RF: run: Always use a string for the command

From the command-line, the run command always comes in as a list.  If
it contains a single item, we unwrap it and pass the string directly
to the runner.  From the python api, the run command can come in as a
string or a list.  Commands in the string form are executed with
shell=True (so underneath with "/bin/sh -c"), which makes it possible
to use things like redirection and pipes in commands.

When we add support for commands with {inputs} and {outputs}
placeholders, the two representations will require separate
handling (e.g., if string, call format directly; if list, map format
call).  Instead of doing that, convert the list representation to the
string representation.

datalad/interface/run.py

@@ -22,6 +22,8 @@
 from os.path import relpath
 from os.path import isabs
 
+from six.moves import shlex_quote
+
 from datalad.interface.base import Interface
 from datalad.interface.utils import eval_results
 from datalad.interface.base import build_doc
@@ -329,8 +331,13 @@ def run_command(cmd, dataset=None, inputs=None, outputs=None, expand=None,
         for res in _unlock_or_remove(ds, rerun_outputs):
             yield res
 
-    # anticipate quoted compound shell commands
-    cmd = cmd[0] if isinstance(cmd, list) and len(cmd) == 1 else cmd
+    if isinstance(cmd, list):
+        if len(cmd) == 1:
+            # This is either a quoted compound shell command or a simple
+            # one-item command. Pass it as is.
+            cmd = cmd[0]
+        else:
+            cmd = " ".join(shlex_quote(c) for c in cmd)
 
     # TODO do our best to guess which files to unlock based on the command string
     #      in many cases this will be impossible (but see rerun). however,

datalad/interface/tests/test_run.py

@@ -102,6 +102,10 @@ def test_basics(path, nodspath):
         res = ds.run('touch empty', message='NOOP_TEST')
         assert_status('notneeded', res)
         eq_(last_state, ds.repo.get_hexsha())
+        # We can also run the command via a single-item list because this is
+        # what the CLI interface passes in for quoted commands.
+        res = ds.run(['touch empty'], message='NOOP_TEST')
+        assert_status('notneeded', res)
 
     # run outside the dataset, should still work but with limitations
     with chpwd(nodspath), \