shell+register+when+模块RETURN变量

# shell
shell模块可以与register和when来结合使用，组合成类似于shell脚本中的 if [ $? -eq 0 ]这种条件判断，根据执行结果来执行playbook中的任务

## 判断nginx配置文件是否正确
```yaml
- name: 启动nginx
  shell: "/usr/sbin/nginx -t"
  register: CONFIGTEST
  ignore_errors: true

- name: 正确则重载nginx
  when: CONFIGTEST.rc == 0
  shell: "nginx -s reload"
```

从帮助文档来看，shell模块会返回很多种变量，rc只是其中的一个，其他包含类似time command的返回shell执行时间的delta变量；返回标准输出的stdout变量等，结合这些返回的变量可以有更多的高级组合操作。

## 帮助文档

```

EXAMPLES:

- name: Execute the command in remote shell; stdout goes to the specified file on the remote.
shell: somescript.sh >> somelog.txt

- name: Change the working directory to somedir/ before executing the command.
shell: somescript.sh >> somelog.txt
args:
chdir: somedir/

# You can also use the 'args' form to provide the options.
- name: This command will change the working directory to somedir/ and will only run when somedir/somelog.txt doesn't exist.
shell: somescript.sh >> somelog.txt
args:
chdir: somedir/
creates: somelog.txt

# You can also use the 'cmd' parameter instead of free form format.
- name: This command will change the working directory to somedir/.
shell:
cmd: ls -l | grep log
chdir: somedir/

- name: Run a command that uses non-posix shell-isms (in this example /bin/sh doesn't handle redirection and wildcards together but bash does)
shell: cat < /tmp/*txt
args:
executable: /bin/bash

- name: Run a command using a templated variable (always use quote filter to avoid injection)
shell: cat {{ myfile|quote }}

# You can use shell to run other executables to perform actions inline
- name: Run expect to wait for a successful PXE boot via out-of-band CIMC
shell: |
set timeout 300
spawn ssh admin@{{ cimc_host }}

expect "password:"
send "{{ cimc_password }}\n"

expect "\n{{ cimc_name }}"
send "connect host\n"

expect "pxeboot.n12"
send "\n"

exit 0
args:
executable: /usr/bin/expect
delegate_to: localhost

# Disabling warnings
- name: Using curl to connect to a host via SOCKS proxy (unsupported in uri). Ordinarily this would throw a warning.
shell: curl --socks5 localhost:9000 http://www.ansible.com
args:
warn: no

RETURN VALUES:

msg:
description: changed
returned: always
type: bool
sample: True
start:
description: The command execution start time
returned: always
type: str
sample: '2016-02-25 09:18:26.429568'
end:
description: The command execution end time
returned: always
type: str
sample: '2016-02-25 09:18:26.755339'
delta:
description: The command execution delta time
returned: always
type: str
sample: '0:00:00.325771'
stdout:
description: The command standard output
returned: always
type: str
sample: 'Clustering node rabbit@slave1 with rabbit@master ...'
stderr:
description: The command standard error
returned: always
type: str
sample: 'ls: cannot access foo: No such file or directory'
cmd:
description: The command executed by the task
returned: always
type: str
sample: 'rabbitmqctl join_cluster rabbit@master'
rc:
description: The command return code (0 means success)
returned: always
type: int
sample: 0
stdout_lines:
description: The command standard output split in lines
returned: always
type: list
sample: [u'Clustering node rabbit@slave1 with rabbit@master ...']

```