3 files changed, 71 insertions, 1 deletions
diff --git a/README.md b/README.md
index e2474b3..711a25c 100644
--- a/README.md
+++ b/README.md
@@ -4,9 +4,30 @@ A dice expression parser and roller.
 
 ## Installation
 
+    # in a local node_modules/
     npm install --save dicebag
+    # globally, to use the CLI
+    npm install -g dicebag
 
-## Usage
+## Command-line usage
+
+    dicebag [-p] [<dice expression>]
+
+If a dice expression is provided, prints the result of rolling those dice and
+exits. Otherwise, reads expressions from `stdin` in a loop.
+
+* `-p` print dice pools (default behavior is to print the dice's sum)
+
+### Examples
+
+    $ dicebag 1d6
+    1
+    $ dicebag "2d8 + 1d4"
+    7
+    $ dicebag -p "2d8 + 1d4"
+    [ 5, 3, 4 ]
+
+## Library usage
 
     const { parse, pool, roll } = require('dicebag')
 
diff --git a/bin/dicebag.js b/bin/dicebag.js
new file mode 100755
index 0000000..f7b0921
--- /dev/null
+++ b/bin/dicebag.js
@@ -0,0 +1,46 @@
+#!/usr/bin/env node
+/* eslint no-console: 0 */
+
+const { parse, roll, pool } = require('../index.js')
+
+const parseArgs = () => {
+  const args = process.argv.slice(2)
+  const parsedArgs = {
+    roller: roll,
+    expression: null
+  }
+
+  while (args.length > 0) {
+    const arg = args.shift()
+    if (arg === '-p') {
+      parsedArgs.roller = pool
+    } else {
+      parsedArgs.expression = arg
+    }
+  }
+
+  return parsedArgs
+}
+
+const rollDie = (string, roller) => {
+  try {
+    const die = parse(string.trim())
+    console.log(roller(die))
+  } catch (error) {
+    console.log(error.message)
+  }
+}
+
+const runIoLoop = (roller) => {
+  process.stdin.setEncoding('utf8')
+  process.stdin.on('data', (string) => {
+    rollDie(string, roller)
+  })
+}
+
+const parsedArgs = parseArgs()
+if (parsedArgs.expression) {
+  rollDie(parsedArgs.expression, parsedArgs.roller)
+} else {
+  runIoLoop(parsedArgs.roller)
+}
diff --git a/package.json b/package.json
index 6179d97..1a41e81 100644
--- a/package.json
+++ b/package.json
@@ -8,6 +8,9 @@
     "test": "jest",
     "lint": "eslint ."
   },
+  "bin": {
+    "dicebag": "./bin/dicebag.js"
+  },
   "repository": {
     "type": "git",
     "url": "git+https://github.com/m-chrzan/dicebag.git"