📋 Linux Commands Cheat Sheet

Quick reference for essential Linux commands from The Linux Terminal guide.

---

📖 Getting Help

Command	Description
man <cmd>	Open manual page for command
man -k <keyword>	Search all man pages
apropos <keyword>	Same as man -k
whatis <cmd>	One-line command description
info <cmd>	GNU-style manual (more detailed)
<cmd> --help	Quick syntax reference
help <builtin>	Help for shell built-ins
type <cmd>	Show command type (alias/builtin/executable)

---

📁 Navigation & File Operations

Navigation

Command	Description
pwd	Print working directory
cd <dir>	Change directory
cd ~ or cd	Go to home directory
cd -	Go to previous directory
cd ..	Go up one directory
ls	List directory contents
ls -l	Long format listing
ls -la	Include hidden files
ls -lh	Human-readable sizes
ls -lSh	Sort by size

File Operations

Command	Description
cp <src> <dest>	Copy file
cp -r <src> <dest>	Copy directory recursively
mv <src> <dest>	Move or rename
rm <file>	Remove file
rm -r <dir>	Remove directory recursively
rm -f <file>	Force remove (no prompt)
mkdir <dir>	Create directory
mkdir -p <path>	Create nested directories
touch <file>	Create empty file / update timestamp

---

📄 Viewing & Editing Files

Command	Description
cat <file>	Display entire file
less <file>	Page through file
head <file>	First 10 lines
head -n 20 <file>	First 20 lines
tail <file>	Last 10 lines
tail -n 20 <file>	Last 20 lines
tail -f <file>	Follow file (live updates)
tail -F <file>	Follow with retry (log rotation)
wc <file>	Line, word, byte count
wc -l <file>	Line count only

---

🔍 Finding Files

Quick Lookup

Command	Description
which <cmd>	Find executable in PATH
which -a <cmd>	Find all executables in PATH
whereis <cmd>	Find binary, man page, source
locate <pattern>	Search filename database (fast)
locate -i <pattern>	Case-insensitive
sudo updatedb	Update locate database

find — Real-time Search

find <path> [options] [expression]

Option	Description
-name "pattern"	Match filename (case-sensitive)
-iname "pattern"	Match filename (case-insensitive)
-type f	Files only
-type d	Directories only
-size +100M	Larger than 100MB
-size -1k	Smaller than 1KB
-mtime -7	Modified in last 7 days
-mtime +30	Modified over 30 days ago
-user <name>	Owned by user
-perm 644	Exact permissions
-empty	Empty files/directories
-maxdepth n	Limit search depth
-exec cmd {} \;	Execute command on each match
-delete	Delete matching files

Examples:

find /var/log -name "*.log"
find . -type f -size +100M 2>/dev/null
find . -mtime -1
find . -type d -empty -delete
find . -name "*.sh" -exec chmod +x {} \;

---

🔎 Searching Content (grep)

grep [options] "pattern" <file(s)>

Option	Description
-i	Case-insensitive
-v	Invert match (show non-matching)
-n	Show line numbers
-c	Count matches
-l	List filenames with matches
-r / -R	Recursive search
-w	Match whole words
-E	Extended regex (egrep)
-A n	Show n lines after match
-B n	Show n lines before match
-C n	Show n lines around match
-o	Show only matching part
--color	Highlight matches

Examples:

grep "error" logfile.txt
grep -in "warning" /var/log/syslog
grep -r "TODO" ./src/
grep -E "error|warning" log.txt
grep -C 3 "Exception" app.log
ps aux | grep nginx

Regular Expressions

Pattern	Meaning
.	Any single character
*	Zero or more of previous
+	One or more (use -E)
^	Start of line
$	End of line
[abc]	Any char in brackets
[^abc]	Any char NOT in brackets
[a-z]	Range of characters

---

🔀 Piping & Redirection

Piping

command1 | command2 | command3

Example	Description
ls -la | less	Browse long output
cat file | sort | uniq	Sort and dedupe
ps aux | grep nginx	Find processes
history | tail -20	Last 20 commands

Output Redirection

Operator	Description
>	Redirect stdout (overwrite)
>>	Redirect stdout (append)
2>	Redirect stderr
2>>	Append stderr
&>	Redirect both stdout and stderr
&>>	Append both

Input Redirection

Operator	Description
<	Redirect stdin from file
<<	Here document (heredoc)
<<<	Here string

Special

Command	Description
command 2>&1	Redirect stderr to stdout
command > file 2>&1	Both to file
command &> file	Both to file (modern)
tee file	Write to stdout AND file
tee -a file	Append to file

---

📜 Command History

Command	Description
history	Display command history
history 20	Last 20 commands
history -d <n>	Delete line n
history -c	Clear history

Bang Commands

Syntax	Description
!!	Repeat last command
!n	Execute command #n
!-n	Execute nth previous command
!string	Last command starting with string
!$	Last argument of previous command
!*	All arguments of previous command
^old^new	Replace in last command
sudo !!	Run last command with sudo

---

🔐 User & Privileges

Command	Description
whoami	Current username
id	User ID, group ID, groups
groups	Groups you belong to
sudo <cmd>	Execute as root
sudo -i	Interactive root shell
sudo su -	Switch to root
sudo -k	Invalidate sudo cache
sudo -v	Extend sudo timeout
sudo -l	List your sudo privileges
sudo visudo	Safely edit sudoers

---

🛠️ Text Processing

Command	Description
sort <file>	Sort lines alphabetically
sort -n <file>	Sort numerically
sort -r <file>	Sort reverse
sort -u <file>	Sort and remove duplicates
sort -k2 <file>	Sort by 2nd column
uniq	Remove adjacent duplicates
uniq -c	Count occurrences
uniq -d	Show only duplicates
cut -d':' -f1 <file>	Extract first field
cut -c1-10 <file>	Extract characters 1-10
strings <binary>	Extract readable text from binary

xargs — Build Commands

find . -name "*.tmp" | xargs rm
cat urls.txt | xargs -P 4 -I {} curl {}
find . -name "*.txt" -print0 | xargs -0 cat

---

⌨️ Keyboard Shortcuts

Navigation

Shortcut	Action
Ctrl + A	Beginning of line
Ctrl + E	End of line
Alt + B	Back one word
Alt + F	Forward one word

Editing

Shortcut	Action
Ctrl + U	Delete before cursor
Ctrl + K	Delete after cursor
Ctrl + W	Delete word before
Ctrl + Y	Paste deleted text
Ctrl + _	Undo

Control

Shortcut	Action
Ctrl + L	Clear screen
Ctrl + C	Interrupt/kill process
Ctrl + Z	Suspend process
Ctrl + D	Exit shell / EOF
Ctrl + R	Reverse history search

---

📊 Quick Examples

# Find large files
find / -type f -size +100M 2>/dev/null

# Search recursively for pattern
grep -rn "TODO" ./src/

# Count lines in all Python files
find . -name "*.py" | xargs wc -l

# Last 20 commands containing "git"
history | grep git | tail -20

# Monitor log file live
tail -f /var/log/syslog

# Find and delete old temp files
find /tmp -type f -mtime +7 -delete

---

📝 For detailed explanations, see The Linux Terminal guide.