From: Brian Palmer <rubytalk@...>
Date: 2006-08-02T13:14:09+09:00
Subject: Re: How to auto-locate interpreter image

On Aug 1, 2006, at 9:15 PM, Scheming Commie wrote:

> On Sat, 15 Jul 2006 21:06:25 +0000, Just Another Victim of the Ambient
> Morality wrote:
>>     I'm pretty sure the "#!" line is meaningless on Windows and  
>> the shell
>> doesn't even bother looking for it.  Indeed, it always struck me a  
>> little
>> weird that every script knows exactly where the interpreter image  
>> is.  What
>> if it were to move?  All your scripts will suddenly break!  An  
>> annoying,
>> albeit, unlikely scenario...
>
> #!/usr/bin/env perl
> #!/usr/bin/env ruby
> .. etc
>
> env finds the interpreter wherever it is and runs it, as you'd expect.
>
> A neat trick, I don't know why it isn't used, well, universally.
>
> Of course it relies on env being in /usr/bin but, that changes less
> (never) than where particular interpreters are.
>
>

When you use a line like #!/usr/bin/env ruby, env searches each  
directory on your path for a program called ruby -- but in some  
situations, such as running under a web server like Apache or from a  
remote ssh session, your path isn't set, or is set to a restricted  
subset of your normal path, so /usr/bin/env won't find what it's  
looking for. As I understand it, that's why it's not more universally  
used.

For instance, on the web hosting service I often use Apache doesn't  
set any path at all, so while /usr/bin/env exists, it can't be used  
in this way.

-- Brian