C Shell

Note: This shell code has been written to be run on a computer with the Microsoft Windows Operating System. Commands are likely to not run on other operating systems.

Table of contents

• C Shell
  • Table of contents
  • Compilation instructions
  • List of commands
    • echo command
      • Usage of echo
      • Available features in echo
      • Unavailable features in echo
      • Examples for echo
    • pwd command
      • Usage of pwd
      • Example for pwd
    • cd command
      • Usage of cd
      • Available features in cd
      • Unavailable features in cd
      • Examples for cd
    • history command
      • Usage of history
      • Example for history
    • exit command
      • Usage of exit
  • Directory structure

Compilation instructions

1. Open your preferred terminal which can detect the gcc command.
2. Navigate to the current c-shell folder.
3. Run the make all command.
4. Open the shell using ./shell.exe.
   • Alternatively, you can also double click and run the executable file.
5. To clear the files, run make clear.
   • Note: A helper file named cmd_hist.txt is created in the user's Documents folder on the first run of the shell, which does not get automatically deleted when the make clear command is run.

List of commands

1. echo
2. pwd
3. cd
4. history
5. exit

echo command

Prints back the user input with formatting if necessary.

Note: Even though the shell is configured to run in Windows OS, the echo command is designed to simulate the functioning of echo in a Linux environment.

Usage of echo

echo <prompt>

echo "<prompt_line_1>
> <prompt_line_2>
> ..."

Available features in echo

• Truncates extra white spaces.
• Handling of quotes, i.e. when a double quote is started, characters are read as is without any truncation/modification until double quotes are closed.

Unavailable features in echo

• If a user starts a double quote and enters a new line, then they cannot cancel the new line.
• Cannot parse escape sharacters such as \b, \t, \r, etc. if entered manually as text in the prompt.

Examples for echo

<USERNAME@WINDOWS:~> echo Hi!
Hi!
<USERNAME@WINDOWS:~> 

<USERNAME@WINDOWS:~> echo Hi! "My name is:
> FirstName   LastName."    Nice to meet you!
Hi! My name is:
FirstName   LastName. Nice to meet you!
<USERNAME@WINDOWS:~> 

pwd command

Prints the current working directory of the shell.

Usage of pwd

pwd

Example for pwd

<USERNAME@WINDOWS:~> pwd
C:\Users\USERNAME
<USERNAME@WINDOWS:~> 

cd command

Navigates to the specified directory.

Usage of cd

cd <prompt>

Available features in cd

• Parses special inputs such as ., .., -, ~ and empty input.
• Remembers the entire history of changes in directory in a shell session.
• Can handle nested directories.

Unavailable features in cd

• Cannot navigate to directories which have spaces in their name, regardless of the presence of double quotes.
• Cannot navigate above the home directory.
• If an error occurs in the middle of executing a nested file path, then the shell's working directory is set to the sub-path till which execution was successful.

Examples for cd

<USERNAME@WINDOWS:~> cd .
<USERNAME@WINDOWS:~> cd folder
<USERNAME@WINDOWS:~\folder> cd
<USERNAME@WINDOWS:~> cd -
<USERNAME@WINDOWS:~\folder> cd ~
<USERNAME@WINDOWS:~> cd folder/nested_folder_1/
<USERNAME@WINDOWS:~\folder\nested_folder_1> cd ../nested_folder_2
<USERNAME@WINDOWS:~\folder\nested_folder_2>

<USERNAME@WINDOWS:~> cd folder
<USERNAME@WINDOWS:~\folder> cd nested_folder_1
<USERNAME@WINDOWS:~\folder\nested_folder_1> cd ../nested_folder_2
<USERNAME@WINDOWS:~\folder\nested_folder_2> cd -
<USERNAME@WINDOWS:~\folder\nested_folder_1> cd -
<USERNAME@WINDOWS:~\folder> cd -
<USERNAME@WINDOWS:~>

history command

Lists the history of commands previously run on the shell across sessions.

Usage of history

history

Example for history

<USERNAME@WINDOWS:~> echo Hi!
Hi!
<USERNAME@WINDOWS:~> pwd       
C:\Users\USERNAME
<USERNAME@WINDOWS:~> echo Greetings.
Greetings.
<USERNAME@WINDOWS:~> echo Hello! 
Hello!
<USERNAME@WINDOWS:~> history
echo
pwd
echo
history
<USERNAME@WINDOWS:~> exit

Upon running the shell again,

<USERNAME@WINDOWS:~> history
echo
pwd
echo
history
exit
history
<USERNAME@WINDOWS:~>

exit command

Exits the shell.

Usage of exit

exit

Directory structure

c-shell
|_cd_code
  |_cd.c
  |_cd.h
|_echo_code
  |_echo.c
  _|echo.h
|_pwd_code
  |_pwd.c
  |_pwd.h
|_shell_code
  |_shell.c
.gitignore
makefile
README.md

The *_code folders, where * is a placeholder for the command name, contain the files specifying the declarations and definitions of the functions of the respective commands.

The .gitignore file is for specifying the files to ignore if a git repository is initialised in the folder.

The makefile file contains the commands for compilation and deletion of the shell.

The README.md file contains the compilation instructions, description of the commands and the file structure.