tox.ini: Prevent casual addition of bash dependency

While bash is not available on every environments, there seems to be
a tendency to introduce more bash dependency very casually.  This check
is intended to be a reminder to give people a chance to consider
alternatives.

Related-Bug: #1398266
Change-Id: I5103e0d7c111880d9a02dd93de56c567066ed14c

tools/check_bash.sh

@@ -0,0 +1,31 @@
+#! /bin/sh
+
+# Copyright (C) 2014 VA Linux Systems Japan K.K.
+# Copyright (C) 2014 YAMAMOTO Takashi <yamamoto at valinux co jp>
+# All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+# The purpose of this script is to avoid casual introduction of more
+# bash dependency.  Please consider alternatives before commiting code
+# which uses bash specific features.
+
+# Ignore comments, but include shebangs
+OBSERVED=$(grep -E '^([^#]|#!).*bash' tox.ini tools/* | wc -l)
+EXPECTED=5
+if [ ${EXPECTED} -ne ${OBSERVED} ]; then
+    echo Unexpected number of bash usages are detected.
+    echo Please read the comment in $0
+    exit 1
+fi
+exit 0

tox.ini

@@ -44,6 +44,7 @@ downloadcache = ~/cache/pip
 
 [testenv:pep8]
 commands =
+  sh ./tools/check_bash.sh
   flake8
   neutron-db-manage check_migration
   sh -c "find neutron -type f -regex '.*\.pot?' -print0|xargs -0 -n 1 msgfmt --check-format -o /dev/null"