Do not display the output of a command in pipe mode

CHANGELOG.md

@@ -2,7 +2,10 @@
 ------------------
 
 **Added**
--  Script of script (SoS) notebooks are now supported. Thanks to Thomas Pernet-coudrier for contributing the sample notebook (#453).
+- Script of script (SoS) notebooks are now supported. Thanks to Thomas Pernet-coudrier for contributing the sample notebook (#453).
+
+**Fixed**
+- When using `jupytext --pipe cmd`, the output of `cmd` should not appear in the terminal (#432)
 
 
 1.4.0 (2020-03-09)

jupytext/cli.py

@@ -621,15 +621,15 @@ def load_paired_notebook(notebook, fmt, nb_file, log):
     return notebook, latest_inputs, latest_outputs
 
 
-def exec_command(command, input=None):
+def exec_command(command, input=None, capture=False):
     """Execute the desired command, and pipe the given input into it"""
     if not isinstance(command, list):
         command = command.split(' ')
     sys.stdout.write("[jupytext] Executing {}\n".format(' '.join(command)))
     process = subprocess.Popen(command,
                                **(dict(stdout=subprocess.PIPE, stdin=subprocess.PIPE) if input is not None else {}))
     out, err = process.communicate(input=input)
-    if out:
+    if out and not capture:
         sys.stdout.write(out.decode('utf-8'))
     if err:
         sys.stderr.write(err.decode('utf-8'))
@@ -673,7 +673,7 @@ def pipe_notebook(notebook, command, fmt='py:percent', update=True, prefix=None)
             tmp.write(text)
             tmp.close()
 
-            exec_command([cmd if cmd != '{}' else tmp.name for cmd in command])
+            exec_command([cmd if cmd != '{}' else tmp.name for cmd in command], capture=update)
 
             if not update:
                 return notebook
@@ -682,7 +682,7 @@ def pipe_notebook(notebook, command, fmt='py:percent', update=True, prefix=None)
         finally:
             os.remove(tmp.name)
     else:
-        cmd_output = exec_command(command, text.encode('utf-8'))
+        cmd_output = exec_command(command, text.encode('utf-8'), capture=update)
 
         if not update:
             return notebook