The minishell project was done in collaboration with Renan Guillen, a follow cadet at 42. Together, we aimed to create a program that emulates the default behaviour of a shell script command line prompt, executing binaries throught pipes and conditionals, dealing with environment variables and manipulating files through redirections and heredocs. This was the most complex project that we had to dwell upon so far, not only because of its code complexity, but more so bacause it is really hard to know when to stop: Minishell can be infinite, and is, by all means, always incomplete.

The main idea behind minishell is the ability to decipher what is being written on the prompt by the user, translating it into a structure of data that will be easily understandable by the computer, and therefore appropriately executed.

Your shell should:

• Display a prompt when waiting for a new command.
• Have a working history.
• Search and launch the right executable (based on the PATH variable or using a relative or an absolute path).
• Not use more than one global variable. Think about it. You will have to explain its purpose.
• Not interpret unclosed quotes or special characters which are not required by the subject such as \ (backslash) or ; (semicolon).
• Handle ’ (single quote) which should prevent the shell from interpreting the metacharacters in the quoted sequence.
• Handle " (double quote) which should prevent the shell from interpreting the metacharacters in the quoted sequence except for $ (dollarsign).
• Implement redirections:
  • < should redirect input.
  • > should redirect output.
  • << should be given a delimiter, then read the input until a line containing the delimiter is seen. However, it doesn’t have to update the history!
  • >> should redirect output in append mode.
• Implement pipes ( | character). The output of each command in the pipeline is connected to the input of the next command via a pipe.
• Handle environment variables ( $ followed by a sequence of characters) which should expand to their values.
• Handle $? which should expand to the exit status of the most recently executed foreground pipeline.
• Handle ctrl-C, ctrl-D and ctrl-\ which should behave like in bash.
• Ininteractive mode:
  • ctrl-C displays a new prompt on a new line.
  • ctrl-D exits the shell.
  • ctrl-\ does nothing.
• Your shell must implement the following 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