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From: emmonsl@athena.ecs.csus.edu (L. Scott Emmons)
Newsgroups: comp.unix.programmer
Subject: Re: system() question
Message-ID: <1991Mar2.181423.13981@csusac.csus.edu>
Date: 2 Mar 91 18:14:23 GMT
References: <9321@hub.ucsb.edu>
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Organization: California State University, Sacramento
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In article <9321@hub.ucsb.edu> 6600bori@ucsbuxa.ucsb.edu (Boris Burtin) writes:
>Can anyone tell me why I get a core dump
>when I try to do :
>
> system("last [username] > ~/filename");

News has been stacked up here, so there's probably already been a reply
to this (since it's been a week since your original post), but
anyway...

system() uses /bin/sh to execute the command, and sh doesn't know ~.

Also, you are _much_ better off doing a fork() and then an exec()
instead of a system()...system just does the equivalent of a fork() and
an exec(), just _much_ less efficiently...If you need some help on
using fork() and exec() please send me some mail and I'll be happy to
give you a hand. (The reason that this is more efficient is because with
exec() you don't fork a shell, you just execute the program directly).

There is a story (well, a truth) around campus here.  Someone needed to
delete a file via a program.  Instead of using unlink() they
system("rm") the file...  rm is just a program which calls unlink(),
but with millions of times the overhead, because they used system()
(ok, well not quite that much)...Anyway, avoid system() where exec() or
a direct system call will do.

Hope this offers you some help...

			L. Scott Emmons
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