minishell

Build a simplified version of a shell - (under development ⚙️)

Our shell should:

• Not interpret unclosed quotes or unspecified special characters like \ or ;.
• Not use more than one global variable, think about it and be ready to explain why you do it.
• Show a prompt when waiting for a new command.
• Have a working History.
• Search and launch the right executable (based on the PATH variable or by using relative or absolute path)
• It must implement the builtins:
• echo with option -n
• cd with only a relative or absolute path
• pwd with no options
• export with no options
• unset with no options
• env with no options or arguments
• exit with no options
• ’ inhibit all interpretation of a sequence of characters.
• " inhibit all interpretation of a sequence of characters except for $.
• Redirections:
• "<" should redirect input.
• ">" should redirect output.
• “<<” read input from the current source until a line containing only the delimiter is seen. it doesn’t need to update history!
• “>>” should redirect output with append mode.
• Pipes
  • "|". The output of each command in the pipeline is connected via a pipe to the input of the next command.
• Environment variables ($ followed by characters) should expand to their values.
• $? should expand to the exit status of the most recently executed foreground pipeline.
• ctrl-C ctrl-D ctrl-\ should work like in bash.
• When interactive:
  • ctrl-C print a new prompt on a newline.
  • ctrl-D exit the shell.
  • ctrl-\ do nothing.

readline function can produce some leaks, no need to fix this.

For every point, if you have any doubt take bash as a reference.

File Organization

Folder	Description
Parser	Contains a parser and a lexer that build an Abstract Syntax Tree. The goal is to read the input provided from the user and separate it into actionable commands. Also checks for syntax errors.
Cleaning	Contains functions to make sure that we go into the next phase (i.e. exiting or new line from user) cleanly. Frees any unnecessary memory.
Commands	Contains functions to replicate bash commands that need to be hardcoded. "cd" is a good example, since we cannot fork and then call chdir because when we exit the fork we'll be left in the same directory.
Executing	Executes commands given by the parser via execve.
Redirecting	Takes care of redirecting STDIN and STDOUT when necessary. A good example is that it creates the pipes needed between two processes when givne the pipe command.
Reader	Uses the readline functions to read a line from the user and create a working history.
Utils	Helpful everyday functions.

Usage

This project uses a makefile, so to run the program you can compile with make and then enter ./minishell. Minishell usually runs with no arguments but for debugging you can use the -debug flag (i.e. ./minishell -debug).

External functions that are allowed

• readline, rl_clear_history, rl_on_new_line, rl_replace_line, rl_redisplay, add_history,
• printf, malloc, free, write,
• access, open, read, close,
• fork, wait, waitpid, wait3, wait4,
• signal, sigaction, kill,
• exit,
• getcwd,
• chdir,
• stat, lstat, fstat,
• unlink,
• execve, dup, dup2, pipe,
• opendir, readdir, closedir,
• strerror, perror,
• isatty, ttyname, ttyslot,
• ioctl, getenv, tcsetattr, tcgetattr, tgetent, tgetflag, tgetnum, tgetstr, tgoto, tputs.