main.py

#!/bin/python3

'''
main source code of nemsh
'''
import subprocess
import os
import sys


alias_table = {} # note: here aliases are stored right now

PS1 = False # note: don't touch this

# executing NOT built-in commands
def exec_cmd(command):
    '''
    this function execute every other command (that isn't implemented to nemsh)
    '''
    try:
        if len(command.split()) == 1:
            subprocess.run(command, check=True)
        else:
            subprocess.run(command.split(), check=True)
    except subprocess.CalledProcessError as e:
        print(f"=> [error]: {e}.")
    except FileNotFoundError:
        print(f"=> [error]: Command not found. ({command})")

# implementing simple shell commands (echo, cd, improved ls)
def echo(args):
    '''
    this function prints echo output to stdout
    '''
    if len(args) == 1 and args[0][0] == "$":
        print(os.getenv(args[0][1:]))
    else:
        print(" ".join(args))

def change_dir(directory):
    '''
    this is nemsh's cd implementation
    '''
    if not directory:
        os.chdir(f"/home/{os.getlogin()}")
    else:
        try:
            os.chdir(directory[0])
        except (NotADirectoryError, FileNotFoundError):
            print("=> [error] No such file or directory.")
        except IndexError:
            print("=> Usage: cd <directory>.")

def export_var():
    '''
    this function adds environment variables support
    '''
    var_name = input("\x1b[32m>\x1b[0m variable name: ")
    var_val = input("\x1b[32m>\x1b[0m value: ")
    os.environ[var_name] = var_val

def alias():
    '''
    this function adds alias to nemsh
    '''
    global alias_table

    alias_name = input("\x1b[32m>\x1b[0m name: ")
    alias_val = input("\x1b[32m>\x1b[0m value: ")
    alias_table[alias_name] = alias_val

# shell loop
def sh_loop():
    '''
    the shell loop
    '''
    global PS1

    if not PS1:
         PS1 = f"\x1b[32m{os.getcwd()}\x1b[0m ({os.getlogin()}@{os.uname()[1]}) $ "
    while True:
        command = input(PS1)
        if not command:
            continue
        args = command.split()

        if len(args) == 1 and args[0] == "exit":
            sys.exit()
        elif len(args) == 2 and args[0] == "exit":
            try:
                if int(args[1]) > 255:
                    print("=> [error] Avialable exit codes are in range from 0 to 255")
                else:
                    sys.exit(args[1])
            except ValueError:
                print("[e] Exit code expected to be an integer.")
        elif args[0] == "cd":
            change_dir(args[1:])
        elif args[0] == "echo":
            echo(args[1:])
        elif args[0] == "export":
            export_var()
        elif args[0] == "alias":
            alias()
        elif args[0] in list(alias_table.keys()):
            exec_cmd(alias_table[args[0]])
        else:
            exec_cmd(command)

if __name__ == "__main__":
    try:
        sys.path.append(f"/home/{os.getlogin()}/.config/nemsh/")
        import rc
        PS1 = rc.PS1
        rc.main()
    except Exception:
        # pass because user may not have the rc file (it is not necessary to have one)
        pass
    sh_loop()