Overview
The shell is the primary interface between an administrator and a Linux system. While graphical tools exist for specific tasks, the command line offers precision, repeatability, and the ability to combine tools in ways no GUI anticipates. Bash — the Bourne Again Shell — is the default interactive shell on RHEL and the one you will spend the most time in. Understanding how Bash processes input, how to navigate history without retyping, and which keyboard shortcuts accelerate common operations separates slow, error-prone sessions from efficient ones.
Bash Shell Basics
When you open a terminal on RHEL, Bash presents a prompt. The default prompt shows your username, the hostname, and your current working directory:
student@servera:~$The $ at the end signals a regular user session. The root prompt ends in #. Everything you type before pressing Enter is a command line, and Bash parses it according to a consistent structure:
command [options] [arguments]Options modify how a command behaves. Short options are prefixed with a single dash (-l, -a, -h) and can usually be combined (-lh). Long options use two dashes (--human-readable). Arguments are the targets the command acts on — files, directories, usernames. Bash processes metacharacters that control flow between commands:
| Metacharacter | Meaning |
|---|---|
; | Run commands sequentially regardless of exit status |
&& | Run second command only if first succeeds (exit 0) |
|| | Run second command only if first fails (exit non-zero) |
| | Pipe stdout of left command to stdin of right command |
Command Types
Not every command on RHEL is a file on disk. Bash distinguishes two types:
External commands are binary executables stored in directories listed in $PATH. When you type ls, Bash searches each directory in $PATH in order until it finds /usr/bin/ls and executes it. which ls shows which file would be run.
Built-in commands are part of the Bash interpreter itself — cd, echo, pwd, export, alias, source, and others. They run faster than external commands because no new process is forked. type command reports whether a command is a built-in, an external file, or an alias.
Essential Commands
| Command | What It Does |
|---|---|
whoami | Print the current username |
hostname | Print the system’s hostname |
date | Display the current date and time; date +%Y-%m-%d for custom format |
passwd | Change your own password; passwd username changes another user’s (root only) |
id | Show current UID, primary GID, and all supplementary group memberships |
uname -r | Print the running kernel version |
uptime | Show how long the system has been running, plus the 1/5/15-minute load averages |
These commands require no arguments and produce immediate, useful output — they are diagnostic first steps when logging into an unfamiliar system.
Command History
Bash records every command you run in an in-memory history list and writes it to ~/.bash_history when the session ends. The number of entries kept in memory is controlled by HISTSIZE; the number written to disk is controlled by HISTFILESIZE. On RHEL the defaults are 1000 in memory and 2000 on disk.
| History Syntax | Effect |
|---|---|
history | Print the numbered history list |
!N | Re-run command number N from history |
!! | Re-run the immediately previous command |
!string | Re-run the most recent command that begins with string |
!string:p | Print (but do not run) the command that would be recalled by !string |
history -c | Clear the in-memory history list |
The most powerful history tool is reverse incremental search: press Ctrl+R, then start typing any substring of a previous command. Bash displays the most recent match and updates it as you type. Press Ctrl+R again to cycle to the next earlier match. Press Enter to execute, or Esc to edit the recalled command before running it.
Keyboard Shortcuts
The Bash readline library provides a set of keyboard shortcuts for editing the current command line and controlling the terminal session. These are worth memorising because they eliminate the need to retype long commands when a small change is needed.
| Shortcut | Action |
|---|---|
Ctrl+A | Move cursor to the beginning of the line |
Ctrl+E | Move cursor to the end of the line |
Alt+B | Move cursor back one word |
Alt+F | Move cursor forward one word |
Ctrl+U | Delete everything from the cursor to the beginning of the line |
Ctrl+K | Delete everything from the cursor to the end of the line |
Ctrl+W | Delete the word immediately before the cursor |
Ctrl+Y | Paste (yank) text that was previously deleted with Ctrl+U, Ctrl+K, or Ctrl+W |
Ctrl+C | Send SIGINT to the foreground process — interrupt and terminate it |
Ctrl+D | Send EOF — exits the current shell if the line is empty |
Ctrl+Z | Suspend the foreground process (send SIGTSTP); resume with fg or bg |
Ctrl+L | Clear the screen, equivalent to running clear |
Ctrl+R | Enter reverse incremental history search |
Ctrl+X Ctrl+E | Open the current command line in $EDITOR for multi-line editing |
The delete-and-yank shortcuts (Ctrl+U / Ctrl+K / Ctrl+W paired with Ctrl+Y) function as a simple cut-and-paste buffer. This is useful when you need to move an argument from one part of a command to another without retyping it.
Tab Completion
Bash can complete commands, file paths, and variable names automatically. Press Tab once to complete a unique match instantly. If multiple completions are possible, a single Tab does nothing — press Tab a second time to list all candidates. This works for:
- Commands: typing
systhen Tab Tab lists all commands starting withsys - File paths: typing
/etc/systhen Tab lists matching files and directories under/etc/ - Variables: typing
$HIthen Tab expands to$HISTSIZEif that is the only match
Some tools extend Tab completion to cover their own options and subcommands. dnf install followed by Tab Tab, for example, can suggest package names if the completion package for dnf is installed.
Summary
Bash processes commands as a command options arguments structure, distinguishes built-in commands from external binaries, and records every command in a history list accessible via history, !N, and Ctrl+R incremental search. The readline keyboard shortcuts — particularly the cursor-movement pairs (Ctrl+A/Ctrl+E, Alt+B/Alt+F) and the delete-and-yank pairs (Ctrl+U/Ctrl+K with Ctrl+Y) — eliminate most of the friction in working with long command lines. Tab completion reduces both typing time and the risk of path typos. These habits compound across every session.