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From: mwette@mr-ed.jpl.nasa.gov (Matt Wette)
Newsgroups: comp.windows.x
Subject: <None>
Message-ID: <1990Oct16.160553.12020@jato.jpl.nasa.gov>
Date: 16 Oct 90 21:00:21 GMT
References: <m0iOhip-00013UC@aleytys.uu.net>
Sender: news@jato.jpl.nasa.gov
Organization: Jet Propulsion Laboratory
Lines: 187
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 GMT
Message-ID: <1990Oct16.090021@mr-ed.jpl.nasa.gov>
Reply-To: mwette@mr-ed.jpl.nasa.gov (Matt Wette)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Subject: Re: rlogin and the DISPLAY variable
Keywords: 

In article <m0iOhip-00013UC@aleytys.uu.net>, mike%aleytys@UUNET.UU.NET
(Michael Kent) writes:
|> I appologize if this is a FAQ, but:
|> 
|> I need to rlogin to a remote X Workstation from my local X
Workstation,
|> and have the DISPLAY environmental variable properly set so that any
|> X apps I run on the remote machine will display on my local machine.
|> The setting of DISPLAY must happen without operator intervention,
and
|> must be correct no matter which of several local machines rlogin to
the
|> remote machine.
|> 
|> Using the remote shell command is out, since the primary app to be
run
|> on the remote machine is interactive in the manner of 'vi', and is a
|> 'tty'-based app which is best run via rlogin.  Having the user's
profile
|> set DISPLAY is out, as the user can be logging in from several
different
|> local machines.
|> 
|> Any ideas?
|> -- 
|> Michael Kent			INTERNET: mike@aleytys.uu.net
|> Center for M.C.E.		UUCP:     ...!{uunet, uflorida}!aleytys!mike
|> 2521 N.W. 57th Pl		MA BELL:  +1-904-335-1573
|> Gainesville, Fl  32606		"...yes, we have no bananas..."

You may want to try the included program.  It tries to get a reasonable
display name by reading /etc/utmp.   Basically, you put 
	setenv DISPLAY `echodpy` 
in your .cshrc file. 

Matt
 _______________________________________________________________________
_______
 Matthew R. Wette			| Jet Propulsion Laboratory, 198-326
 mwette@csi.jpl.nasa.gov                | 4800 Oak Grove Dr, Pasadena,CA
91109
 -----------------------------------------------------------------------
-------


/* echodpy.c - echo reasonable DISPLAY variable, if possible
 *
 * Copyright (c) 1990 Matthew R. Wette
 * Permission for use and distribution granted provided this copyright
notice
 * and source code accompany distribution.
 *
 * in your .cshrc file put:
 *
 *	set dpy=`echodpy`
 *	if ( "$dpy" != "" ) then
 *		setenv DISPLAY $dpy
 *	endif
 *	unset dpy
 *
 * history -
 *	16Oct90	M.Wette: created.
 *
 * version -
 *      $Id: echodpy.c,v 1.2 90/10/16 09:07:40 mwette Exp $
 *
 * notes -
 *  	1.  probably not the best implementation
 *
 */
#include <utmp.h>
#include <unistd.h>
#include <stdarg.h>
#include <stdio.h>

#define UTMP "/etc/utmp"

void
error(char *fmt, ...)
{
  va_list ap;
  char *p;

  fprintf(stderr, "echodpy: ");
  va_start(ap, fmt);
  for (p = fmt; *p; p++) {
    if (*p != '%') { putc(*p, stderr); continue; }
    switch (*++p) {
    case 'c': putc(va_arg(ap, char), stderr); break;
    case 'd': fprintf(stderr, "%d", va_arg(ap, int)); break;
    case 'f': fprintf(stderr, "%f", va_arg(ap, double)); break;
    case 's': fprintf(stderr, "%s", va_arg(ap, char *)); break;
    default: putc(*p, stderr); break;
    }
  }
  putc('\n', stderr);
}


char *
utmphost(char *line)
{
  FILE *fp;
  struct utmp ut;
  char *host;

# ifdef DEBUG
  error("in utmphost: match line=%s", line);
# endif
  if (access(UTMP, R_OK) != 0) {
    error("access denied to \"%s\"", UTMP);
    return((char *) NULL);
  }
  if ((fp = fopen(UTMP, "r")) == NULL) {
    error("couldn't open \"%s\"", UTMP);
    return((char *) NULL);
  }
  while (fread(&ut, sizeof(struct utmp), 1, fp) > 0) {
#   ifdef DEBUG
    if (ut.ut_line[0] != '\0')
      error("in utmphost: line=%s, host=%s", ut.ut_line, ut.ut_host);
#   endif
    if (strcmp(ut.ut_line, line)==0 && ut.ut_name[0]!='\0') {
      host = (char *) malloc(strlen(ut.ut_host + 1));
      strcpy(host, ut.ut_host);
      return(host);
    }
  }
  return((char *) NULL);
}


int
main(int argc, char *argv[])
{
  char buf[128], *bufp, *ttyn, *line, *host;

  if (isatty(0)) {
    ttyn = ttyname(0);
  } else if (isatty(1)) {
    ttyn = ttyname(1);
  } else if (isatty(2)) {
    ttyn = ttyname(2);
  } else {
#   ifdef DEBUG
    error("can't establish ttyname\n");
#   endif
    exit(1);
  }
# ifdef DEBUG
  error("ttyname=\"%s\"", ttyn);
# endif

  strcpy(buf, &ttyn[5]);
  line = buf;
  if ((host = utmphost(line)) == (char *) NULL) {
#   ifdef DEBUG
    error("couldn't get hostname");
#   endif
    exit(1);
  }
# ifdef DEBUG
  error("host=\"%s\"", host);
# endif

  bufp = buf;
  while (*host != ':' && *host != '\0') *bufp++ = *host++;
  *bufp++ = ':';
  *bufp++ = '0';
  *bufp++ = '.';
  *bufp++ = '0';
  *bufp = '\0';
# ifdef DEBUG
  error("dpy env=\"%s\"", buf);
# endif
  printf(buf);
}

/* --- last line of echodpy.c --- */