Make help message generation robust.

code/iottb-project/iottb/commands/sniff.py

@@ -46,6 +46,14 @@ def validate_sniff(ctx, param, value):
     return value
 
 
+def run_pre(pre):
+    pass
+
+
+def run_post(post):
+    pass
+
+
 @click.command('sniff', help='Sniff packets with tcpdump')
 @optgroup.group('Testbed sources')
 @optgroup.option('--db', '--database', type=str, envvar='IOTTB_DB', show_envvar=True,
@@ -79,10 +87,13 @@ def validate_sniff(ctx, param, value):
 @click.argument('device', required=False)
 @click.pass_context
 def sniff(ctx, device, interface, print_pacno, ff, count, monitor_mode, print_ll, address, db, unsafe, guided,
-          app, tcpdump_args, **params):
+          app, tcpdump_args, pre, post, **params):
     """ Sniff packets from a device """
     logger.info('sniff command invoked')
-
+    # Step 0: run pre script:
+    if pre:
+        click.echo(f'Running pre command {pre}')
+        run_pre(pre)
     # Step1: Load Config
     config = ctx.obj['CONFIG']
     logger.debug(f'Config loaded: {config}')
@@ -325,3 +336,6 @@ def sniff(ctx, device, interface, print_pacno, ff, count, monitor_mode, print_ll
         json.dump(metadata, f, indent=4)
 
     click.echo(f'END  SNIFF SUBCOMMAND')
+    if post:
+        click.echo(f'Running post command {post}')
+        run_post(post)