From: Ken Bloom <kbloom@...>
Date: 2007-12-14T00:25:04+09:00
Subject: Re: system(), syscall(), and Shells

On Wed, 12 Dec 2007 18:21:51 -0500, thefed wrote:

> Hello all
> 
> I have a rather quick question.
> 
> As a part of the ruby unix team, we need to be able to execute commands.
> One way to do this is through system. The other way is through syscall.
> 
> First: does a call of system() open up a new process in the current
> shell or does it make a system call? I tested this out with this
> command:
> 
> system('cat csh.cshrc | wc') and got back a legitimate response. I'm
> assuming, since I used pipelines, that this gets opened in a new shell.
> I am asking here just to be safe.
> 
> Second: How exactly do I use syscall() in Ruby? Partically using syscall
> for the exec command. I could get write to work, but not exec. Help?
> 
> I have researched using syscall, and have only found documentation for
> using it in C. C != Ruby # => true

Syscall in ruby works exactly like it does in C.

Ruby (ri Kernel#syscall)
     Calls the operating system function identified by _fixnum_, passing
     in the arguments, which must be either +String+ objects, or
     +Integer+ objects that ultimately fit within a native +long+. Up to
     nine parameters may be passed (14 on the Atari-ST). The function
     identified by _fixnum_ is system dependent. On some Unix systems,
     the numbers may be obtained from a header file called +syscall.h+.

C (man 2 syscall)
       syscall()   performs  the  system  call  whose
       assembly language interface has the  specified
       number with the specified arguments.  Symbolic
       constants for system calls can be found in the
       header file <sys/syscall.h>.

--Ken

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