How to implement your own cd command in your own shell [duplicate]

问题

I am working in a mini project: "MY OWN COMMAND INTERPRETER (SHELL)", like the Bash shell or Sh shell. Till now it can execute every predefined commands like ls, ps, pwd, date. Except this I have implemented some other operations like Input Redirection(<), output redirection(>), PIPE (|) features. Along with this i have implemented my own user-commands like pid, ppid, quit, hist.

vvdnlt208@vvdnlt208-Vostro-3446:~/project/Vector/sourabh/unix/proj2$ ./my_sh  
<1 SOURABH> ls
 a     cd.c       execute.o  inredir.c  main.o   multiexec.o  my_sh   sh.c                sigign.c  test.c
addhist.c  dir        header.h   inredir.o  Makefile     mypipe.c     outredir.c  showhist.c  sigign.o  tetest.c
addhist.o  execute.c  inredir    main.c     multiexec.c  mypipe.o     outredir.o    showhist.o  test2.c
<2 SOURABH> ps
PID TTY          TIME CMD
6120 pts/10   00:00:01 bash
6510 pts/10   00:00:00 grep
6512 pts/10   00:00:00 grep
6514 pts/10   00:00:00 grep
6516 pts/10   00:00:00 grep
7772 pts/10   00:00:00 my_sh
7774 pts/10   00:00:00 ps
<3 SOURABH> pwd
/home/vvdnlt208/project/Vector/sourabh/unix/proj2
<4 SOURABH> date
Fri Nov 14 16:44:24 IST 2014
<5 SOURABH> 
<6 SOURABH> 
<7 SOURABH> 
<8 SOURABH> hist
1 ls
2 ps
3 pwd
4 date
8 hist
<9 SOURABH> ls >a.txt
<10 SOURABH> pid
7772
<11 SOURABH> ppid

But I am facing some difficulty in executing the cd command...

<12 SOURABH> cd
cd: No such file or directory
<13 SOURABH> cd dir
cd: No such file or directory
<14 SOURABH>

Someone told me to implement it by my own... Please help me in doing this. Thanks in advance.

回答1:

cd is not a program, it's a built-in command. The built-in command are directly built into the shell.

To implement cd, you basically need to

Use chdir() to change the current directory
Update some environment variables (like Klas Lindback said: OLDPWD and PWD)

回答2:

You may wish to have a look at the chdir function in unistd.h. This changes the working directory of the current process.

回答3:

In my project I have used chdir() to implement my cd command and it works. Every process has its own PWD(Present Working Directory). A shell is also a process and its default PWD is the PWD of its parent (bash shell where I have executed ./my_sh).

来源：https://stackoverflow.com/questions/26928907/how-to-implement-your-own-cd-command-in-your-own-shell

标签

Linux

shell

pwd