Prevent require-ing bin/shjs (#848)

* Prevent require-ing bin/shjs

* Move require guard up, and improve function name

* Move require up and clarify comment

bin/shjs

@@ -1,12 +1,23 @@
 #!/usr/bin/env node
+
+if (require.main !== module) {
+  throw new Error('Executable-only module should not be required');
+}
+
+// we must import global ShellJS methods after the require.main check to prevent the global
+// namespace from being polluted if the error is caught
 require('../global');
 
-if (process.argv.length < 3) {
-  console.log('ShellJS: missing argument (script name)');
+function exitWithErrorMessage(msg) {
+  console.log(msg);
   console.log();
   process.exit(1);
 }
 
+if (process.argv.length < 3) {
+  exitWithErrorMessage('ShellJS: missing argument (script name)');
+}
+
 var args,
   scriptName = process.argv[2];
 env['NODE_PATH'] = __dirname + '/../..';
@@ -19,9 +30,7 @@ if (!scriptName.match(/\.js/) && !scriptName.match(/\.coffee/)) {
 }
 
 if (!test('-f', scriptName)) {
-  console.log('ShellJS: script not found ('+scriptName+')');
-  console.log();
-  process.exit(1);
+  exitWithErrorMessage('ShellJS: script not found ('+scriptName+')');
 }
 
 args = process.argv.slice(3);

test/shjs.js

@@ -4,9 +4,10 @@ import test from 'ava';
 
 import shell from '..';
 
+const binPath = path.resolve(__dirname, '../bin/shjs');
+
 function runWithShjs(name) {
   // prefix with 'node ' for Windows, don't prefix for unix
-  const binPath = path.resolve(__dirname, '../bin/shjs');
   const execPath = process.platform === 'win32'
     ? `${JSON.stringify(shell.config.execPath)} `
     : '';
@@ -52,3 +53,11 @@ test('Extension detection', t => {
   t.is(result.stdout, 'OK!\n');
   t.falsy(result.stderr);
 });
+
+//
+// Invalids
+//
+
+test('disallow require-ing', t => {
+  t.throws(() => require(binPath), 'Executable-only module should not be required');
+});