Operating System Shell Features

Questions and Answers

What must be unique within the shell or script?

The body of a function

The exit status of a command

The name of the routine (correct)

The commands in a function

What does the exit status of a function reflect?

The number of commands in the function

The exit status of the entire script

The status of the shell where the function is declared

The exit status of the last command executed in the function (correct)

Which of the following is an example of correct function syntax?

function myFunction; { echo 'Hello'; }

myFunction() { echo 'Hello';

myFunction() { echo 'Hello'; } (correct)

myFunction { echo 'Hello'; }

What is a common mistake when defining functions?

Failing to separate curly braces from the body by spaces Signup and view all the answers

What does the symbol $* represent in a function definition?

It includes command line switches entered after the command Signup and view all the answers

Match the following function syntax with their descriptions:

function FUNCTION { COMMANDS; } = Defines a shell function using the 'function' keyword FUNCTION () { COMMANDS; } = Defines a shell function using parentheses COMMANDS; = Represents the body of the function $u = Calls the function named 'u' Signup and view all the answers

Match the following components of function definitions with their purposes:

Curly braces = Contain the body of the function Exit status = Determined by the last command executed in the body $* = Represents all parameters passed to the function Semicolon or newline = Indicates the end of the function body Signup and view all the answers

Match the following common mistakes in function definitions with their corrections:

No space between braces and body = Add a space between curly braces and the body Missing semicolon or newline = Ensure the body ends with a semicolon or newline Using incorrect syntax = Use either 'function FUNCTION' or 'FUNCTION ()' Incorrect use of parameters = Correctly define parameters using $* Signup and view all the answers

Match the following function examples with their descriptions:

$u() { ls -l; } = Function 'u' executes 'ls -l' $u() { ls --l $*; } = Function 'u' executes 'ls --l' with parameters $u --a = Calls function 'u' with the '-a' switch vi.bash_profile = Opens the bash_profile file with vi editor Signup and view all the answers

Match the following terms related to shell function creation with their definitions:

Function name = Must be unique within the shell or script Body of the function = List of commands that execute when function is called Exit status = Result of the last command executed in the function Shell = Environment where the function is declared and executed Signup and view all the answers

Study Notes

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.