Finding and Changing the Current Working Directory

Problem

You want to see which directory the Ruby process considers its current working directory, or change that directory.

Solution

To find the current working directory, use Dir.getwd:

 
Dir.getwd # => "/home/leonardr"

To change the current working directory, use Dir.chdir:

	 
Dir.chdir("/bin")
	Dir.getwd # => "/bin"
	File.exists? "ls" # => true

Discussion

The current working directory of a Ruby process starts out as the directory you were in when you started the Ruby interpreter. When you refer to a file without providing an absolute pathname, Ruby assumes you want a file by that name in the current working directory. Ruby also checks the current working directory when you require a library that can't be found anywhere else.

The current working directory is a useful default. If you're writing a Ruby script that operates on a directory tree, you might start from the current working directory if the user doesn't specify one.

However, you shouldn't rely on the current working directory being set to any particular value: this makes scripts brittle, and prone to break when run from a different directory. If your Ruby script comes bundled with libraries, or needs to load additional files from subdirectories of the script directory, you should set the working directory in code.

You can change the working directory as often as necessary, but it's more reliable to use absolute pathnames, even though this can make your code less portable. This is especially true if you're writing multithreaded code.

The current working directory is global to a process. If multiple threads are running code that changes the working directory to different values, you'll never know for sure what the working directory is at any given moment.