Introduction

This is a Linux shell implemented in C.

Running the Shell

1. Clone the repository using the following command: git clone https://github.com/siddharth-mavani/Linux-C-Shell.git
2. cd into the directory containing all the source files
3. run the command make
4. run ./a.out

Functionality

1. ls

   • This commands Lists all the files and directories.
   • Using it with flags gives additional information such as hidden files, last edit date etc.
   • Flags implemented are -l and -a
   • General Usage: ls [flags] [Directory[/File_name]]
   • Usage Examples:

       $ ls
       $ ls -a
       $ ls -l
       $ ls -a -l
       $ ls -al / ls -la
       $ ls .
       $ ls ..
       $ ls <dir>
       $ ls [-flags] <dir_1/dir_2>

2. echo

   • Prints the string specified after removing extra spaces and tabs
   • General Usage; echo <string>
   • Usage Exampls:

       $ echo "hey"
       $ echo "hey 'my 'name "is bond,    James       Bondd!

3. pwd

   • Gives the full path of the present working directory
   • Usage: pwd

4. history

   • Gives a list of the latest commands entered in the shell.
   • User can specify a number upto 20.
   • If no number is specified, last 10 commands are printed.
   • General Usage: history [Number]
   • Usage Examples:

       $ history
       $ history 5
       $ history 10
       $ history 20

5. cd

   • Current working directory changes to the input directory.
   • General Usage: cd [Directory]
   • Usage Examples:

       $ cd
       $ cd .
       $ cd ..
       $ cd ~
       $ cd -
       $ cd temp
       $ cd temp/temp1

6. Foreground Process

   • Runs the command inputted
   • General Usage: <command> [flags]
   • Usage Examples:

       $ gedit
       $ firefox
       $ clear
       $ clear -X

7. Foreground Process

   • Runs the inputted command in the background
   • General Usage: <command> [flags] &
   • Usage Examples:

       $ gedit &
       $ firefox &
       $ sleep 10 &

8. Multiple Commands

   • User can run multiple commands in a single input.
   • Each command should be seperated by a semi-colon.
   • General Usage: <command_1> ; <command_2> [; [command_n]]
   • Usage Examples:

       $ ls; sleep 5; firefox &

9. Process Information

   • Gives information about the process specified by pid
   • If no pid is given, then information about currently running process is given.
   • General usage: pinfo [pid]
   • Usage Examples:

       $ pinfo
       $ pinfo 6921

10. Repeat

    • Repeats the inputted command specified number of times
    • General Usage: repeat <Num_Repeat> <command>
    • Usage Examples:

        $ repeat 2 echo hello
        $ repeat 3 sleep 5

11. Input/Output Redirection

    • User can use contents of a file as input.
    • User can redirect output of a command into a file.
    • < is used to specidy input file
    • > is used to specify output file
    • >> is used to specify to concatenate to output file.
    • General Usage: <command> < <input_file> > <output_file>
    • Usage Examples:

        $ echo Hello > 1.txt
        $ cat < 1.txt
        $ sort < test.txt >> sorted.txt

12. Pipelining

    • Ouput of one command can be provided as input of other command
    • General Usage: <command_1> | <command_2>
    • Usage Examples:

        $ cat 1.txt | wc
        $ cat 2.txt | head -7 | tail -5
        $ cat < 3.txt | wc -l | lines.txt

13. jobs

    • This command gives basic information about all background jobs
    • Has 2 flags: -r and -l
    • -r gives information about running background jobs
    • -s gives information about sleeping background jobs
    • General Usage: jobs [-rs]
    • Usage Examples:

        $ jobs
        $ jobs -r
        $ jobs -s

14. sig

    • This command sends signal to a background job specified by job number
    • General Usage: sig <Job_Number> <Signal_Number>
    • Usage Examples:

        $ sig 2 9
        $ sig 1 12

15. fg

    • fg brings the running or stopped background job corresponding to ​j​ob number​​ to the foreground, and changes its state to ​r​running.​
    • The shell throws an error if no job with the given job number exists.
    • General Usage: fg <Job_Number>
    • Usage Example:

        $ fg 1

16. bg

    • bg changes the state of a stopped background job to running (in the background).
    • The shell throws an error if no background job corresponding to the given job number exists
    • The shell does nothing if the job is already running in the background.
    • General Usage: bg <Job_Number>
    • Usage Example:

        $ bg 1

17. Signal Handling

    • CTRL-Z
      • Pushes any currently running foreground job into the background, and changes its state from running to stopped.
      • This havs no effect on the shell if there is no foreground process running.
    • CTRL-C
      • This interrupts any currently running foreground job by sending it the ​S​SIGINT​​ signal.
      • This has no effect on the shell if there is no foreground process running.
    • CTRL-D
      • Logs the user out of the shell.
      • Has no effect on the actual shell.

18. Replay

    • command executes a particular command in fixed time interval for a certain period.
    • General Usage: replay -command <command> -interval <Interval_Number> -period <Period_Number>
    • Usage Examples:

        $ replay -command echo "hi" -interval 3 -period 6
        $ replay -command sleep 2 -interval 2 -period 11

19. exit

    • This command exits the shell.

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File Structure

• main.c contains code to initiate the shell and calls functions to set it up.
• utils.c contains inplementation of the driver functions that help initiate and run the shell
• headers.h contains all the headers required by the shell.
• Each function has a file corrsponding to it.
• <command>.c contains code to implement <command>
• For example:
  • ls.c contains code to implement ls