https://github.com/daisvke/minishell
This project involves creating a simple shell in C.
https://github.com/daisvke/minishell
42school custom-shell minishell shell
Last synced: 11 months ago
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This project involves creating a simple shell in C.
- Host: GitHub
- URL: https://github.com/daisvke/minishell
- Owner: daisvke
- Created: 2021-12-14T04:19:59.000Z (about 4 years ago)
- Default Branch: main
- Last Pushed: 2025-01-24T13:57:48.000Z (12 months ago)
- Last Synced: 2025-01-24T14:35:01.507Z (12 months ago)
- Topics: 42school, custom-shell, minishell, shell
- Language: C
- Homepage:
- Size: 404 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# **minishell**
## **Description**
This project involves creating a simple shell in **C**.
---
## **Commands**
### **Running the Program**
To compile and run the program, use:
```bash
make
./minishell
```
Alternatively, you can run a command directly through **minishell** with:
```bash
make
./minishell [command]
```
---
### **envp**
- `$HOME` is initialized as the `$PWD` (path) of the project's root directory.
---
### **Command Prompt Format**
The command prompt is composed of:
```plaintext
[$LOGNAME]@[$NAME / $SESSION_MANAGER]:[PATH]$
```
- `$NAME` or `$SESSION_MANAGER` is used, depending on the system.
- Unsetting `$LOGNAME` or `$NAME/$SESSION_MANAGER` does not change this part.
- If `$HOME` is unset, the **absolute current path** is used.
- If the current directory is the same as `$HOME`, the path is replaced by a tilde (`~`).
- If the current directory is the root directory, [PATH] only shows `/$`.
---
## **Implemented Commands**
### **cd**
- The `cd` command updates `$PWD` and changes the command prompt's path when the directory is altered.
- `cd ..` works as expected (using `chdir()`), navigating to the parent directory.
- `cd -` is implemented. It replaces the '`-`' argument by the $OLDPWD value.
- If `cd` is called with more than one argument, it will return an error.
- Running `cd` alone brings the user to `$HOME`.
### **exit**
- Any argument passed to the `exit` command is ignored.
### **export**
- Every valid argument is exported to **minishell's envp**.
- Arguments are **invalid** if:
1. The variable's name begins with a digit.
2. The variable's name contains non-alphanumeric characters (except underscores `_`).
3. The argument begins with the equal sign `=`.
4. There are spaces before the equal sign.
### **unset**
- Unsetting `$PATH` and then trying to run a command (except for built-in commands: `cd`, `echo`, `exit`, `export`, `unset`) will throw an error. This mimics bash behavior.
- Arguments are **unset** from **minishell's envp** unless:
1. The variable is not found.
2. The variable is invalid (see **export** above).
### **pwd**
- If `$PWD` is unset, the `pwd` command will print the **current absolute path**, using `getcwd()`.
### **echo**
- All arguments are printed with spaces in between unless the `-n` option is used (to omit the trailing newline).
- The backslash character (`\`) is not echoed, similar to bash behavior.
### **env**
- This command ignores any arguments and prints all active environment variables within **minishell**.
#### Advantages of Using Linked Lists
Using a linked list to manage environment variables in a C shell offers several key benefits:
1. **Dynamic Size**
Easily add or remove variables without wasting memory.
2. **Efficient Modifications**
Insertions and deletions occur in constant time (O(1)).
3. **Easy Traversal**
Supports sequential access without the need for fixed indexing.
4. **Better Memory Management**
Allows for precise memory allocation and reduces the risk of memory leaks.
5. **Simpler Implementation**
Operations are easier due to the inherent structure of linked lists.
---
## Environment Variable Expansion
We have added comprehensive support for environment variable expansion, enabling dynamic substitution of variables within commands and scripts.
### Features
1. **Environment Variable Expansion**
- Any variable prefixed with a `$` and defined in the environment is expanded to its corresponding value. For example:
```bash
echo $HOME
```
will display the value of the `HOME` environment variable.
- Variables enclosed in quotes, such as `"$HOME"`, are also expanded correctly. The quotes are preserved, but the variable is substituted with its value. For example:
```bash
export MY_VAR=hello
echo "$MY_VAR"
```
Output:
```
hello
```
2. **Special Variable Expansion**
- The `$?` variable is expanded to represent the exit status of the last executed command. For example:
```bash
ls /nonexistent
echo $?
```
would output `2`, as the `ls` command failed to find the specified path.
3. **Undefined Variables**
- If a variable is not defined in the environment or is invalid, it is replaced with an empty string (`""`) during expansion. For example:
```bash
echo $UNSET_VAR
```
results in:
```
(no output, replaced by an empty string followed by a newline character)
```
## **Leaks**
To check for memory leaks (excluding those due to `readline()`), create a suppression file with the following content:
```plaintext
{
ignore_readline_leaks
Memcheck:Leak
...
obj:/lib/x86_64-linux-gnu/libreadline.so.7.0
}
```
You can name this file anything you'd like.
Make sure to replace the last line with the correct path for your system.
You can find this in the **valgrind** reports. For instance:
```
// With this output:
==356791== by 0x4890CD4: readline (in /usr/lib/x86_64-linux-gnu/libreadline.so.8.1)
```
You will replace `obj:/lib/x86_64-linux-gnu/libreadline.so.7.0` by `obj:/usr/lib/x86_64-linux-gnu/libreadline.so.8.1`
Then, run:
```bash
valgrind --leak-check=full --show-leak-kinds=all --track-fds=yes --suppressions=ignore_readline_leaks ./minishell
```
This will suppress the specific leaks caused by `readline()` while checking for other memory issues.