Open Source OS Lab 6: The Shell

The Shell

• Acts as an interface between the user and the kernel of the operating system.
• Prompts for input, processes commands, and executes actions before prompting again.

Shell Features

• Combining Commands: Use ; to execute multiple commands in a single line.
• Command Line Completion: Pressing Tab after typing an unambiguous prefix autocompletes the command.
• Command Line Edition: Navigate and edit commands using arrows and key combinations like Ctrl+A (to start) and Delete to erase characters.

Command History

• Stores previously executed commands for easy access using Up and Down arrow keys.
• Command history displays the list of past commands, each with an associated event number.
• Re-execute commands using !event_number or !! for the last command.

Running Commands in Background

• Add & at the end of a command to run it in the background without waiting for it to complete.

Command Substitution

• Use $(command) or backticks `command` to use output of one command as an argument in another.
• Example: ls -l $(locate manual.html) lists all manual.html files.

Using Pipes

• Use | to send the output of one command to another, allowing commands to be executed concurrently.
• Example: echo Happy Birthday! | rev reverses the string output.

Redirecting Input and Output

• Standard Output: Redirect using > to save output to a file; use >> to append.
• Standard Error: Redirect using 2> to capture error messages to a file.
• Example: cat nonexistent 2>errors saves error messages to the file named errors.

Adding Aliases

• Simplify complex commands by creating aliases with alias name='command'.
• Example: alias p='pwd; ls --CF' enables p to execute both commands in sequence.

Shell Functions

• Group commands for repetitive tasks, executed with a single name.
• Function syntax: function FUNCTION { COMMANDS; } or FUNCTION () { COMMANDS; }.
• Example: u() { ls -l; } allows you to use u as a shortcut for ls -l.

Common Shell Command Usage

• History: Use history to display commands; press Up/Down for navigation.
• Background Commands: Use & to run tasks simultaneously.
• Pipes: Create command chains for more efficient output handling.
• Input/Output Redirection: Efficiently manage where command outputs/errors are stored.
• Aliases and Functions: Streamline command use for efficiency and simplicity.

Explore the fundamentals of shell programs in this lab quiz. Test your knowledge on command features like combining commands, command line completion, and using pipes. Learn to manage command history, background processes, and input/output redirection effectively.