I'm try to install rails on Debian. when run this command

`gem install rails`

I gave this error:

```
ERROR:  Loading command: install (LoadError)
    cannot load such file -- zlib
ERROR:  While executing gem ... (NoMethodError)
    undefined method ``invoke_with_build_args' for nil:NilClass

```

even when I try this command:
`gem install`
I gave this error:

```
ERROR:  Loading command: install (LoadError)
    cannot load such file -- zlib
ERROR:  While executing gem ... (NoMethodError)
    undefined method ``invoke_with_build_args' for nil:NilClass

```

I used this link to build ruby from sources [ruby 2.1.2 build instruction](https://gorails.com/setup/ubuntu/14.10)

what can I do to overcome this error?