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Tutorial2

This tutorial introduces "the shell," a powerful command-line interface for Linux and Unix systems. The shell allows users to interact with the operating system by entering commands that the shell interprets and executes. Unlike graphical user interfaces (GUIs), the shell operates in a text-based environment, making it essential for performing tasks efficiently. The tutorial provides examples, including the implementation of a basic shell in Python, demonstrating how to break down user input into commands and execute them. Resources for further learning are also mentioned.

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Tutorial2

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Presentation Transcript

  1. Tutorial2 Discussing Assignment 1

  2. What is "the shell"? • The Linux/Unix shell refers to a special program that allows you to interact with it by entering certain commands from the keyboard; the shell will execute the commands and display its output on the monitor. The environment of interaction is text-based unlike the GUI • Retrieved from: http://linux.about.com/od/linux101/a/desktop11.htm

  3. Where can I learn about the shell? • Linux Man Pages • Official Ubuntu Documentation • Using The Terminal

  4. # The start of the shell while True: line = input('psh> ') print(line) python3 tut2_1.py

  5. # Non class version: Break the line into shell words. import shlex defword_list(line): lexer= shlex.shlex(line, posix=True) lexer.whitespace_split = False lexer.wordchars += '#$+-,./?@^=' args = list(lexer) return args while True: line = input('psh> ') print(word_list(line)) python3 tut2_2.py

  6. # Class version: Break the line into shell words. import shlex class PShell(): defread_loop(self): while True: line = input('psh> ') print(self.word_list(line)) defword_list(self, line): lexer= shlex.shlex(line, posix=True) lexer.whitespace_split = False lexer.wordchars += '#$+-,./?@^=' args = list(lexer) return args my_shell = PShell() my_shell.read_loop() python3 tut2_3.py

  7. # Executing only the first command on the line import shlex import os class PShell(): defread_loop(self): while True: line = input('psh> ') words = self.word_list(line) print(words) command = words[0] child = os.fork() if child == 0: # we are in the child os.execvp(command, words) else: os.waitpid(child, 0) defword_list(self, line): lexer = shlex.shlex(line, posix=True) lexer.whitespace_split = False lexer.wordchars += '#$+-,./?@^=' args = list(lexer) return args my_shell = PShell() my_shell.read_loop() python3 tut2_4.py

  8. Python exception handling # Class version # executing only the first command on the line import shlex import os class PShell(): defread_loop(self): while True: line = input('psh> ') words = self.word_list(line) print(words) command = words[0] try: child = os.fork() if child == 0: # we are in the child os.execvp(command, words) else: os.waitpid(child, 0) except OSError: print('Caught an OSError.') defword_list(self, line): """Break the line into shell words. """ lexer = shlex.shlex(line, posix=True) lexer.whitespace_split = False lexer.wordchars += '#$+-,./?@^=' args = list(lexer) return args my_shell = PShell() my_shell.read_loop() python3 tut2_5.py

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