diff --git a/pipreqs/pipreqs.py b/pipreqs/pipreqs.py
index d21b071..c0f9c55 100755
--- a/pipreqs/pipreqs.py
+++ b/pipreqs/pipreqs.py
@@ -33,6 +33,7 @@ Options:
                           that are not imported in project.
 """
 from __future__ import print_function, absolute_import
+from contextlib import contextmanager
 import os
 import sys
 import re
@@ -61,6 +62,37 @@ else:
     py2_exclude = ["concurrent", "concurrent.futures"]
 
 
+@contextmanager
+def _open(filename=None, mode='r'):
+    """Open a file or ``sys.stdout`` depending on the provided filename.
+
+    Args:
+        filename (str): The path to the file that should be opened. If
+            ``None`` or ``'-'``, ``sys.stdout`` or ``sys.stdin`` is
+            returned depending on the desired mode. Defaults to ``None``.
+        mode (str): The mode that should be used to open the file.
+
+    Yields:
+        A file handle.
+
+    """
+    if not filename or filename == '-':
+        if not mode or 'r' in mode:
+            file = sys.stdin
+        elif 'w' in mode:
+            file = sys.stdout
+        else:
+            raise ValueError('Invalid mode for file: {}'.format(mode))
+    else:
+        file = open(filename, mode)
+
+    try:
+        yield file
+    finally:
+        if file not in (sys.stdin, sys.stdout):
+            file.close()
+
+
 def get_all_imports(
         path, encoding=None, extra_ignore_dirs=None, follow_links=True):
     imports = set()
@@ -128,7 +160,7 @@ def filter_line(l):
 
 
 def generate_requirements_file(path, imports):
-    with open(path, "w") as out_file:
+    with _open(path, "w") as out_file:
         logging.debug('Writing {num} requirements: {imports} to {file}'.format(
             num=len(imports),
             file=path,
@@ -141,14 +173,7 @@ def generate_requirements_file(path, imports):
 
 
 def output_requirements(imports):
-    logging.debug('Writing {num} requirements: {imports} to stdout'.format(
-        num=len(imports),
-        imports=", ".join([x['name'] for x in imports])
-    ))
-    fmt = '{name}=={version}'
-    print('\n'.join(
-        fmt.format(**item) if item['version'] else '{name}'.format(**item)
-        for item in imports))
+    generate_requirements_file('-', imports)
 
 
 def get_imports_info(