Simple list of Linux commands which are frequently used.

Introduction to the Unix/Linux command line. even if you are familiar with these bash commands its a good overview of all these commands.

Some Required Commands

Command	Action	Options
List	ls	-a (all files), -l (long format)
Make directory	mkdir [OPT] DIR	-p (make parents)
Change directory	cd PATH	. (current dir), .. (parent dir), ~ (home dir), - (last dir)
Print working directory	pwd
Create empty file	touch FILE
Copy	cp [OPT] FROM TO	-r (copy directories recursively)
Move or rename	mv FROM TO
Remove	rm [OPT] FILE	-r (recursively remove directories), -f (force)
Remove directory	rmdir [OPT] DIR	-p (parents)
Concatenate and print files	cat [OPT] FILES	-l (number the output lines)
View file	less [OPT] FILE	-N (number the output lines)

Less Frequent Commands

Key	Command	Key	Command
Space	Next page	/<text>	Forward search for <text>
b	Previous page	?<text>	Backward search for <text>
j	Next line	n	Next search match
k	Previous line	N	Previous search match
g	First line	=	File information
G	Last line	h	Help
<n>G	Line <n>	q	Quit

Command	Action	Options
Display first lines	head [OPT] FILE	-n (first n lines )
Display last lines	tail [OPT] FILE	-n (last n lines)
Print lines matching a pattern	grep [OPT] PATTERN [FILE...]	-c (display the number of matched lines), -i (ignore case sensitivity), -l (display the filenames), -n (display the line numbers), -w (match whole word)
Word count	wc [OPT] FILE	-l (line count), -c (byte count), -m (character count), -w (word count)

Control Key Commands

Command	Action
Kill process	CTRL + C
Stop process	CTRL + Z
End of file	CTRL + D

I/O Redirection

Redirection	Action	Description
STDOUT to a file	COMMAND > FILE	Overwrite
STDOUT to a file	COMMAND >> FILE	Append
STDIN to a file	COMMAND < FILE

In order to redirect the output from one command as input to the next one write COMMAND1 | COMMAND2 | COMMAND3.

Wildcards

Symbol	Matches
*	Any number of characters
?	Any single character

System and Security

UNIX Permissions

sudo [OPT] [USER] COMMAND allows users to run programs with the security privileges of another user (normally the root).

u	g	o
user	group	others
r w x	r w x	r w x
4 2 1	4 2 1	4 2 1
7	7	7

Command	Action	Options
Change permissions	chmod [OPT] MODE FILE	-r (recursively)

Command	MODE
Read and execute for all	+rx
Deny write access for group	g-w
Read, write and execute for all	777

UNIX Processes

Command	Action	Options
Run process in background	COMMAND &
Background or suspended processes	jobs
Send signal to a process	kill SIGNAL PROCESS
Kill process by name	killall PROCESS
Display top CPU processes	top
Reports the process status	ps	-f (full listing), -e (all processes)

Other

Command	Action	Options
Last commands used	history	-c (clear)
Last matched command	!*
Time command execution	time COMMAND
Compare files line by line	diff
Walk a file hierarchy	find PATH [OPT] [EXPRESSION]	-name (find by name), -size (find by size), -iname (case sensitive mode)