Bin bash edit file4/23/2024 ![]() All the application, including X, is built over shell and Linux shell is so powerful that the whole Linux system can be controlled precisely, using it. UID: The User Identifier of the current user.Linux Shell is one of the most fascinating and powerful GNU/ Linux powered tool. ![]() SHELLOPTS: Shell options you can set using the set option.The PS2 environment variable holds the definition of this secondary prompt, which, by default, is the greater than sign ( >). PS2: When a command spans more than one line and more input is expected, the secondary command prompt is shown.They represent such things as the host- and username, the current working directory, and the time. A set of tokens called escape sequences can be included in the definition of your command prompt. PS1: The PS1 environment variable holds the definition for the primary, default, and command prompt.IFS: The Internal Field Separator used to separate input on the command line. ![]() HOSTNAME: The hostname of the computer.HISTSIZE: Number of lines of history allowed in memory.HISTFILESIZE: Maximum number of lines permitted in the history file.DIRSTACK: The directories that have been added to the directory stack by the pushd command.COLUMNS: The current width of the terminal window.BASH_VERSINFO: The bash version as a digit.BASH_VERSION: The bash version number as a string of words and numbers.BASHOPTS: The command-line options that were used when bash was launched.For example, the COLUMNS environment variable will be updated to reflect changes you might make to the width of the terminal window: Some of the values are updated as you use the terminal. These are some of the shell environment variables used in bash to dictate or record its behavior and functionality. _: The underscore ( _) environment variable holds the last command that was typed.HOME: The home directory of the current user.LANG: The language, localization, and character encoding settings.PATH: A list of directories that the shell will search through to find command executables.MAIL: If the mail system has been set up on your Linux computer (by default, it isn't), this will hold the path to the current user's mailbox.LS_COLORS: The list of color codes used by the ls highlight different file types.OLDPWD: The directory you were in prior to moving to the current working directory.PWD: The path to the current working directory.USER: The username of the current person using the system.This holds the type of hardware terminal that will be emulated. TERM: Terminal windows are actually emulations of a hardware terminal.On most Linux distributions, this will be bash unless you changed it from the default. SHELL: The name of the shell that will launch when you open a terminal window.Your locale, time zone, and keyboard settings, the set of directories searched when the shell tries to find a command, and your default editor, are all stored in shell environment variables. There's a third set of environment variables defined within the shell. Others can't reference your session environment variables. ![]() ![]() Others are session-wide and can only be seen by you. Some environment variables are system-wide, or global. So, naturally, they're referred to as environment variables. Collectively, these variables hold settings that define the environment you find inside your terminal window, right down to the look of the command prompt. These variables also ensure that any information to which the terminal window and shell might need to refer is available. When you launch a terminal window and the shell inside it, a collection of variables is referenced to ensure the shell is configured correctly. Learn how to see them, create them for local and remote logins, and make them survive reboots. There's more than one type of environment variable on Linux. ![]()
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