myshell

Description

This is a simple shell written in C.

How To Run

make to compile the source code. ./myshell to run after compiling.

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Alternatively make run to compile and run

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make clean to clean the repository from object, executable, alias and history files

Features

• The prompt string: username@hostname:cwd ---
• > - redirect output to a file (overwrite)
• >> - redirect output to a file (append)
• >>> - redirect output to a file (append, but invert the order of all letters in the output)
• & - run the command in the background
• alias x = y - create an alias for the command y, named x
• bello - run the bello program

• Bello Program: Displays various information about the user and system:

1. Username: Retrieved using getenv("USER").
2. Hostname: Retrieved using gethostname().
3. Last Executed Command: Read from a file called .history
4. TTY
5. Current Shell Name
6. Home Location
7. Current Time and Date
8. Current Number of Processes: Retrieved by executing the 'ps -e' command and counting lines of output.

Some Design Decisions and Specifications

• It works in a fork-exec manner, meaning that it creates a child process for each command.
• It can run each and every command in the PATH environment variable.
• In case of a collision between an alias and a command, the alias should take precedence.
• Use of getcwd() as cwd for the prompt string. This is done to make sure that the prompt string is always up to date.
• Process count takes into account the zombie processes as well since they are not waited for.
• Last executed command resolves into a raw command from the user, including all the arguments. (i.e. input: ls -l >> a.txt, output: ls -l >> a.txt)
• Background processing yields prompt string to be printed before the command is finished executing, similar to how bash handles.
• Alias resolves into corresponding command and arguments while right after getting the input from the user. (i.e. input: ls -l, alias: ls = ls -a, output: ls -l -a)
• Bello functionality is provided as an executable file in the same directory as the myshell executable. After it is compiled with the same makefile, the directory /bin is added to the PATH. Therefore, whenever bello is called, there guaranteed to be at least 1 child process.
• Last executed command is stored in a file called .history in the same directory as the myshell executable. It is created if it does not exist. It is overwritten if it exists.

Author

Umit Can Evleksiz - 2020400114 Bogazici University - Computer Engineering Department