diff --git a/cli.js b/cli.js
index b75c955d..4d96f3aa 100755
--- a/cli.js
+++ b/cli.js
@@ -4,29 +4,155 @@
 /* eslint no-console:0 */
 
 const katex = require("./");
-let input = "";
+const fs = require("fs");
 
-// Skip the first two args, which are just "node" and "cli.js"
-const args = process.argv.slice(2);
+const options = require("nomnom")
+    .option("displayMode", {
+        full: "display-mode",
+        abbr: "d",
+        flag: true,
+        default: false,
+        help: "If true the math will be rendered in display " +
+              "mode, which will put the math in display style " +
+              "(so \\int and \\sum are large, for example), and " +
+              "will center the math on the page on its own line.",
+    })
+    .option("throwOnError", {
+        full: "no-throw-on-error",
+        abbr: "t",
+        flag: true,
+        default: true,
+        transform: function(t) {
+            return !t;
+        },
+        help: "If true, KaTeX will throw a ParseError when it " +
+              "encounters an unsupported command. If false, KaTeX " +
+              "will render the unsupported command as text in the " +
+              "color given by errorColor.",
+    })
+    .option("errorColor", {
+        full: "error-color",
+        abbr: "c",
+        metavar: "color",
+        default: "#cc0000",
+        transform: function(color) {
+            return "#" + color;
+        },
+        help: "A color string given in the format 'rgb' or 'rrggbb'. " +
+              "This option determines the color which unsupported " +
+              "commands are rendered in.",
+    })
+    .option("colorIsTextColor", {
+        full: "color-is-text-color",
+        abbr: "b",
+        flag: true,
+        default: false,
+        help: "Restores the old behavior of (pre-0.8.0) KaTeX.",
+    })
+    .option("maxSize", {
+        full: "max-size",
+        abbr: "s",
+        metavar: "size",
+        default: 0,
+        help: "If non-zero, all user-specified sizes, e.g. in " +
+              "\\rule{500em}{500em}, will be capped to maxSize ems. " +
+              "Otherwise, elements and spaces can be arbitrarily large",
+    })
+    .option("macros", {
+        full: "macro",
+        abbr: "m",
+        metavar: "macro:expansion",
+        list: true,
+        default: [],
+        help: "A custom macro. Each macro is a property with a name " +
+              "like \\name which maps to a string that " +
+              "describes the expansion of the macro.",
+    })
+    .option("macroFile", {
+        full: "macro-file",
+        abbr: "f",
+        metavar: "path",
+        default: null,
+        help: "Read macro definitions from the given file.",
+    })
+    .option("inputFile", {
+        full: "input",
+        abbr: "i",
+        metavar: "path",
+        default: null,
+        help: "Read LaTeX input from the given file.",
+    })
+    .option("outputFile", {
+        full: "output",
+        abbr: "o",
+        metavar: "path",
+        default: null,
+        help: "Write html output to the given file.",
+    })
+    .parse();
 
-if (args.indexOf("--help") !== -1) {
-    console.log(process.argv[0] + " " + process.argv[1] +
-                " [ --help ]" +
-                " [ --display-mode ]");
 
-    console.log("\n" +
-                "Options:");
-    console.log("  --help            Display this help message");
-    console.log("  --display-mode    Render in display mode (not inline mode)");
-    process.exit();
+function readMacros() {
+    if (options.macroFile) {
+        fs.readFile(options.macroFile, "utf-8", function(err, data) {
+            if (err) {throw err;}
+            splitMacros(data.toString().split('\n'));
+        });
+    } else {
+        splitMacros([]);
+    }
 }
 
-process.stdin.on("data", function(chunk) {
-    input += chunk.toString();
-});
+function splitMacros(macroStrings) {
+    // Override macros from macro file (if any)
+    // with macros from command line (if any)
+    macroStrings = macroStrings.concat(options.macros);
 
-process.stdin.on("end", function() {
-    const options = { displayMode: args.indexOf("--display-mode") !== -1 };
-    const output = katex.renderToString(input, options);
-    console.log(output);
-});
+    const macros = {};
+
+    for (const m of macroStrings) {
+        const i = m.search(":");
+        if (i !== -1) {
+            macros[m.substring(0, i).trim()] = m.substring(i + 1).trim();
+        }
+    }
+
+    options.macros = macros;
+    readInput();
+}
+
+function readInput() {
+    let input = "";
+
+    if (options.inputFile) {
+        fs.readFile(options.inputFile, "utf-8", function(err, data) {
+            if (err) {throw err;}
+            input = data.toString();
+            writeOutput(input);
+        });
+    } else {
+        process.stdin.on("data", function(chunk) {
+            input += chunk.toString();
+        });
+
+        process.stdin.on("end", function() {
+            writeOutput(input);
+        });
+    }
+}
+
+function writeOutput(input) {
+    const output = katex.renderToString(input, options) + "\n";
+
+    if (options.outputFile) {
+        fs.writeFile(options.outputFile, output, function(err) {
+            if (err) {
+                return console.log(err);
+            }
+        });
+    } else {
+        console.log(output);
+    }
+}
+
+readMacros();