Added replace module

Heavily based on existing lineinfile module, but where it literally tests a regexp against
*each individual line* of a file, this replace module is more analogous to common uses of
a `sed` or `perl` match + replacement of all instances of a pattern anywhere in the file.

Was debating adding `all` boolean or `count` numeric options to control how many
replacements to make in the destfile (vs currently replacing all instances)

Noted use of MULTILINE mode in docs, per suggestion from @jarv

files/replace

@@ -0,0 +1,160 @@
+#!/usr/bin/python
+# -*- coding: utf-8 -*-
+
+# (c) 2013, Evan Kaufman <evan@digitalflophouse.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/>.
+
+import re
+import os
+import tempfile
+
+DOCUMENTATION = """
+---
+module: replace
+author: Evan Kaufman
+short_description: Replace all instances of a particular string in a
+                   file using a back-referenced regular expression.
+description:
+  - This module will replace all instances of a pattern within a file.
+  - It is up to the user to maintain idempotence by ensuring that the
+    same pattern would never match any replacements made.
+version_added: "1.4"
+options:
+  dest:
+    required: true
+    aliases: [ name, destfile ]
+    description:
+      - The file to modify.
+  regexp:
+    required: true
+    description:
+      - The regular expression to look for in the contents of the file.
+        Uses Python regular expressions; see
+        U(http://docs.python.org/2/library/re.html).
+        Uses multiline mode, which means C(^) and C($) match the beginning
+        and end respectively of I(each line) of the file.
+  replace:
+    required: false
+    description:
+      - The string to replace regexp matches. May contain backreferences
+        that will get expanded with the regexp capture groups if the regexp
+        matches. If not set, matches are removed entirely.
+  backup:
+    required: false
+    default: "no"
+    choices: [ "yes", "no" ]
+    description:
+      - Create a backup file including the timestamp information so you can
+        get the original file back if you somehow clobbered it incorrectly.
+  validate:
+    required: false
+    description:
+      - validation to run before copying into place
+    required: false
+    default: None
+  others:
+    description:
+      - All arguments accepted by the M(file) module also work here.
+    required: false
+"""
+
+EXAMPLES = r"""
+- replace: dest=/etc/hosts regexp='(\s+)old\.host\.name(\s+.*)?$' replace='\1new.host.name\2' backup=yes
+
+- replace: dest=/home/jdoe/.ssh/known_hosts regexp='^old\.host\.name[^\n]*\n' owner=jdoe group=jdoe mode=644
+
+- replace: dest=/etc/apache/ports regexp='^(NameVirtualHost|Listen)\s+80\s*$' replace='\1 127.0.0.1:8080' validate='/usr/sbin/apache2ctl -f %s -t'
+"""
+
+def write_changes(module,contents,dest):
+
+    tmpfd, tmpfile = tempfile.mkstemp()
+    f = os.fdopen(tmpfd,'wb')
+    f.write(contents)
+    f.close()
+
+    validate = module.params.get('validate', None)
+    valid = not validate
+    if validate:
+        (rc, out, err) = module.run_command(validate % tmpfile)
+        valid = rc == 0
+        if rc != 0:
+            module.fail_json(msg='failed to validate: '
+                                 'rc:%s error:%s' % (rc,err))
+    if valid:
+        module.atomic_move(tmpfile, dest)
+
+def check_file_attrs(module, changed, message):
+
+    file_args = module.load_file_common_arguments(module.params)
+    if module.set_file_attributes_if_different(file_args, False):
+
+        if changed:
+            message += " and "
+        changed = True
+        message += "ownership, perms or SE linux context changed"
+
+    return message, changed
+
+def main():
+    module = AnsibleModule(
+        argument_spec=dict(
+            dest=dict(required=True, aliases=['name', 'destfile']),
+            regexp=dict(required=True),
+            replace=dict(default='', type='str'),
+            backup=dict(default=False, type='bool'),
+            validate=dict(default=None, type='str'),
+        ),
+        add_file_common_args=True,
+        supports_check_mode=True
+    )
+
+    params = module.params
+    dest = os.path.expanduser(params['dest'])
+
+    if os.path.isdir(dest):
+        module.fail_json(rc=256, msg='Destination %s is a directory !' % dest)
+
+    if not os.path.exists(dest):
+        module.fail_json(rc=257, msg='Destination %s does not exist !' % dest)
+    else:
+        f = open(dest, 'rb')
+        contents = f.read()
+        f.close()
+
+    mre = re.compile(params['regexp'], re.MULTILINE)
+    result = re.subn(mre, params['replace'], contents, 0)
+
+    if result[1] > 0:
+        msg = '%s replacements made' % result[1]
+        changed = True
+    else:
+        msg = ''
+        changed = False
+
+    if changed and not module.check_mode:
+        if params['backup'] and os.path.exists(dest):
+            module.backup_local(dest)
+        write_changes(module, result[0], dest)
+
+    msg, changed = check_file_attrs(module, changed, msg)
+    module.exit_json(changed=changed, msg=msg)
+
+# this is magic, see lib/ansible/module_common.py
+#<<INCLUDE_ANSIBLE_MODULE_COMMON>>
+
+main()