Redirect command output to file (existing command)

Question

To write the stdout of a command (in this case, echo hi) to a file, you can do:

echo hi > outfile

I would like a command instead of a redirection or pipe so that I do not need to invoke a shell. This is eventually for use with Ansible, which calls python's subprocess.POpen.

I am looking for:

stdout-to-file outfile echo hi

tee makes copying stdout to a file easy enough, but it accepts stdin, not a separate command.

Is there a common, portable command that does this? It's easy enough to write one, of course, but that's not the question. Ultimately, in Ansible, I want to do:

command: to-file /opt/binary_data base64 -d {{ base64_secret }}

Instead of:

shell: base64 -d {{ base64_secret }} > /opt/binary_data

Edit: Looking for a command available on RHEL 7, Fedora 21

You should specify what operating system you're using, since that will make a difference to what commands are available. — Barmar, Feb 28 '15 at 02:15
There is a portable command that does this with a slightly different syntax. It is called a shell, and the syntax is: `sh -c ' > outfile echo hi'` — William Pursell, Feb 28 '15 at 03:48
Except then you have the responsibility of translating the command into a string... Though there may not actually be edge cases, do you see why that's scary, and why one would look for a better alternative? — ToBeReplaced, Feb 28 '15 at 04:16

score 15 · Answer 1 · answered Feb 28 '15 at 04:26

What you are actually looking for, is a Ansible Module, which takes two parameters,

The actual command
A file to redirect the output of above command

In this case, you could use shell module instead of command module, which allows such redirections.

e.g.

- shell: /usr/bin/your_command >> output.log

You could check the source and example documentation here.

This is the simplest. And I believe you are aware of this. I am just putting this across for anyone new to shell/command modules reading this thread.

If you don't like to do it that way, you could still write a wrapper module, which accepts the "file name" as an argument and will run as,

- custommodule: output.log /usr/bin/your_command

All you may need to do is fork the repo, look into existing modules, and customize yours accordingly.

score 7 · Answer 2 · edited May 23 '17 at 12:01

Not sure if that is what you want, but in Ansible - Save registered variable to file I have found what I have needed:

- name: "Gather lsof"
  command: lsof
  register: lsof_command
- name: "Save lsof log"
  local_command:
    copy content="{{ lsof_command.stdout }}" dest="/root/lsof.log"

Or, in my specific case (might be useful for you as well) playbook was running on system A, but I needed the log from B and having it saved to localhost (because A system is hitting B and I want to log B's state):

- name: "Gather lsof on B"
  delegate_to: B
  command: lsof
  register: lsof_command
  run_once: true
- name: "Save lsof log"
  local_action:
    copy content="{{ lsof_command.stdout }}" dest="/root/lsof.log"
  run_once: true

IMO run_once: true is required in my case, as I want the log gathered only once per playbook run (not say 10 times if playbook is running on 10 systems).

Space for improvement would be to save stderr as well or possibly failing "Save lsof log" task when it is not empty.

Redirect command output to file (existing command)

2 Answers2