Code / Linux Fundamentals / Chapter 5

Shell & Command Basics

Companion resources for Chapter 5 — shell basics, essential commands, file viewing, getting help, redirection, wildcards, and command history quick reference.

nextsteplinux.com/lf5
You scanned the QR code from Chapter 5 of Linux Fundamentals. This page is a quick reference companion — it does not replace the chapter. Full explanations, exam objectives, practice questions, and glossary are in the book.

Quick Reference · Navigation

Filesystem Navigation

The three commands you use constantly to move around and see where you are. Know every flag — these appear in exam questions regularly.

pwd · cd · ls	Navigation
Command	What It Does
pwd	Print current working directory (absolute path)
cd /path	Change to absolute path
cd subdir	Change to relative path
cd ~	Go to your home directory
cd ..	Go up one directory level
cd –	Return to previous directory
ls	List directory contents
ls -l	Long format — permissions, owner, size, date
ls -a	Show hidden files (names starting with .)
ls -la	Long format + hidden files (most common)
ls -lh	Human-readable sizes (KB, MB, GB)
ls -R	Recursive — list all subdirectories

Quick Reference · Files

Essential File Operations

Create, copy, move, remove. Know the key flags for each — especially the difference between cp -r and cp -a, and why rm -rf has no undo.

mkdir · touch · cp · mv · rm	File Ops
Command	What It Does
mkdir dir	Create a directory
mkdir -p a/b/c	Create nested dirs — no error if they exist
touch file	Create empty file or update its timestamp
cp src dst	Copy a file
cp -r src/ dst/	Copy directory recursively (no attribute preservation)
cp -a src/ dst/	Archive copy — recursive + all attributes preserved
cp -p src dst	Preserve timestamps, ownership, permissions
mv old new	Rename a file
mv file dir/	Move file into directory
mv -i src dst	Prompt before overwriting
rm file	Remove a file (no recycle bin)
rm -i file	Ask for confirmation first
rm -r dir/	Remove directory recursively
rm -rf dir/	Recursive + force — no prompts, no undo
rmdir dir	Remove an EMPTY directory only

Visual Reference · Filesystem

Viewing File Contents

Know which viewer to reach for: cat for short files, less for long files, tail -f for live log monitoring. The less navigation keys are the same as man pages.

cat · less · head · tail · grep	File Viewing
Command	What It Does
cat file	Print entire file to terminal
cat -n file	Print with line numbers
less file	Page through file — supports forward AND backward
less -N file	Page through file with line numbers
less +F file	Follow file as it grows (like tail -f)
head file	Show first 10 lines
head -n 20 file	Show first 20 lines
tail file	Show last 10 lines
tail -n 50 file	Show last 50 lines
tail -f file	Follow file in real time (Ctrl+C to stop)
tail -F file	Follow by filename — reconnects if file is rotated
grep pattern file	Print lines matching pattern
grep -i pattern file	Remove directory recursively
grep -r pattern dir/	Recursive search through directory
grep -v pattern file	Invert — show lines that do NOT match
grep -n pattern file	Show line numbers with matches

A “Hidden” Pro Feature: F (Tail)

If you are viewing a log file with less, pressing Shift + F puts less into “follow” mode (similar to tail -f). It will wait for new data to be appended to the file and display it in real-time. Press Ctrl + C to stop following and go back to normal navigation.

Visual Reference · Filesystem

Linux Directory Hierarchy (FHS)

The Filesystem Hierarchy Standard defines where things live. These directories and their purposes come up frequently — know the highlighted ones especially well.

Directory	Contents	Exam Weight
/	Root — top of the entire filesystem tree	★★★
/etc	System-wide configuration files — sshd_config, fstab, passwd, hostname	★★★
/var/log	Log files — syslog, auth.log, nginx/, journal/	★★★
/tmp	Temporary files — world-writable, cleared on reboot	★★★
/proc	Virtual filesystem — kernel and process info (not on disk)	★★★
/dev	Device files — /dev/sda, /dev/null, /dev/random	★★★
/home	User home directories — /home/username	★★
/root	Root user’s home directory (not inside /home)	★★
/bin	Essential user commands — ls, cp, mv, cat (symlink → /usr/bin on modern distros)	★★
/sbin	System admin commands — fdisk, ip (symlink → /usr/sbin on modern distros)	★★
/usr	User programs — /usr/bin, /usr/lib, /usr/share	★★
/boot	Boot files — kernel (vmlinuz), initrd, GRUB	★★
/sys	Virtual filesystem — hardware/driver info (not on disk)	★★
/lib	Shared libraries required by /bin and /sbin	★
/mnt	Temporary manual mount point	★
/media	Removable media — USB drives, optical discs	★
/opt	Optional third-party software	★

Quick Reference · I/O

Redirection and Pipes

Standard streams, redirection operators, and pipes. The order of 2>&1 matters — this is one of the most tested redirection patterns.

stdin · stdout · stderr · pipes	I/O Redirection
Operator	Meaning
>	Redirect stdout to file (overwrite)
>>	Redirect stdout to file (append)
2>	Redirect stderr to file
2>>	Append stderr to file
> file 2>&1	Redirect stdout AND stderr to file (correct order)
&>	Redirect both stdout and stderr (Bash 4+ shorthand)
<	Redirect file as stdin to command
\|	Pipe — stdout of left becomes stdin of right
tee file	Show hidden files (names starting with .)
ls -la	Long format + hidden files (most common)
ls -lh	Human-readable sizes (KB, MB, GB)
ls -R	Recursive — list all subdirectories

1. The Redirection Logic: Why Order is King

In Linux, the shell processes redirections from left to right. Think of it as a plumber connecting pipes one by one.

The Correct Way: > file 2>&1

1) > file: The shell looks at File Descriptor 1 (STDOUT) and points it to file.

2) 2>&1: The shell looks at File Descriptor 2 (STDERR) and says, “Point this to wherever FD1 is currently pointing.” Since FD1 is already pointing to the file, FD2 follows suit.

Result: Everything (output and errors) ends up in the file.

The Wrong Way: 2>&1 > file

1) 2>&1: The shell looks at FD2 and points it to wherever FD1 is currently pointing. By default, FD1 points to your Terminal. So, FD2 is now locked onto your screen.

2) > file: The shell then moves FD1 to the file.

Result: Regular output goes to the file, but errors are still dumped onto your screen.

Pattern	The “Human” Translation	Pro-Tip
`ps aux \| grep nginx`	“Show me every process, then filter for the one named nginx.”	Add `\| grep -v grep` to remove the grep command itself from the results.
`cat syslog \| grep error \| tail -20`	“Read the log, find the errors, and show me only the most recent 20.”	Using `grep --color` makes the errors pop visually in the terminal.
`ls -la \| tee list.txt \| grep ".conf"`	“List files, save the FULL list to a file, but only show me .conf files on screen.”	`tee` acts like a physical “T” junction in plumbing, splitting the data flow.

Quick Reference · Productivity

Essential Keyboard Shortcuts

These shortcuts work in Bash on any Linux system. Ctrl+R alone will save you more time than almost anything else you learn in this chapter.

Ctrl+R

Reverse history search — type to find a previous command

↑/↓

Scroll through previous / next commands

Tab

Autocomplete command name or filename

Tab Tab

Show all possible completions when ambiguous

Ctrl+A

Move cursor to beginning of line

Ctrl+E

Move cursor to end of line

Ctrl+U

Delete from cursor to beginning of line

Ctrl+K

Delete from cursor to end of line

Ctrl+W

Delete the word before the cursor

Ctrl+L

Clear the screen (same as the clear command)

Ctrl+C

Cancel / kill the running command

Ctrl+D

End of input / logout from shell session

Command

What it Does

history

Lists your command history with line numbers.

history 20

Shows only the last 20 commands you ran.

!503

Re-runs the command at line 503 in your history.

!!

Re-runs the very last command.

sudo !!

Re-runs the last command with root privileges.

!grep

Re-runs the most recent command starting with “grep”.

[!TIP]
The “Invisible” Command
If you need to type a command that contains a password, API key, or sensitive data, start the command with a leading space.
$ mysql -u admin -p'Secret123'
Because of the space before mysql, the shell will execute it but will not save it to your .bash_history file. This is a vital security habit for any Linux admin.

Quick Reference · Help

Getting Help from the System

You never need to memorize every flag. Know how to find what you need quickly — man, –help, and apropos are the three tools that matter most.

man · –help · apropos · whatis	Help System
Command	What It Does
man command	Full manual page for a command
man 5 passwd	Manual page in section 5 (file formats)
man 1 passwd	Manual page in section 1 (commands)
man -k keyword	Search man pages by keyword (same as apropos)
command –help	Quick usage summary and flag list
apropos keyword	Search man page descriptions for keyword
whatis command	One-line description from man page database
sudo mandb	Rebuild the whatis database (if apropos fails)
type command	Show whether it’s a binary, builtin, or alias
which command	Full path to a command binary

For the Linux+ (XK0-005) and LPIC-1 exams

memorizing these specific section numbers is non-negotiable. It’s a favorite topic for multiple-choice questions because it tests whether you understand the difference between a standard command and an administrative tool.

Man Page Section Numbers: The Essential Map

Section

Category

Key Examples

Why it Matters

User Commands

ls, cp, grep, passwd

Commands available to all users.

System Calls

open, read, fork, exec

Functions that talk directly to the Kernel.

Library Functions

printf, malloc, scanf

Functions used by C/C++ developers (standard libraries).

File Formats

/etc/passwd, /etc/fstab

Describes the structure of configuration files.

Admin Commands

fdisk, mount, useradd

Commands intended only for the root/superuser.

[!IMPORTANT]

EXAM PRO-TIP: The passwd Confusion

The exams love to trick you with the passwd command.

• man 1 passwd : Shows you how to use the command to change a password.
• man 5 passwd : Shows you the structure of the /etc/passwd text file.

If you just type man passwd, Linux defaults to the lowest number (Section 1).
To see the file format, you must specify the section: man 5 passwd.

Practice · Scripts

Practice Scripts

These scripts build hands-on familiarity with the commands in Chapter 5. Run them on any of the three distributions covered in the book — all commands are universal.

01-navigation-drill.sh

⬇Navigation-drill

Practice Drill 01: Filesystem Navigation
File Name: 01-navigation-drill.sh

Goal: Master moving through the Linux tree using cd, pwd, and ls.

Step

Command

What you are observing

pwd

Your current location (Print Working Directory).

ls -la ~

Your Home directory. Look for “hidden” files starting with a .

ls /etc | head -15

Piping output. Only seeing the first 15 files of the config directory.

cd -

The “Back” button. It toggles between your current and previous directory.

cd ../bin

Relative pathing. Moving up one level (..) then down into bin.

[!NOTE]
Pro-Tip: Path Logic
Absolute Paths always start with / and work from anywhere.

Relative Paths are based on where you are currently standing. Use ../ to move up to the parent directory.

02-file-ops-drill.sh

⬇file-ops-drill

Practice Drill 02: File Operations Sandbox
File Name: 02-file-ops-drill.sh

Goal: Master mkdir, touch, cp, mv, and rm within a safe /tmp environment

Oppo Reno 15

Command Flag	Why the Exam Cares	Book Reference
mkdir -p	Creates full paths without failing if they already exist.	Section 5.3.1
`cp -a`	“Archive” mode. Essential for backups; preserves timestamps and permissions.	Section 5.3.3
`rm -rf`	Recursive and Force. The most dangerous command; has no “undo.”	Section 5.3.5

[!CAUTION]
The rm -rf / Nightmare
As noted in the book, a simple typo like rm -rf / path/to/dir (adding a space before the slash) tells Linux to delete everything starting from the Root directory. Always double-check your paths before hitting Enter when using the -r (recursive) flag.

03-redirection-drill.sh

⬇redirection-drill

Practice Drill 03: I/O Redirection & Pipes
File Name: 03-redirection-drill.sh

Goal: Master the flow of data between commands, files, and the terminal.

#!/bin/bash
# 03-redirection-drill.sh — I/O redirection practice
# Companion to Chapter 5: Shell & Command Basics
# nextsteplinux.com/lf5

# Create a fresh workspace in /tmp
mkdir -p /tmp/lf5-io && cd /tmp/lf5-io

echo "=== STEP 1: Standard Output (stdout) Redirection ==="
# > overwrites the file [cite: 320]
ls /etc > etc-list.txt
echo "File 'etc-list.txt' created with $(wc -l < etc-list.txt) lines."

echo -e "\n=== STEP 2: Appending Output (>>) ==="
# >> adds to the end of the file instead of overwriting [cite: 323]
echo "--- appended mark ---" >> etc-list.txt
tail -n 3 etc-list.txt

echo -e "\n=== STEP 3: Standard Error (stderr) & /dev/null ==="
# 2> redirects errors; /dev/null discards them [cite: 331, 349]
echo "Searching /etc for .conf files (silencing permission errors)..."
find /etc -name "*.conf" 2>/dev/null | head -n 10

echo -e "\n=== STEP 4: Merging Streams (2>&1) ==="
# CORRECT ORDER: > file 2>&1 
# Redirects both regular output and errors to combined.txt
ls /etc /nonexistent > combined.txt 2>&1
echo "Contents of combined.txt (should show success and error):"
cat combined.txt

echo -e "\n=== STEP 5: Complex Pipes & Filters ==="
# Piping stdout of one command to stdin of the next [cite: 341]
echo "Finding recent errors in system logs..."
journalctl -n 100 2>/dev/null | grep -i error | head -n 5

echo -e "\n=== STEP 6: Using 'tee' for Dual Output ==="
# tee writes to a file AND continues the pipe [cite: 347, 348]
ls /usr/bin | tee binlist.txt | wc -l
echo "Total binaries counted and full list saved to 'binlist.txt'."

# Cleanup
cd ~ && rm -rf /tmp/lf5-io
echo -e "\n=== DRILL COMPLETE: Workspace /tmp/lf5-io removed. ==="

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Chapter 4: Installing Arch Linux

Chapter 6 File Permissions & Ownership