This is a minishell, a 42 school project that reproduce a basic shell, or command interpreter. we did all the bonuses except for the HERE_DOCUMENT ("<<" operator). So we handle the line editing like in the real bash, with the history and some custom copy past, go-to-the-end (ctrl+e or END key), go-to-the-beginning (ctrl + a or HOME key), navigate between words (ctrl + left and ctrl + right), navigate between lines (ctrl + up, ctrl + down). we handle the multiline edition and the use of the PS2 prompt. We also handle the pathname expansions. alowing multiple '/' in a raw like in the real bash. quoted stars are differenciated from wild cards, therefore not expanded. We also handle the "&&" and "||" and the parenthesis for complexe commands and subshells trhough the use of an abstract synthax tree. we added extra bonuses like the tild expansion, field splitting when doing variable expansions, the shlvl environment variable is updated, the possibility to update the prompt PS1 and PS2, the ability to change the window size, similar shell error messages like ambiguous redirections, "cd -", "cd ~"
Main behavior of the minishell:
the parsing happens in two disctinct STEPS 1) lexer (lexical analizer) => creates tokens 2) parser => process the tokens acording to a grammar and builds an abstract synthax tree of all the commands we need to run. note: we do hande the "&&" and "||" operators, as well as the parenthesis to start subshells.
I] getting the next command line: the terminal is put in raw mode in order to have an exact bash like input interface. - we have a history of the last commands launched. (ctrl up and ctrl down). that could be the only difference between the real bash, if we go up in the history and sart to edit a command line, then change to an other line in history back and forth, the edition we just did gets lost. Except for that every features of bash is reproduced. note: hitting the tab key doesnt do the autocompletion of file names or commands. The trailing and are removed before splitting the input into tokens.
II] tokenisation (aka lexing)
1) char by char, create tokens with the lexer. If the tokens arent finished
at the end of the user's input (unmatching quotes or parenthesis,
escaped new-line...):
--> prompt a PS2. redo it UNTIL the all the tokens are closed.
note: fix set of metacharacter to separate tokens (unquoted and unescaped)
<space>, <tab>, <newline>, ;, (, ), |, &, <, >.
2) then when the token constructs are fully complete we can stop getting
the user 's input, and start to parse the command.
3) categorizing the tokens as we creat them from left to right.
Once a token is delimited, make sure its being categorized as required by
the shell grammar.
4) separate in between: OPERATOR (including IO_NUMBER...) or TOKEN
III] build an abstract tree in the parser section. thanks to the operators, we can identify the begining and end of jobs.
IV] in each simple commands the tokens list is subject to word expansion:
1) tild expansion is done at the begining of a potential path, or after
the first '=' sign that is in between a label=value pattern.
ex: echo salut=:/Projects:~/hey ->
salut=/HOME/charmstr:/HOME/charmstr/Projects:/HOME/charmstr/hey
2) parameter expansion
example: $PWD -> /home/...
3) field splitting, applied to the parameter expansion, only if in an
unquoted section of text.
example: export hey="one two"
echo $hey --> one two
the spaces are removed, expansion got split in two.
echo "$hey" --> one two
the spaces arent removed. still one uniq string.
note: portion of the new strings that come from an expansion are
marked as protected against late quote removal. every char is
to be taken litteraly.
4) pathname expansion
example: ls -> salut salop salt samy
echo sal* -> salut salop salt
note: it only applies if the '*' is unquoted (unescaped etc).
if it doesnt apply, we jump to step 5.
also note that some quote removal is done before
this action occurs.
5) quote removal (not on the protected strings parts resulting
from the parameter expansion).
V] Redirection is performed if necessary. they are separated from the argv, but kept in the order of appearance. redirecting stdin and stdout temporary
VI] Commands are executed. then a new prompt is displayed.