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From: LEICHTER-JERRY@YALE.ARPA.UUCP
Newsgroups: comp.os.vms
Subject: Re: redirection of stdio, et al.
Message-ID: <8704281049.AA16383@ucbvax.Berkeley.EDU>
Date: Tue, 28-Apr-87 06:50:12 EDT
Article-I.D.: ucbvax.8704281049.AA16383
Posted: Tue Apr 28 06:50:12 1987
Date-Received: Wed, 29-Apr-87 06:20:24 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: <LEICHTER-JERRY@YALE.ARPA>
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To: unc!mcguffey@mcnc.org (Michael McGuffey)
    Does anyone know of any tools that allow command line redirection of
    stdio under VMS. Something similar to the way unix and msdos does it is
    preferable to some of the methods that have previously been proposed.

The following is from the DECUS C library; it's meant for programs written
in C - which seems to be what you have in mind - though it could be adapted
for other languages.

getredirection() was written by Martin Minow.  Note that the code dates
back to V1 of C; some of it could be simplified, as you no longer need to
creat/fdopen's to get at various RMS options.

							-- Jerry

/*
 * getredirection() is intended to aid in porting C programs
 * to VMS (Vax-11 C) which does not support '>' and '<'
 * I/O redirection.  With suitable modification, it may
 * useful for other portability problems as well.
 *
 * Modified, 24-Jan-86 by Jerry Leichter
 *	When creating a new output file, force the maximum record size to
 *	512; otherwise, it ends up as 0 (though the C I/O system won't write
 *	a record longer than 512 bytes anyway) which will cause problems if
 *	the file is later opened for APPEND - if the maximum record size is
 *	0, C will use the length of the longest record written to the file
 *	for its buffer!  [This was a C RTL bug, probably since fixed.]
 */

#ifdef	vms
#include	<stdio.h>
#include	<errno.h>

int
getredirection(argc, argv)
int		argc;
char		**argv;
/*
 * Process vms redirection arg's.  Exit if any error is seen.
 * If getredirection() processes an argument, it is erased
 * from the vector.  getredirection() returns a new argc value.
 *
 * Warning: do not try to simplify the code for vms.  The code
 * presupposes that getredirection() is called before any data is
 * read from stdin or written to stdout.
 *
 * Normal usage is as follows:
 *
 *	main(argc, argv)
 *	int		argc;
 *	char		*argv[];
 *	{
 *		argc = getredirection(argc, argv);
 *	}
 */
{
	register char		*ap;	/* Argument pointer	*/
	int			i;	/* argv[] index		*/
	int			j;	/* Output index		*/
	int			file;	/* File_descriptor 	*/

	for (j = i = 1; i < argc; i++) {   /* Do all arguments	*/
	    switch (*(ap = argv[i])) {
	    case '<':			/* <file		*/
		if (freopen(++ap, "r", stdin) == NULL) {
		    perror(ap);		/* Can't find file	*/
		    exit(errno);	/* Is a fatal error	*/
		}
		break;

	    case '>':			/* >file or >>file	*/
		if (*++ap == '>') {	/* >>file		*/
		    /*
		     * If the file exists, and is writable by us,
		     * call freopen to append to the file (using the
		     * file's current attributes).  Otherwise, create
		     * a new file with "vanilla" attributes as if
		     * the argument was given as ">filename".
		     * access(name, 2) is TRUE if we can write on
		     * the specified file.
		     */
		    if (access(++ap, 2) == 0) {
			if (freopen(ap, "a", stdout) != NULL)
			    break;	/* Exit case statement	*/
			perror(ap);	/* Error, can't append	*/
			exit(errno);	/* After access test	*/
		    }			/* If file accessable	*/
		}
		/*
		 * On vms, we want to create the file using "standard"
		 * record attributes.  create(...) creates the file
		 * using the caller's default protection mask and
		 * "variable length, implied carriage return"
		 * attributes. dup2() associates the file with stdout.
		 */
		if ((file = creat(ap, 0, "rat=cr", "rfm=var", "mrs=512"))
			== -1
		 || dup2(file, fileno(stdout)) == -1) {
		    perror(ap);		/* Can't create file	*/
		    exit(errno);	/* is a fatal error	*/
		}			/* If '>' creation	*/
		break;			/* Exit case test	*/

	    default:
		argv[j++] = ap;		/* Not a redirector	*/
		break;			/* Exit case test	*/
	    }
	}				/* For all arguments	*/
	argv[j] = NULL;			/* Terminate argv[]	*/
	return (j);			/* Return new argc	*/
}
#else
getredirection(argc, argv)
int		argc;
char		*argv[];
/*
 * Dummy routine.
 */
{
	return (argv[0], argc);
}
#endif
-------