Harley Hahn's Guide to Unix and Linux

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Appendix D...

The ASCII Code

Before the 1990s, the character encoding used by Unix (and most computer systems) was the ASCII CODE, often referred to as ASCII. The name stands for "American Standard Code for Information Interchange".

The ASCII code was created in 1967. It specifies a 7-bit pattern for every character, 128 in all. These bit patterns range from 0000000 (0 in decimal) to 1111111 (127 in decimal). For this reason, the 128 ASCII characters are numbered from 0 to 127.

The 128 characters that comprise the ASCII code consist of 33 "control characters" and 95 "printable characters". The control characters are discussed in see Chapter 7. The printable characters, shown below, are the 52 letters of the alphabet (26 uppercase, 26 lowercase), 10 numbers, 32 punctuation symbols, and the space character (listed first below):

!"#$%&'()*+,-./0123456789:;<=>? @ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_ 'abcdefghijklmnopqrstuvwxyz{|}~

As a convenience, most Unix systems have a reference page showing the ASCII code to allow you to look at it quickly whenever you want. Unfortunately, the ASCII reference page is not standardized, so the way in which you display it depends on which system you are using. You can see the details in Figure 19-1 or Figure 20-5.

For reference, the tables below contain the 128 characters of the ASCII code along with their decimal (base 10), hexadecimal (base 16), octal (base 8), and binary (base 2) equivalents. For a discussion of the binary, octal, and hexadecimal number systems see Chapter 21.

Character	Decimal	Hex	Octal	Binary
	0	00	000	0000 0000	(null)
Ctrl-A	1	01	001	0000 0001
Ctrl-B	2	02	002	0000 0010
Ctrl-C	3	03	003	0000 0011
Ctrl-D	4	04	004	0000 0100
Ctrl-E	5	05	005	0000 0101
Ctrl-F	6	06	006	0000 0110
Ctrl-G	7	07	007	0000 0111	(beep)
Ctrl-H	8	08	010	0000 1000	backspace
Ctrl-I	9	09	011	0000 1001	tab
Ctrl-J	10	0A	012	0000 1010
Ctrl-K	11	0B	013	0000 1011
Ctrl-L	12	0C	014	0000 1100
Ctrl-M	13	0D	015	0000 1101	return
Ctrl-N	14	0E	016	0000 1110
Ctrl-O	15	0F	017	0000 1111
Ctrl-P	16	10	020	0001 0000
Ctrl-Q	17	11	021	0001 0001
Ctrl-R	18	12	022	0001 0010
Ctrl-S	19	13	023	0001 0011
Ctrl-T	10	14	024	0001 0100
Ctrl-U	21	15	025	0001 0101
Ctrl-V	22	16	026	0001 0110
Ctrl-W	23	17	027	0001 0111
Ctrl-X	24	18	020	0001 1000
Ctrl-Y	25	19	021	0001 1001
Ctrl-Z	26	1A	022	0001 1010
Ctrl-[	27	1B	023	0001 1011	escape
Ctrl-\	28	1C	024	0001 1100
Ctrl-]	29	1D	025	0001 1101
Ctrl-^	30	1E	026	0001 1110
Ctrl-_	31	1F	027	0001 1111

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Character	Decimal	Hex	Octal	Binary
(space)	32	20	040	0010 0000	space
!	33	21	041	0010 0001	(exclamation mark)
"	34	22	042	0010 0010	(double quote)
#	35	23	043	0010 0011	(number sign)
$	36	24	044	0010 0100	(dollar sign)
%	37	25	045	0010 0101	(percent)
&	38	26	046	0010 0110	(ampersand)
'	39	27	047	0010 0111	(single quote)
(	40	28	050	0010 1000	(left parenthesis)
)	41	29	051	0010 1001	(right parenthesis)
*	42	2A	052	0010 1010	(asterisk)
+	43	2B	053	0010 1011	(plus)
,	44	2C	054	0010 1100	(comma)
-	45	2D	055	0010 1101	(minus/hyphen)
.	46	2E	056	0010 1110	(period)
/	47	2F	057	0010 1111	(slash)
0	48	30	060	0011 0000
1	49	31	061	0011 0001
2	50	32	062	0011 0010
3	51	33	063	0011 0011
4	52	34	064	0011 0100
5	53	35	065	0011 0101
6	54	36	066	0011 0110
7	55	37	067	0011 0111
8	56	38	070	0011 1000
9	57	39	071	0011 1001
:	58	3A	072	0011 1010	(colon)
;	59	3B	073	0011 1011	(semicolon)
<	60	3C	074	0011 1100	(less than)
=	61	3D	075	0011 1101	(equals)
>	62	3E	076	0011 1110	(greater than)
?	63	3F	077	0011 1111	(question mark)

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Character	Decimal	Hex	Octal	Binary
@	64	40	100	0100 0000	(at sign)
A	65	41	101	0100 0001
B	66	42	102	0100 0010
C	67	43	103	0100 0011
D	68	44	104	0100 0100
E	69	45	105	0100 0101
F	70	46	106	0100 0110
G	71	47	107	0100 0111
H	72	48	110	0100 1000
I	73	49	111	0100 1001
J	74	4A	112	0100 1010
K	75	4B	113	0100 1011
L	76	4C	114	0100 1100
M	77	4D	115	0100 1101
N	78	4E	116	0100 1110
O	79	4F	117	0100 1111
P	80	50	120	0101 0000
Q	81	51	121	0101 0001
R	82	52	122	0101 0010
S	83	53	123	0101 0011
T	84	54	124	0101 0100
U	85	55	125	0101 0101
V	86	56	126	0101 0110
W	87	57	127	0101 0111
X	88	58	130	0101 1000
Y	89	59	131	0101 1001
Z	90	5A	132	0101 1010	(left square bracket)
[	91	5B	133	0101 1011	(backslash)
\	92	5C	134	0101 1100	(right square bracket)
]	93	5D	135	0101 1101	(circumflex)
^	94	5E	136	0101 1110	(underscore)
_	95	5F	137	0101 1111

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Character	Decimal	Hex	Octal	Binary
`	96	60	140	0110 0000	(back quote)
a	97	61	141	0110 0001
b	98	62	142	0110 0010
c	99	63	143	0110 0011
d	100	64	144	0110 0100
e	101	65	145	0110 0101
f	102	66	146	0110 0110
g	103	67	147	0110 0111
h	104	68	150	0110 1000
i	105	69	151	0110 1001
j	106	6A	152	0110 1010
k	107	6B	153	0110 1011
l	108	6C	154	0110 1100
m	109	6D	155	0110 1101
n	110	6E	156	0110 1110
o	111	6F	157	0110 1111
p	112	70	160	0111 0000
q	113	71	161	0111 0001
r	114	72	162	0111 0010
s	115	73	163	0111 0011
t	116	74	164	0111 0100
u	117	75	165	0111 0101
v	118	76	166	0111 0110
w	119	77	167	0111 0111
x	120	78	170	0111 1000
y	121	79	171	0111 1001
z	122	7A	172	0111 1010
{	123	7B	173	0111 1011	(left brace bracket)
\|	124	7C	174	0111 1100	(vertical bar)
}	125	7D	175	0111 1101	(right brace bracket)
~	126	7E	176	0111 1110	(tilde)
	127	7F	177	0111 1111	del

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Jump to Appendix E
What to Do If You Forget the Root Password

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