Hi,
I want to assert a file exists - but in a way that doesn't have the potential to
create conflicting resource definitions.
I know this has been asked many times before:
"How can I check whether a file exists, like 'File.exists?(file)'
or '-f $file'?"
My very specific use case is with a user-account define. I want something like
this:
define user_account($name, $shell = '/bin/bash', /* ... */) {
/* ... */
assert file_exists($shell) # make sure the shell is available
/* ... */
}
I don't want to create the file $shell, nor do I care how it gets there, but I
want it to be there (and ideally, executable). Declaring a resource user("foo":
shell = $shell) doesn't appear to assert this by itself (trying in 2.7.9).
Just to be clear, "require File[$shell]" and equivalents are no good, because
they force me to define a File resource which "owns" the file $shell, and since
there can only be one of those I am in trouble if something else wants to define
the same condition. In general I cannot know if this is being asserted
elsewhere by the author of another module.
However, the question has a more general aspect. Why doesn't core Puppet make
assertions like this easy? It seems a simple, obvious, and common thing to
want. And not just for files - I often want to express similar assertions about
users, groups, packages, and probably other resources.
This question seems like it ought to be addressed in the puppet FAQ [1], but I
can't find any discussion of it there, nor in the puppet cookbook [2], puppet
language guide [3], nor the "Puppet types" reference page [4].
I know there are workarounds of sorts:
- if !defined(File[$shell]) { file{ $shell: ensure => 'exists' } }
- Exec { "check ${shell} exists for ${user}":
command => "/usr/bin/test -f '${shell}'" }
- if inline_template("<% File.exists?(shell)? 'true':'false' %>") == "true"
{ /* fail somehow */ }
- define a custom function which simply does File.exists?(shell) and fails if
false
They are all sledgehammers to crack a nut, the first is apparently dangerous and
another thread on this list is proposing to outlaw it.
To sum up, it appears that this feature is missing for a reason, but why? And
what's the best workaround available?
Cheers,
N
1. http://docs.puppetlabs.com/guides/faq.html
2. http://www.puppetcookbook.com/
3. http://docs.puppetlabs.com/guides/language_guide.html
4. http://docs.puppetlabs.com/references/2.7.9/type.html
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