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shell.c

/*
 * Copyright 1989 - 1991, Julianne Frances Haugh
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of Julianne F. Haugh nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY JULIE HAUGH AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL JULIE HAUGH OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <config.h>

#include "rcsid.h"
RCSID("$Id: shell.c 6 2005-03-20 15:34:28Z bubulle $")

#include <stdio.h>
#include <errno.h>
#include "prototypes.h"
#include "defines.h"


extern char **newenvp;
extern size_t newenvc;

/*
 * shell - execute the named program
 *
 *    shell begins by trying to figure out what argv[0] is going to
 *    be for the named process.  The user may pass in that argument,
 *    or it will be the last pathname component of the file with a
 *    '-' prepended.  The first attempt is to just execute the named
 *    file.  If the errno comes back "ENOEXEC", the file is assumed
 *    at first glance to be a shell script.  The first two characters
 *    must be "#!", in which case "/bin/sh" is executed to process
 *    the file.  If all that fails, give up in disgust ...
 */

void
shell(const char *file, const char *arg)
{
      char arg0[1024];
      int err;

      if (file == (char *) 0)
            exit (1);

      /*
       * The argv[0]'th entry is usually the path name, but
       * for various reasons the invoker may want to override
       * that.  So, we determine the 0'th entry only if they
       * don't want to tell us what it is themselves.
       */

      if (arg == (char *) 0) {
            snprintf(arg0, sizeof arg0, "-%s", Basename((char *) file));
            arg = arg0;
      }
#ifdef DEBUG
      printf (_("Executing shell %s\n"), file);
#endif

      /*
       * First we try the direct approach.  The system should be
       * able to figure out what we are up to without too much
       * grief.
       */

      execle (file, arg, (char *) 0, newenvp);
      err = errno;

      /* Linux handles #! in the kernel, and bash doesn't make
         sense of "#!" so it wouldn't work anyway...  --marekm */
#ifndef __linux__
      /*
       * It is perfectly OK to have a shell script for a login
       * shell, and this code attempts to support that.  It
       * relies on the standard shell being able to make sense
       * of the "#!" magic number.
       */

      if (err == ENOEXEC) {
            FILE  *fp;

            if ((fp = fopen (file, "r"))) {
                  if (getc (fp) == '#' && getc (fp) == '!') {
                        fclose (fp);
                        execle ("/bin/sh", "sh",
                              file, (char *) 0, newenvp);
                        err = errno;
                  } else {
                        fclose (fp);
                  }
            }
      }
#endif

      /*
       * Obviously something is really wrong - I can't figure out
       * how to execute this stupid shell, so I might as well give
       * up in disgust ...
       */

      snprintf(arg0, sizeof arg0, _("Cannot execute %s"), file);
      errno = err;
      perror(arg0);
      exit(1);
}

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