Add MD014 with tests.

lib/markdownlint.js

@@ -18,7 +18,7 @@ function lintFile(file, config, callback) {
       callback(err);
     } else {
       var tokens = md.parse(contents, {});
-      var lines = contents.split(/\r\n|\r|\n/g);
+      var lines = contents.split(/\r\n|\r|\n/);
       tokens.forEach(function forToken(token) {
         if (token.lines) {
           token.line = lines[token.lines[0]];

lib/rules.js

@@ -246,6 +246,25 @@ module.exports = [
     }
   },
 
+  {
+    "name": "MD014",
+    "desc": "Dollar signs used before commands without showing output",
+    "func": function MD014(params, errors) {
+      filterTokens(params.tokens, "code_block", "fence")
+        .forEach(function forToken(token) {
+          if (token.content && token.content
+            .split(/\r\n|\r|\n/)
+            .filter(function filterLine(line) {
+              return line;
+            }).every(function forLine(line) {
+              return /^\$\s/.test(line);
+            })) {
+            errors.push(token.lines[0] + 1);
+          }
+        });
+    }
+  },
+
   {
     "name": "MD028",
     "desc": "Blank line inside blockquote",

test/code_block_dollar.md

@@ -0,0 +1,33 @@
+The following code block shouldn't have $ before the commands:
+
+    $ ls {MD014}
+    $ less foo
+
+    $ cat bar
+
+However the following code block shows output, and $ can be used to
+distinguish between command and output:
+
+    $ ls
+    foo bar
+    $ less foo
+    Hello world
+
+    $ cat bar
+    baz
+
+The following code block uses variable names, and likewise shouldn't fire:
+
+    $foo = 'bar';
+    $baz = 'qux';
+
+The following code block doesn't have any dollar signs, and shouldn't fire:
+
+    ls foo
+    cat bar
+
+The following (fenced) code block doesn't have any content at all, and
+shouldn't fire:
+
+```
+```

test/markdownlint-test.js

@@ -31,7 +31,7 @@ function createTestForFile(file) {
     var expectedPromise = Q.nfcall(fs.readFile, file, { "encoding": "utf8" })
       .then(
         function fileContents(contents) {
-          var lines = contents.split(/\r\n|\r|\n/g);
+          var lines = contents.split(/\r\n|\r|\n/);
           var results = {};
           lines.forEach(function forLine(line, lineNum) {
             var regex = /\{(MD\d+)(?::(\d+))?\}/g;