We dynamically compute the name of a directory at run-time from some attributes:
var1 = (node['foo']['bar']).to_s
var2 = (node['foo']['baz']).to_s
app_dir = "/var/#{var1}/#{var2}
Copying this code block to all of the recipes that needs it works. When we have tried to clean this up, it bombs with "No resource, or local variable named 'app_dir'.
We have tried the following:
1) Move the block of code into attributes/default.rb
2) Move the block of code into recipes/default.rb
3) Same as 2 above, but adding require_relative 'default' in the recipes that require the variable
If you're requiring from a separate file (e.g. require_relative) you need to make the variable something that gets exported. You can try making it a constant instead e.g. AppDir =, or a method. Local variables are not loaded with require.
There isn't really a good way to do this in Chef. Recipe and attributes files run in very different contexts so your best bet is either copy-pasta the boiler plate (if it really is as small as your example, do that) or otherwise maybe a global helper method but those are hard to write safely. Ping me on Slack and we can talk about the right kind of helper method for your exact situation (covering all of them isn't really practical for an SO answer).
If you need to share some code between a bunch of different recipes, you can try using a library loaded from a common cookbook dependency.
Related
For work purposes I need to link against an object file generated by another program and found in its folder, the case is that I did not find information about this kind of linkage. I think that if I hardcode the paths and put the name-of-obj.o in front of the package_LDADD variable should work, but the case is that I don't want to do it that way.
If the object is not found I want the configure to fail and tell the user that the name-of-obj.o is missing.
I tried by using AC_LIBOBJ([name-of-obj.o]) but this will try to find in the root directory a name-of-obj.c and compile it.
Any tip or solution around this issue?
Thank you!
I need to link against an object file generated by another program and
found in its folder
What you describe is a very unusual requirement, not among those that the Autotools are designed to handle cleanly or easily. In particular, Autoconf has no mechanisms specifically applicable to searching for bare object files, as opposed to libraries, and Automake has no particular automation around including such objects when it links. Nevertheless, these tools do have enough general purpose functionality to do what you want; it just won't be as tidy as you might like.
I think that if I hardcode the paths and put the
name-of-obj.o in front of the package_LDADD variable should work, but
the case is that I don't want to do it that way.
I take it that it is the "hardcode the paths" part that you want to avoid. Adding an item to an appropriate LDADD variable is not negotiable; it is the right way to get your object included in the link.
If the object is not found I want the configure to fail and tell the
user that the name-of-obj.o is missing.
Well, then, the key thing appears to be to get configure to perform a search for your object file. Autoconf does not have a built-in mechanism to perform such a search, but it's just a macro-based shell-script generator, so you can write such a search in shell script + Autoconf, maybe something like this:
AC_MSG_CHECKING([for name-of-obj.o])
OTHER_LOCATION=
for my_dir in
/some/location/other_program/src
/another/location/other_program.12345/src
$srcdir/../relative/location/other_program/src; do
AS_IF([test -r "${my_dir}/name-of-obj.o"], [
# optionally, perform any desired test to check that the object is usable
# ... perhaps one using AC_LINK_IFELSE ...
# if it passes, then
OTHER_LOCATION=${my_dir}
break
])
done
# Check whether the object was in fact discovered, and act appropriately
AS_IF([test "x${OTHER_LOCATION}" = x], [
# Not found
AC_MSG_RESULT([not found])
AC_MSG_ERROR([Cannot configure without name-of-obj.o])
], [
AC_MSG_RESULT([${OTHER_LOCATION}/name-of-obj.o])
AC_SUBST([OTHER_LOCATION])
])
That's functional, but of course you could embellish, such as by providing for the package builder to specify a location to use via a command-line argument (AC_ARG_WITH(...)). And if you want to do this for multiple objects, then you would probably want to wrap up at least some of that into a custom macro.
The Automake side is much less involved. To get the object linked, you just need to add it to the appropriate LDADD variable, using the output variable created by the above, such as:
foo_LDADD = $(OTHER_LOCATION)/name-of-obj.o
Note that if you're building just one program target then you can use the general LDADD instead of foo_LDADD, but note that by default these are alternatives not complements.
With that said, this is a bad idea overall. If you want to link something that is not part of your project, then you should get it from an installed library. That can be a local, custom-built library, of course, so long as it is a library, not a bare object file, and it is installed. It can be a static library if you don't want to rely on or distribute a separate shared library.
On the other hand, if your project is part of a larger build, then the best approach is probably to integrate it into that build, maybe as a subproject. It would still be best to link a library instead of a bare object file, but in a subproject context it might make sense to use a lib that was not installed to the build system. In conjunction with a command-line argument that tells it where to find the wanted lib, this could make the needed Autoconf code much cleaner and clearer.
I work on a team that decided long ago to use Chef's template resource to make dynamic scripts to be executed in an execute reource block.
I know this feature was only built to generate config files and the like, but I have to work with what I've got here.
Basically I need to know how to write to Chef::Log from a Ruby script generated from a template block. The script is not in the same context as the cookbook that generated it, so I can't just call require 'chef/log' in the script. I also do not want to just append the chef-run.log because that runs into timing problems.
Is there any way to accomplish this as cleanly as possible without appending to chef-run.log?
Thank you for your time.
Chef::Log is a global, so technically you can just call its methods directly from inside a template, but this is really weird and you probably shouldn't. Do whatever logging you need from the recipe code instead. If you need to log some values, compute them in the recipe and them pass them in using variables.
I'm wondering what benefit discriminating between local and global variables provides. It seems to me that if everything were made a global variable, there would be a lot less confusion.
Wouldn't declaring everything a global variable result in fewer errors because one wouldn't mistakenly call a local variable in a global instance, thereby encountering fewer errors?
Where is my logic wrong on this?
Some of this boils down to good coding practices. Keeping variables local also means it becomes simpler to share code from one application to another without having to worry about code conflicts. While its simpler to make everything global, getting into the habit of only using global variables when you actually have to will force you to code more efficiently and will make your code more structured.
I think your key oversight is thinking that an error telling you a local variable doesn't exist is a bad thing - it isn't. You've made a mistake and ruby is telling you so. This type of mistake is usually easy to fix: you've misspelled something or you're using something that you forgot to create.
Global variables everywhere might remove those errors but they would replace them with a far harder set of errors to reason about: accidentally using a variable that another bit of code is using. Imagine if every time you called a function (one of your own or a standard library one or one from a gem) you had to check which global variables it might change (and which functions it called, since it might also change global variables) If you make a mistake then you might get an error message (if the class of the object in the variable changes enough) but often you would just silently get incorrect results (if the value of a variable you were using changes unexpectedly).
In general global variables are much harder to work with and people avoid them when possible.
If all variables are global, every line of code in every program (including those which haven't been written yet) written by every programmer on the planet (including those who haven't been born yet or are already dead) must universally, uniquely agree on the names of variables. If you use a variable name that someone else on a different continent two years from now will also use, both of your programs will break, when used together.
For reasons that are a little hard to explain, I need to do the following: I have a master.rb file that sets some global like: a = 1. I want to call another file other_file.rb that will run with the globals that were set in the master file. In python I'd use runpy.run_module( 'other_module', globals() ).
Can anyone think of an equivalent in Ruby? I've looked at require, include, and load, but none seem to do quite what I need, specifically they don't pull the globals into the other_file.rb. Note that I am not trying to fork a new process, just hand execution over to "other_module" while maintaining the state of the globals.
a=1 is not a global variable, it is a local variable that gets scoped to the file. If you really nee this behavior, use $a=1 to set global variables.
If you absolutely must, you can use globals, and they're declared with the $ prefix. They are highly discouraged because there is only one global namespace, which makes collisions possible. Generally they are used for interpreter configuration, like $LOAD_PATH.
A better approach is to use a module that has instance variables:
module MyContainer
def self.settings
#settings ||= { }
end
end
MyContainer.settings[:foo] = :bar
This has the advantage of keeping your variables contained in a namespace while not preventing other sub-programs from accessing them.
Keep in mind this will only work within the context of the same Ruby process or children created using fork, so using system or exec will not work. Remember also that forked processes need to use IPC to communicate with their parent.
I have seen two commonly used techniques for adding the directory of the file currently being executed to the $LOAD_PATH (or $:). I see the advantages of doing this in case you're not working with a gem. One seems more verbose than the other, obviously, but is there a reason to go with one over the other?
The first, verbose method (could be overkill):
$LOAD_PATH.unshift(File.expand_path(File.dirname(__FILE__))) unless $LOAD_PATH.include?(File.expand_path(File.dirname(__FILE__)))
and the more straightforward, quick-and-dirty:
$:.unshift File.dirname(__FILE__)
Any reason to go with one over the other?
The Ruby load path is very commonly seen written as $: , but just because it is short, does not make it better. If you prefer clarity to cleverness, or if brevity for its own sake makes you itchy, you needn't do it just because everyone else is.
Say hello to ...
$LOAD_PATH
... and say goodbye to ...
# I don't quite understand what this is doing...
$:
I would say go with $:.unshift File.dirname(__FILE__) over the other one, simply because I've seen much more usage of it in code than the $LOAD_PATH one, and it's shorter too!
I'm not too fond on the 'quick-and-dirty' way.
Anyone new to Ruby will be pondering what $:. is.
I find this more obvious.
libdir = File.dirname(__FILE__)
$LOAD_PATH.unshift(libdir) unless $LOAD_PATH.include?(libdir)
Or if I care about having the full path...
libdir = File.expand_path(File.dirname(__FILE__))
$LOAD_PATH.unshift(libdir) unless $LOAD_PATH.include?(libdir)
UPDATE 2009/09/10
As of late I've been doing the following:
$:.unshift(File.expand_path(File.dirname(__FILE__))) unless
$:.include?(File.dirname(__FILE__)) || $:.include?(File.expand_path(File.dirname(__FILE__)))
I've seen it in a whole bunch of different ruby projects while browsing GitHub.
Seems to be the convention?
If you type script/console in your Rails project and enter $:, you'll get an array that includes all the directories needed to load Ruby. The take-away from this little exercise is that $: is an array. That being so, you can perform functions on it like prepending other directories with the unshift method or the << operator. As you implied in your statement $: and $LOAD_PATH are the same.
The disadvantage with doing it the quick and dirty way as you mentioned is this: if you already have the directory in your boot path, it will repeat itself.
Example:
I have a plugin I created called todo. My directory is structured like so:
/---vendor
|
|---/plugins
|
|---/todo
|
|---/lib
|
|---/app
|
|---/models
|---/controllers
|
|---/rails
|
|---init.rb
In the init.rb file I entered the following code:
## In vendor/plugins/todo/rails/init.rb
%w{ models controllers models }.each do |dir|
path = File.expand_path(File.join(File.dirname(__FILE__), '../lib', 'app', dir))
$LOAD_PATH << path
ActiveSupport::Dependencies.load_paths << path
ActiveSupport::Dependencies.load_once_paths.delete(path)
end
Note how I tell the code block to perform the actions inside the block to the strings 'models', 'controllers', and 'models', where I repeat 'models'. (FYI, %w{ ... } is just another way to tell Ruby to hold an array of strings). When I run script/console, I type the following:
>> puts $:
And I type this so that it is easier to read the contents in the string. The output I get is:
...
...
./Users/Me/mySites/myRailsApp/vendor/plugins/todo/lib/app/models
./Users/Me/mySites/myRailsApp/vendor/plugins/todo/lib/app/controllers
./Users/Me/mySites/myRailsApp/vendor/plugins/todo/lib/app/models
As you can see, though this is as simple an example I could create while using a project I'm currently working on, if you're not careful the quick and dirty way will lead to repeated paths. The longer way will check for repeated paths and make sure they don't occur.
If you're an experienced Rails programmer, you probably have a very good idea of what you're doing and likely not make the mistake of repeating paths. If you're a newbie, I would go with the longer way until you understand really what you're doing.
Best I have come across for adding a dir via relative path when using Rspec. I find it verbose enough but also still a nice one liner.
$LOAD_PATH.unshift(File.join(File.dirname(__FILE__), '..', 'lib'))
There is a gem which will let you setup your load path with nicer and cleaner code. Check this out: https://github.com/nayyara-samuel/load-path.
It also has good documentation
My 2ยข: I like $LOAD_PATH rather than $:. I'm getting old... I've studied 92,000 languages. I find it hard to keep track of all the customs and idioms.
I've come to abhor namespace pollution.
Last, when I deal with paths, I always delete and then either append or prepend -- depending upon how I want the search to proceed. Thus, I do:
1.times do
models_dir = "#{File.expand_path(File.dirname(__FILE__))}/models"
$LOAD_PATH.delete(models_dir)
$LOAD_PATH.unshift(models_dir)
end
I know it's been a long time since this question was first asked, but I have an additional answer that I want to share.
I have several Ruby applications that were developed by another programmer over several years, and they re-use the same classes in the different applications although they might access the same database. Since this violates the DRY rule, I decided to create a class library to be shared by all of the Ruby applications. I could have put it in the main Ruby library, but that would hide custom code in the common codebase which I didn't want to do.
I had a problem where I had a name conflict between an already defined name "profile.rb", and a class I was using. This conflict wasn't a problem until I tried to create the common code library. Normally, Ruby searches application locations first, then goes to the $LOAD_PATH locations.
The application_controller.rb could not find the class I created, and threw an error on the original definition because it is not a class. Since I removed the class definition from the app/models section of the application, Ruby could not find it there and went looking for it in the Ruby paths.
So, I modified the $LOAD_PATH variable to include a path to the library directory I was using. This can be done in the environment.rb file at initialization time.
Even with the new directory added to the search path, Ruby was throwing an error because it was preferentially taking the system-defined file first. The search path in the $LOAD_PATH variable preferentially searches the Ruby paths first.
So, I needed to change the search order so that Ruby found the class in my common library before it searched the built-in libraries.
This code did it in the environment.rb file:
Rails::Initializer.run do |config|
* * * * *
path = []
path.concat($LOAD_PATH)
$LOAD_PATH.clear
$LOAD_PATH << 'C:\web\common\lib'
$LOAD_PATH << 'C:\web\common'
$LOAD_PATH.concat(path)
* * * * *
end
I don't think you can use any of the advanced coding constructs given before at this level, but it works just fine if you want to setup something at initialization time in your app. You must maintain the original order of the original $LOAD_PATH variable when it is added back to the new variable otherwise some of the main Ruby classes get lost.
In the application_controller.rb file, I simply use a
require 'profile'
require 'etc' #etc
and this loads the custom library files for the entire application, i.e., I don't have to use require commands in every controller.
For me, this was the solution I was looking for, and I thought I would add it to this answer to pass the information along.