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Unix文件与目录简介

By Wu Yudong on March 07, 2016

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

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