAssembly from Bash
 
-... more coming soon
+## Getting started and simple example
+
+First up you'll want to start a new module:
+
+```text
+$ mkdir -p gcd-bash
+$ cd gcd-bash
+$ touch gcd.wat gcd.sh
+```
+
+Next, copy this example WebAssembly text module into your project. It exports a function for calculating the greatest common denominator of two numbers.
+
+## `gcd.wat`
+
+```wat
+{{#include ../examples/gcd.wat}}
+```
+
+Create a bash script that will invoke GCD three times.
+
+## `gcd.sh`
+
+```bash
+#!/bin/bash
+
+function gcd() {
+  # Cast to number; default = 0
+  local x=$(($1))
+  local y=$(($2))
+  # Invoke GCD from module; suppress stderr
+  local result=$(wasmtime examples/gcd.wat --invoke gcd $x $y 2>/dev/null)
+  echo "$result"
+}
+
+# main
+for num in "27 6" "6 27" "42 12"; do
+  set -- $num
+  echo "gcd($1, $2) = $(gcd "$1" "$2")"
+done
+```