add a module for update-alternatives

library/system/alternatives

+#!/usr/bin/python
+# -*- coding: utf-8 -*-
+
+"""
+Ansible module to manage symbolic link alternatives.
+(c) 2014, Gabe Mulley <gabe.mulley@gmail.com>
+
+This file is part of Ansible
+
+Ansible is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+Ansible is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
+"""
+
+DOCUMENTATION = '''
+---
+module: alternatives
+short_description: Manages symbolic links
+description:
+    - Manages symbolic links using the 'update-alternatives' tool provided on debian-like systems.
+    - Useful when multiple programs are installed but provide similar functionality (e.g. different editors).
+version_added: "1.5"
+options:
+  name:
+    description:
+      - The generic name of the link.
+    required: true
+  path:
+    description:
+      - The path to the real executable that the link should point to.
+    required: true
+  link:
+    description:
+      - The path to the symbolic link that should point to the real executable.
+    required: false
+requirements: [ update-alternatives ]
+'''
+
+EXAMPLES = '''
+- name: correct java version selected
+  alternatives: name=java path=/usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java
+
+- name: alternatives link created
+  alternatives: name=hadoop-conf link=/etc/hadoop/conf path=/etc/hadoop/conf.ansible
+'''
+
+UPDATE_ALTERNATIVES = '/usr/sbin/update-alternatives'
+DEFAULT_LINK_PRIORITY = 50
+
+def main():
+
+    module = AnsibleModule(
+        argument_spec = dict(
+            name = dict(required=True),
+            path  = dict(required=True),
+            link = dict(required=False),
+        )
+    )
+
+    params = module.params
+    name = params['name']
+    path = params['path']
+    link = params['link']
+
+    current_path = None
+    all_alternatives = []
+
+    (rc, query_output, query_error) = module.run_command(
+        [UPDATE_ALTERNATIVES, '--query', name]
+    )
+
+    # Gather the current setting and all alternatives from the query output.
+    # Query output should look something like this:
+
+        # Name: java
+        # Link: /usr/bin/java
+        # Slaves:
+        #  java.1.gz /usr/share/man/man1/java.1.gz
+        # Status: manual
+        # Best: /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java
+        # Value: /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java
+
+        # Alternative: /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java
+        # Priority: 1061
+        # Slaves:
+        #  java.1.gz /usr/lib/jvm/java-6-openjdk-amd64/jre/man/man1/java.1.gz
+
+        # Alternative: /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java
+        # Priority: 1071
+        # Slaves:
+        #  java.1.gz /usr/lib/jvm/java-7-openjdk-amd64/jre/man/man1/java.1.gz
+
+    if rc == 0:
+        for line in query_output.splitlines():
+            split_line = line.split(':')
+            if len(split_line) == 2:
+                key = split_line[0]
+                value = split_line[1].strip()
+                if key == 'Value':
+                    current_path = value
+                elif key == 'Alternative':
+                    all_alternatives.append(value)
+
+    if current_path != path:
+        try:
+            # install the requested path if necessary
+            if path not in all_alternatives:
+                module.run_command(
+                    [UPDATE_ALTERNATIVES, '--install', link, name, path, str(DEFAULT_LINK_PRIORITY)],
+                    check_rc=True
+                )
+
+            # select the requested path
+            module.run_command(
+                [UPDATE_ALTERNATIVES, '--set', name, path],
+                check_rc=True
+            )
+
+            module.exit_json(changed=True)
+        except subprocess.CalledProcessError as cpe:
+            module.fail_json(msg=str(dir(cpe)))
+    else:
+        module.exit_json(changed=False)
+
+
+# import module snippets
+from ansible.module_utils.basic import *
+main()