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From: stevesu@copper.UUCP
Newsgroups: comp.os.vms
Subject: Re: Why no system() under VAX C
Message-ID: <1106@copper.TEK.COM>
Date: Wed, 10-Jun-87 00:56:06 EDT
Article-I.D.: copper.1106
Posted: Wed Jun 10 00:56:06 1987
Date-Received: Sat, 13-Jun-87 03:45:04 EDT
References: <12308535119.47.AWALKER@RED.RUTGERS.EDU> <552@unc.cs.unc.edu> <3322@sri-unix.ARPA>
Distribution: na
Organization: Tektronix Inc., Beaverton, Or.
Lines: 65
Summary: here's one

In article <3322@sri-unix.ARPA>, ubi@sri-unix.ARPA (Ron Ueberschaer) writes:
> Speaking of glaring, why did DEC decide not to implement system()
> under VMS???  It's bad enough that I can't exec anything except
> C programs.

I suspect they left it out because you probably don't want to use
it.  The only way to implement system() is with lib$spawn(),
which is notoriously slow.  Here's one I use, which I call
"vmssystem" so that I have to think about it before using it.
(A program containing "system" won't automatically link, without
some attention.)  Besides thinking about whether you can afford
to spend several seconds in a lib$spawn, you may also need to
change the string actually passed to system(), which is usually a
Unix command of some sort.  (For example, just because you had a
working "system" wouldn't mean that you could port the tar
utility, which contains this gem:

	sprintf(buf, "sort +0 -1 +1nr %s -o %s; \
		awk '$1 != prev {print; prev=$1}' %s >%sX; mv %sX %s",
				tname, tname, tname, tname, tname, tname);
	system(buf);

                                           Steve Summit
                                           stevesu@copper.tek.com

#define NULL 0

struct descriptor
	{
        short dsc_length;
        char dsc_type;
        char dsc_class;
        char *dsc_addr;
	};

vmssystem(command)
char *command;
{
int r;
long int status;
struct descriptor vmscmd;

vmscmd.dsc_addr = command;
vmscmd.dsc_length = strlen(command);
vmscmd.dsc_type = vmscmd.dsc_class = 0;

r = lib$spawn(&vmscmd,			/* command string */
	(struct descriptor *)NULL,	/* input file */
	(struct descriptor *)NULL,	/* output file */
	(long int *)NULL,		/* flags */
	(struct descriptor *)NULL,	/* process name */
	(long int *)NULL,		/* process id */
	&status,			/* completion status */
	(unsigned char *)NULL,		/* completion efn */
	(int (*)())NULL,		/* completion astadr */
	0,				/* completion astarg */
	(struct descriptor *)NULL,	/* prompt */
	(struct descriptor *)NULL);	/* CLI */


if(!(r & 01))
	return -1;

return status;
}