Simple Linux Shell

Hey! Here's a Command Line Interface application I've written in C language that works like a Linux shell

Preview

Here are some important Linux commands that I've tested on my Linux shell application

Code Explanation

• The main( ) function executes a while loop We need this loop to run the shell input command infinitely after execution of each command
• The shell function does the following job :
  • It stores the user input in the character array cmd[100] (string)
  • length of this string cmd is stored in l
• We pass this string cmd and its length l to a token function tok(cmd,l)
• The tok(cmd, l) function's return type is a 2D array (an array of strings)
  • This function takes the cmd string and tokenizes it into a group of strings
  • A global variable g is used to store the number of tokens obtained
• The array of strings returned by token function is stored in a
• Now, we compare the first token a[0] given by the user with cd, echo, pwd, If the token matches with any one of them, its respective function is called :
  • Cd(a) function uses chdir(a[1]), an in-built function to change the directory
  • Echo(a) function concats all the tokens from a[1] to a[g-1] and stores in a string b
  • A for loop is used to remove " character
  • Pwd( ) function uses getcwd( ), an in-built function to get the current working directory
  • Cmd(a) function is used to access commands like mkdir, ls, cat, rm, date executables in the bin folder using execvp( )
    • In this Cmd(a) function, fork( ) function is used to initialize a child process
    • In the child process execvp is used. Its return value is stored in a variable z
    • If z != 0, It displays an error
    • execvp takes the input command and the array of strings as arguments
    • execvp function calls the file from bin folder according to the user input
    • Meanwhile, the parent process waits for the child process to exit
• After leaving the if-else loop and executing one of the Cd( ), Pwd( ), Echo( ), Cmd( ) functions, the array a memory is freed
• Because we have a while loop in our Main function and it breaks only when character ch != '\n'
• At each step, it calls the shell function again