/SHELL

Primary LanguageC

Shell

This is a Shell developed entirely in C. The shell emulates the normal bash in linux systems. It is able to handle bakground processes, foreground processes, input-output redirection, command redirection etc.

Features

##Display

  • The format is <username@system_name:curr_dir>
  • ~ signifies the address of Home Directory.

Commands

pwd

  • Prints the path present working directory.

cd

  • cd changes the pwd to the specified directory path.

ls [al]

  • lists all the file in the pwd.

pinfo

  • Prints the process related info of Shell program.

pinfo

  • prints the process info about given pid.

history

  • Tells the last 10 commands executed on shell.

history

  • Prints the last 'n' commands.
  • 'n' is specified by user.

All Other General shell commands.

  • All other commands like cat, grep, etc. can be executed through the shell.
  • The difference is that they are builtin and ls, pwd, cd were built by me.

setenv var [value] :

  • If the enviroment variable does not exist, then creates it.
  • Modifies the existing value if the environment variable already exists.

unsetenv var

  • Destroys the evironment variable if exists.

jobs

  • prints all the currently running jobs along with their pids.

kjob

  • Takes the job number of the process and sends the signal specified by signalNumber to it.

fg

  • Brings the job running in background to the foreground.

bg

  • Changes a stopped background job to a running background job.

overkill

  • Kills all background process at once.

quit

  • Exits the shell.

CTRL-Z

  • Changes teh currently running job to stop, and pushes it to background process.

CTRL-C

  • Sends a SIGINT signal to the current forground job of this shell.
  • If there is no foreground process currently this should have no effect.

Foreground Processes

  • Just type the command's name you want to run.
  • These processes have the access of input and output on the terminal window.
  • Example
vim bello;ls;

Background Processes

  • Type the command's name you want to execute. End it with a &.
  • These processes run in the background meaning they do not have input and output accesses from the terminal window.
  • Example
vim bello &

Input/Output Redirection.

  • Input Redirection
sort < lines.txt
  • Output Redirection
cat bello.txt > hello.txt  //Overwriting hello.txt
cat bello.txt >> hello.txt  //Appending to hello.txt
  • Input-Output Redirection
sort < lines.txt > output.txt

Command Redirection Using Pipes

  • A pipe is a basically a channel of communication between two processes.
  • Identified by '|'
  • Example
cat bello.txt | grep hello
ls | grep *.txt > out.txt

SHELL