C- Simple Shell

An ALX Africa Software Engineering Program project.

Project Overview

This is a collaborative project to build a custom bash shell in C, to simulate basic shell functionality!

It allows users to execute commands, manage paths, handle user input, and perform memory management operations.

The goal is to deepen understanding of C programming and explore the intricacies of shell development.

Project Contributors

• Meet the amazing individuals contributing to this project:
  • @dahunsi-dami
  • @mikoiyke

Technologies Used

• This project leverages the following technologies:
  • Programming Language: C
  • Operating System: Ubuntu 20.04

Functions Overview

We built several functions from scratch, each prefixed with an underscore _, to handle different aspects of the custom simple_shell functionality.

Here is a table summarizing the key functions used in this project.

Functions we built from scratch start with the underscore _ character.

Function Name	Description
_write	Writes a given string to the standard output (stdout).
_tokenizeinput	Tokenizes an input string based on a specified delimiter, allocates memory for the tokens, and returns an array of tokenized strings.
_checkgetfail	Checks if getline function fails, handles the error by freeing the buffer and exiting the program, and checks if the input is the "exit" command to terminate the program.
_putchar	Writes a given character to the standard output (stdout) and returns 1 on success or -1 if an error occurs.
_strcmp	Compares 2 strings character and returns the difference between the first non-matching characers or 0 if the strings are identical.
_strlen	Calculates and returns the length of a string by counting the number of characters before the null terminator.
_strncmp	Compares the first n characters of 2 strings and returns the difference between the 1st mismatched characters, or 0 if the strings are identical within the first n characters.
_readinput	Reads input from the user, optionally prompts the user if the input is from the terminal, and returns the number of characters read into the provided buffer.
_getline	Dynamically allocates memory for a string, reads input from a specified file stream, adjust the buffer size as needed, and returns the number of character read (excluding the newline character).
_promptuser	Prompts the user with the shell input symbol hsh > by calling the _write function.
_realloc	Reallocates memory for a buffer, adjusting its size based on the provided new size, and returns a pointer to the newly allocated buffer (copying the old content if the size increases).
_strcpy	Copies the string pointed to by src into the buffer pointed to by dest, and then returns a pointer to dest.
_strcat	Concatenates the string pointed to by src to the end of the string pointed to by dest, and then returns a pointer to dest.
_executecommand	Executes a command by forking a new process, checks if the command exists using _checkcmdexists, and then runs the command using execve. It waits for the command to finish and fress the allocated memory for the command path.
_isabspath	Checks if the given path (the 1st argument in argv) is absolute using the stat function. If the path exists, it allocates memory for it, copies the path into the allocated memory, and returns it; otherwise, it returns NULL.
_mallocchar	Allocates memory for a copy of the string _envp and returns a pointer to the allocated memory, or NULL if allocation fails, after freeing _envp and printing an error message.
_appendtopath	Attempts to find a valid directory for a relative path by appending the command to each token in the parsed array and checking if the resulting path exists.
_checkcmdexists	Checks if a command exists as an executable either by verifying its absolute path or searching the directories listed in the PATH environment variable.
_findpathenv	Searches the environment variables for the PATH value, allocates memory for it, and returns the path or NULL if not found.

Compilation

The shell is compiled this way: gcc -Wall -Werror -Wextra -pedantic -std=gnu89 *.c -o hsh

Testing

It works like this in interactive mode:

$ ./hsh
($) /bin/ls
hsh main.c shell.c
($)
($) exit
$

But also in non-interactive mode like this:

$ echo "/bin/ls" | ./hsh
hsh main.c shell.c test_ls_2
$
$ cat test_ls_2
/bin/ls
/bin/ls
$
$ cat test_ls_2 | ./hsh
hsh main.c shell.c test_ls_2
hsh main.c shell.c test_ls_2
$

Requirements

• The code uses the Betty style. It's checked using betty-style.pl and betty-doc.pl.
• No more than 5 functions per file.
• All header files are include guarded.
• System calls are used only when we need to.
• There, ideally, should be no memory leaks.