M I N I S H E L L
1- LEXER
We made lexer pace for split our input to commands. While doing this, we paid attention to quotations, special characters such as |, >, >>, <, <<. We have also separated these special characters and kept them in a linked list structure for easier access.
2- EXPANDER
As we can understand from the name in this pace we expanded $ENV_KEYS, tilda (~) and deleted quote signs for print or use them. While we do this paid attention for quote hierarchy. For example:
"$USER" -> pragmataW
'$USER' -> $USER
"hello'world'!" -> hello'world'!
3- PARSER
In this pace we create a command table for execve function. In this command table have 4 attribute.
1 - cmd_path = it's important for execve function. For exemple when we execute "ls" command our shell search for ls command's executable path like "/bin/ls" because ls is actually a program like our programs. The pats are in the $PATH variables. Even if you unset $PATH variable u cant execute any commands in bash (don't try this).
2- full_cmd = it's for execve function -btw, execve function is execute some shell commands in c code-. The second parameter of the execve function is which command will be executed in the path we give in the first parameter. For example i will execute ls -a in the /bin/ls.
3- infile = We use this for redirec and heredoc (<, <<) In this case we redirec our program's input to specified file in executer pace. If there is a heredoc or redirec i'm opening a file and give file's descriptor to infile attribute.
4- outfile = We use this for redirec like >> or >. In this case we redirec our program output to the specified file in executer pace. So if there is a redirec i'm opening a file and give file's descriptor to outfile attribute.
4- EXECUTER
We are ready for execute our commands. We can call execve functions. But we should now some tricks. Firstly after we called execve function, our process self-destructs. So we must open a new child process and call the execve function in here.
Also we should made our pipe and redirec struct. For example when we try to execute ls -a | wc -l, ls should be another process, wc should be another process. And ls's output should be wc's input. For this we use "dup2" and "pipe" functions.
For redirec we should control command table's infile and output attributes. If they are not normal values we should use dup2 like dup2(infile, STDINFILENO) or dup2(outfile, STDOUTFILENO)
then we can execute our commands. We have some built-in functions like echo, pwd, cd etc. If our commands are built'in, i called my own built-in execve function, if our command is not built'in i called default execve function for execute.