File Operations

Command	Action
`cp file dest`	Copy file
`cp -r dir dest`	Copy directory recursively
`mv file dest`	Move or rename
`rm file`	Delete file
`rm -rf dir`	Delete directory recursively
`mkdir -p a/b/c`	Create nested directories
`touch file`	Create empty file or update timestamp
`ln -s target link`	Create symbolic link
`find . -name "*.py"`	Find files by name pattern
`find . -type f -mtime -7`	Files modified in last 7 days
`find . -size +10M`	Files larger than 10MB
`du -sh *`	Directory sizes
`df -h`	Disk usage by filesystem
`stat file`	Detailed file metadata

Text Processing

Command	Action
`cat file`	Print file contents
`less file`	Paginate file (q to quit)
`head -n 20 file`	First 20 lines
`tail -n 20 file`	Last 20 lines
`tail -f file`	Follow file (live updates)
`grep "pattern" file`	Search for pattern
`grep -r "pattern" .`	Recursive search
`grep -i "pattern"`	Case-insensitive
`grep -v "pattern"`	Invert: lines NOT matching
`grep -n "pattern"`	Show line numbers
`grep -c "pattern"`	Count matching lines
`wc -l file`	Count lines
`wc -w file`	Count words
`sort file`	Sort lines alphabetically
`sort -n`	Numeric sort
`sort -r`	Reverse sort
`uniq`	Remove duplicate adjacent lines
`uniq -c`	Count occurrences
`cut -d: -f1 file`	Cut field 1 with `:` delimiter
`awk '{print $1}' file`	Print first field
`awk -F: '{print $1, $3}'`	Custom delimiter, multiple fields
`sed 's/old/new/g' file`	Replace text (in output)
`sed -i 's/old/new/g' file`	Replace text in-place
`tr 'a-z' 'A-Z'`	Translate characters

Syntax	Action
`cmd1 \| cmd2`	Pipe stdout of cmd1 to cmd2
`cmd > file`	Redirect stdout to file (overwrite)
`cmd >> file`	Redirect stdout to file (append)
`cmd 2> file`	Redirect stderr to file
`cmd 2>&1`	Redirect stderr to stdout
`cmd &> file`	Redirect both stdout and stderr
`cmd < file`	Use file as stdin
`cmd \| tee file`	Print and also save to file
`cmd1 && cmd2`	Run cmd2 only if cmd1 succeeds
`cmd1 \|\| cmd2`	Run cmd2 only if cmd1 fails
`cmd1 ; cmd2`	Run cmd2 regardless of cmd1 result

Command	Action
`cmd &`	Run command in background
`jobs`	List background jobs
`fg %1`	Bring job 1 to foreground
`bg %1`	Resume job 1 in background
`Ctrl+Z`	Suspend current process
`Ctrl+C`	Kill current process
`ps aux`	List all processes
`ps aux \| grep name`	Find process by name
`top`	Interactive process viewer
`htop`	Better interactive viewer (if installed)
`kill <pid>`	Send SIGTERM to process
`kill -9 <pid>`	Send SIGKILL (force)
`killall name`	Kill all processes by name
`pkill name`	Kill processes matching name
`nohup cmd &`	Run command immune to hangup

Permission bits: 4 = read, 2 = write, 1 = execute. Add for each group (owner/group/others).

Command	Action
`curl https://url`	Fetch URL
`curl -O url`	Download file keeping name
`curl -L url`	Follow redirects
`curl -H "Auth: token" url`	Custom header
`curl -X POST -d '{}' url`	POST with body
`wget url`	Download file
`ssh user@host`	SSH login
`ssh -p 2222 user@host`	SSH on custom port
`scp file user@host:/path`	Copy file to remote
`scp user@host:/path file`	Copy file from remote
`ping host`	Test connectivity
`traceroute host`	Trace network path
`netstat -tulnp`	Open ports and listeners
`ss -tulnp`	Faster alternative to netstat
`nmap -sn 192.168.1.0/24`	Scan local network

Shortcut	Action
`Ctrl+A`	Jump to line start
`Ctrl+E`	Jump to line end
`Ctrl+K`	Delete from cursor to end
`Ctrl+U`	Delete from cursor to start
`Ctrl+W`	Delete word before cursor
`Alt+.`	Insert last argument of previous command
`Ctrl+R`	Reverse search command history
`!!`	Repeat last command
`!$`	Last argument of previous command
`!string`	Run last command starting with string
`Ctrl+L`	Clear screen

Variable	Value
`$?`	Exit code of last command (0 = success)
`$!`	PID of last background process
`$$`	PID of current shell
`$0`	Script name
`$1`, `$2`	Script arguments
`$@`	All arguments as separate words
`$#`	Number of arguments
`$HOME`	Home directory
`$PATH`	Executable search path
`$PWD`	Current directory