Minishell

Lexer

lexical analysis is the process of converting a sequence of characters (such as in a computer program or web page) into a sequence of tokens (strings with an identified "meaning").

Normally we represent the token as a pair: (token type, token value). For example, if a program's source file contains string: "998", the lexer will treat it as token (Number, 998) meaning it is a number with value of 998.

Lexer vs Compiler

Let's first look at the structure of a compiler:

                   +-------+                      +--------+
-- source code --> | lexer | --> token stream --> | parser | --> assembly
                   +-------+                      +--------+

The Compiler can be treated as a transformer that transform C source code into assembly. In this sense, lexer and parser are transformers as well: Lexer takes C source code as input and output token stream; Parser will consume the token stream and generate assembly code.

Then why do we need lexer and a parser? Well the Compiler's job is hard! So we recruit lexer to do part of the job and parser to do the rest so that each will need to deal with simple one only.

That's the value of a lexer: to simplify the parser by converting the stream of source code into token stream.

`Exit` :

The exit command in a shell is used to exit the current shell session gracefully. It allows you to terminate the shell and return an optional exit status to the calling process.

How `exit` Works in a Shell:

Syntax :
```
   exit [status]
```
[status] is an optional integer argument that represents the exit status of the shell. If not provided, the exit status defaults to 0.
Functionality : - The exit command is used to gracefully terminate the current shell session. - It allows the shell to return an exit status to the parent process or terminal from which it was launched.
Exit Status : - The exit status is an integer value that typically indicates the success or failure of the shell's execution. A status of 0 often indicates success, while non-zero values typically represent errors or abnormal termination. - You can use exit statuses to convey information about the outcome of a script or a series of commands executed within the shell.
Termination : - When the exit command is executed, the shell terminates immediately, and the control is returned to the parent process (e.g., the terminal or a script). - Any unsaved data, environment variables, and changes made during the shell session are discarded.

Using `exit` in a Shell:

Here are some common use cases and tips for using the exit command in a shell:

Exit with Default Status :
- To exit the shell with the default exit status (0), simply type exit and press Enter.
```
    exit
```
Specify an Exit Status :
- To exit the shell with a specific exit status, use exit followed by the desired integer status, e.g., exit 1 or exit 42.
```
    exit 1      # Indicates an error or failure
    exit 42     # Custom exit status
```
Checking the Exit Status :
- you can check the exit status of the last executed command by using the special variable $?.
```
echo $?
```

MarouanDoulahiane/MiniShell

Minishell

Lexer

Lexer vs Compiler

Exit :

How exit Works in a Shell:

Using exit in a Shell:

`Exit` :

How `exit` Works in a Shell:

Using `exit` in a Shell: