lang.py

import os
import sys
variables = {}

def rchop(string, suffix):
    if suffix and string.endswith(suffix):
        return string[:-len(suffix)]
    return string

while True:
    # debug
    #print(variables)
    try:
        if not sys.argv[1] == "-c":
            inp = input(">>").lstrip()
        else:
            inp = input().lstrip()
        variable_assigned = False
        
        # replace variable names with values
        for var_name, var_value in variables.items():
            inp = inp.replace(f"{var_name}$", var_value)
        
        # variable handler
        if ":=" in inp:
            var_name, *var_value = inp.split(":=")
            var_name, var_value = var_name.strip(), ':='.join(var_value)
            if ' ' not in var_name and var_value:
                variables[var_name] = var_value
                variable_assigned = True
        
        inp = inp or "No content"
        keyword = inp.split(" ")[0]
        # commands
        if inp == "exit":
            if not sys.argv[1] == "-c":
                print("Exiting.")
            break
        elif keyword == "print":
            print(inp[6:])
        elif inp == "ls":
            directories = [f for f in os.listdir('.') if not os.path.isfile(f)]
            files = [f for f in os.listdir('.') if os.path.isfile(f)]
            for d in directories:
                print(f'{d}/')
            for f in files:
                print(f)
        elif keyword == "cd":
            targetdirectory = inp[3:]
            try:
                os.chdir(targetdirectory)
                if not sys.argv[1] == "-c":
                    print("Directory changed to %s" % os.getcwd())
            except:
                print(f'Unable to change directory to {targetdirectory}. Does the directory exist?')
        elif inp.startswith("shell ") and inp.endswith(" shell"):
            command = rchop(inp[6:], " shell")
            os.system(command)
        elif keyword == "pwd":
            print(os.getcwd())
        elif keyword == "calc":
            expr = inp[5:]
            print(expr, "=", eval(expr))
        elif not variable_assigned:
            print(f"syntax error - ({inp})")
    except:
        if not sys.argv[1] == "-c":
            print("\nExiting.")
        break