Variables & File Name Expansion in Linux

When using shell scripting in Linux, variables and file name expansion play very important roles. Variables help us store and manage data, while file name expansion gives us the ability to find and manage files in a directory.

Variables are used to store a value in a script or shell. This value can be input from a user, a system value, or a value generated during the execution of a program.

Declaring and Using Variables: In Linux shell scripting, variables are created directly without any keyword (`variable_name=value`). They are accessed using the `$` symbol (e.g., `echo $variable_name`).

Types of Variables: There are two main types: Local Variables (valid only within the current script or shell) and Environment Variables (available to all shells and scripts system-wide, created with `export`).

Arithmetic Operations: Mathematical operations on variables can be performed using the `expr` command or `$((expression))` syntax.

File name expansion in Linux is used to easily manage files and directories without typing their full names. This is also known as "globbing." Using shell globbing, we can select multiple files based on a pattern.

Wildcards: Special characters used for pattern-matching.

Brace Expansion: Used to perform actions on multiple files or directories in a single command (e.g., `mkdir project_{A,B,C}` creates `project_A`, `project_B`, and `project_C`).

Tilde Expansion: The tilde (~) is used to refer to the user's home directory (e.g., `cd ~`).