From: Joel VanderWerf <joelvanderwerf@...>
Date: 2010-07-29T07:14:59+09:00
Subject: Re: Which Ruby is in use?

Caleb Clausen wrote:
> On 7/28/10, Roger Pack <rogerpack2005@gmail.com> wrote:
>>> I haven't checked yet whether there's a bug filed against JRuby
>>> for the lack of support for ENV['_'], which obviously wins the
>>> minimalist contest  :-)
>> ENV['_'] doesn't seem to work for me on windows at all:
>> 
>>>> ENV['_']
>> => nil
>> 
>> Thought it might still be a bug in jruby that it not have one under
>>  linux, I'm not entirely sure.
> 
> I just did a quick check, and I'm not seeing anywhere in the ruby 
> source where it sets an envvar named _. Perhaps this envvar is a 
> feature of bash or linux or something other than ruby.
> 

Yeah, I think it's just a shell feature:

$ ruby -e 'p ENV["_"]'
"/usr/local/bin/ruby"
$ env ruby -e 'p ENV["_"]'
"/usr/bin/env"

That's the behavior in both zsh and bash.

Found this in some bash docs:

> The underscore variable is set at shell startup and contains the
> absolute file name of the shell or script being executed as passed in
> the argument list. Subsequently, it expands to the last argument to
> the previous command, after expansion. It is also set to the full
> pathname of each command executed and placed in the environment
> exported to that command. When checking mail, this parameter holds
> the name of the mail file.