Shell V0.1

Author: pxlgenesis

README.md

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+Shell building project using python.
+
+NOTE TO SELF: 
+1.PYTHON IS CASE SENSITIVE.
+2.For some reason program doesnt terminate on sys.exit(0) or return 0 in the main() for some reason while using visual studio but works fine in the terminal.
+3.Used def func for each command.
+4.Split is is used to cut commands into multiple parts. and then dictionary can be used to match it out.
+5.regex is the way to go but too complex.
+6. os.path.isfile: to check if file is present. os.access(path,os.X_OK) to check that the user privilages are enough.
+7.shutil is used for high level operations for the file.
+8.os.[] has important file handing functions.
+9.isdir checks for directory and isfile checks for a executable file.
+10.Join is can be used to join variables in a list with desired separator.
+11.prompttoolkit is useful during user input operations.
+
+v[0.1]
+Task-To-Implement:
+1.REPL (READ-EVAL-PRINT-LOOP): executes command after command like a terminal does.
+2.EXIT: Implemented status 0 on typin "exit 0". 
+3.ECHO: 1. implemented to read echo and differentiate from illegal      words like "echo34" or "echo%" for now. and changed both of them to be executed as functions.(echo strips the first 5 words of each message)
+        2.Rewored echo to recognizse seprators.
+        3.Reworked echo to recognize Redirect stdout & stdin
+
+4.TYPE: Shows if or not the command is present in the shell.
+5.CUSTOM COMMANDS: 1. checks for command and command path in bin. if present executes the command. 
+                   2. Reworked to distinguished quoted commands.
+6.PWD: outputs current working directory from os. 
+7.CD: 1.changes directory on absolute path, relative and ~ for home.
+      2.Reworked cd to recognize seprators.
+8.AUTOCOMPLETE: autocompletes all builting commands.
+    

app/main.py

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+import sys
+import os 
+import shutil #shell utilities.
+import shlex #Simple lexical analysis.
+from prompt_toolkit import prompt #toolkit used to autocomplete words.
+from prompt_toolkit.completion import WordCompleter
+
+def main():
+        #REPL
+    completer = WordCompleter(builtin,ignore_case=True)
+    while True:
+
+        # "$" initiation
+        #Takes in an input
+        command = prompt("$ ",completer=completer) 
+        sys.stdout.flush()
+
+        #Recognises status 0 on "exit 0"
+        if command == "": #Blank input resets.
+            main()
+        elif  command.startswith("exit"):
+            handle_exit(command)
+
+        elif command.startswith("pwd"):
+            handle_pwd(command)
+
+        elif command.startswith("cd"):
+            handle_cd(command)
+
+        elif command.startswith("echo"):
+            handle_echo(command)
+        
+        elif command.startswith("type"):
+            handle_typecmd(command)
+        
+        elif handle_systemcommand(command):
+            os.system(command) #Automatically prints output but print(os.system(command)) causes it to return code 0.
+        else:
+            #f"{}" stands for formmated string
+            print_cmd_error(command)
+    
+def debug():
+    print("works!")
+
+def handle_systemcommand(message):
+    message = shlex.split(message)
+    if shutil.which(message[0]):
+        return True
+    return False
+
+#Prints error message
+def print_cmd_error(message):
+    print(f"{message}: command not found")
+    sys.stdout.flush()
+    
+#ECHO command to print out the message    
+def handle_echo(message): #Searches for "<" anad ">" in echo command and redirects to os shell.
+    if "<" in message  or ">" in message:
+        os.system(message)
+        return
+    elif message.startswith("echo "): 
+        message=message[5:].strip() 
+        message=shlex.split(message)
+        print(" ".join(message))
+    elif message == "echo":
+        print("")
+    else:
+        print_cmd_error(message)
+
+#EXIT command to exit the program
+def handle_exit(message):        
+    if len(message)<5:
+        print_cmd_error(message)
+        return
+
+    message=message.split(maxsplit=1)
+    if len(message)==2 and message[1] =="0":    
+        #Exiting with system(0)
+        sys.exit(0)
+    else:
+        print_cmd_error(message[1])
+
+#All commands in shell
+builtin={"echo","exit","type","pwd","cd"}
+
+#finding inbuilt commands and searches for given path and command in envior path.
+def handle_typecmd(message):
+    #splits message into "type" & follow up "command"
+    message = message.split(maxsplit=1)
+    
+    #Checks if it split into two
+    if len(message)==2:
+        
+        #Checks for command in builtin commands
+        if message[1] in builtin:
+            print(f"{message[1]} is a shell builtin")
+            return
+        
+        #Retrive and Split current path, pathsep auto detects win or linux sepration
+        path_dictry = os.environ.get("PATH","").split(os.pathsep)
+        
+
+        #Process and match the path
+        for directory in path_dictry:
+            Potential_path=os.path.join(directory,message[1])
+
+            #Is file gives boolean if the path exists
+            #Access does the same but for if the user can has exucatable access
+            if os.path.isfile(Potential_path) and os.access(Potential_path,os.X_OK): #Is there a file and can we access it.
+                print(f"{message[1]} is {Potential_path}")
+                return
+             
+        print(f"{message[1]}: not found")
+    else:
+        print_cmd_error(message[0])
+
+#shows current directory
+def handle_pwd(message):
+    message = message.split(maxsplit=1)
+    if len(message) > 1:
+        print_cmd_error(message[0])
+        return
+    elif message[0] == "pwd":
+        #used to check current directory
+        print(os.getcwd())  
+        return
+    else:
+        print_cmd_error(message[0])
+
+#handles cd commands for absoute, relative and HOME
+def handle_cd(message):
+    message = message.split(maxsplit=1)
+    if (len(message) < 2):
+        print_cmd_error(message[0])
+        return
+    if(len(message) == 2) and (message[1]=="~"):
+        os.chdir(os.path.expanduser("~"))
+        return
+
+    if ((len(message) >= 2) and (os.path.isdir(message[1]) == True)):
+        os.chdir(message[1])
+        return
+    else:
+        print(f"cd: {message[1]}: No such file or directory")
+        return
+
+if __name__ == "__main__":
+    main()
+432