diff --git a/setup.cfg b/setup.cfg
index 6dac5bf..86bd85a 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -32,4 +32,4 @@ patterns =
 [pycalver:file:README.rst]
 patterns =
     badge/CalVer-{calver}{build}-{release}-blue.svg
-    :alt: CalVer {version}
+    :alt: CalVer {version}
\ No newline at end of file
diff --git a/src/pycalver/__main__.py b/src/pycalver/__main__.py
index a196558..a73be68 100644
--- a/src/pycalver/__main__.py
+++ b/src/pycalver/__main__.py
@@ -146,7 +146,7 @@ def init(dry: bool) -> None:
     "--commit",
     default=True,
     is_flag=True,
-    help="Tag the commit.",
+    help="Commit after updating version strings.",
 )
 @click.option(
     "--tag",
@@ -154,7 +154,24 @@ def init(dry: bool) -> None:
     is_flag=True,
     help="Tag the commit.",
 )
-def bump(release: str, verbose: bool, dry: bool, commit: bool, tag: bool) -> None:
+@click.option(
+    "--allow-dirty",
+    default=False,
+    is_flag=True,
+    help=(
+        "Commit even when working directory is has uncomitted changes. "
+        "(WARNING: The commit will still be aborted if there are uncomitted "
+        "to files with version strings."
+    ),
+)
+def bump(
+    release: str,
+    verbose: bool,
+    dry: bool,
+    commit: bool,
+    tag: bool,
+    allow_dirty: bool,
+) -> None:
     _init_loggers(verbose)
 
     if release and release not in parse.VALID_RELESE_VALUES:
@@ -179,6 +196,25 @@ def bump(release: str, verbose: bool, dry: bool, commit: bool, tag: bool) -> Non
     if dry:
         log.info("Running with '--dry', showing diffs instead of updating files.")
 
+    _vcs = vcs.get_vcs()
+    dirty_files = _vcs.dirty_files()
+
+    if dirty_files:
+        log.warn(f"{_vcs.__name__} working directory is not clean:")
+        for file in dirty_files:
+            log.warn("    " + file)
+
+    if not allow_dirty and dirty_files:
+        sys.exit(1)
+
+    pattern_files = cfg["file_patterns"].keys()
+    dirty_pattern_files = set(dirty_files) & set(pattern_files)
+    if dirty_pattern_files:
+        log.error("Not commiting when pattern files are dirty:")
+        for file in dirty_pattern_files:
+            log.warn("    " + file)
+        sys.exit(1)
+
     matches: typ.List[parse.PatternMatch]
     for filepath, patterns in cfg["file_patterns"].items():
         with io.open(filepath, mode="rt", encoding="utf-8") as fh:
@@ -203,10 +239,10 @@ def bump(release: str, verbose: bool, dry: bool, commit: bool, tag: bool) -> Non
                 tofile="b/" + filepath,
             )))
 
-        # if not dry:
-        #     new_content = "\n".join(new_lines)
-        #     with io.open(filepath, mode="wt", encoding="utf-8") as fh:
-        #         fh.write(new_content)
+        if not dry:
+            new_content = "\n".join(new_lines)
+            with io.open(filepath, mode="wt", encoding="utf-8") as fh:
+                fh.write(new_content)
 
     if dry:
         return
@@ -214,7 +250,6 @@ def bump(release: str, verbose: bool, dry: bool, commit: bool, tag: bool) -> Non
     if not commit:
         return
 
-    v = vcs.get_vcs()
-    if v is None:
+    if _vcs is None:
         log.warn("Version Control System not found, aborting commit.")
         return
diff --git a/src/pycalver/vcs.py b/src/pycalver/vcs.py
index 42ce2da..2be6797 100644
--- a/src/pycalver/vcs.py
+++ b/src/pycalver/vcs.py
@@ -17,12 +17,6 @@ import subprocess as sp
 log = logging.getLogger("pycalver.vcs")
 
 
-class WorkingDirectoryIsDirtyException(Exception):
-
-    def __init__(self, message):
-        self.message = message
-
-
 class BaseVCS:
 
     @classmethod
@@ -50,21 +44,14 @@ class BaseVCS:
             raise
 
     @classmethod
-    def assert_nondirty(cls):
+    def dirty_files(cls):
         status_output = sp.check_output(cls._STATUS_COMMAND)
-        lines = [
-            line.strip()
+        return [
+            line.decode("utf-8")[2:].strip()
             for line in status_output.splitlines()
             if not line.strip().startswith(b"??")
         ]
 
-        if lines:
-            cleaned_output = b"\n".join(lines)
-            cls_name = cls.__name__
-            raise WorkingDirectoryIsDirtyException(
-                f"{cls_name} working directory is not clean:\n{cleaned_output}"
-            )
-
 
 class Git(BaseVCS):
 
@@ -76,6 +63,10 @@ class Git(BaseVCS):
     def tag(cls, name):
         sp.check_output(["git", "tag", name])
 
+    @classmethod
+    def add_path(cls, path):
+        sp.check_output(["git", "add", "--update", path])
+
 
 class Mercurial(BaseVCS):
 
@@ -87,25 +78,17 @@ class Mercurial(BaseVCS):
     def tag(cls, name):
         sp.check_output(["hg", "tag", name])
 
+    @classmethod
+    def add_path(cls, path):
+        pass
+
 
 VCS = [Git, Mercurial]
 
 
-def get_vcs(allow_dirty=False):
+def get_vcs():
     for vcs in VCS:
-        if not vcs.is_usable():
-            continue
-
-        if not allow_dirty:
-            try:
-                vcs.assert_nondirty()
-            except WorkingDirectoryIsDirtyException as e:
-                log.warn(
-                    f"{e.message}\n\n"
-                    f"Use --allow-dirty to override this if you know what you're doing."
-                )
-                raise
-
-        return vcs
+        if vcs.is_usable():
+            return vcs
 
     return None
diff --git a/test/test_parse.py b/test/test_parse.py
new file mode 100644
index 0000000..e69de29