Advanced Programming in the UNIX® Environment

ptg10805159

Section 4.23 chdir,fchdir,andgetcwdFunctions 135

To illustrate theftwandnftwfunctions, we have provided moregenerality in this

program than needed. For example, the functionmyfunc always returns 0, even

though the function that calls it is prepared to handle a nonzeroreturn.

For additional information on descending through a file system and using this

technique in many standardUNIX System commands —find, ls, tar,and so

on — refer to Fowler,Korn, and Vo[ 1989 ].

4.23 chdir,fchdir,and getcwdFunctions

Every process has a current working directory.This directory is wherethe search for all

relative pathnames starts (i.e., with all pathnames that do not begin with a slash). When

auser logs in to a UNIX system, the current working directory normally starts at the

directory specified by the sixth field in the/etc/passwd file — the user ’s home

directory.The current working directory is an attribute of a process; the home directory

is an attribute of a login name.

We can change the current working directory of the calling process by calling the

chdirorfchdirfunction.

#include <unistd.h>

int chdir(const char *pathname);

int fchdir(intfd);

Both return: 0 if OK,−1 on error

We can specify the new current working directory either as apathnameor through an

open file descriptor.

Example

Because it is an attribute of a process, the current working directory cannot affect

processes that invoke the process that executes the chdir.(We describe the

relationship between processes in moredetail in Chapter 8.) As a result, the program in

Figure4.23 doesn’t do what we might expect.

#include "apue.h"

int

main(void)

{

if (chdir("/tmp") < 0)

err_sys("chdir failed");

printf("chdir to /tmp succeeded\n");

exit(0);

}

Figure 4.23Example ofchdirfunction