It's common to want to find the current user's home directory, for instance to read or write a config file.
config_file = File.join(Dir.home, ".rubytapas") # => "/home/avdi/.rubytapas"
So you might think is going to be an extra short episode! But there's a small complication.
Dir.home depends on the
$HOME environment variable being set. We can demonstrate this fact by removing the
$HOME variable and trying to use
ENV.delete('HOME') config_file = File.join(Dir.home, ".rubytapas") # ~> -:2:in `home': couldn't find HOME environment -- expanding `~' (ArgumentError) # ~> from -:2:in `<main>'
Actually, that's not completely true.
Dir.home doesn't need the
$HOME environment variable to be set if you pass it an explicit username.
ENV.delete('HOME') config_file = File.join(Dir.home("avdi"), ".rubytapas") # => "/home/avdi/.rubytapas"
So now the question becomes: how do we get a hold of the current user's login? We might look at the $USER variable, but in a situation where the
$HOME variable isn't set, I wouldn't rely on the
$USER variable being available either.
Of course, the operating system knows who the current user is. Can't we ask it? As a matter of fact we can. To do so, we use the
etc standard library.
etc provides a module called (surprise)
Etc, which exposes a method called
#getlogin which returns the login of the current user.
require 'etc' user = Etc.getlogin # => "avdi" config_file = File.join(Dir.home(user), ".rubytapas") # => "/home/avdi/.rubytapas"
Etc, we can reliably find the current user's home directory without depending on environment variables. This technique should work on any UNIX-like operating system, including Linux and Mac OS X. It does not work on Windows.
OK, that's all for today. Happy hacking!