Glossary of Linux Command Line Terms
A
Absolute Path: Specifies the complete path to a file or directory from the root directory (/). It always starts with a slash. For example, /home/user/documents.
Alias: A shortcut or substitute name for one or more commands. Aliases allow users to create simple names for long and complex commands. For example, alias ll='ls -l' creates an alias ll for the command ls -l.
Argument: An input provided to a command that specifies data for the command to process. Arguments often include filenames or options that modify the command’s behavior.
AWK: A powerful programming language and utility used for pattern scanning and processing. It is commonly used for manipulating data and generating reports.
B
Background Process: A process that runs independently of the user’s direct interaction. It allows the user to continue using the shell while the process executes. Initiated by adding & at the end of a command.
Bash: Bourne Again SHell, the default command-line shell on many Linux distributions. It interprets and executes user commands and scripts.
C
Command Line Interface (CLI): A text-based interface where the user interacts with the computer’s operating system by typing commands.
Cron: A time-based job scheduler in Unix-like systems that executes commands or scripts at specified times and dates. It is used for automating recurring tasks.
Current Working Directory: The directory in which a user is currently operating. Commands without specified paths act relative to this directory. Use pwd to display it.
D
Daemon: A background process that runs continuously and performs specific operations or awaits certain conditions. Commonly used for services like web servers.
Directory: A location in the file system used to store files and other directories. Directories help organize files in a hierarchical structure.
E
Environment Variable: A dynamic value that can affect the way running processes behave on a computer. Examples include PATH, HOME, and LANG.
Executable: A file that can be run as a program or command. In Linux, a file must have execute permissions to be considered executable.
F
File Permissions: Rules that define who can read, write, or execute a file or directory. Permissions are assigned to user, group, and others.
Filesystem: The method and data structure that the operating system uses to control how data is stored and retrieved. Examples include ext4, NTFS, and FAT32.
Foreground Process: A process that occupies the terminal for user input and output. The shell waits for the process to complete before returning to the command prompt.
G
Glob: A pattern used to match filenames with wildcard characters like *, ?, and []. Also known as wildcard patterns.
GNU: A recursive acronym for “GNU’s Not Unix!”, representing a free software movement that provides a collection of software for Unix-like operating systems.
GREP: Global Regular Expression Print. A command-line utility for searching plain-text data sets for lines that match a regular expression.
H
Home Directory: The personal directory assigned to a user account for storing files and personal settings. Typically located at /home/username.
Hostname: The unique name assigned to a computer on a network. It is used to identify the device in communications over a network.
I
J
K
L
Link: A pointer or reference to a file or directory. There are two types: hard links and symbolic (soft) links.
Linux: An open-source operating system kernel that, combined with GNU software and other components, forms a complete operating system.
M
Man Page: Short for manual page, it is documentation that provides detailed information about commands and programs. Accessed using the man command.
Mount: The process of making a file system accessible at a certain point in the directory tree. The mount command attaches a file system to a specified directory.
Multiuser: A system that allows multiple users to access and use computing resources simultaneously.
N
Nano: A simple and user-friendly text editor used in the command line. It is suitable for beginners due to its ease of use.
Network Interface: A software or hardware interface between two systems communicating over a network.
O
P
Path: A string that represents the location of a file or directory in the file system. It can be absolute or relative.
Pipeline: A sequence of one or more commands separated by the pipe character |, where the output of one command serves as the input to the next.
Process: An executing instance of a program. Each process is assigned a unique process identifier (PID).
R
Regular Expression: A sequence of characters that defines a search pattern, mainly used for pattern matching with strings.
Relative Path: A file or directory location relative to the current working directory, does not begin with /.
S
Script: A file containing a sequence of commands that are executed by the shell interpreter.
Shell: A program that provides the command line interface for users to interact with the operating system.
Standard Error (stderr): The default error output stream where a program writes its error messages.
Standard Input (stdin): The default input stream where a program reads its input data.
Standard Output (stdout): The default output stream where a program writes its output data.
Sudo: Stands for “superuser do.” A command that allows a permitted user to execute a command with the privileges of another user, typically the superuser.
T
Terminal: An application that provides a text-based interface to the shell. Users enter commands via the terminal.
Text Editor: A program used for editing plain text files. Examples include nano, vim, and gedit.
U
User: An individual who uses the computer system. Each user has a unique username and home directory.
User Permissions: The access rights granted to a user, determining what actions they can perform on files and directories.
V
Variable: A named object that contains data used by one or more programs. Environment variables are a type of variable used by the shell and applications.
VI/Vim: A text editor that is more advanced and feature-rich than nano. Vim stands for “Vi Improved”.
W
* (matches any number of characters) and ? (matches any single character).X
Y
apt instead.Z
Special Terms
Command Line Interface (CLI): A means of interacting with a computer program by issuing commands in the form of successive text lines.
Man Page: Manual pages that provide documentation about commands and software programs. Accessed using the man command.
Wildcard: A character or set of characters that can be used to substitute for other characters in command arguments.
Mount: To make a storage device accessible to the system. Mounting integrates the device’s file system into the directory structure.