C Shell

Installation:

To run the code, use the given makefile, which generates main as output file.

Files and their uses:

Headers

• headerlist.h contains all the system header files to be included
• listing.h is the header corresponding to listing.c
• printuser.h is the header corresponding to printuser.c
• tokenize.h is the header corresponding to tokenize.c

C files:

• listing.c contains the functions for ls incl its both flags
• printuser.c includes the functions for printing user and host along with current working dir.
• tokenize.c contains the functions for tokenizing a string by ';', ' ' or newline. It also includes a function to trim leading and trailing spaces.
• main.c is the main program

Basic Working

The Shell program runs on an infinite loop and takes input from stdin using getline(), which is further tokenized into semicolon-separated commands, which are run in order. Each command is tokenized separating the commands,flags(if any) and the arguments(if any). Switch-case is used in order to select from the executable commands like rm,mkdir etc and other self-defined commands pwd, ls, cd, echo, pinfo and history.

Assumptions :

• /proc filesystem is accessible as is to any standard linux user. - no of semicolon separated commands is maximum 50, with 2000 char as max length for each. - each command can have maximum value of x as 50, where argv[x]. - username, hostname and cwd are 1000 characters at max.

Other Functionalities added:

• input/output redirection
• piping
• User defined commands:
  • setenv
  • unsetenv
  • jobs
  • kjob
  • fg
  • bg
  • overkill
  • quit
• signal handling
  • ctrl+c
  • ctrl+d
  • ctrl+z