readme

Name - Vedant Gaurang Shah
Roll No. - 200101115:

Program written in C language
meant to be compiled like gcc 200101115_Assign02.c
and excecuted by ./a.out

OVERVIEW
--------
when executed the shell starts with a "welcome to my mini shell" 
on the next line user name and then the present working directory is printed, waiting for input from the user
like 
user: /home/user/Desktop $> 

Assumptions :
The User must enter all words with space apart.
e.g. sentenv TERM = vt100
also in redirection, appending and piping...
 >, <  , >> & | should be space separated from the rest text.
 e.g. echo hello world > output

 (
     NOTE : echo hello world >output is not valid command
            cat input |grep hello is also not valid command
 )


COMMANDS IMPLEMENTED :

Internal Commands 
-----------------

history:
outputs all the history of commands written before          // history file is temporarily created in the same folder as the ./a.out folder and this folder is visible when 'ls' command is run. the history file gets removed once the program gets exited

exit:
exits from the mini shell and removes the history file created before

pwd:
when command is only 'pwd' then the present working directorys path is printed

cd:
when commanded as "cd Directory1" , it changes the directory to Directory1
only "cd" brings to home directory
"cd .." brings back two parent directory 

ls:
only "ls" prints lists all files and directory in  the current directory.
extra feature supported for ls:
ls -l : prints the files & directories all in new line
ls -a : prints the hidden files as well

help:
this prints this same README file for help for the valid commands and the syntax used



External Commands
-----------------

all external commands are available 
many are coded by myself like :
date
touch
clear (or cls)
cat
rm
dir
rmdir
mv

and the rest external commands are covered by exec command:
like:
shutdown
which
chsh
wheris
apropos
more
less
script
find
chmod



ENVIRONMENT VARIABLES
---------------------

printenv TYPE
this command prints ( or gets) the environment variable TYPE.this command is alias to getenv so  getenv command is not explicitly implemented

setenv TERM = vt100
this sets a new TERM as environment variable and assings it value vt100. when prompted with printenv TERM, it outputs vt100
space between each word is mandatory. ALSO THE EQUAL TO SIGN (=) should be space separated, or else this wont work.
For saftey purpose the setenv doesnt overwrite any pre=existing env var.

unsetenv TERM
this will remove the set environment variable name TERM.(if it exists)


REDIRECTION AND PIPING
---------------------

using < redirects the input to the next file pointed after '<'
using >> appends the ouput to the next file pointed after '>>'
using > redirects the output to the next file pointed after '>'

e.g.
./a.out < input > output
[NOTE the SPACE is REQUIRED]
similarly
./a.out < input >> output
this will append to output file

pipe ( | )
this command also requires space between | .
assumption only 1 pipe is handled, multiple pipes cannot be handled ( as told by prof via mail )
this pipes the output of commands on left of pipe and inputs it as input of right of pipe commands.
e.g.
cat input | grep hello
cat input | wc
cat input | head -5
cat input | tail -4
[NOTE THE SPACE RQUIRED]