cli: don't print result of --eval unless -p or --print is given

Fixes #572.

src/node.cc

@@ -111,6 +111,7 @@ static Persistent<String> uncaught_exception_symbol;
 static Persistent<String> emit_symbol;
 
 
+static int eval_print = 0;
 static char *eval_string = NULL;
 static int option_end_index = 0;
 static bool use_debug_agent = false;
@@ -2120,6 +2121,7 @@ Handle<Object> SetupProcessObject(int argc, char *argv[]) {
   // -e, --eval
   if (eval_string) {
     process->Set(String::NewSymbol("_eval"), String::New(eval_string));
+    process->Set(String::NewSymbol("_print"), Boolean::New(eval_print));
   }
 
   size_t size = 2*PATH_MAX;
@@ -2252,6 +2254,7 @@ static void PrintHelp() {
          "Options:\n"
          "  -v, --version        print node's version\n"
          "  -e, --eval script    evaluate script\n"
+         "  -p, --print          print result of --eval\n"
          "  --v8-options         print v8 command line options\n"
          "  --vars               print various compiled-in variables\n"
          "  --max-stack-size=val set max v8 stack size (bytes)\n"
@@ -2295,13 +2298,19 @@ static void ParseArgs(int argc, char **argv) {
     } else if (strcmp(arg, "--help") == 0 || strcmp(arg, "-h") == 0) {
       PrintHelp();
       exit(0);
-    } else if (strcmp(arg, "--eval") == 0 || strcmp(arg, "-e") == 0) {
+    } else if (strcmp(arg, "--eval") == 0 ||
+        strcmp(arg, "-e") == 0 ||
+        strcmp(arg, "-pe") == 0) {
       if (argc <= i + 1) {
         fprintf(stderr, "Error: --eval requires an argument\n");
         exit(1);
       }
+      eval_print |= ('p' == argv[i][1]); // node -pe 42 # prints 42
       argv[i] = const_cast<char*>("");
       eval_string = argv[++i];
+    } else if (strcmp(arg, "--print") == 0 || strcmp(arg, "-p") == 0) {
+      argv[i] = const_cast<char*>("");
+      eval_print = 1;
     } else if (strcmp(arg, "--v8-options") == 0) {
       argv[i] = const_cast<char*>("--help");
     } else if (argv[i][0] != '-') {

src/node.js

@@ -80,8 +80,11 @@
       var module = new Module('eval');
       module.filename = path.join(cwd, 'eval');
       module.paths = Module._nodeModulePaths(cwd);
+
       var rv = module._compile('return eval(process._eval)', 'eval');
-      console.log(rv);
+      if (process._print) {
+        console.log(rv);
+      }
 
     } else if (process.argv[1]) {
       // make process.argv[1] into a full path

test/simple/test-cli-eval.js

@@ -31,25 +31,41 @@ if (module.parent) {
 }
 
 // assert that the result of the final expression is written to stdout
-child.exec(nodejs + ' --eval "1337; 42"',
+child.exec(nodejs + ' --print --eval "1337; 42"',
     function(err, stdout, stderr) {
       assert.equal(parseInt(stdout), 42);
     });
 
 // assert that module loading works
-child.exec(nodejs + ' --eval "require(\'' + __filename + '\')"',
+child.exec(nodejs + ' --print --eval "require(\'' + __filename + '\')"',
     function(status, stdout, stderr) {
       assert.equal(status.code, 42);
     });
 
 // module path resolve bug, regression test
-child.exec(nodejs + ' --eval "require(\'./test/simple/test-cli-eval.js\')"',
+child.exec(nodejs + ' --print --eval "require(\'./test/simple/test-cli-eval.js\')"',
     function(status, stdout, stderr) {
       assert.equal(status.code, 42);
     });
 
 // empty program should do nothing
-child.exec(nodejs + ' -e ""', function(status, stdout, stderr) {
+child.exec(nodejs + ' -p -e ""', function(status, stdout, stderr) {
   assert.equal(stdout, 'undefined\n');
   assert.equal(stderr, '');
 });
+
+// this shouldn't print anything...
+'-e|--eval'.split('|').forEach(function(args) {
+  child.exec(nodejs + ' ' + args + ' 42', function(status, stdout, stderr) {
+    assert.equal(stdout, '');
+    assert.equal(stderr, '');
+  });
+});
+
+// ...while this should
+'-pe|-p -e|--print --eval'.split('|').forEach(function(args) {
+  child.exec(nodejs + ' ' + args + ' 42', function(status, stdout, stderr) {
+    assert.equal(stdout, '42\n');
+    assert.equal(stderr, '');
+  });
+});