C Shell

Overview

This custom shell is designed to support a variety of functionalities including command execution, piping, redirection, background and foreground process management, and more. The shell allows you to execute built-in commands as well as external commands with various options for redirection and background execution.

Features

• Command Execution: Execute external commands and built-in commands.
• Piping: Support for piping between commands using |.
• Redirection: Input and output redirection with <, >, and >>.
• Background Jobs: Execute commands in the background using &.
• Foreground Jobs: Bring background jobs to the foreground using fg.
• Process Management: List and manage processes.
• Custom Commands: Includes custom commands like hop, reveal, proclore, seek, log, iMan, activities, ping, and neonate.

Commands

Built-in Commands

• hop: Changes the working directory. Usage: hop <path>
• reveal: Displays information about the system or environment. Usage: reveal <options>
• proclore: Lists current processes. Usage: proclore
• seek: Searches for a pattern in files or directories. Usage: seek <pattern>
• log: Handles log files. Usage: log <options>
• iMan: Displays information about the manual. Usage: iMan <options>
• activities: Lists recent activities. Usage: activities
• ping: Pings a specified target. Usage: ping <target>
• neonate: Creates a new neonate process. Usage: neonate -n <time>

External Commands

You can execute any external command using the shell. External commands are executed using the execvp system call.

Usage

1. Starting the Shell: Compile the shell and run the executable.
2. Executing Commands: Type commands directly into the shell prompt.
3. Piping Commands: Use | to pipe output from one command to another.
4. Redirecting Output: Use > to redirect output to a file and >> to append to a file.
5. Redirecting Input: Use < to redirect input from a file.
6. Background Execution: Append & to a command to run it in the background.
7. Foreground Execution: Use fg <pid> to bring a background process to the foreground.

Prompt Function

File: prompt.h

Function: prompt

• Purpose: Displays a shell prompt with the username, hostname, and current working directory, using color formatting.

• Parameters:

  • char* home: User’s home directory for abbreviation.

• Logic:

  1. Retrieve User/Host Info:
     • Uses getpwuid() for username and gethostname() for hostname.
  2. Handle CWD:
     • Retrieves the current directory using getcwd().
     • If inside home, abbreviates path with ~, else shows the full path.
  3. Display Prompt:
     • Uses ANSI color codes to style the username (blue), hostname (green), and directory (cyan).
  4. Error Handling:
     • Prints errors if fetching username, hostname, or CWD fails.

• Color Reset: After each segment, terminal colors are reset using the RESET macro.

Hop Function

File: hop.h

Function: hop

• Purpose: Changes the current working directory based on input arguments.

• Parameters:

  • char* argum: The command input, e.g., hop or a directory path.
  • char* home: User’s home directory for ~ expansion.
  • char* pevcwd: Previous working directory, used for - option.

• Logic:

  1. Default to Home:
     • If argum is "hop", changes to the home directory and prints the path.
  2. Process Arguments:
     • Splits argum using strtok_r().
     • Handles special cases:
       • "-": Switches to the previous directory.
       • "~": Switches to the home directory.
       • Otherwise, changes to the provided path.
  3. Update Previous Directory:
     • Stores the current working directory in pevcwd before changing to the new path.
  4. Error Handling:
     • Prints an error if directory change (chdir()) fails.
     • Prints the current directory on successful change.

• Return: Returns the updated previous working directory (pevcwd).

Reveal Functions

File: reveal.h

Functions:

list

• Purpose: Lists files in a directory with optional hidden file filtering.
• Parameters:
  • int hidden_flag: If set, includes hidden files.
  • const char* dir_path: Path of the directory to list.
  • char* home: User’s home directory for ~ expansion.
  • char* prevcd: Previous working directory for - option.
• Logic:
  • Resolves - and ~ to proper paths.
  • Filters hidden files based on hidden_flag.
  • Prints directory contents with color-coding: Blue (directories), Green (executables), White (regular files).

print_file_info

• Purpose: Prints detailed file info (permissions, owner, size, etc.).
• Parameters:
  • const char* name: File name.
  • const struct stat* sb: File status info (metadata).

list_all

• Purpose: Lists all files with detailed info, using print_file_info().
• Parameters: Same as list.

exec_list

• Purpose: Parses and executes the list command, supporting flags like -a (show hidden) and -l (long format).
• Parameters:
  • char* cmd: The full command input (e.g., ls -al).
  • char* home, char* prevcd: Same as list.

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Log Functions

File: log.h

Functions:

logcmd

• Purpose: Logs executed commands, avoiding duplicates.
• Parameters:
  • char* cmd: Command to log.
  • const char* log_file: Log file path.

writecmd

• Purpose: Writes a command to the log file, maintaining a fixed log size.
• Parameters: Same as logcmd.

purge

• Purpose: Clears the log file.
• Parameters:
  • const char* log_file: Log file path.

handle_log

• Purpose: Manages log commands like viewing and purging.
• Parameters:
  • char* cmd_token: The log command.
  • const char* log_file: Log file path.

execute

• Purpose: Retrieves and executes a command from the log by number.
• Parameters:
  • int number: The command index.
  • const char* log_file: Log file path.
• Returns: The command string at the specified log index.

Proclore Functions

File: proclore.h

Functions:

get_process_info

• Purpose: Retrieves and displays information about a process by its PID.
• Parameters:
  • pid_t pid: The process ID to query.
• Logic:
  1. Process Status: Reads from /proc/[pid]/status to extract:
     • Process state.
     • Process group ID (Tgid).
     • Virtual memory size (VmSize).
  2. Executable Path: Reads the symbolic link from /proc/[pid]/exe to display the path of the executable.
  3. Error Handling: Prints an error if the process does not exist or if it fails to read the executable path.

print_proc

• Purpose: Parses a command to print process information for a given or current PID.
• Parameters:
  • char* cmd: Command input that optionally includes a PID.
• Logic:
  • Extracts the PID from the command, defaults to the current process ID if no PID is provided.
  • Calls get_process_info() to display process details.

Code Explanation

Seek Functions

colorprint

• Purpose: Prints the file or directory name with a color based on its type (directory or file).
• Parameters:
  • char *path: Path or name of the file/directory.
  • int is_dir: Flag to indicate if the path is a directory (prints blue) or a file (prints green).

check_file

• Purpose: Compares a file name with a target file, accounting for possible extensions.
• Parameters:
  • char *a: The base name to check.
  • char *target: The target file name.
• Logic:
  • If the base name contains an extension, it checks for an exact match.
  • If the base name doesn't have an extension, it checks if the base name matches the beginning of the target name with a . added.

recurse

• Purpose: Recursively searches through directories to find files or directories matching the target name.
• Parameters:
  • char *base_path: The starting directory path.
  • char *target: The name of the file or directory to search for.
  • int search_files: Whether to search for files.
  • int search_dirs: Whether to search for directories.
  • int *found_count: Tracks the number of matches found.
  • char *invoke: The current working directory.
  • char *found_path: Stores the first found path.

seek

• Purpose: Parses the input command and initiates a search for a file or directory within the target directory.
• Parameters:
  • char *command_string: The command input that includes options (-d, -f, -e), target file or directory, and search directory.
• Flags:
  • -d: Search for directories only.
  • -f: Search for files only.
  • -e: Execute the found file or change directory to the found directory.

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Process Management (activities.h)

add_process

• Purpose: Adds a process to the process management system.
• Parameters:
  • pid_t pid: The process ID of the process.
  • const char *command: The command associated with the process.

update_process_status

• Purpose: Checks the status of all tracked processes, updating whether they are running, stopped, or terminated.
• Logic:
  • Uses waitpid to check for process status changes and updates the internal process list accordingly.
  • Handles processes that have exited or have been stopped/continued.

compare_processes

• Purpose: Helper function for sorting processes based on their command names.
• Parameters:
  • Two Process structures to be compared.

fg_command

• Purpose: Brings a process to the foreground and resumes it if it was stopped.
• Parameters:
  • pid_t pid: The process ID to bring to the foreground.
• Logic:
  • Sets the terminal's foreground process group to the specified process.
  • Sends the SIGCONT signal to resume the process if it was stopped.

activities

• Purpose: Displays a list of all running and stopped processes, sorted by command name.
• Logic:
  • Calls update_process_status to ensure process statuses are up-to-date.
  • Sorts the process list using qsort and compare_processes.
  • Displays each process, its PID, command, and whether it's stopped or running.

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Code Explanation

Ping Functions

ping

• Purpose: Sends a signal to a process.
• Parameters:
  • int pid: The process ID to which the signal will be sent.
  • int sig: The signal number to send (e.g., SIGKILL, SIGTERM).
• Logic:
  • Uses the kill system call to send a signal to the process.
  • If the process doesn't exist or an error occurs, it prints an error message.
  • Otherwise, it prints a success message indicating that the signal was sent.

execping

• Purpose: Parses a command string and sends a signal to a process.
• Parameters:
  • char *cmd: The command string, which includes the process ID and signal.
• Logic:
  • The command string is split using strtok to extract the PID and signal number.
  • The ping function is called with these extracted values.

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Neonate Functions

handle_signal

• Purpose: Handles signals sent to the process.
• Parameters:
  • int sig: The signal number (e.g., SIGUSR1).
• Logic:
  • If the signal is SIGUSR1, it sets the running flag to 0, which can be used to terminate the loop in the child process.

get_most_recent_pid

• Purpose: Retrieves the most recent PID from the system.
• Logic:
  • Reads the /proc/sys/kernel/pid_max file to get the most recent PID.
  • If successful, returns the PID. Otherwise, returns -1.

getch

• Purpose: Captures a single character input from the user without echoing it to the screen.
• Logic:
  • Uses tcgetattr and tcsetattr to modify terminal settings, disabling canonical mode and echo.
  • Returns the captured character.

neonate_command

• Purpose: Continuously prints the most recent process ID at specified intervals until the user presses the 'x' key.
• Parameters:
  • const char *time_arg: The time interval (in seconds) between prints.
• Logic:
  • Parses the time argument, ensuring it's a valid positive integer.
  • Uses fork to create a child process:
    • Child Process:
      • Continuously fetches and prints the most recent PID every interval seconds until it receives a SIGUSR1 signal.
    • Parent Process:
      • Waits for user input. If the 'x' key is pressed, the parent sends a SIGUSR1 signal to the child process, terminating it.
  • If the fork fails, prints an error message.

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IMAN Function

fetch_data_from_url

Purpose

Sends an HTTP GET request to a given URL and prints the text content of the response while ignoring HTML tags, scripts, and styles.

Parameters

• const char *hostname: The hostname of the server to connect to.
• const char *path: The path of the resource on the server.

Functionality

1. Prepare Address Info:

   • Initializes hints for getaddrinfo to handle both IPv4 and IPv6 addresses and TCP stream sockets.

2. Get Address Information:

   • Calls getaddrinfo to resolve the hostname into an address structure.

3. Create Socket:

   • Creates a socket using the resolved address information.

4. Connect to Server:

   • Connects the socket to the server's address.

5. Prepare and Send HTTP GET Request:

   • Constructs an HTTP GET request string.
   • Sends the request using the socket.

6. Receive and Process Response:

   • Receives the response in chunks.
   • Parses the response to extract and print text content, ignoring HTML tags, scripts, and styles.

7. Close Socket:

   • Closes the socket after receiving the response.

Error Handling

• Prints error messages if getaddrinfo, socket, connect, or send fail.
• Prints an error message if receiving the response fails.

executeman

Purpose

Constructs a URL path based on a command argument and fetches data from the URL using the fetch_data_from_url function.

Parameters

• char* cmd: The command string containing the argument for the URL path.

Functionality

1. Parse Command String:

   • Splits the command string into tokens using strtok.
   • Extracts the argument for the URL path.

2. Construct URL Path:

   • Uses snprintf to create the URL path with the given argument.

3. Fetch Data:

   • Calls fetch_data_from_url with the hostname (man.he.net) and the constructed path.

Example Usage

If cmd is "manpage topic", it will construct the path /?topic=topic&section=all and fetch data from man.he.net using this path.

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Shell Functions and Signal Handlers

Signal Handlers

handle_sigint

Purpose: Handles the SIGINT signal (usually generated by pressing Ctrl+C).

Functionality:

• Sets the global flag ctrl_c_pressed.
• Sends SIGINT to the foreground process if it exists.
• Prints a new line if no foreground process is running.

handle_sigtstp

Purpose: Handles the SIGTSTP signal (usually generated by pressing Ctrl+Z).

Functionality:

• Sets the global flag ctrl_z_pressed.
• Sends SIGTSTP to the foreground process if it exists.

handle_sigchld

Purpose: Handles the SIGCHLD signal, which is sent to a process when a child process terminates or stops.

Functionality:

• Reaps all terminated child processes.
• Prints status messages based on the termination status:
  • Exit Status: Prints when a background process exits normally.
  • Signal Termination: Prints when a background process is terminated by a signal.
  • Stopped: Prints when a process is stopped; adds the process to the background processes list.

Utility Functions

is_command_valid

Purpose: Checks if a command is valid by verifying if it is a known command or if it exists in the system's PATH.

Parameters:

• const char *command: The command to check.

Returns:

• 1 if the command is valid.
• 0 otherwise.

get_part_before_whitespace

Purpose: Extracts the part of a string before the first whitespace.

Parameters:

• const char *str: The input string.
• char *result: Buffer to store the result.

Functionality:

• Copies the substring before the first whitespace into the result buffer.
• If no whitespace is found, copies the entire string.

trim_whitespace

Purpose: Trims leading and trailing whitespace from a string.

Parameters:

• char *str: The string to trim.

Functionality:

• Removes leading and trailing spaces from the string.
• Modifies the original string in place.

count_char_occurrences

Purpose: Counts occurrences of a specific character in a string.

Parameters:

• const char *str: The input string.
• char ch: The character to count.

Returns:

• The number of occurrences of the specified character.

Notes

• Global Variables:

  • volatile sig_atomic_t ctrl_c_pressed: Flag set when Ctrl+C is pressed.
  • volatile sig_atomic_t ctrl_z_pressed: Flag set when Ctrl+Z is pressed.
  • pid_t foreground_pid: Stores the PID of the foreground process.

• Signal Handling:

  • Ensure proper handling of child processes and background tasks by implementing appropriate functions to manage process states and interactions.