Re: [Fab-user] constructing host lists from a file

[Jeff Forcier]

Hi Martin,

On Tue, Aug 10, 2010 at 4:27 PM, Martin-Louis Bright <address@hidden> wrote:
> it would be nice if I could specify the file
> on the command line and be done with it... Is there a disadvantage to
> this approach?

Nope, that would work just fine. You could do something like this:

    def set_hosts(filename):
        with open(filename) as fd:
            env.hosts = [x.strip for x in fd.readlines()]

    def do_stuff():
        run("foo")

and then execute it like this:

    $ fab set_hosts:/path/to/hosts_file.txt do_stuff

Which would execute "foo" on every host[1] defined in /path/to/hosts_file.txt.

That approach works because:

* By the time Fabric goes to execute do_stuff(), your set_hosts() has
already run, and has thus modified env.hosts. (This is a common
idiom.)
* Task functions can take arguments on the command line[2]
* Fabfiles are Just Python(tm) and so stuff like opening and reading
in external files works just fine and is totally encouraged.


All of that said -- there've been occasional discussions about various
other ways of pre-setting or bootstrapping your execution environment,
via config files or importing additional Python files. So this is
likely to get even easier in the future.

Hope that helps,
Jeff

[1] http://docs.fabfile.org/0.9.1/usage/execution.html#hosts
[2] http://docs.fabfile.org/0.9.1/usage/fab.html#per-task-arguments

-- 
Jeff Forcier
Unix sysadmin; Python/Ruby developer
http://bitprophet.org