Pry実行時のエラー「Sorry, you can't use Pry without Readline or a compatible library.･･･」を解決する ref: http://qiita.com/y-temp4/items/7f3d394cfed83c486f15

file0.txt

$ pry
Sorry, you can't use Pry without Readline or a compatible library.
Possible solutions:
 * Rebuild Ruby with Readline support using `--with-readline`
 * Use the rb-readline gem, which is a pure-Ruby port of Readline
 * Use the pry-coolline gem, a pure-ruby alternative to Readline
...

file1.txt

$ gem install rb-readline
Fetching: rb-readline-0.5.3.gem (100%)
Successfully installed rb-readline-0.5.3
Parsing documentation for rb-readline-0.5.3
Installing ri documentation for rb-readline-0.5.3
Done installing documentation for rb-readline after 3 seconds
1 gem installed

file2.txt

$ rbenv install -f 2.3.1

file3.txt

$ pry
[1] pry(main)>