From: Ken Bloom <kbloom@...>
Date: 2006-08-11T23:30:06+09:00
Subject: Re: access built-in shell commands like 'history' or 'fc'

On Wed, 09 Aug 2006 12:28:44 -0700, bwv549 wrote:

> How do I access built-in shell commands (like 'history' or 'fc') with a
> system call?
> 
> Not what I was expecting:
>   % ruby -e 'puts `history`'
>       -e:1: command not found: history
> 
> But this works fine:
> 
>   % ruby -e 'puts `pwd`'
>       /home/john
> 
> I've tried this:
> 
>   % ruby -e 'system "history >tmp.tmp"; puts IO.read("tmp.tmp")'
> 
> And no errors are generated, but there is nothing in tmp.tmp, either.
> 
> Thanks

I think under certain circumstances either ruby doesn't call the shell
(and just calls the executable) or the shell doesn't recognize builtin
commands when called as sh -c

For example:
irb(main):001:0> puts `cd scratch`
(irb):1: command not found: cd scratch

=> nil
irb(main):002:0> puts `pwd`
/home/bloom
=> nil
irb(main):003:0> puts `type pwd`
(irb):3: command not found: type pwd

=> nil
irb(main):004:0> puts `type pwd && echo`
pwd is a shell builtin

=> nil
irb(main):005:0> puts `which pwd`
/bin/pwd
=> nil

pwd works because it also happens to be a binary in /bin

--Ken Bloom

-- 
Ken Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/