cmd/std/mesg.c

/***********************************************************************
*                                                                      *
*               This software is part of the ast package               *
*          Copyright (c) 1989-2011 AT&T Intellectual Property          *
*                      and is licensed under the                       *
*                 Eclipse Public License, Version 1.0                  *
*                    by AT&T Intellectual Property                     *
*                                                                      *
*                A copy of the License is available at                 *
*          http://www.eclipse.org/org/documents/epl-v10.html           *
*         (with md5 checksum b35adb5213ca9657e911e9befb180842)         *
*                                                                      *
*              Information and Software Systems Research               *
*                            AT&T Research                             *
*                           Florham Park NJ                            *
*                                                                      *
*                 Glenn Fowler <gsf@research.att.com>                  *
*                                                                      *
***********************************************************************/
#pragma prototyped
/*
 * mesg.c
 * Written by David Korn
 * Thu Aug 15 15:25:29 EDT 1996
 */

static const char usage[] =
"[-?\n@(#)$Id: mesg (AT&T Research) 1999-04-28 $\n]"
USAGE_LICENSE
"[+NAME?mesg - permit or deny messages to the terminal]"
"[+DESCRIPTION?\bmesg\b controls whether other users are allowed to send"
"   messages via \bwrite\b(1), \btalk\b(1) or other commands to the"
"   terminal device. The terminal device affected is determined by"
"   searching for the first terminal in the sequence of devices"
"   associated with standard input, standard output and standard error,"
"   respectively. With no arguments, \bmesg\b reports the current state"
"   without changing it. Processes with appropriate privileges may be"
"   able to send messages to the terminal independent of the"
"   current state.]"

"\n"
"\n[ y | n ]\n"
"\n"

"[+OPERANDS?The following operands are supported:]{"
"   [+y?Grant permission to other users to send messages to the terminal.]"
"   [+n?Deny permission to other users to send messages to the terminal.]"
"}"
"[+SEE ALSO?\btalk\b(1), \bwrite\b(1)]"
;

#include    <cmd.h>
#include    <ls.h>

static int mesg(int  mode)
{
    struct stat statb;
    char *tty = ttyname(2);
    if(!tty)
        tty = ttyname(0);
    if(!tty)
        tty = ttyname(1);
    if(!tty)
        error(ERROR_exit(1),"cannot find terminal");
    if(stat(tty,&statb)<0)
        error(ERROR_system(1),"%s: cannot stat",tty);
    switch(mode)
    {
        case 'n':
        case 'y':
        if(mode=='y')
            statb.st_mode |= S_IWGRP;
        else
            statb.st_mode &= ~S_IWGRP;
        if(chmod(tty, statb.st_mode) < 0)
            error(ERROR_system(1),"%s: cannot stat",tty);
        break;
        case 0:
        sfprintf(sfstdout,"%c\n",(statb.st_mode&S_IWGRP)?'y':'n');
    }
    return((statb.st_mode&S_IWGRP)==0);
}

int
main(int argc, char *argv[])
{
    register int n;

    NoP(argc);
    error_info.id = "mesg";
    for (;;)
    {
        switch (optget(argv, usage))
        {
        case ':':
            error(2, "%s", opt_info.arg);
            break;
        case '?':
            error(ERROR_usage(2), "%s", opt_info.arg);
            break;
        }
        break;
    }
    argv += opt_info.index;
    n = 0;
    if(error_info.errors || (*argv && (n= **argv) !='y' && n!='n'))
        error(ERROR_usage(2), "%s", optusage(NiL));
    return mesg(n);
}