What Is Minishell ? (subject)
Minishell refers to a minimalistic shell or command-line interface program for Unix-like operating systems.A shell is a user interface that allows users to interact with the operating system by executing commandsand managing various tasks.
A Minishell typically provides basic functionality similar to a standard shell, such as executing commands, handling input and output redirection, managing processes, and supporting various shell features like command history and tab completion. However, it may not have all the advanced features of a full-featured shell like Bash or Zsh.
The shell implementation is divided into three parts: The Parser, The Executor, and Shell
Subsystems.
The Parser is the software component that reads the command line such as “ls -al” and puts it into a data structure called Command Table that will store the commands that will be executed.
The executor will take the command table generated by the parser and for every SimpleCommand in the array it will create a new process. It will also if necessary create pipes to communicate the output of one process to the input of the next one. Additionally, it will redirect the standard input, standard output, and standard error if there are any redirections.
Other subsystems that complete your shell are:
● Environment Variables: Expressions of the form${VAR}are expanded with the corresponding environment variable. Also the shell should be able to set, expand and print environment vars.
● Wildcards: Arguments of the forma*aare expanded to all the files that match them in the local directory and in multiple directories .
● Subshells: Arguments between `` (backticks) are executed and the output is sent as input to the shell.
| Function | Manual Page | From lib | Description |
|---|---|---|---|
| printf | man 3 printf |
<stdio.h> |
write output to stdout |
| malloc | man malloc |
<stdlib.h> |
allocate dynamic memory |
| free | man 3 free |
<stdlib.h> |
free dynamic memory |
| read | man 2 read |
<unistd.h> |
read from a file descriptor |
| write | man 2 write |
<unistd.h> |
write to a file descriptor |
| open | man 2 open |
<fcntl.h> |
open and possibly create a file |
| close | man 2 open |
<unistd.h> |
close a file descriptor |
| fork | man fork |
<unistd.h> |
create a child process |
| wait | man wait |
<sys/wait.h> |
wait for process to change state |
| waitpid | man waitpid |
<sys/wait.h> |
wait for process to change state |
| wait3 | man wait3 |
<sys/wait.h> |
(obsolete) wait for process to change state, BSD style |
| wait4 | man wait4 |
<sys/wait.h> |
(obsolete) wait for process to change state, BSD style |
| signal | man signal |
<signal.h> |
ANSI C signal handling |
| kill | man 2 kill |
<signal.h> |
send signal to a process |
| exit | man exit |
<stdlib.h> |
cause normal process termination |
| getcwd | man getcwd |
<unistd.h> |
get current working directory |
| chdir | man chdir |
<unistd.h> |
change working directory |
| stat | man 2 stat |
<sys/stat.h> |
get file status by pathname |
| lstat | man lstat |
<sys/stat.h> |
get file status by pathname (for symlinks) |
| fstat | man fstat |
<sys/stat.h> |
get file status by fd |
| execve | man execve |
<unistd.h> |
execute program |
| dup | man dup |
<unistd.h> |
duplicate a file descriptor |
| dup2 | man dup2 |
<unistd.h> |
duplicate a file descriptor |
| pipe | man pipe |
<unistd.h> |
create pipe |
| opendir | man opendir |
<dirent.h> |
open a directory |
| readdir | man readdir |
<dirent.h> |
read a directory |
| closedir | man closedir |
<dirent.h> |
close a directory |
| strerror | man strerror |
<string.h> |
return string describing error number |
| errno | man errno |
<errno.h> |
number of last error |
| termcap | man termcap, man termios |
<term.h> |
direct curses interface to the terminfo capability database |