ALX Simple Shell Team Project

This is an ALX collaboration project on Shell. We were tasked to create a simple shell that mimics the Bash shell.

Our shell shall be called hsh.

Introduction

This repository is a ALX Holberton School Project. The school project consisted in writing a shell like sh (Bourne Shell) by Stephen Bourne , in C, using a limited number of standard library functions, so instead we used our own function that we rewrited over the past three month Here.

The goal in this project is to make us understand how a shell works.

• To single out some core topics which includes;
  • What is the environment?
  • The difference between functions and system calls.
  • How to create processes using execve...

General Requirements

• README file, at the root of the folder of the project is mandatory.
• Allowed editors: vi, vim, emacs
• Compiler;
  • Ubuntu 20.04 LTS using gcc.
  • Using the options -Wall -Werror -Wextra -pedantic -std=gnu89
• Coding style;
  • Betty Style.
• Shell should not have any memory leaks.
• No more than 5 functions per file.
• All header files should be include guarded.

How hsh works

• Prints a prompt and waits for a command from the user.
• Creates a child process in which the command is checked.
• Checks for built-ins, aliases in the PATH, and local executable programs.
• The child process is replaced by the command, which accepts arguments.
• When the command is done, the program returns to the parent process and prints the prompt.
• The program is ready to receive a new command.
• To exit: press Ctrl-D or enter "exit" (with or without a status).
• Works also in non interactive mode.

Usage

In order to run this program,

Clone This Repo;

git clone https://github.com/TosinISOGUN/simple_shell.git

Compile it with;

gcc 4.8.4 -Wall -Werror -Wextra -pedantic *.c -o hsh.

You can then run it by invoking ./hsh in that same directory.

How to use it In order to use this shell, in a terminal, first run the program: prompt$ ./hsh It wil then display a simple prompt and wait for commands. $ A command will be of the type $ command

To invoke hsh, compile all .c files in the repository and run the resulting executable.

hsh can be invoked both interactively and non-interactively. If hsh is invoked with standard input not connected to a terminal, it reads and executes received commands in order.

Example:

$ echo "echo 'hello'" | ./hsh
'hello'
$

If hsh is invoked with standard input connected to a terminal (determined by isatty(3)), an interactive shell is opened. When executing interactively, hsh displays the prompt $ when it is ready to read a command.

Example:

$./hsh
$

Alternatively, if command line arguments are supplied upon invocation, hsh treats the first argument as a file from which to read commands. The supplied file should contain one command per line. hsh runs each of the commands contained in the file in order before exiting.

Example:

$ cat test
echo 'hello'
$ ./hsh test
'hello'
$

Environment

Upon invocation, hsh receives and copies the environment of the parent process in which it was executed. This environment is an array of name-value strings describing variables in the format NAME=VALUE. A few key environmental variables are:

HOME

The home directory of the current user and the default directory argument for the cd builtin command.

$ echo "echo $HOME" | ./hsh
/home/projects

PWD

The current working directory as set by the cd command.

$ echo "echo $PWD" | ./hsh
/home/projects/alx/simple_shell

OLDPWD

The previous working directory as set by the cd command.

$ echo "echo $OLDPWD" | ./hsh
/home/projects/alx/printf

PATH

A colon-separated list of directories in which the shell looks for commands. A null directory name in the path (represented by any of two adjacent colons, an initial colon, or a trailing colon) indicates the current directory.

$ echo "echo $PATH" | ./hsh
/home/projects/.cargo/bin:/home/projects/.local/bin:/home/projects/.rbenv/plugins/ruby-build/bin:/home/projects/.rbenv/shims:/home/projects/.rbenv/bin:/home/projects/.nvm/versions/node/v10.15.3/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/home/projects/.cargo/bin:/home/projects/workflow:/home/projects/.local/bin

hsh Builtin Commands

cd

• Usage: cd [DIRECTORY]
• Changes the current directory of the process to DIRECTORY.
• If no argument is given, the command is interpreted as cd $HOME.
• If the argument - is given, the command is interpreted as cd $OLDPWD and the pathname of the new working directory is printed to standad output.
• If the argument, -- is given, the command is interpreted as cd $OLDPWD but the pathname of the new working directory is not printed.
• The environment variables PWD and OLDPWD are updated after a change of directory.

Example:

$ ./hsh
$ pwd
/home/projects/alx/simple_shell
$ cd ../
$ pwd
/home/projects/alx
$ cd -
$ pwd
/home/projects/alx/simple_shell

alias

• Usage: alias [NAME[='VALUE'] ...]
• Handles aliases.
• alias: Prints a list of all aliases, one per line, in the form NAME='VALUE'.
• alias NAME [NAME2 ...]: Prints the aliases NAME, NAME2, etc. one per line, in the form NAME='VALUE'.
• alias NAME='VALUE' [...]: Defines an alias for each NAME whose VALUE is given. If name is already an alias, its value is replaced with VALUE.

Example:

$ ./hsh
$ alias show=ls
$ show
AUTHORS            builtins_help_2.c  errors.c         linkedlist.c        shell.h       test
README.md          env_builtins.c     getline.c        locate.c            hsh
alias_builtins.c   environ.c          helper.c         main.c              split.c
builtin.c          err_msgs1.c        helpers_2.c      man_1_simple_shell  str_funcs1.c
builtins_help_1.c  err_msgs2.c        input_helpers.c  proc_file_comm.c    str_funcs2.c

exit

• Usage: exit [STATUS]
• Exits the shell.
• The STATUS argument is the integer used to exit the shell.
• If no argument is given, the command is interpreted as exit 0.

Example:

$ ./hsh
$ exit

env

• Usage: env
• Prints the current environment.

Example:

$ ./hsh
$ env
NVM_DIR=/home/projects/.nvm
...

setenv

• Usage: setenv [VARIABLE] [VALUE]
• Initializes a new environment variable, or modifies an existing one.
• Upon failure, prints a message to stderr.

Example:

$ ./hsh
$ setenv NAME Poppy
$ echo $NAME
Poppy

unsetenv

• Usage: unsetenv [VARIABLE]
• Removes an environmental variable.
• Upon failure, prints a message to stderr.

Example:

$ ./hsh
$ setenv NAME Poppy
$ unsetenv NAME
$ echo $NAME
$

Thank you for going through our shell documentation.

AUTHORS

🤵🏼 Christian Freeman Balogun

• GitHub
• LinkedIn

🤵🏻‍ Onome Mafuru

• GitHub
• LinkedIn