本文主要简单介绍Unix文件与目录
文件系统
Unix文件系统是目录和文件的一种层次结构，所有东西的起点是称为根的目录，此目录的名称是一个字符"/"
文件名
创建新目录时会自动创建了两个文件名：.（点）和..（点点），点指向当前目录，点点指向父目录
路径名
由斜线分隔的一个或多个文件名组成的序列构成路径名，以斜线开头的路径名成为绝对路径名，否则称为相对路径名
举个例子：
实现列举一个目录中所有的文件的名字（ls命令的简要实现）
#include<dirent.h>
#include"apue.h"
#include<errno.h>
int main(int argc, char *argv[])
{
DIR *dp;
struct dirent *dirp;
if(argc != 2)
err_quit("usage: ls directory_name");
if((dp = opendir(argv[1])) == NULL)
err_sys("can't open %s", argv[1]);
while((dirp = readdir(dp)) != NULL)
printf("%s\n", dirp->d_name);
closedir(dp);
exit(0);
}编译运行：
wu@ubuntu:~/opt/Cproject/apue/cp1$ gcc error.c myls.c -o a.out
wu@ubuntu:~/opt/Cproject/apue/cp1$ ./a.out /dev
其中apue.h主要是一个宏定义、常量定义等，代码如下：
/*
* Our own header, to be included before all standard system headers.
*/
#ifndef _APUE_H
#define _APUE_H
#define _POSIX_C_SOURCE 200809L
#if defined(SOLARIS) /* Solaris 10 */
#define _XOPEN_SOURCE 600
#else
#define _XOPEN_SOURCE 700
#endif
#include <sys/types.h> /* some systems still require this */
#include <sys/stat.h>
#include <sys/termios.h> /* for winsize */
#if defined(MACOS) || !defined(TIOCGWINSZ)
#include <sys/ioctl.h>
#endif
#include <stdio.h> /* for convenience */
#include <stdlib.h> /* for convenience */
#include <stddef.h> /* for offsetof */
#include <string.h> /* for convenience */
#include <unistd.h> /* for convenience */
#include <signal.h> /* for SIG_ERR */
#define MAXLINE 4096 /* max line length */
/*
* Default file access permissions for new files.
*/
#define FILE_MODE (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)
/*
* Default permissions for new directories.
*/
#define DIR_MODE (FILE_MODE | S_IXUSR | S_IXGRP | S_IXOTH)
typedef void Sigfunc(int); /* for signal handlers */
#define min(a,b) ((a) < (b) ? (a) : (b))
#define max(a,b) ((a) > (b) ? (a) : (b))
/*
* Prototypes for our own functions.
*/
char *path_alloc(size_t *); /* {Prog pathalloc} */
long open_max(void); /* {Prog openmax} */
int set_cloexec(int); /* {Prog setfd} */
void clr_fl(int, int);
void set_fl(int, int); /* {Prog setfl} */
void pr_exit(int); /* {Prog prexit} */
void pr_mask(const char *); /* {Prog prmask} */
Sigfunc *signal_intr(int, Sigfunc *); /* {Prog signal_intr_function} */
void daemonize(const char *); /* {Prog daemoninit} */
void sleep_us(unsigned int); /* {Ex sleepus} */
ssize_t readn(int, void *, size_t); /* {Prog readn_writen} */
ssize_t writen(int, const void *, size_t); /* {Prog readn_writen} */
int fd_pipe(int *); /* {Prog sock_fdpipe} */
int recv_fd(int, ssize_t (*func)(int,
const void *, size_t)); /* {Prog recvfd_sockets} */
int send_fd(int, int); /* {Prog sendfd_sockets} */
int send_err(int, int,
const char *); /* {Prog senderr} */
int serv_listen(const char *); /* {Prog servlisten_sockets} */
int serv_accept(int, uid_t *); /* {Prog servaccept_sockets} */
int cli_conn(const char *); /* {Prog cliconn_sockets} */
int buf_args(char *, int (*func)(int,
char **)); /* {Prog bufargs} */
int tty_cbreak(int); /* {Prog raw} */
int tty_raw(int); /* {Prog raw} */
int tty_reset(int); /* {Prog raw} */
void tty_atexit(void); /* {Prog raw} */
struct termios *tty_termios(void); /* {Prog raw} */
int ptym_open(char *, int); /* {Prog ptyopen} */
int ptys_open(char *); /* {Prog ptyopen} */
#ifdef TIOCGWINSZ
pid_t pty_fork(int *, char *, int, const struct termios *,
const struct winsize *); /* {Prog ptyfork} */
#endif
int lock_reg(int, int, int, off_t, int, off_t); /* {Prog lockreg} */
#define read_lock(fd, offset, whence, len) \
lock_reg((fd), F_SETLK, F_RDLCK, (offset), (whence), (len))
#define readw_lock(fd, offset, whence, len) \
lock_reg((fd), F_SETLKW, F_RDLCK, (offset), (whence), (len))
#define write_lock(fd, offset, whence, len) \
lock_reg((fd), F_SETLK, F_WRLCK, (offset), (whence), (len))
#define writew_lock(fd, offset, whence, len) \
lock_reg((fd), F_SETLKW, F_WRLCK, (offset), (whence), (len))
#define un_lock(fd, offset, whence, len) \
lock_reg((fd), F_SETLK, F_UNLCK, (offset), (whence), (len))
pid_t lock_test(int, int, off_t, int, off_t); /* {Prog locktest} */
#define is_read_lockable(fd, offset, whence, len) \
(lock_test((fd), F_RDLCK, (offset), (whence), (len)) == 0)
#define is_write_lockable(fd, offset, whence, len) \
(lock_test((fd), F_WRLCK, (offset), (whence), (len)) == 0)
void err_msg(const char *, ...); /* {App misc_source} */
void err_dump(const char *, ...) __attribute__((noreturn));
void err_quit(const char *, ...) __attribute__((noreturn));
void err_cont(int, const char *, ...);
void err_exit(int, const char *, ...) __attribute__((noreturn));
void err_ret(const char *, ...);
void err_sys(const char *, ...) __attribute__((noreturn));
void log_msg(const char *, ...); /* {App misc_source} */
void log_open(const char *, int, int);
void log_quit(const char *, ...) __attribute__((noreturn));
void log_ret(const char *, ...);
void log_sys(const char *, ...) __attribute__((noreturn));
void log_exit(int, const char *, ...) __attribute__((noreturn));
void TELL_WAIT(void); /* parent/child from {Sec race_conditions} */
void TELL_PARENT(pid_t);
void TELL_CHILD(pid_t);
void WAIT_PARENT(void);
void WAIT_CHILD(void);
#endif /* _APUE_H */工作目录
每一个进程都有一个工作目录，所有的相对路径都从工作目录开始解释。
起始目录
登录时，工作目录设置为其实目录
