42_minishell

This project is about creating a simple shell. Our own little bash with limited functionalities.

Team project with Orezek at 42Prague.

What kind of features our minishell have?

• displays prompt as a bash - with path to current directory
• working history
• working redirections (<, >, >>), heredoc (<<), pipes (||)
• execute commands as bash with argumets - ls, cat, head, git ...
• launch executables - try launch ./minishell in ./minishell
• handle environmental variables
• woking expansion of environmental variables ($) as bash
• handle CTRL-C, CTRL-D, CTRL-\ as bash
• working 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

What our minishell cannot do?

• Cannot handle open quotes or open double quotes
• Cannot handle special characters such as backslash \ or semicolon ;
• NO BONUS - Cannot handle &&, || and wildcards *

How to run minishell

• You have to have readline installed. If not, install it with

sudo apt install libreadline-dev

• Make the minishell with command

Make

• Run the program

./minishell

Examples

Aditional test cases

cat | cat - should hang and after pressing CTRL+C should end execution and show prompt again

cat /dev/urandom | head -5
/bin/ls src
/bin/pwd hello
/bin/date
/usr/bin/head -n 10 Makefile
/bin/grep # Makefile
/usr/bin/uname -a
/usr/bin/head Makefile
/usr/bin/tail Makefile

How to debug? Use valgrind!

Use this prompt to check for leaks, open fds, etc. (It requires minishell.supp file in minishell root directory)

valgrind -s --leak-check=full --show-reachable=yes --error-limit=no --suppressions=minishell.supp --trace-children=yes --track-fds=yes ./minishell

• -s same as --show-error-list=yes that shows detected errors list and suppression count at exit
• --leak-check=full shows a full list of memory leaks
• --show-reachable=yes same as --show-leak-kinds=all that shows all kinds of memory leaks
• --error-limit=no won't stop showing errors if too many
• --suppressions=minishell.supp suppresses memory leaks from in-built functions (readline and add_history)
• --trace-children=yes checks memory leaks in child process too
• --track-fds=yes tracks open and closed file descriptors

What we learned during coding minishell

• Understand bash better, how it works underneath
• Better understanding of processes, forks, wait, waitpid, exit statuses, etc.
• Learned what signals are and how to handle them
• Learned to use static variable within clean functions to store a pointer to a struct for later use (see for example the exit_minishell() function)
• Become more familiar with structs and linked lists

Contributors

• m-bartos - parser - splitter, expander, heredoc; prompt construction
• orezek - execution, built-ins, signals, environmental variables

Thanks and kudos

• Thanks LukasKuhn for the minishell tester
• Appreciate the project discussions, testing and hints provided by our fellow 42Prague students - andreaulicna, loudapet - Thanks you for your insights!