O-shell: 自己搓的玩具shell
Note: this is the Experiment 1 of the OS course.
O-shell is a shell that performs basic functions of a UNIX shell (e.g. bash, zsh)
There are several built-in commands supported and O-shell also supports commands that are already in operating system path.
Installation
Prerequisites
Your operating system must be GNU/Linux, UNIX, macOS or other POSIX compatible OSs.
Compile
If you are using GNU/Linux, UNIX or macOS, there are no more compile flags needed because all headers in the source code are included in the path by default by the operating system and compilers.
Open system terminal in the folder, then run:
1 | |
Run
You can run O-shell in system terminal directly:
1 | |
If the program runs normally, it shows the prompt
o-shell ->.
Features
Run system executables
As long as the command/executable can be found by system, the O-shell can fork a new child process and execute it.
If the execution is not successful, the O-shell will print the reason for the error occurred.
Built-in commands
pwd
This command shows the current working directory using system call
getcwd().
When executing this command, O-shell prints the working directory in the terminal.
cd
This command changes the current working directory using system call
chdir().
When executing this command, O-shell changes the working directory.
If the given directory is not found, O-shell will print the error using
perror().
This command can be combined with pwd and
ls to access the whole file system.
exit
This command terminates the O-shell process.
history
This command shows the most recent history.
When executing this command, O-shell shows recent command in
decending order, from the most recent to the last recent. Each history
command has a index, representing the index from the first command. The
history command supports most 10 history commands. When
there are more than 10 history commands, O-shell will forget the least
recent history while memorizing the most recent history.
When there is no history command, O-shell prints
No history command yet. .
!!
This command executes the most recent command.
If no recent command is found, O-shell prints
No history command yet. .
![index]
This command execute the recent command depending on the the index value.
If the command index is not found, the O-shell prints
No history command yet. .
Run without waiting
Enter any command following with '&', the O-shell
will not wait for the child process to complete.
This will result in format error because the O-shell tends to print the next prompt before the completion of the child process.
The solution of zsh or bash is to fork few
child process(es), the shell waits for all child process(es) to
complete, and each child process creates a new child process on its own
based on the command. This prevents the format error and thus more
safe.
References
Textbook (Operating System Concepts 9th Edition)
Tokenize a string in C (and a Safer Version)