The csh command on Linux invokes the C Shell, a Unix shell created by Bill Joy in the late 1970s, characterized by its C-like syntax. It serves as both a command interpreter and a scripting language, offering features such as command history, job control, and aliasing. Unlike the more commonly used Bourne Again Shell (bash), csh is known for its syntax that resembles the C programming language, making it intuitive for those familiar with C. The C Shell supports interactive use and scripting with features like built-in arithmetic and advanced control structures, but it has been critiqued for its inconsistent syntax and limited scripting capabilities compared to other shells.

Features

  • Interactive Use: csh can be used interactively to execute commands typed by the user.
  • Scripting: You can write scripts (collections of commands) that csh will execute.
  • Command History: Allows users to recall, edit, and re-execute previous commands.
  • Job Control: Users can stop, resume, and background processes.
  • Alias Mechanism: Users can create aliases for commands or sets of commands.
  • C-like Syntax: The syntax for control structures (like loops and conditionals) resembles the C programming language.

To start the C shell, simply type csh in your terminal. Here’s an example of starting csh and executing a simple command:

$ csh

% echo "Hello, world!"

Hello, world!

% exit

$

In this example:

  • Typing csh starts the C shell.
  • The % prompt indicates you are now in the C shell.
  • The echo command prints “Hello, world!” to the screen.
  • Typing exit exits the C shell and returns to the original shell.

Overall, csh is a powerful shell that combines the features of both interactive command processing and script execution with a syntax familiar to those who know the C programming language.

Change Linux Shell using csh Command

The csh command can indeed be used to change the shell on a Linux system to the C shell. When you run the csh command in a terminal, a new shell session is started using the C shell. This contrasts other standard shells like bash (Bourne Again Shell) or zsh (Z Shell).

Here’s a more detailed explanation of how `csh` works as a command to change the shell:

Starting C Shell

When you type csh in your terminal, it starts a new shell session using the C shell. This can be useful if you prefer the syntax or features of the C shell over your current shell.

$ csh

%

In this example, the `%` prompt indicates that you are now in the C shell.

Exiting C Shell

To exit the C shell and return to your previous shell (e.g., bash), type exit or press Ctrl-D.

% exit

$

Changing Default Shell with csh

To permanently change your default login shell to csh, you can use the chsh (change shell) command. This command changes the shell specified in your user account settings.

 $ chsh -s /bin/csh

After running this command, you must log out and back in for the change to take effect. The path /bin/csh might vary depending on your system configuration, so you should verify the correct path to the C shell executable using:

which csh

Using a Different Shell Temporarily

If you want to temporarily use the C shell for a particular session, you can invoke csh and then exit when you’re done, as described above.

In summary, while csh can temporarily change the shell by starting a new C shell session, the csh command permanently changes your default login shell to the C shell.

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