--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -2653,35 +2653,8 @@ def tag(ui, repo, name, rev_=None, **opt
     else:
         r = hex(repo.changelog.tip())
 
-    disallowed = (revrangesep, '\r', '\n')
-    for c in disallowed:
-        if c in name:
-            raise util.Abort(_("%s cannot be used in a tag name") % repr(c))
-
-    repo.hook('pretag', throw=True, node=r, tag=name,
-              local=int(not not opts['local']))
-
-    if opts['local']:
-        repo.opener("localtags", "a").write("%s %s\n" % (r, name))
-        repo.hook('tag', node=r, tag=name, local=1)
-        return
-
-    for x in repo.changes():
-        if ".hgtags" in x:
-            raise util.Abort(_("working copy of .hgtags is changed "
-                               "(please commit .hgtags manually)"))
-
-    repo.wfile(".hgtags", "ab").write("%s %s\n" % (r, name))
-    if repo.dirstate.state(".hgtags") == '?':
-        repo.add([".hgtags"])
-
-    message = (opts['message'] or
-               _("Added tag %s for changeset %s") % (name, r))
-    try:
-        repo.commit([".hgtags"], message, opts['user'], opts['date'])
-        repo.hook('tag', node=r, tag=name, local=0)
-    except ValueError, inst:
-        raise util.Abort(str(inst))
+    repo.tag(name, r, opts['local'], opts['message'], opts['user'],
+             opts['date'])
 
 def tags(ui, repo):
     """list repository tags

--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -162,6 +162,52 @@ class localrepository(object):
                 r = runhook(hname, cmd) or r
         return r
 
+    tag_disallowed = ':\r\n'
+
+    def tag(self, name, node, local=False, message=None, user=None, date=None):
+        '''tag a revision with a symbolic name.
+
+        if local is True, the tag is stored in a per-repository file.
+        otherwise, it is stored in the .hgtags file, and a new
+        changeset is committed with the change.
+
+        keyword arguments:
+
+        local: whether to store tag in non-version-controlled file
+        (default False)
+
+        message: commit message to use if committing
+
+        user: name of user to use if committing
+
+        date: date tuple to use if committing'''
+
+        for c in self.tag_disallowed:
+            if c in name:
+                raise util.Abort(_('%r cannot be used in a tag name') % c)
+
+        self.hook('pretag', throw=True, node=node, tag=name, local=local)
+
+        if local:
+            self.opener('localtags', 'a').write('%s %s\n' % (node, name))
+            self.hook('tag', node=node, tag=name, local=local)
+            return
+
+        for x in self.changes():
+            if '.hgtags' in x:
+                raise util.Abort(_('working copy of .hgtags is changed '
+                                   '(please commit .hgtags manually)'))
+
+        self.wfile('.hgtags', 'ab').write('%s %s\n' % (node, name))
+        if self.dirstate.state('.hgtags') == '?':
+            self.add(['.hgtags'])
+
+        if not message:
+            message = _('Added tag %s for changeset %s') % (name, node)
+
+        self.commit(['.hgtags'], message, user, date)
+        self.hook('tag', node=node, tag=name, local=local)
+
     def tags(self):
         '''return a mapping of tag to node'''
         if not self.tagscache:

--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -378,6 +378,13 @@ def system(cmd, environ={}, cwd=None, on
     if command fails and onerr is None, return status.  if ui object,
     print error message and return status, else raise onerr object as
     exception.'''
+    def py2shell(val):
+        'convert python object into string that is useful to shell'
+        if val in (None, False):
+            return '0'
+        if val == True:
+            return '1'
+        return str(val)
     oldenv = {}
     for k in environ:
         oldenv[k] = os.environ.get(k)
@@ -385,7 +392,7 @@ def system(cmd, environ={}, cwd=None, on
         oldcwd = os.getcwd()
     try:
         for k, v in environ.iteritems():
-            os.environ[k] = str(v)
+            os.environ[k] = py2shell(v)
         if cwd is not None and oldcwd != cwd:
             os.chdir(cwd)
         rc = os.system(cmd)