hassankyanzi / simple_shell

Simple Shell

Table of Contents

• Project Description
• Requirements
• Authorized functions and system calls
• Compilation
• Tasks
• Authors

Project Description

Simple shell is a group project at ALX SE aimed to write a simple and customized UNIX command interpreter. It is designed to mimic sh and provides an interface between the user and the kernel by executing commands.

Requirements

• Allowed editors: vi, vim, emacs.
• All your files will be compiled on Ubuntu 20.04 LTS using gcc, using the options -Wall -Werror -Wextra -pedantic -std=gnu89.
• Your code should use the Betty style. It will be checked using betty-style.pl and betty-doc.pl.
• All your files should end with a new line.
• You are not allowed to use global variables.
• No more than 5 functions per file.
• All your header files should be include guarded.
• You should have an AUTHORS file at the root of your repository, listing all individuals having contributed content to the repository. Format, see Docker.

Authorized functions and system calls

• access (man 2 access)
• chdir (man 2 chdir)
• close (man 2 close)
• closedir (man 3 closedir)
• execve (man 2 execve)
• exit (man 3 exit)
• _exit (man 2 _exit)
• fflush (man 3 fflush)
• fork (man 2 fork)
• free (man 3 free)
• getcwd (man 3 getcwd)
• getline (man 3 getline)
• getpid (man 2 getpid)
• isatty (man 3 isatty)
• kill (man 2 kill)
• malloc (man 3 malloc)
• open (man 2 open)
• opendir (man 3 opendir)
• perror (man 3 perror)
• read (man 2 read)
• readdir (man 3 readdir)
• signal (man 2 signal)
• stat (__xstat) (man 2 stat)
• lstat (__lxstat) (man 2 lstat)
• fstat (__fxstat) (man 2 fstat)
• strtok (man 3 strtok)
• wait (man 2 wait)
• waitpid (man 2 waitpid)
• wait3 (man 2 wait3)
• wait4 (man 2 wait4)
• write (man 2 write)

Compilation

Your code will be compiled this way:

$ gcc -Wall -Werror -Wextra -pedantic -std=gnu89 *.c -o hsh

Tasks

0. Betty would be proud

Write a beautiful code that passes the Betty checks.

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1. Simple shell 0.1

Write a UNIX command line interpreter.

• Usage: simple_shell

Your Shell should:

• 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.
• The command lines are simple, no semicolons, no pipes, no redirections or any other advanced features.
• The command lines are made only of one word. No arguments will be passed to programs.
• 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)

You don’t have to:

• Use the PATH.
• Implement built-ins.
• Handle special characters : ", ', `, \, *, &, #.
• Be able to move the cursor
• Handle commands with arguments

2. Simple shell 0.2

Simple shell 0.1 +

• Handle command lines with arguments.

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3. Simple shell 0.3

Simple shell 0.2 +

• Handle the PATH.
• fork must not be called if the command doesn’t exist.

4. Simple shell 0.4

Simple shell 0.3 +

• Implement the exit built-in, that exits the shell.
• Usage: exit.
• You don’t have to handle any argument to the built-in exit.

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5. Simple shell 1.0

Simple shell 0.4 +

• Implement the env built-in, that prints the current environment.

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6. Simple shell 0.1.1

Simple shell 0.1 +

• Write your own getline function.
• Use a buffer to read many chars at once and call the least possible the read system call.
• You will need to use static variables.
• You are not allowed to use getline. You don’t have to:
• Be able to move the cursor.

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7. Simple shell 0.2.1

Simple shell 0.2 +

• Write your own strtok function.
• You are not allowed to use strtok.

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8. Simple shell 0.4.1

Simple shell 0.4 +

• handle arguments for the built-in exit.
• Usage: exit status, where status is an integer used to exit the shell.

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9. setenv, unsetenv

Simple shell 1.0 +

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 an environment variable.
  • Command syntax: unsetenv VARIABLE.
  • Should print something on stderr on failure.

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10. cd

Simple shell 1.0 +

Implement the builtin command cd:

• Changes the current directory of the process.
• Command syntax: cd [DIRECTORY].
• 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. man chdir, man getcwd

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11. ;

Simple shell 1.0 +

• Handle the commands separator ;.

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12. && and ||

Simple shell 1.0 +

• Handle the && and || shell logical operators.

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13. alias

Simple shell 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.

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14. Variables

Simple shell 1.0 +

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

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15. Comments

Simple shell 1.0 +

• Handle comments (#)

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16. File as input

Simple shell 1.0 +

• Usage: simple_shell [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.

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Authors:

• Kyanzi Hassan Musisi