Accessing the Command Line

CIS126RH · Red Hat System Administration I

The bash shell · Command syntax · Getting help

Goal: log in to RHEL's graphical and command-line environments and run simple commands correctly.

• Access a RHEL graphical environment.
• Access a command-line environment.
• Use the bash shell.
• Use basic command syntax correctly.
• Use built-in documentation to get help.

Key commands: bash, pwd, echo, history, man, apropos, which

The shell is a command interpreter.

1. Reads what you type
2. Runs the corresponding program
3. Displays the results
4. Shows a new prompt when ready

On RHEL, the default shell is bash — the Bourne Again SHell.

• Installing software
• Managing users
• Configuring services
• Automating tasks

The GUI is optional; the command line is not.

Most production RHEL servers are headless: they run without a graphical desktop.

[student@server1 ~]$

[root@server1 ~]#

Always check the prompt. A # means you are root and a mistyped command can damage the system.

RHEL provides multiple virtual consoles.

• From the graphical desktop: Ctrl+Alt+F3 through F6
• Return to the graphical session with Ctrl+Alt+F1 or F2

Virtual consoles provide direct text-mode access without requiring a GUI.

command [options] [arguments]

pwd
ls -l
ls --all
ls -la
ls -l /etc

• pwd: no option or argument
• -l: short option
• --all: long option
• -la: combined short options
• /etc: argument

The shell treats spaces, quotes, and characters such as *, $, and > specially.

echo Hello World
echo "Hello World"
echo '$HOME stays literal here'
echo "$HOME expands here"

Exam note: Single quotes are fully literal; double quotes still allow variable expansion and command substitution.

history
!482
!!

• history displays recent commands.
• !482 re-runs command 482.
• !! re-runs the most recent command.

Ctrl+R is your friend: search backward through command history instead of pressing ↑ repeatedly.

Commands can use absolute or relative paths.

cd /etc/ssh

cd ../ssh

Press Tab while typing a command, file name, or path.

cd /etc/ss[Tab]
# becomes:
cd /etc/ssh/

Press Tab twice to list all possible matches when more than one exists.

Tab completion reduces typing, prevents path typos, and helps confirm that a file or directory exists.

man ssh
ssh --help
apropos partition
which ssh

• Use man for detailed documentation.
• Use --help for a quick reference.
• Use apropos when you know the topic but not the command.
• Use which to locate the executable.

Man pages have sections. For the file-format version of passwd, use man 5 passwd.

shell

Command interpreter that reads, executes, and returns output.

bash

The Bourne Again SHell; RHEL's default shell.

prompt

Text shown when the shell is ready for input; ends in $ or #.

option

Flag that modifies command behavior.

argument

Value, file, or directory a command acts on.

absolute path

Path beginning at /.

relative path

Path interpreted from the current directory.

man page

Built-in manual documentation.

1. What is the difference between a $ prompt and a # prompt?
2. Name two ways to reach a shell when no GUI is installed.
3. How do single and double quotes handle $HOME differently?
4. Name two ways to re-run a recent command.
5. What does pressing Tab twice do?
6. What is the difference between absolute and relative paths?
7. How would you get the file-format version of the passwd man page?

• bash is the default RHEL shell.
• Know what your prompt tells you, especially $ vs. #.
• Understand command [options] [arguments].
• Use history, editing shortcuts, and Ctrl+R efficiently.
• Distinguish absolute and relative paths.
• Use Tab completion to work accurately.
• Use man, --help, apropos, and which to find answers without leaving the command line.

The goal is not to memorize every command. Learn how to work effectively at the shell and how to find the information you need.