مهارات سطر الأوامر - الوحدة 05

Module 05: Command Line Skills

• This module covers the basics of the command line interface (CLI), including the shell, commands, variables, command types, quoting, and control statements.
• The Linux community promotes the CLI for its power, speed, and ability to accomplish tasks with single commands, especially for server environments that do not require graphical interfaces.
• The CLI provides precise control, speed, and easier automation through scripting. This makes Linux users highly productive almost instantly.

Command Line Interface

• The CLI is a powerful tool for interacting with a computer's operating system.
• It allows users to perform tasks via commands rather than a graphical user interface.
• The CLI is beneficial for tasks that require precise control or speed.

The Shell

• The shell is a command-line interpreter which converts commands typed by the user to actions performed by the operating system.
• It's a crucial part of the CLI.
• Linux allows many different shells, and the most common is the Bash shell. This shell has features such as command history, inline editing, scripting, aliases, and variables for storing information for the shell and the user itself, enabling many commands to be completed.

The Prompt

• The prompt displays information about the user and system.
• A typical structure includes username, system name(hostname), and current directory. The ~ symbol represents the user's home directory.

Commands

• A command is a software program that executes an action on the computer when run in the CLI
• To execute a command, type its name and press Enter.
• Some commands require additional input like options and arguments to work correctly.

Arguments

• Used to specify what the command should act upon.
• For example, if ls (list directory contents) is given a directory name as an argument, it lists that directory.
• Some commands may accept multiple arguments.

Options

• Options modify how commands behave.
• They often use single letters (e.g., -l for a long listing) or complete words (e.g., --help).
• Options can be used in conjunction with each other.

Commands Types

• Commands are categorized as internal (built-in) or external (stored elsewhere).
• Using the type command, you can find out a command's type.

Internal Commands

• These commands are built into the shell.
• cd (change directory) and ls (list directory contents) are examples.

External Commands

• These are commands stored in files.
• You can use which to find the location of an external command. The location is stored in an environment variable called the PATH variable, a very important variable, which contains a list of directories where the system looks for programs.

Aliases

• An alias creates a shortcut for a longer command.
• You can set aliases using the alias command.
• You can delete an alias using the unalias command.

Functions

• Functions let you group several commands into a single command.
• They are often loaded from shell initialization files when the shell starts up.

Variables

• Variables are used to store data.
• There are two types: local (temporal/lost when the terminal is closed) and environment (global/system wide.)

Globbing

• Glob characters (wildcards like * and ?) are symbols with special meaning in the shell.
• They can be used as patterns to match filenames.
• Using glob characters, you can control commands and affect multiple files at once.

Quoting

• Quoting characters (", ') prevent the shell from interpreting special characters in the string.
• " (double quotes) stop the shell from interpreting special characters in strings.
• ' (single quotes) stop the shell from interpreting special characters at all, including glob characters.
• \ (backslash) can be used to escape special characters in the string.

Control Statements

• Control statements allow for running multiple commands simultaneously or conditionally.
• Important control statements include semicolon (;), double ampersand (&&) and double pipe (||).