pmthang99/OS-Shell

Shell C Interface

Requirement

• Unix
• Gcc

Installation

gcc -o shellfinal shellfinal.c

Command

• exit
• cd
• pwd
• env
• export
• set
• unset
• history
• background process (&)

Usage

To start simple shell, run the command below:

./shellfinal

1. For internal command pwd, cd, set, unset, export

$ pwd
$ cd 
$ export
$ export MYVAR="abcd"
$ set MYVAR="abcd"
$ unset MYVAR
$ sleep 30 &
$ cat log.txt &

2. For external command

$ ls
$ ls -l
$ ps
$ cat README.md

3. Execute history

$ !!

4. Single redirection

$ ls -l > output
$ grep README < output

5. Single pipe

$ cat output | grep README
$ cat > file.txt
abc
hsds
bbcb
asdas
pofas
$ cat file.txt | sort

How to implement

1. Creating the child process and executing the command in the child

   • pid_t fork(void);
     • Call once, return twice
     • Concurrent excution
     • Duplicate but separate address spaces
     • Shared files
   • pid_t waitpid(pid_t pid, int *startup, int options); -> background process
   • pid_t wait(int *startus); Calling wait(&status) is equivalent to calling waitpid(-1, &status, 0).

   Problem internal command pwd, cd

   • Implement internal command: pwd, cd, exit, export, set, unset

2. Providing a history feature

   • Save command in log.txt
   • !! excute the last command in log.txt

3. Adding support of input and output redirection

   • int creat(char *filename, mode_t mode);
   • int open (const char* Path, int flags [, int mode ]);
   • int dup2(int oldfd, int newfd);

4. Allowing the parent and child processes to communicate via a pipe

   • int pipe(int fds[2]);
     • fds[0] for read
     • fds[1] for write
   • Backup file description STDIN and STDOUT
   • Open pipe and exec

Credit

• 1712689 Huỳnh Ngọc Quân
• 1712759 Phạm Minh Thắng
• 1712698 Võ Văn Quân

Ho Chi Minh University of Science