Show commandline being executed with :spawn.

Closes #616.

CHANGELOG.asciidoc

@@ -26,6 +26,7 @@ Changed
 ~~~~~~~
 
 - `QUTE_HTML` and `QUTE_TEXT` for userscripts now don't store the contents directly, and instead contain a filename.
+- `:spawn` now shows the command being executed in the statusbar, use `-q`/`--quiet` for the old behavior.
 
 https://github.com/The-Compiler/qutebrowser/releases/tag/v0.2.1[v0.2.1]
 -----------------------------------------------------------------------

doc/help/commands.asciidoc

@@ -510,7 +510,7 @@ Preset the statusbar to some text.
 
 [[spawn]]
 === spawn
-Syntax: +:spawn [*--userscript*] 'args' ['args' ...]+
+Syntax: +:spawn [*--userscript*] [*--quiet*] 'args' ['args' ...]+
 
 Spawn a command in a shell.
 
@@ -521,6 +521,7 @@ Note the {url} variable which gets replaced by the current URL might be useful h
 
 ==== optional arguments
 * +*-u*+, +*--userscript*+: Run the command as an userscript.
+* +*-q*+, +*--quiet*+: Don't print the commandline being executed.
 
 [[stop]]
 === stop

qutebrowser/browser/commands.py

@@ -21,6 +21,7 @@
 
 import re
 import os
+import shlex
 import subprocess
 import posixpath
 import functools
@@ -823,7 +824,8 @@ class CommandDispatcher:
             tabbed_browser.setUpdatesEnabled(True)
 
     @cmdutils.register(instance='command-dispatcher', scope='window')
-    def spawn(self, userscript=False, *args):
+    def spawn(self, win_id: {'special': 'win_id'}, userscript=False,
+              quiet=False, *args):
         """Spawn a command in a shell.
 
         Note the {url} variable which gets replaced by the current URL might be
@@ -836,10 +838,14 @@ class CommandDispatcher:
 
         Args:
             userscript: Run the command as an userscript.
+            quiet: Don't print the commandline being executed.
             *args: The commandline to execute.
         """
         log.procs.debug("Executing: {}, userscript={}".format(
             args, userscript))
+        if not quiet:
+            fake_cmdline = ' '.join(shlex.quote(arg) for arg in args)
+            message.info(win_id, 'Executing: ' + fake_cmdline)
         if userscript:
             cmd = args[0]
             args = [] if not args else args[1:]