diff --git a/main.py b/main.py
index ee2d828..4b10af8 100644
--- a/main.py
+++ b/main.py
@@ -2,7 +2,12 @@
 
 import yaml
 import pypandoc
+import os
 import re
+import sys
+
+root = ""
+lang = "de"
 
 # Compiles a presentation in the given language from the given directory and
 # stores it in a corresponding slides.lang.html file inside the same directory.
@@ -11,14 +16,14 @@ def compile(directory, language='en'):
     root = directory
     global lang
     lang = language
-    wrapper = open(root + 'layouts/root.html', 'r').read()
+    wrapper = open(os.path.join(root, 'layouts/root.html'), 'r').read()
     wrapper = wrapper.replace('@slides', compile_chapters())
     wrapper = insert_metadata(wrapper, lang=lang)
-    with open(root + 'slides.' + lang + '.html', 'w+') as output:
+    with open(os.path.join(root, 'slides.' + lang + '.html'), 'w+') as output:
         output.write(wrapper)
     print('done')
 
-# Replaces the placeholders in the given content with corresponding values in 
+# Replaces the placeholders in the given content with corresponding values in
 # the given language from the meta.yml and returns the filled content.
 def insert_metadata(content, lang=None):
     metadata = read_yaml('meta.yml')
@@ -42,10 +47,11 @@ def compile_chapters():
 # Compiles a presentation's chapter (given its name) by splitting it into
 # slides, compiling those, and returning them as a string of <article>s.
 def compile_chapter(chapter):
+    global root
     if type(chapter) != str:
         raise Exception('Chapters with attributes are not supported yet.\n' +
                 str(chapter))
-    chapter_file = open(root + 'slides/' + chapter + '.' + lang + '.md', 'r')
+    chapter_file = open(os.path.join(root, 'slides/' + chapter + '.' + lang + '.md'), 'r')
     delimiter = '\n@slide'
     chapter_input = ('\n' + chapter_file.read()).split(delimiter)
     slides = [delimiter + slide for slide in chapter_input][1:]
@@ -73,7 +79,7 @@ def compile_slide(slide):
     return slide
 
 # Parses the metadata passage of a given slide and returns the metadata as a
-# dictionary. For some items, default values are used if the slide does not 
+# dictionary. For some items, default values are used if the slide does not
 # contain them.
 def get_slide_metadata(slide):
     metadata = { 'layout': 'default' }
@@ -96,8 +102,9 @@ def get_slide_data(slide):
 # Reads the layout file for a given layout name and returns its content as a
 # string.
 def get_slide_layout(layout_name):
+    global root
     try:
-        return open(root + 'layouts/' + layout_name + '.html', 'r').read()
+        return open(os.path.join(root, 'layouts/' + layout_name + '.html'), 'r').read()
     except FileNotFoundError:
         raise Exception('Layout ' + layout_name + ' not found!')
 
@@ -106,16 +113,25 @@ def get_slide_layout(layout_name):
 def convert_slide_content(content):
     return pypandoc.convert_text(content, 'html', format='md')
 
-# Calls a YAML parser for the given relativ path inside the presentation root
+# Calls a YAML parser for the given relative path inside the presentation root
 # directory. Returns a dictionary with the YAML content.
 def read_yaml(path):
-    with open(root + path, 'r') as stream:
+    global root
+    with open(os.path.join(root, path), 'r') as stream:
         try:
             return yaml.safe_load(stream)
         except yaml.YAMLError as exc:
             print(exc)
 
-if __name__ == '__main__':
-    compile('../test/', language='de')
-    compile('../test/', language='en')
+# Print information on how to use this program.
+def print_usage():
+    print("Usage: python3 main.py <root-directory>")
+
+if __name__ == '__main__':
+    if len(sys.argv) != 2:
+        print_usage()
+    else:
+        compile(sys.argv[1], language='de')
+        # TODO: Handle multiple languages
+        # compile(sys.argv[1], language='en')