usr/klibc/execvpe.c

/*
 * execvpe.c
 *
 * execvpe() function (from which we build execlp, execlpe, execvp).
 *
 * This version of execvpe() will *not* spawn /bin/sh if the command
 * return ENOEXEC.  That's what #! is for, folks!
 *
 * Since execlpe() and execvpe() aren't in POSIX, nor in glibc,
 * I have followed QNX precedent in the implementation of the PATH:
 * the PATH that is used is the one in the current environment, not
 * in the new environment.  Otherwise it would be impossible to pass
 * a different PATH to the new process than the one one would want to
 * use to search.
 */

#include <errno.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>

#define DEFAULT_PATH 	"/bin:/usr/bin:."

int execvpe(const char *file, char *const *argv, char *const *envp)
{
	char path[PATH_MAX];
	const char *searchpath, *esp;
	size_t prefixlen, filelen, totallen;

	if (strchr(file, '/'))	/* Specific path */
		return execve(file, argv, envp);

	filelen = strlen(file);

	searchpath = getenv("PATH");
	if (!searchpath)
		searchpath = DEFAULT_PATH;

	errno = ENOENT;		/* Default errno, if execve() doesn't
				   change it */

	do {
		esp = strchr(searchpath, ':');
		if (esp)
			prefixlen = esp - searchpath;
		else
			prefixlen = strlen(searchpath);

		if (prefixlen == 0 || searchpath[prefixlen - 1] == '/') {
			totallen = prefixlen + filelen;
			if (totallen >= PATH_MAX)
				continue;
			memcpy(path, searchpath, prefixlen);
			memcpy(path + prefixlen, file, filelen);
		} else {
			totallen = prefixlen + filelen + 1;
			if (totallen >= PATH_MAX)
				continue;
			memcpy(path, searchpath, prefixlen);
			path[prefixlen] = '/';
			memcpy(path + prefixlen + 1, file, filelen);
		}
		path[totallen] = '\0';

		execve(path, argv, envp);
		if (errno == E2BIG  || errno == ENOEXEC ||
		    errno == ENOMEM || errno == ETXTBSY)
			break;	/* Report this as an error, no more search */

		searchpath = esp + 1;
	} while (esp);

	return -1;
}