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 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 necessary. 

There are two other commands:

[?/]w value
Write the two-byte ­value to the addressed location. 

[?/]W value
Write the four-byte ­value to the addressed location. 

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 justify. 

Plan 9  —  June 29, 2000