If you are not familiar with modules, check out Ansible - Getting Started with Modules.
Typically, the shell, command, or script modules are used to invoke a command on a managed node (e.g. target systems).
Python (e.g. /usr/bin/python) needs to exist on the managed node to use these modules.
- shell
- command (this article)
Python is not need to use these modules.
In this example, the ps command will be invoked on the managed nodes.
---
- hosts: localhost
tasks:
- name: ps command
command: ps
...
The following should be produced.
TASK [ps command]
changed: [localhost]
By default, no stdout is printed. register and debug can be used to print output to the console.
---
- hosts: localhost
tasks:
- name: ps command
command: ps
register: out
- name: print out
debug:
var: out
...
Which should return something like this.
TASK [print out]
ok: [localhost] => {
"out": {
"changed": true,
"cmd": "ps",
"delta": "0:00:02.674260",
"end": "2021-08-03 23:34:44.388683",
"failed": false,
"failed_when_result": false,
"msg": "non-zero return code",
"rc": 1,
"start": "2021-08-03 23:34:41.714423",
"stderr": "",
"stderr_lines": [],
"stdout": "root 122418 122378 0 23:41 ? 00:00:00 bash",
"stdout_lines": [
"root 122418 122378 0 23:41 ? 00:00:00 bash"
]
}
}
Often, you just want to get the rc (return code) and stdout and stderr. For debugging purposes, you may need to include ignore_errors: true so that errors are ignored so that you can print the rc (return code), stdout and stderr. Then, use meta: end_play so that the playbook does not continue through the next tasks.
---
- hosts: localhost
tasks:
- name: ps command
command: ps
register: out
ignore_errors: true
- name: return code
debug:
var: out.rc
- name: stdout
debug:
var: out.stdout
- name: stderr
debug:
var: out.stderr
- meta: end_play
...
Often, a return code of 0 or 1 is ok when using the command module. failed_when can be used to fail when the rc (return code) is not 0 or 1. Check out my article on resolving non-zero return code.
---
- hosts: localhost
tasks:
- name: ps command
command: ps
register: out
failed_when: out.rc not in [ 0, 1 ]
...
Become (root, sudo)
If you do not have permission to issue a certain shell command, permission denied will be returned. To resolve this, the become module can be used to become root.
The chdir argument can be used to change into a certain directory on the managed node before running the command.
---
- hosts: localhost
tasks:
- name: invoke example.sh
command: example.sh
args:
chdir: /tmp
...
Let's say the creates parameter contains /tmp/foo.txt. If /tmp/foo.txt exists, the task will not be run. If /tmp/foo.txt does not exist, the task will be run.
---
- hosts: localhost
tasks:
- name: invoke example.sh
command: example.sh
args:
creates: /tmp/foo.txt
...
Let's say the removes parameter contains /tmp/foo.txt. If /tmp/foo.txt exists, the task will be run. If /tmp/foo.txt does not exist, the task will not be run.
---
- hosts: localhost
tasks:
- name: invoke example.sh
command: example.sh
args:
removes: /tmp/foo.txt
...
Let's say you have a script that prompts for input, like this.
What is your name?
The stdin parameter can be used to pass standard input to the script.
---
- hosts: localhost
tasks:
- name: invoke example.sh
command: example.sh
args:
stdin: "John Doe"
...
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