simple_shell

A simple UNIX command interpreter.

Description

This project was created as part of the third month curriculum at Holberton School, San Francisco. In short, we we're required to write a UNIX command interpreter. Our shell replicates (to a certain degree) the sh shell.

Due to it's simplicity, our custom-built shell has some of the functionalities of a normal shell, but not all of them. Down below we will describe each feature our shell contains.

Compilation

To create an executable, compile the C files like this:

gcc -Wall -Werror -Wextra -pedantic *.c -o hsh (or any other name you desire)

Or this way (without error checking):

gcc *.c -o hsh

Entering the Shell

Once compiled, use the executable file hsh to enter. Your output for the shell should look something like this:

$ ./hsh
($hell) 

If the prompt ($hell) shows up and not the normal $, you'll know that you are in our custom shell.

Example Usage

Exiting the Shell

To exit out of the shell, you can use either CTRL + D, or CTRL + Z or by typing in the built-in exit to the command line.

Do take note that the shell ignores the CTRL + C signal. When entered, the signal ^C will be printed without exiting. To exit, use one of the inputs explained above.

Files

The following table describes in short the contents of each file in this repository.

File Name	Description
builtin_f.c	Contains the commands exit, setenv and unsetenv, as well as other helpful functions.
builtin_f2.c	Contains the command cd builtin for change directory, as well as other helpful functions.
handle_path.c	Contains functions that handle the PATH environment variable.
help_main.c	Contains various helpful functions for the main.c file (main functionality of the program).
int_string.c	Contains itoa and atoi functions.
list_array.c	Contains functions to converts an array of strings into a linked list and vice versa.
list_f.c	Contains various linked lists functions.
list_f2.c	Contains more function for linked lists operations.
main.c	Entry point for the shell, and main loop for the program.
man_1_simple_shell	The man page for our simple shell. Type in man ./man_1_simple_shell to see the man page.
modify_env.c	Contains functions that are used for thr setenv and unsetenv built-in commands.
shell_head.h	Header file that contains all libraries, function prototypes, and structs definitions.
string_f.c	Contains custom built string functions- _strlen, _puts (personalized versions of built-in functions).
string_f2.c	Contains more custom built string functions.
string_split.c	Contains custom built strtok function - strtow.
var_replace.c	Handles variable replacements. Mainly, used for the echo $? command.

Output

Once compiling our program, you can see that our shell has the same output and same error messages as the normal shell would.

sh

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

• The error message is personalized to your exacutable filename, in this case hsh.

./hsh (our shell)

($hell) echo "qwerty" | ./hsh
./hsh: 1: qwerty: not found
($hell) echo "qwerty" | ./././hsh
./././hsh: 1: qwerty: not found
($hell)

Interactive vs Non-Interactive

Our shell works in two different modes, interactive and non-interactive.

Interactive Mode

The classic shell. Every time a command is entered, the prompt appears again and waits for the next user input:

$ ./hsh
($hell) /bin/ls
AUTHORS handle_path.c  int_string.c  main.c
($hell)
($hell) exit
$

Non-Interactive Mode

Piping a command into the executable file. Our shell executes the command, and exits the shell.

$ echo "/bin/ls" | ./hsh
AUTHORS handle_path.c  int_string.c  main.c
$
$ echo "pwd" | ./hsh
/vagrant/home/
$
$ echo "ls -a" | ./hsh
AUTHORS handle_path.c  int_string.c  main.c .git . ..
$

Built-in Commands

The shell includes the following built-in commands.

Each one of the custom built-in commands can be compared to the the normal sh shell output.

• exit

  • Usage - $ exit or $ exit [VALUE]
  • When entered correctly (valid exit value or nothing), the user exits the shell. The exit value will be the parameter passed, or the return value of the latest command if no value was passed.
  • You can see the exit value by entering echo $? after exiting the shell.

• env

  • Usage - $ env
  • When entered, all of the current environment variables and their values are displayed.

• setenv

  • Usage - $ setenv [VARIABLE] [VALUE]
  • When entered, either a new environment variable is created, or an existing one is modified.
  • If an error occurs (e.g. no parameters included), a message is displayed in the standard error output.

• unsetenv

  • Usage - $ unsetenv [VARIABLE]
  • When entered, an environment variable is removed.
  • If an error occurs (e.g. variable not found, no parameters included), a message is displayed in the standard error output.

• cd

  • Usage - $ cd [DIRECTORY]
  • When entered, the current working directory is changed.
  • cd -: changes the working directory to the previous one.
  • cd: if no argument is entered, the command is interpreted as cd $HOME
  • If an error occurs (e.g. directory is not valid), a message is displayed in the standard error output.

Variable Replacements

Our shell knows to replace variables with $.

• echo $PATH: the variable PATH gets replaced with its value.
• echo $$: the current process ID is displayed.
• echo $?: the return/exit value of the last command entered is displayed.

Authors

• Ethan Mayer - |
• Jun Zhu - VieetBubbles

License

This project is licensed under the MIT License - see the LICENSE file for details.