Description.txt

SYSTEM DESCRIPTION
Implemented a Linux Based Shell using Linux System Calls and Inbuilt Libraries of C- 5 internal & external commands. 

Internal Commands
1. exit-  This command calls the system call exit(0). The shell will continue to run unless we call this command. 
2. history-  This command stores the history of the shell uptil now. Basically, we write every command written onto the shell to a file named writehistory.txt. History command prints this file onto the text.
Options handled-
* --help flag - used to display the information about the command by writing from a text file onto the shell, done using I/O in C
* -c flag- used to clear the history- erase the contents of writehistory.txt
       
3. Pwd- This prints the current directory using getcwd() command.
Options handled-
* --help flag - used to display the information about the command by writing from a text file onto the shell
* -L flag- it is a default flag, a softlink for the pwd command.
    
4. echo- this is used to print any string onto the shell, done using write calls in I/O in C
Options handled-
* -e flag - this flag interprets \n as a new line character and prints everything after \n in a new line, doesn’t take inverted commas into account.
* -E flag- this flag, similarly to echo prints everything and doesn’t take inverted commas into account.
     
5. cd - this is used to change the current directory to the string value provided using chdir()
Options handled-
* --help flag - used to display the information about the command by writing from a text file onto the shell
* -L flag- it is a default flag, a softlink for the cd command as well.


External Commands
1. date- used to print date, time values in the local time zone, done using time functions.
Options handled-
* --help flag - used to display the information about the command by writing from a text file onto the shell
* -u flag- used to display date, time in UTC.

2. cat- used to read files, done using read, I/O in C 
Options handled-
* --help flag - used to display the information about the command by writing from a text file onto the shell.
* -n flag- used to append a serial number in front of each line that is being written to the shell using cat command, done using I/O in C.
    
3. mkdir- we make directories using mkdir function  in C
Options handled-
* --help flag - used to display the information about the command by writing from a text file onto the shell.
* -v flag- tells the status of every directory- if it’s creation was successful or not
   
4. ls- we list the directories using readdir and opendir functions in C
Options handled-
* --help flag - used to display the information about the command by writing from a text file onto the shell.
* -1 flag- used to list each directory in a new line.

5. rm- used to delete files using remove(file) in C
Options handled-
* --help flag - used to display the information about the command by writing from a text file onto the shell.
* -i flag- prompts the user before every removal. If a character other than y is inputted, the file/folder is not deleted.
  
NOTE
* After writing the command, give a space and then enter for proper execution.
* We cannot exit the shell unless we type in “exit \n”


Sample Test Case
echo hello world 
ls -1 
date -u
mkdir five six seven
pwd --help 
cat -n date.txt 
date 
history
cd five
pwd
rm five
exit