0x02-shell_v2

(327) 0x02. C - Shell v2

Specializations > System programming & Algorithm > Linux Programming

Project author

Alexandre Gautier

Assignment dates

12-15-2020 to 01-12-2021

Description

Revisiting (235) 0x16. C - Simple Shell to build a second clone of dash/Ubuntu sh, now with logical operators, piping, and input/output redirections.

Requirements

• Allowed Functions and System Calls:

access	chdir	close	execve	fork
stat	lstat	fstat	kill	open
read	signal	wait	waitpid	wait3
wait4	write	_exit	dup	dup2
pipe	unlink	time	gethostname	geteuid
sigaction	sigemptyset	select	getpid	__errno_location (errno macros)
closedir	exit	free	getcwd	getline
malloc	opendir	perror	readdir	strtok
localtime	getpwuid	isatty	printf	fflush
fprintf	vfprintf	sprintf

• Error printing should mimic sh:

$ echo "qwerty" | /bin/sh
/bin/sh: 1: qwerty: not found
$ echo "qwerty" | /bin/../bin/sh
/bin/../bin/sh: 1: qwerty: not found
$

Note

This project can be found in a separate repository: shell_v2. This README is to provide the project profile separate from the README originally included with the project itself.

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Mandatory Tasks

✅ 0. README, man, AUTHORS

• Write a README
• Write a man for your shell.
• You should have an AUTHORS.md file at the root of your repository, listing all individuals having contributed content to the repository. Format, see Docker

File(s): README.md man_1_hsh AUTHORS.md

✅ 1. Betty would be proud

Write a beautiful code that passes the betty linter checks

Be aware that every single C source file (*.c and *.h) inside your repository will be checked

Compiled: make all

⬜ 2. hsh 1.0

Write a UNIX command line interpreter.

• Usage: hsh

Your shell must:

• Display a prompt and wait for the user to type a command. A command line always ends with a new line.
• The prompt is displayed again each time a command has been executed.
• If an executable cannot be found, print an error message and display the prompt again.
• Handle errors.
• You have to handle the “end of file” condition (Ctrl+D)
• Handle command lines with arguments
• Handle and parse the PATH environment variable

Builtins

• Implement the built-in command exit:

  • Your exit built-in must behave exactly like sh‘s
  • You have to handle arguments

• Implement the built-in command cd:

  • Changes the current directory of the process.
  • Command syntax: cd [path]
  • If no argument is given to cd the command must be interpreted like cd $HOME
  • You have to handle the command cd -
  • You have to update the environment variable PWD when you change directory

• Implement the built-in command env:

  • Prints the current environment

You don’t have to:

• handle special characters : ", ', \``, `, *, &, #
• be able to move the cursor
• handle pipes and redirections

Compiled: make all

✅ 3. hsh 1.1

hsh 1.0 +

• Handle the right stream redirection >
• Usage: command > output_file

Compiled: make all

✅ 5. hsh 1.2

hsh 1.1 +

• Handle the double right stream redirection >>
• Usage: command >> output_file
• You don’t have to handle the syntax: >> output_file command

Compiled: make all

✅ 6. hsh 1.3

hsh 1.2 +

• Handle the left stream redirection <
• Usage: command < input_file

Compiled: make all

✅ 7. hsh 1.4

hsh 1.3 +

• Handle the double left stream redirection << (also known as heredoc)
• Usage: command << delimiter

Compiled: make all

✅ 8. hsh 1.5

hsh 1.4 +

• Handle the pipe stream redirection |
• Usage: command1 | command2

Compiled: make all

✅ 9. hsh 1.6

hsh 1.5 +

• Handle the commands separator ;

Compiled: make all

✅ 10. hsh 1.7

hsh 1.6 +

• Handle the && logical operator

Compiled: make all

✅ 11. hsh 1.8

hsh 1.7 +

• Handle the || logical operator

Compiled: make all

✅ 12. hsh 2.0

hsh 1.8 +

Implement the setenv and unsetenv builtin commands

• setenv
  • Initialize a new environment variable, or modify an existing one
  • Command syntax: setenv VARIABLE VALUE
  • Should print something on stderr on failure
• unsetenv
  • Remove a environment variable
  • Command syntax: unsetenv VARIABLE
  • Should print something on stderr on failure

Compiled: make all

Advanced Tasks

⬜ 4. hsh 1.1.1

hsh 1.1 +

• Handle the right stream redirection >
• Usage: command n> output_file
  • Where n is the file descriptor of the file to redirect the output from
  • n is a number between 0 and 9

Compiled: make all

⬜ 13. Ctrl + C

hsh 1.0 +

• Handle Ctrl+C: your shell should not quit when the user inputs ^C
• Hint: man 2 signal

Compiled: make all

⬜ 14. Aliases

hsh 1.0 +

• Implement the alias builtin command
• Usage: alias [name[='value'] ...]
  • alias: Prints a list of all aliases, one per line, in the form name='value'
  • alias name [name2 ...]: Prints the aliases name, name2, etc 1 per line, in the form name='value'
  • alias name='value' [...]: Defines an alias for each name whose value is given. If name is already an alias, replaces its value with value

Compiled: make all

⬜ 15. $VARIABLES

hsh 1.0 +

• Handle variables replacement
• Handle the $? variable
• Handle the $$ variable

Compiled: make all

✅ 16. #Comments

hsh 1.0 +

• Handle comments (#)

Compiled: make all

✅ 17. Help !

hsh 1.0 +

• Implement the help builtin command
• Usage: help [BUILTIN]

Compiled: make all

⬜ 18. Move on

hsh 1.0 +

• Implement the history builtin command, without any argument
• The history builtin displays the history list, one command by line, preceded with line numbers (starting at 0)
• On exit, write the entire history, without line numbers, to a file named .hsh_history in the directory $HOME
• When the shell starts, read the file .hsh_history in the directory $HOME if it exists, and set the first line number of the current session to the total number of lines in the file modulo 4096

Compiled: make all

✅ 19. Try to run this!

hsh 1.0 +

• Usage: hsh [filename]
• Your shell can take a file as a command line argument
• The file contains all the commands that your shell should run before exiting
• The file should contain one command per line
• In this mode, the shell should not print a prompt and should not read from stdin

Compiled: make all

⬜ 20. . .hshrc

hsh 1.0 +

• At startup, your shell must open the file .hshrc located in the $HOME directory, and execute it
• Since this task requires only hsh 1.0, there won’t be any advanced content in .hshrc file during the correction (no aliases, no redirections, …)

Compiled: make all

✅ 21. $PS1

hsh 1.0 +

• When executing interactively, your shell must displays the primary prompt PS1 when it is ready to read a command
• The PS1 variable can be customized by inserting a number of backslash-escaped special characters
• You must handle the following backslash-escaped characters:
  • \d: The date in “Weekday Month Date” format (e.g., “Tue Feb 05”, “Sat Jul 26”)
  • \H: The hostname
  • \s: The name of the shell
  • \u: The username of the current user
  • \w: The current working directory, with $HOME abbreviated with a tilde (~)

Compiled: make all

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Student

• Samuel Pomeroy - allelomorph