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.

2. 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

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

3. 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.

4. Pathname expansion

$ ls # foo foobar foobar2
$ echo fo* # -> foo foobar foobar2

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

5. 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.