"invalid gem" with different versions of ruby and its packages - ruby

Question

I know very little about ruby and its package management. On a Ubuntu 16.04 system, there seems to be something messed up with different versions of ruby. I tried to run pdfbeads ruby program.
$ pdfbeads -o all.pdf
/home/t/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:54:in `require': iconv will be deprecated in the future, use String#encode instead.
/home/t/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:128:in `require': libMagickCore.so.5: cannot open shared object file: No such file or directory - /home/t/.rvm/gems/ruby-1.9.3-p551/extensions/x86_64-linux/1.9.1/rmagick-2.13.4/RMagick2.so (LoadError)
from /home/t/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:128:in `rescue in require'
from /home/t/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:39:in `require'
from /home/t/.rvm/gems/ruby-1.9.3-p551/gems/rmagick-2.13.4/lib/rmagick_internal.rb:11:in `<top (required)>'
from /home/t/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/t/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/t/.rvm/gems/ruby-1.9.3-p551/gems/rmagick-2.13.4/lib/RMagick.rb:1:in `<top (required)>'
from /home/t/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/t/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/t/.rvm/gems/ruby-1.9.3-p551/gems/pdfbeads-1.1.1/lib/pdfbeads.rb:35:in `<top (required)>'
from /home/t/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/t/.rvm/rubies/ruby-1.9.3-p551/lib/ruby/site_ruby/1.9.1/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/t/.rvm/gems/ruby-1.9.3-p551/gems/pdfbeads-1.1.1/bin/pdfbeads:38:in `<top (required)>'
from /home/t/.rvm/gems/ruby-1.9.3-p551/bin/pdfbeads:23:in `load'
from /home/t/.rvm/gems/ruby-1.9.3-p551/bin/pdfbeads:23:in `<main>'
from /home/t/.rvm/gems/ruby-1.9.3-p551/bin/ruby_executable_hooks:15:in `eval'
from /home/t/.rvm/gems/ruby-1.9.3-p551/bin/ruby_executable_hooks:15:in `<main>'
I first found that the default pdfbeads isn't the one for the latest version of ruby, so I call the latter directly:
$ which pdfbeads
/home/t/.rvm/gems/ruby-1.9.3-p551/bin/pdfbeads
$ whereis pdfbeads
pdfbeads: /usr/local/bin/pdfbeads /home/t/.rvm/gems/ruby-1.9.3-p551/bin/pdfbeads
$ whereis gem
gem: /usr/bin/gem2.3 /usr/bin/gem /home/t/.rvm/rubies/ruby-1.9.3-p551/bin/gem /usr/share/man/man1/gem.1.gz
$ gem --version
2.4.3
$ /usr/local/bin/pdfbeads -o all.pdf
Ignoring executable-hooks-1.3.2 because its extensions are not built. Try: gem pristine executable-hooks --version 1.3.2
Ignoring gem-wrappers-1.2.7 because its extensions are not built. Try: gem pristine gem-wrappers --version 1.2.7
Ignoring nokogiri-1.6.6.2 because its extensions are not built. Try: gem pristine nokogiri --version 1.6.6.2
Ignoring rmagick-2.13.4 because its extensions are not built. Try: gem pristine rmagick --version 2.13.4
/usr/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- iconv (LoadError)
from /usr/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /home/t/.rvm/gems/ruby-1.9.3-p551/gems/pdfbeads-1.1.1/bin/pdfbeads:35:in `<top (required)>'
from /usr/local/bin/pdfbeads:23:in `load'
from /usr/local/bin/pdfbeads:23:in `<main>'
Hoping to solve the problem, I run the suggested gem command, but what does the error mean here?
$ gem pristine executable-hooks --version 1.3.2
Restoring gems to pristine condition...
Cached gem for executable-hooks-1.3.2 not found, attempting to fetch...
Fetching: executable-hooks-1.3.2.gem (100%)
ERROR: While executing gem ... (Gem::InstallError)
invalid gem: No such file or directory - /home/t/.rvm/gems/ruby-1.9.3-p551#global/cache/executable-hooks-1.3.2.gem
How can I clean up the old version of ruby and its packages, if I only need the newer version?
Thanks.

Answer 1

You are missing some libraries (imagemagick). Please try installing them:
sudo apt-get install imagemagick libmagickwand-dev
After that try again to install your gem.
To cleanup old version of a gem run:
gem cleanup pdfbeads
To uninstall a specific ruby version run:
rvm remove 1.9.3
You can also take a look in the folder /home/t/.rvm/ and clean up by hand. But do that with care. Or just take a look in this folder to find out which ruby versions and gemsets are installed and clean up with the rvm commands.