Linux cheat sheet

A Standard Linux Directory Structure

Below is a reference to the basic structure of directories for most Linux distributions. Find more at the Linux Filesystem Hierarchy Standard, on Wikipedia.

/ – the root or base of the filesystem
/bin – operating system binaries
/boot – Linux kernel and programs run at startup
/dev – devices
/etc – system configuration files
/home – user working directories
/lib – library files shared across installed programs
/media – removable media devices
/mnt – removable device mount points
/opt – for optional software
/proc – Linux kernel files
/root – home directory for root user
/sbin – system binaries
/usr – program and support files
- /usr/bin – programs installed by the Linux distribution
- /usr/lib – shared libraries
- /usr/local – programs for system-wide use
- /usr/sbin – system administration binaries
- /usr/share – shared data used by programs including documentation
/var – dynamic data, including mail, databases and log files

Commonly Used Wildcards

Linux offers extensive search capabilities using wildcards and the following characters are frequently used.

* – matches any character
? – matches a single character
[set] – matches a set of characters
[!set] – matches those not in the set

Metacharacters

These 10 metacharacters have special meaning to the bash shell program and must be quoted with ' or " to not be interpreted as metacharacters.

space tab newline | & ; ( ) < >

Keystroke Combinations

These keystroke combinations are helpful in the bash shell.

Ctrl-c – stop a process
Ctrl-d – exit the terminal
Ctrl-z – pause a process
Ctrl-a – go to start of line
Ctrl-e – go to end of line

Reserved Words

Reserved words are commonly used for looping and conditional constructs when writing functions and scripts.

! – negation or not
[[ ]] – conditional expression
{ } – command grouping
function – define a function
select do done – create a menu
time – for timing statistics
case in esac – conditional construct
if then elif else fi – conditional construct
for in do done – looping construct
until do done – looping construct
while do done – looping construct

File and Directory Modes and Permissions

Permissions can be set with any one of three modes: octal, binary and mode.

Octal	Binary	Mode
0	000	—
1	001	–x
2	010	-w-
3	011	-wx
4	100	r–
5	101	r-x
6	110	rw-
7	111	rwx

Non-Alphanumeric Characters and Meanings

The following 32 non-alphanumeric characters have special meaning in the bash shell depending on context. The Context Key below is used to cross-reference the context under which each character has special meaning. See GNU Bash Manual for more complete information.

Symbol	Name(s)	Context
`	backtick	I
~	tilde	M
!	exclamation, bang	O, S
@	ampersand, at symbol	H, O
#	number, pound, sharp, hash	B, H
$	dollar symbol	H, I, L, O, Q, S
%	percent	J, H, U
^	caret	H, J
&	ampersand, and symbol	D, J
*	asterisk, star	J, H, L, O
(	open parenthesis	H, J, S
)	close parenthesis	H, J, S
_	underscore	(no special meaning)
–	dash, minus, hyphen	J, M, O, S, U
+	plus	J, O, P, U
=	equal	J, Q, R, S
\|	pipe, vertical bar	D, J
\	backslash	I, T
/	forward slash	J, H, M
{	open brace, curly bracket	F, H, S
}	close brace, curly bracket	D, H, L, O, S
[	open bracket	D, H, L, O, S
]	close bracket	D, H, L, O, S
“	quote, double quote	A, P, S, T
‘	apostrophe, single quote	A, O, P, S, T
:	colon	C, F, H, S, T
;	semi-colon	E, S
?	question mark	O
<	less than	D, N
>	greater than	D, N
.	period, dot	C, M
,	comma	J

Context Key

quoting
comments
command shortcuts
redirection
compound commands
brace expansion
tilde expansion
parameter and variable expansion
command substitution
arithmetic expansion
word splitting
filename expansion
directories
process substitution
pattern matching
command options
environment
variables
expessions
escape sequences
job control

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