cd

README

Written as a demo of how a shell would implement this, and why it needs
to be a shell builtin.

This won't actually work as a standalone program; chdir(3) only changes
the directory of the current process. As soon as the program exits, it
returns control to the parent process (the shell). If this is executed
as a shell builtin, the shell process's working directory is changed.

cd.c

/*
 * Copyright (c) 2015 Kyle Isom <kyle@tyrfingr.is>
 *  
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *  
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *  
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */


#include <sys/types.h>

#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>


int
main(int argc, char *argv[])
{
	int		 ret = -1;
	char		*newdir = NULL;
	struct passwd	*pw = NULL;

	switch (argc) {
	case 1:
		newdir = getenv("HOME");
		if (NULL != newdir) {
			break;
		}

		pw = getpwuid(getuid());
		if (NULL == pw) {
			fprintf(stderr, "cd: cannot find home\n");
			exit(1);
		}

		newdir = pw->pw_dir;
		if (NULL == newdir) {
			fprintf(stderr, "cd: HOME not set\n");
			exit(1);
		}
		break;
	case 2:
		newdir = argv[1];
		break;
	default:
		fprintf(stderr, "cd: cannot chdir to multiple paths\n");
		fprintf(stderr,
		    "    (did you mean to enclose the path in quotes?)\n");
		exit(1);
	}

	ret = chdir(newdir);
	if (-1 == ret) {
		perror("cd");
		exit(1);
	}

	return 0;
}