diff --git a/borg/archiver.py b/borg/archiver.py
index e189d02eb..728b85482 100644
--- a/borg/archiver.py
+++ b/borg/archiver.py
@@ -560,7 +560,7 @@ def run(self, args=None):
                                           description=self.do_init.__doc__, epilog=init_epilog,
                                           formatter_class=argparse.RawDescriptionHelpFormatter)
         subparser.set_defaults(func=self.do_init)
-        subparser.add_argument('repository', metavar='REPOSITORY',
+        subparser.add_argument('repository', metavar='REPOSITORY', nargs='?', default='',
                                type=location_validator(archive=False),
                                help='repository to create')
         subparser.add_argument('-e', '--encryption', dest='encryption',
@@ -608,7 +608,7 @@ def run(self, args=None):
                                           epilog=check_epilog,
                                           formatter_class=argparse.RawDescriptionHelpFormatter)
         subparser.set_defaults(func=self.do_check)
-        subparser.add_argument('repository', metavar='REPOSITORY_OR_ARCHIVE',
+        subparser.add_argument('repository', metavar='REPOSITORY_OR_ARCHIVE', nargs='?', default='',
                                type=location_validator(),
                                help='repository or archive to check consistency of')
         subparser.add_argument('--repository-only', dest='repo_only', action='store_true',
@@ -633,7 +633,7 @@ def run(self, args=None):
                                           epilog=change_passphrase_epilog,
                                           formatter_class=argparse.RawDescriptionHelpFormatter)
         subparser.set_defaults(func=self.do_change_passphrase)
-        subparser.add_argument('repository', metavar='REPOSITORY',
+        subparser.add_argument('repository', metavar='REPOSITORY', nargs='?', default='',
                                type=location_validator(archive=False))
 
         create_epilog = textwrap.dedent("""
@@ -767,7 +767,7 @@ def run(self, args=None):
         subparser.add_argument('-s', '--stats', dest='stats',
                                action='store_true', default=False,
                                help='print statistics for the deleted archive')
-        subparser.add_argument('target', metavar='TARGET',
+        subparser.add_argument('target', metavar='TARGET', nargs='?', default='',
                                type=location_validator(),
                                help='archive or repository to delete')
 
@@ -782,7 +782,8 @@ def run(self, args=None):
         subparser.add_argument('--short', dest='short',
                                action='store_true', default=False,
                                help='only print file/directory names, nothing else')
-        subparser.add_argument('src', metavar='REPOSITORY_OR_ARCHIVE', type=location_validator(),
+        subparser.add_argument('src', metavar='REPOSITORY_OR_ARCHIVE', nargs='?', default='',
+                               type=location_validator(),
                                help='repository/archive to list contents of')
         mount_epilog = textwrap.dedent("""
         This command mounts an archive as a FUSE filesystem. This can be useful for
@@ -865,7 +866,7 @@ def run(self, args=None):
                                help='number of yearly archives to keep')
         subparser.add_argument('-p', '--prefix', dest='prefix', type=str,
                                help='only consider archive names starting with this prefix')
-        subparser.add_argument('repository', metavar='REPOSITORY',
+        subparser.add_argument('repository', metavar='REPOSITORY', nargs='?', default='',
                                type=location_validator(archive=False),
                                help='repository to prune')
 
diff --git a/borg/helpers.py b/borg/helpers.py
index 6d2b81736..aa5bead0b 100644
--- a/borg/helpers.py
+++ b/borg/helpers.py
@@ -466,13 +466,34 @@ class Location:
                          r'(?P<path>[^:]+)(?:::(?P<archive>.+))?$')
     scp_re = re.compile(r'((?:(?P<user>[^@]+)@)?(?P<host>[^:/]+):)?'
                         r'(?P<path>[^:]+)(?:::(?P<archive>.+))?$')
+    # get the repo from BORG_RE env and the optional archive from param.
+    # if the syntax requires giving REPOSITORY (see "borg mount"),
+    # use "::" to let it use the env var.
+    # if REPOSITORY argument is optional, it'll automatically use the env.
+    env_re = re.compile(r'(?:::(?P<archive>.+)?)?$')
 
-    def __init__(self, text):
+    def __init__(self, text=''):
         self.orig = text
-        if not self.parse(text):
+        if not self.parse(self.orig):
             raise ValueError
 
     def parse(self, text):
+        valid = self._parse(text)
+        if valid:
+            return True
+        m = self.env_re.match(text)
+        if not m:
+            return False
+        repo = os.environ.get('BORG_REPO')
+        if repo is None:
+            return False
+        valid = self._parse(repo)
+        if not valid:
+            return False
+        self.archive = m.group('archive')
+        return True
+
+    def _parse(self, text):
         m = self.ssh_re.match(text)
         if m:
             self.proto = m.group('proto')
diff --git a/borg/testsuite/helpers.py b/borg/testsuite/helpers.py
index b61a8268f..95531df83 100644
--- a/borg/testsuite/helpers.py
+++ b/borg/testsuite/helpers.py
@@ -23,42 +23,115 @@ def test_bigint(self):
         self.assert_equal(bigint_to_int(int_to_bigint(2**70)), 2**70)
 
 
-class LocationTestCase(BaseTestCase):
+class TestLocationWithoutEnv:
+    def test_ssh(self, monkeypatch):
+        monkeypatch.delenv('BORG_REPO', raising=False)
+        assert repr(Location('ssh://user@host:1234/some/path::archive')) == \
+               "Location(proto='ssh', user='user', host='host', port=1234, path='/some/path', archive='archive')"
+        assert repr(Location('ssh://user@host:1234/some/path')) == \
+               "Location(proto='ssh', user='user', host='host', port=1234, path='/some/path', archive=None)"
 
-    def test(self):
-        self.assert_equal(
-            repr(Location('ssh://user@host:1234/some/path::archive')),
-            "Location(proto='ssh', user='user', host='host', port=1234, path='/some/path', archive='archive')"
-        )
-        self.assert_equal(
-            repr(Location('file:///some/path::archive')),
-            "Location(proto='file', user=None, host=None, port=None, path='/some/path', archive='archive')"
-        )
-        self.assert_equal(
-            repr(Location('user@host:/some/path::archive')),
-            "Location(proto='ssh', user='user', host='host', port=None, path='/some/path', archive='archive')"
-        )
-        self.assert_equal(
-            repr(Location('path::archive')),
-            "Location(proto='file', user=None, host=None, port=None, path='path', archive='archive')"
-        )
-        self.assert_equal(
-            repr(Location('/some/absolute/path::archive')),
-            "Location(proto='file', user=None, host=None, port=None, path='/some/absolute/path', archive='archive')"
-        )
-        self.assert_equal(
-            repr(Location('some/relative/path::archive')),
-            "Location(proto='file', user=None, host=None, port=None, path='some/relative/path', archive='archive')"
-        )
-        self.assert_raises(ValueError, lambda: Location('ssh://localhost:22/path:archive'))
+    def test_file(self, monkeypatch):
+        monkeypatch.delenv('BORG_REPO', raising=False)
+        assert repr(Location('file:///some/path::archive')) == \
+               "Location(proto='file', user=None, host=None, port=None, path='/some/path', archive='archive')"
+        assert repr(Location('file:///some/path')) == \
+               "Location(proto='file', user=None, host=None, port=None, path='/some/path', archive=None)"
 
-    def test_canonical_path(self):
+    def test_scp(self, monkeypatch):
+        monkeypatch.delenv('BORG_REPO', raising=False)
+        assert repr(Location('user@host:/some/path::archive')) == \
+               "Location(proto='ssh', user='user', host='host', port=None, path='/some/path', archive='archive')"
+        assert repr(Location('user@host:/some/path')) == \
+               "Location(proto='ssh', user='user', host='host', port=None, path='/some/path', archive=None)"
+
+    def test_folder(self, monkeypatch):
+        monkeypatch.delenv('BORG_REPO', raising=False)
+        assert repr(Location('path::archive')) == \
+               "Location(proto='file', user=None, host=None, port=None, path='path', archive='archive')"
+        assert repr(Location('path')) == \
+               "Location(proto='file', user=None, host=None, port=None, path='path', archive=None)"
+
+    def test_abspath(self, monkeypatch):
+        monkeypatch.delenv('BORG_REPO', raising=False)
+        assert repr(Location('/some/absolute/path::archive')) == \
+               "Location(proto='file', user=None, host=None, port=None, path='/some/absolute/path', archive='archive')"
+        assert repr(Location('/some/absolute/path')) == \
+               "Location(proto='file', user=None, host=None, port=None, path='/some/absolute/path', archive=None)"
+
+    def test_relpath(self, monkeypatch):
+        monkeypatch.delenv('BORG_REPO', raising=False)
+        assert repr(Location('some/relative/path::archive')) == \
+               "Location(proto='file', user=None, host=None, port=None, path='some/relative/path', archive='archive')"
+        assert repr(Location('some/relative/path')) == \
+               "Location(proto='file', user=None, host=None, port=None, path='some/relative/path', archive=None)"
+
+    def test_underspecified(self, monkeypatch):
+        monkeypatch.delenv('BORG_REPO', raising=False)
+        with pytest.raises(ValueError):
+            Location('::archive')
+        with pytest.raises(ValueError):
+            Location('::')
+        with pytest.raises(ValueError):
+            Location()
+
+    def test_no_double_colon(self, monkeypatch):
+        monkeypatch.delenv('BORG_REPO', raising=False)
+        with pytest.raises(ValueError):
+            Location('ssh://localhost:22/path:archive')
+
+    def test_canonical_path(self, monkeypatch):
+        monkeypatch.delenv('BORG_REPO', raising=False)
         locations = ['some/path::archive', 'file://some/path::archive', 'host:some/path::archive',
                      'host:~user/some/path::archive', 'ssh://host/some/path::archive',
                      'ssh://user@host:1234/some/path::archive']
         for location in locations:
-            self.assert_equal(Location(location).canonical_path(),
-                              Location(Location(location).canonical_path()).canonical_path())
+            assert Location(location).canonical_path() == \
+                   Location(Location(location).canonical_path()).canonical_path()
+
+
+class TestLocationWithEnv:
+    def test_ssh(self, monkeypatch):
+        monkeypatch.setenv('BORG_REPO', 'ssh://user@host:1234/some/path')
+        assert repr(Location('::archive')) == \
+               "Location(proto='ssh', user='user', host='host', port=1234, path='/some/path', archive='archive')"
+        assert repr(Location()) == \
+               "Location(proto='ssh', user='user', host='host', port=1234, path='/some/path', archive=None)"
+
+    def test_file(self, monkeypatch):
+        monkeypatch.setenv('BORG_REPO', 'file:///some/path')
+        assert repr(Location('::archive')) == \
+               "Location(proto='file', user=None, host=None, port=None, path='/some/path', archive='archive')"
+        assert repr(Location()) == \
+               "Location(proto='file', user=None, host=None, port=None, path='/some/path', archive=None)"
+
+    def test_scp(self, monkeypatch):
+        monkeypatch.setenv('BORG_REPO', 'user@host:/some/path')
+        assert repr(Location('::archive')) == \
+               "Location(proto='ssh', user='user', host='host', port=None, path='/some/path', archive='archive')"
+        assert repr(Location()) == \
+               "Location(proto='ssh', user='user', host='host', port=None, path='/some/path', archive=None)"
+
+    def test_folder(self, monkeypatch):
+        monkeypatch.setenv('BORG_REPO', 'path')
+        assert repr(Location('::archive')) == \
+               "Location(proto='file', user=None, host=None, port=None, path='path', archive='archive')"
+        assert repr(Location()) == \
+               "Location(proto='file', user=None, host=None, port=None, path='path', archive=None)"
+
+    def test_abspath(self, monkeypatch):
+        monkeypatch.setenv('BORG_REPO', '/some/absolute/path')
+        assert repr(Location('::archive')) == \
+               "Location(proto='file', user=None, host=None, port=None, path='/some/absolute/path', archive='archive')"
+        assert repr(Location()) == \
+               "Location(proto='file', user=None, host=None, port=None, path='/some/absolute/path', archive=None)"
+
+    def test_relpath(self, monkeypatch):
+        monkeypatch.setenv('BORG_REPO', 'some/relative/path')
+        assert repr(Location('::archive')) == \
+               "Location(proto='file', user=None, host=None, port=None, path='some/relative/path', archive='archive')"
+        assert repr(Location()) == \
+               "Location(proto='file', user=None, host=None, port=None, path='some/relative/path', archive=None)"
 
 
 class FormatTimedeltaTestCase(BaseTestCase):
diff --git a/docs/usage.rst b/docs/usage.rst
index 27c258504..0ce547b93 100644
--- a/docs/usage.rst
+++ b/docs/usage.rst
@@ -41,9 +41,15 @@ Environment Variables
 
 |project_name| uses some environment variables for automation:
 
-Specifying a passphrase:
+General:
+    BORG_REPO
+        When set, use the value to give the default repository location. If a command needs an archive
+        parameter, you can abbreviate as `::archive`. If a command needs a repository parameter, you
+        can either leave it away or abbreviate as `::`, if a positional parameter is required.
     BORG_PASSPHRASE
         When set, use the value to answer the passphrase question for encrypted repositories.
+    TMPDIR
+        where temporary files are stored (might need a lot of temporary space for some operations)
 
 Some "yes" sayers (if set, they automatically confirm that you really want to do X even if there is that warning):
     BORG_UNKNOWN_UNENCRYPTED_REPO_ACCESS_IS_OK
@@ -64,10 +70,6 @@ Building:
     BORG_OPENSSL_PREFIX
         Adds given OpenSSL header file directory to the default locations (setup.py).
 
-General:
-    TMPDIR
-        where temporary files are stored (might need a lot of temporary space for some operations)
-
 
 Please note: