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at42minishell

This is a minishell, a 42 school project that reproduce a basic shell (CLI).

We use an AST! (Abstract Syntax Tree)

We did all the bonuses except the HERE_DOCUMENT (<< operator).

Made by charmstr and me.

Usage

# Compile minishell with the Makefile
make -j4

# Start the shell
./minishell

Features

  • Line editing (← / →)

  • History (↑ / ↓)

  • Copy (start: CTRL+K | stop : CTRL+K)

  • Past (CTRL+P)

  • Cut (start: CTRL+K | stop : CTRL+L)

  • Built-ins

    • echo
      • -n flag
    • cd (absolute/relative path + ~/-)
    • pwd
    • export
    • unset
    • env
    • exit

  • Launch binaries from $PATH (of course)

  • Semicolons (;)

  • Pipes (|)

  • Quotes (", ')

  • Redirections (>, >>, <)

  • Signals (CTRL-C / CTRL-\ / CTRL-D)

  • AND operator (&&), OR operator (||)

  • Parenthesis priority, creates a subshell ((cmd))

  • Environment variables (ex: $PATH) + $?

  • Go start of line (CTRL+A or HOME)

  • Go end of line (CTRL+E or END)

  • Navigate between words (CTRL+← and CTRL+→)

  • Navigate between lines (CTRL+↑ and CTRL+↓)

  • Multiline (giving a line with unclosed quote (", ') or backslash (\) prints a PS2 until the line is finished)

  • Pathname expansion. Wildcard * (unquoted)

  • Update SHLVL, the prompts PS1 and PS2

  • Ambiguous Redirections

Main behavior of the minishell:

I] Get the next command line:

  • The terminal is put in raw mode in order to have an exact bash-like input interface.

II] Tokenisation (aka Lexing):

  1. Create tokens with the Lexer (lexical analizer).

If the user's input isn't finished (unmatching quotes or parenthesis, backslash): prompt a PS2 until it's ok.

  1. Categorizing the tokens as we create them from left to right.

III] Parsing:

  • Process the tokens according to a grammar and builds an AST of all the commands to run.

Thanks to the operators, we can identify the beginning and end of jobs.

IV] Word expansion:

  1. Tild expansion (~) is done at the beginning of a potential path, or after the first '=' sign that is in between a label=value pattern:
$ echo salut=~:~/Projects:~/hey # => salut=/HOME/charmstr:/HOME/charmstr/Projects:/HOME/charmstr/hey

  1. Parameter expansion. ex:$PWD becomes /home/...

  2. Field splitting, applied to the parameter expansion, only if in an unquoted section of text.

$ export foo="one       two"
$ echo $foo # Spaces are removed, expansion got split in two: one two
$ echo "$foo" # Spaces aren't removed. still one unique string: one      two

note: new strings that comes from an expansion are marked as protected against late quote removal.

  1. Pathname expansion
$ ls # foo foobar foobar2
$ echo fo* # -> foo foobar foobar2

note: it only applies if the * is unquoted, unescaped, etc.

  1. Quote removal

V] Redirections are performed if necessary.

  • They are separated from the argv, but kept in the order of appearance. Redirecting stdin and stdout.

VI] Commands are executed. A new prompt is displayed.