Sometimes I have seen following code.
gem 'factory_girl','= 1.2.3'
require 'factory_girl'
I tried to look at gem doc but could not find answer to the question of what does the first line do in code above?
What you're looking for in the gem docs is about Coding with Rubygems.
The first line basically says "Hey, go get this gem with this version" from the install directory for gems and load it into the environment. This is mainly to help you add version dependencies to your requires instead of just doing require 'factory_girl' by itself.
Edit: To add on to Jörg's point below, I thought that Ryan Tomayko had a pretty good short and sweet article about why doing this is "wrong".
As #theIV already explained, this activates the factory_girl gem, using exactly (because of the = sign) version 1.2.3.
Note, however, that this is very bad practice and should never be done. If you activate gems manually inside your code, it means that people who do not use RubyGems can no longer use your code.
RubyGems is a package manager. Your code should never care about what package manager was used to install it. Some people prefer RubyGems, some dpkg/APT, some RPM/YUM, some RPM/APT, some RPM/URPMI, some RPM/YaST2, Portage, FreeBSD ports, pkgsrc, MacPorts, slashpackage, CoAPP, Conary, Slackware. There's tons of them. Some people like not to use any package manager at all. Or, they use RubyGems just for downloading, but then unpack the gem into their vendor directory.
All of this cannot possibly work, if you use the gem method in your code.
Related
In our Rails application we do require 'RRD' at some point, but that results in a cannot load such file -- RRD. So obviously I used homebrew to install rrdtool, but the error remains.
The docs at https://oss.oetiker.ch/rrdtool/prog/rrdruby.en.html provide two options:
Either:
$: << '/path/to/rrdtool/lib/ruby/1.8/i386-linux'
require "RRD"
In my /opt/homebrew/Cellar/rrdtool/1.8.0/lib directory there's no mention of ruby, which is because of the --disable-ruby-site-install flag in the formula, because when I skip that flag I do actually get something: /opt/homebrew/Cellar/rrdtool/1.8.0/lib/ruby/2.6.0/universal-darwin21. However replacing the path/to string with this path still gives the error.
Or:
If you use the --ruby-site-install configure option you can drop the $: line since the RRDtool module will be found automatically.
Which is a little confusing (and probably outdated) because here it seems that ruby site install is disabled by default and you have to enable it proactively, whereas in the formula it's actually actively disabled.
Either way: both options didn't do the trick for me and if there's a solution without homebrew that's also fine.
For good measure: I'm on macOS Monterey
TL;DR
For the most part, I'd say that using a non-standard gem without a Ruby version manager is your main issue. There are instructions on the rrdruby site for installing it, but they don't follow typical conventions, so your mileage will vary.
Some Practical Suggestions
The require keyword is for gems, not binaries. You need to have an rrdtool-related gem installed, available to your Ruby instance (usually through a Bundler Gemfile or gemspec, or via the RUBYOPTS environment variable or your in-process Ruby $LOAD_PATH), and then require the correct name of the gem in your code. For example, using the older rrd-ffi gem:
# use sudo if you're installing it to the system,
# but I would strongly recommend a ruby version
# manager instead
gem install rrd-ffi
# in your Ruby class/module file
require "rrd"
For the gem you seem to be using, you have to compile the gem first to make it usable, and then ensure it's available in your Ruby $LOAD_PATH (or other gem lookup mechanism) before trying to require it. The error message you're seeing is basically telling you that a gem with that name is not available as called within any of the standard lookup locations.
Again, I'd suggest reading the build documentation for your gem, and then seeing if you can install it as part of a Bundler bundle, RVM gemset, or other non-system approach if you can. Otherwise, follow the directions for the rrdruby tool, which is not available as a standard Rubygems.org gem, in order to make it available before trying to require it.
Beware of Outdated or Non-Standard Gems
Most of the RRD gems I found were quite old; most were 7-8 years old or older, so their compatibility with current Rubies is potentially suspect. The gem-builder you're using is newer, but doesn't seem to be designed as a standard gem, so you need to build it and install it in a suitable lookup path before it can be required. Installing gems as system gems is almost always a bad idea, so I'd strongly recommend building it from source and using a ruby version manager rather than following the rrdtool author's atypical suggestions. YMMV.
I'm trying to create a gem with Bundler, following this guide: http://rakeroutes.com/blog/lets-write-a-gem-part-one/. In it, it says:
I incorrectly thought after taking my first look through the gemspec
that I would need to add more require statements as I developed my
gem. That isn’t the case: the files just need to be in git.
I am trying to clean up some of my old gems to use this convention, but when I install my gem, the classes from the other files are not available. I have a couple directories nested under my /lib dir, but I wouldnt think that would be an issue. Is there anything simple to overlook that would prevent my other files from being required? Any help would be appreciated.
In the link, when he says he doesn't need to add a lot of "require" statements, he must mean adding files to the s.files, s.executables, and s.test_files arrays--these determine what files get packaged up into the gem and what files get ignored. As you can see from the gem spec, whatever's tracked by git in certain directories is going to be included in the packaged gem.
Ruby's require is a different story. Standard require rules still apply.
Ruby's gem system works by adding a bunch of different places for Ruby to look for "foo.rb" when you run require "foo". If "lib" is your only require path for your gem, when you require "my_gem" Ruby is only going to run the code in lib/my_gem.rb. If lib/my_gem.rb doesn't require any other files in your gem, then Ruby hasn't seen them and so you'll get undefined constant errors when you try to use the classes from those files.
For examples, you might take a look at two simple gems I've written; both were started with bundle gem: HashToHiddenFields and SimpleStats. In both gems, main Ruby file in lib/ requires everything that needs to be loaded for the gem to work correctly. For example, hash_to_hidden_fields.rb requires action_view/helpers/hash_to_hidden_fields so that the ActionView::Helpers::HashToHiddenFields constant+module exists so we can include it into ActionView::Base.
Hope that answers the question. I know Ruby requiring was pretty fuzzy to me for a while.
I have a Gem that I found at RubyForge and want to peek inside to see what code it contains. Is it possible to do this without installing the Gem on my system?
Also, if I use RVM on Mac OS X, does that at all change how my gems get installed (assuming I have one gemset)?
gem unpack unpacks the gem without installing it.
Gems on RubyGems usually have a link to the source code (most often on GitHub), in which case you can easily browse the code (I use this A LOT).
The "homepage" link also tends to link to the repository.
If all else fails, go to GitHub and search for the name of the gem (you may need to match up the authors to ensure it's the right repository for the gem).
Edit:
Just noticed that you asked about gems on Rubyforge. In which case my first step would be to check RubyGems. But otherwise you will need to download the gem and peek inside it (it's just a compressed archive so you can open it up in something like 7-zip).
Many gems have their source freely readable. The way that always works is to install it.
If you just want to browse the source; go to the gem on http://rubygems.org find your gem and use the "Source code" link.
In case of RubyForge you can find the links under the SCM link in the menu.
When I type ri at the command prompt it returns nothing:
Classes and Modules known to ri:
How do I set this up properly?
Many thanks.
You can type gem rdoc --all --overwrite to have gem recreate ri and rdocs for all gems.
You don't say what version of Ruby you have installed, but 1.8.7 seemed to have problems remembering whether it had docs for the core and standard libraries. There was a gem called something like core-data that helped. If I can remember the real name I'll update this.
1.9.2 is better about its docs but I've seen times where I have to force the rebuild using the command above. A gem can act up, causing RDoc to puke, which ends up keeping all the docs from being generated so watch its progress and compare it to what gem list outputs as a sanity check. If that happens I have a shell script I use to walk through all the gems and rebuild their docs one by one. It's an easy piece of code to write and steps around the problem of a single gem killing the processing of everything.
I think you don't have the path to your ruby install folder in your PATH variable.
You have to do it to be allowed to launch ri in your command prompt.
Otherwise you can use the entire path : C:\Ruby\bin\ri.bat
With Jeweler I created a gem folder structure with ease.
However, I still have some questions:
Why are params like --gemcutter and --rubyforge still available for Jeweler. Aren't these replaced by RubyGems? Do I have to specify anything to create a gem for RubyGems?
In the Rakefile I have information about the gem, and when I run "rake install" it created a gemspec. Why is the same information in two places?
What is a manifest? Just read about it, haven't seen such file.
How do I make my gem callable from the shell once I have installed it, like rails. Cause right now it's just accessible through a Ruby script using require.
Should I use "jeweler release" or "gem push" to push my gem to RubyGems.org?
I have to specify "handle" when signing up in RubyGems. What is that?
Thanks.
jeweler was created before RubyGems became what it is, so it still reflects the split. I'm not sure when jeweler was last updated, either. (I think it also still recognizes building gems on Github, which is now disabled.)
I'm not sure I follow what you're saying. The specification in the Rakefile details what the spec that gets written should look like. The spec that gets written details what should be installed and how, I believe.
A manifest is a list of all the files that your gem should ship with. Not everyone uses one. See the hoe documentation for some pro-manifest discussion.
Many Ruby gems are only libraries. If you want yours to also have a program like jeweler or rake or rails that you can call, you have to write the callable program, put it in bin in your gem's layout and specify (in your gemspec) that it should be packaged and installed. See the Gem::Specification reference under files and executable.
Not sure. Consult both jeweler's docs and the docs for RubyGems.
You can give an email address or use a name (a 'handle', like I use Telemachus here), which is all they mean by 'handle'.
For the record, if you are just learning how to write gems, you do not need to upload your first attempts using RubyGems or anything like it. You can simply install the gem on your machine only.