Minix1.5/lib/posix/execlp.c

/* execlp(3) and execvp(3)
 *
 * Author: Terrence W. Holm      July 1988
 */

/* FIXES - Dec 1989 - Jan 1990 Bruce Evans.
 *	 - Don't use search path when file name contains a '/' *anywhere*.
 *	 - Invoke sh(1) on command files.
 *	 - Use PATH_MAX and check strings fit in buffer.
 *	 - Use stdargs, with the unjustified assumption that va_start() turns
 *	   the arg list into a char *[].  Strictly, the arg list should be
 *	   copied, "wasting" up to ARG_MAX bytes.
 */

/*  Execlp(3) and execvp(3) are like execl(3) and execv(3),
 *  except that they use the environment variable $PATH as
 *  a search list of possible locations for the executable
 *  file, if <file> does not contain a '/', and they attempt
 *  to run non-binary executable files using sh(1).
 *
 *  The path search list is a list of directory names separated
 *  by ':'s. If a colon appears at the beginning or end of the
 *  list, or two appear together, then an empty prefix is tried.
 *  If $PATH is not in the environment, it defaults to "".
 *
 *  For example, if <file> is "ls", and the $PATH is
 *  ":/usr/local/bin:/bin:/usr/bin", then  ./ls,
 *  /usr/local/bin/ls, /bin/ls and /usr/bin/ls are tried until
 *  an exectable one is found. If the direct attempt to exec it
 *  fails, the arg list is modified to begin with "sh" and the
 *  absolute name of <file>, and an exec of /bin/sh is tried.
 *  If this fails, no further attempts are made.
 *
 *  This function only returns after an error.  It returns -1
 *  and sets errno like execv().
 */

#include <errno.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdarg.h>

#undef NULL
#define NULL 0			/* kludge for ACK not understanding void * */

extern char **environ;		/* environment pointer */

int execlp(file /* , ... */ )
char *file;
{
  register va_list argp;
  register int result;

  va_start(argp, file);
  result = execvp(file, (char **) argp);
  va_end(argp);
  return(result);
}

int execvp(file, argv)
char *file;
char **argv;
{
  register char **argp;
  char **argtop;
  int best_errno;
  char **envtop;
  size_t flength;
  char *searchpath;
  size_t slength;
  char *split;
  char execpath[PATH_MAX + 1];

  if (strchr(file, '/') != NULL || (searchpath = getenv("PATH")) == NULL)
	searchpath = "";
  flength = strlen(file);
  best_errno = ENOENT;

  while (1) {
	split = strchr(searchpath, ':');
	if (split == NULL)
		slength = strlen(searchpath);
	else
		slength = split - searchpath;
	if (slength + flength >= sizeof execpath - 2) {
		errno = ENAMETOOLONG;	/* too bad if premature */
		return(-1);
	}
	strncpy(execpath, searchpath, slength);
	if (slength != 0) execpath[slength++] = '/';
	strcpy(execpath + slength, file);

	/* Don't try to avoid execv() for non-existent files, since the Minix
	 * shell doesn't, and it is not clear whether access() or stat() work
	 * right when this code is set-uid.
	 */
	execv(execpath, argv);
	switch (errno) {
	    case EACCES:
		best_errno = errno;	/* more useful than ENOENT */
	    case ENOENT:
		if (split == NULL) {
			/* No more path components. */
			errno = best_errno;
			return(-1);
		}
		searchpath = split + 1;	/* try next in path */
		break;
	    case ENOEXEC:
		/* Assume a command file and invoke sh(1) on it.  Replace arg0
		 * (which is usually a short name for the command) by the full
		 * name of the command file.
		 */
		*argv = execpath;

		/* Move the args up by 1, overlaying the assumed NULL at the
		 * end, to make room for "sh" at the beginning.
		 */
		for (argp = argv; *argp != NULL; ) argp++;
		argtop = argp + 1;
		while (argp > argv) {
			*argp = *(argp - 1);
			--argp;
		}
		*argp = "sh";

		/* Count the environment pointers. */
		for (envtop = environ; *envtop != NULL; ) envtop++;

		/* Try only /bin/sh, like the Minix shell.  Lose if the user
		 * has a different shell or the command has #!another/shell.
		 */
		__execve("/bin/sh", argv, environ, argtop - argv,
			 envtop - environ);

		/* Oops, no shell?  Restore argv and give up. */
		--argtop;
		while (argv < argtop) {
			*argp = *(argp + 1);
			++argp;
		}
		*argp = NULL;
		errno = ENOEXEC;
		return(-1);
	    default:
		return(-1);	/* probably  ENOMEM or E2BIG */
	}
  }
}