MDB(1) MDB(1)
NAME
mdb - binary file editor
SYNOPSIS
mdb [ -w ] file [ command ]
DESCRIPTION
Mdb allows inspection of the contents of file. If the -w
option is given, then modification of the contents is also
allowed. Mdb accepts commands of the form
[address] [, count] [command]
If a command is given as an argument, then mdb will execute
that command, otherwise it will read and execute commands
from the standard input. If address is present then the
current position, called `dot', is set to address. Initially
dot is set to 0. Command is repeated count times with dot
advancing between repetitions. The default count is 1.
Address and count are expressions.
Expressions
Expressions take one of the following forms:
. The value of dot.
+ The value of dot.
^ The value of dot.
" The value of the last address typed.
integer A number, decimal by default. A `0' prefix causes
it to be interpreted as octal; a `0x' prefix
causes it to be interpreted as hexadecimal.
(expr) The value of the expression expr.
Operators
e1+e2
Integer addition.
e1-e2
Integer subtraction.
e1*e2
Integer multiplication.
e1%e2
Page 1 Plan 9 (printed 12/22/24)
MDB(1) MDB(1)
Integer division. (N.B. not modulus).
e1|e2
Bitwise disjunction.
e1&e2
Bitwise conjunction.
Commands
Commands have the following syntax:
/f Locations starting at address in file are printed
according to the format f.
?f Same as `/'.
=f The value of address itself is printed according to the
format f.
A format consists of one or more characters that specify a
style of printing. Each format fetches some data, prints it,
and if the command is not `=', advances dot by the amount of
data fetched. All data is assumed to be held in little-
endian form (least significant byte first).
o Print a two-byte integer in octal.
O Print a four-byte integer in octal.
d Print a two-byte integer in decimal.
D Print a four-byte integer in decimal.
u Print a two-byte integer in unsigned decimal.
U Print a four-byte integer in unsigned decimal.
b Print a single byte in hexadecimal.
x Print a two-byte integer in hexadecimal.
X Print a four-byte integer in hexadecimal.
n Prints a newline. No data is fetched.
+ Increments dot by 1. No data is printed.
- Decrements dot by 1. No data is printed.
^ Increments dot by the size of the last format
encountered.
c Prints a single byte as a character.
C Prints a single byte as a printable character,
converting it to backslash escaped hex if neces-
sary.
There are two other commands:
[?/]w value
Write the two-byte value to the addressed loca-
tion.
[?/]W value
Write the four-byte value to the addressed loca-
tion.
Page 2 Plan 9 (printed 12/22/24)
MDB(1) MDB(1)
SOURCE
/appl/cmd/mdb.b
BUGS
Most of the more useful features of mdb's antecedent db are
unimplemented.
It is not possible to print strings or UTF-8 characters.
As there is no ``native'' word format in Inferno, the
assumption that all words are little-endian is hard to jus-
tify.
Page 3 Plan 9 (printed 12/22/24)