Collect all stderrs from pipeline

2 files changed, 20 insertions, 4 deletions

diff --git a/NEWS b/NEWS
index f831ace..0e21b58 100644
--- a/NEWS
+++ b/NEWS
@@ -15,6 +15,10 @@ Version UNRELEASED
   descriptor in the parent results in `SIGPIPE` being sent to the
   `cat` process once `false` terminates.
 
+* Richard Maw changed `cliapp.runcmd` so that the stderr of all
+  commands in the pipeline are collected, when stderr is set to
+  `subprocess.PIPE`.
+
 Version 1.20140719
 ------------------
 
diff --git a/cliapp/runcmd.py b/cliapp/runcmd.py
index 2757068..5ac8da5 100644
--- a/cliapp/runcmd.py
+++ b/cliapp/runcmd.py
@@ -112,23 +112,27 @@ def runcmd_unchecked(argv, *argvs, **kwargs):
 
 def _build_pipeline(argvs, pipe_stdin, pipe_stdout, pipe_stderr, kwargs):
     procs = []
+
+    if pipe_stderr == subprocess.PIPE:
+        # Make pipe for all subprocesses to share
+        rpipe, wpipe = os.pipe()
+        stderr = wpipe
+    else:
+        stderr = pipe_stderr
+
     for i, argv in enumerate(argvs):
         if i == 0 and i == len(argvs) - 1:
             stdin = pipe_stdin
             stdout = pipe_stdout
-            stderr = pipe_stderr
         elif i == 0:
             stdin = pipe_stdin
             stdout = subprocess.PIPE
-            stderr = pipe_stderr
         elif i == len(argvs) - 1:
             stdin = procs[-1].stdout
             stdout = pipe_stdout
-            stderr = pipe_stderr
         else:
             stdin = procs[-1].stdout
             stdout = subprocess.PIPE
-            stderr = pipe_stderr
         p = subprocess.Popen(argv, stdin=stdin, stdout=stdout,
                              stderr=stderr, close_fds=True, **kwargs)
 
@@ -142,6 +146,14 @@ def _build_pipeline(argvs, pipe_stdin, pipe_stdout, pipe_stderr, kwargs):
 
         procs.append(p)
 
+    if pipe_stderr == subprocess.PIPE:
+        # Ensure only subprocesses hold the write end of the pipe, so we get
+        # EOF when they all terminate
+        os.close(wpipe)
+        # Allow reading of the stderr of every process as the stderr of
+        # the last element
+        procs[-1].stderr = os.fdopen(rpipe)
+
     return procs
 
 def _run_pipeline(procs, feed_stdin, pipe_stdin, pipe_stdout, pipe_stderr,