add --list-hosts option to ansible-playbook to dump out the hosts

being run against for each playbook

bin/ansible-playbook

@@ -57,6 +57,8 @@ def main(args):
         help="set additional key=value variables from the CLI")
     parser.add_option('-t', '--tags', dest='tags', default='all',
         help="only run plays and tasks tagged with these values")
+    parser.add_option('--list-hosts', dest='listhosts', action='store_true',
+        help="dump out a list of hosts, each play will run against, does not run playbook!")
 
     options, args = parser.parse_args(args)
 
@@ -66,6 +68,7 @@ def main(args):
 
     sshpass = None
     sudopass = None
+    if not options.listhosts:
         if options.ask_pass:
             sshpass = getpass.getpass(prompt="SSH password: ")
         if options.ask_sudo_pass:
@@ -104,6 +107,21 @@ def main(args):
             only_tags=only_tags,
             subset=options.subset,
         )
+        
+        if options.listhosts:
+            playnum = 0
+            for play in pb.playbook:
+                playnum += 1
+                if 'hosts' in play:
+                    label = 'unnamed'
+                    if 'name' in play:
+                        label = play['name']
+                    print 'hosts in play %s: %s' % (playnum, label)
+                    for host in pb.inventory.list_hosts(play['hosts']):
+                        print '  %s' % host
+                    print '\n'
+            return 0
+            
         try:
 
             pb.run()