https://github.com/kalpishs/Unix-Shell-Implementation-in-C

Simulate the Working of Command Line Interface in Unix-like Environment. Implemented Piping, redirection, history, environment variables,external-internal commands etc using family of system calls.
https://github.com/kalpishs/Unix-Shell-Implementation-in-C

Last synced: 3 months ago
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Simulate the Working of Command Line Interface in Unix-like Environment. Implemented Piping, redirection, history, environment variables,external-internal commands etc using family of system calls.

• Host: GitHub
• URL: https://github.com/kalpishs/Unix-Shell-Implementation-in-C
• Owner: kalpishs
• Created: 2016-05-07T13:26:00.000Z (over 8 years ago)
• Default Branch: master
• Last Pushed: 2016-06-17T18:28:14.000Z (over 8 years ago)
• Last Synced: 2024-02-17T06:36:12.470Z (9 months ago)
• Language: C
• Homepage:
• Size: 122 KB
• Stars: 25
• Watchers: 2
• Forks: 20
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
===========================================================================================================================

                     UNIX SHELL IMPLEMENTATION IN C

=========================================================================================================================== 

This program simulates the working of command line interface in Unix-like environment. Implemented Functionalities are as under:

1. Execute all the External commands (ls, clear, vi etc.)

2. Implement Internal commands: cd, pwd

3. Initialize and use environment variables

4. Print environment variables using echo command

5. Redirection operators: STDIN, STDOUT, STDERR (>>,>,<<,<,2>) 

6. Support for history command and '!' operator (history, !!, !-1, !10,!-10 etc)

7. Pipes “|” (multiple) (Ex: ls | grep 'a' | wc)

===========================================================================================================================

                          Input/Output Format

===========================================================================================================================

Input from the 'stdin' in an infinite loop till an “exit” is entered.

The corresponding output should be printed to 'stdout'.

Ex:

assume that PWD==home/user

Shell name: My_Shell

bash prompt:~$ ./a.out

My_Shell:/home/user$ ls

shell.c history.txt a.out

My_Shell:/home/user$ gfhj

gfhj: command not found

My_Shell:/home/user$ exit

Bye...

bash prompt:~$

===========================================================================================================================

                         Implementation Details

=========================================================================================================================== 

The shell.c contains the main function which takes the input from user and checks it for pipeline. If pipeline exist it processes the data separately else it passes the data to the functions. 

int with_pipe_execute():

This function is the initial function which is called for checking the all the command after initial preprocessing . It passes the processed output to function split

int split(char *cmd_exec, int input, int first, int last):

This function is responsible for splitting of command and passing it to command function

static int command(int input, int first, int last, char *cmd_exec):

this does the major part of the program. It  checks for various possibilities of commands. The types of commands that are checked are as under:

1) Internal commands: pwd and cd

2) echo commands, setting and getting environment variables

3) redirection handler 

4) PIPE

5) External commands

it make use of various funtions like tokenise_redirect_input_output,tokenise_redirect_input,tokenise_redirect_output which internally calls tokenise_commands() for tokenization

Helper functions:

getcwd():

gets the current woring Directory

signal():

Handle Interrupt Signal

void prompt():

initiates new Promt