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src/BNF
151 строка5 KB
Christos Zoulas
A little more grammar from Reuben Thomas
24 окт 2007, 00:00
24 окт 2007, 00:007674a7a
This is a first attempt to document the grammar used by magic(5), with
hopes of eventually incorporating something like this into the manpage.

Note: Currently, the parser varies slightly from this, but only in
very minor ways, e.g., the strflags maybe separated by '/' characters
and at most one strcount is allowed; likewise for regflags.

------------------------------------------------------------------------
magic = 1*query

query = line *( 1*level line )

level = ">"		;; Increment the level by 1.
			;; The first line of a query is at level 0.

line = offset HWS type HWS test HWS message EOL

------------------------------------------------------------------------
offset = absoffset | reloffset | indoffset
			;; The offset in the file at which to apply
			;; the <test>.

absoffset = NUMBER	;; An absolute offset from the start of the file.

reloffset = "&" NUMBER	;; The offset relative to the last match offset
			;; at one level up.
			;; Not allowed at level == 0.

indoffset = indoff | relindoff

indoff = "(" offset1 [ "." size ] [ op disp ] ")"
			;; Read the file at <offset1> of width <size>.
			;; If size is not specified, assume a long.
			;; If <op> is given, then preform that
			;; operation on the result and the <disp>.

offset1 = absoffset | reloffset

size = byte | leshort | beshort | lelong | belong | melong

byte = "B" | "b" | "C" | "c"	;; A one-byte value.
leshort = "s" | "h"		;; A two-byte little-endian value.
beshort = "S" | "H"		;; A two-byte big-endian value.
lelong = "l"			;; A four-byte little-endian value.
belong = "L"			;; A four-byte big-endian value.
melong = "m"			;; A four-byte middle-endian value.

op = [ invert ] ( "+" | "-" | "*" | "/" | "%" | "&" | "|" | "^" )

invert = "~"		;; Flip the bits on result of the <op>.

disp =  NUMBER | memvalue

memvalue = "(" NUMBER ")"
			;; NUMBER is interpreted as an absolute or
			;; relative offset matching that of <offset1>.
			;; Read the file at the resulting offset with
			;; the same size as <offset1>

relindoff = "&" indoff	;; add <indoff> to the last match offset at
			;; one level up.

------------------------------------------------------------------------
type = [ unsigned ] ( numeric | strtype | default )

unsigned = "u"		;; The value is unsigned.
			;; This affects the sign extension of numeric
			;; types and the '<' and '>' compares.  It is
			;; intended for numeric types, but allowed on
			;; all types.

numeric = ( numtype | datatype ) [ nummask ]

numtype = byte | short | long | quad

byte = "byte"
short = "short" | "beshort" | "leshort"
long = "long" | "lelong" | "belong" | "melong"
quad = "quad" | "lequad" | "bequad"

datetype = udate32 | ldate32 | udate64 | ldate64

udate32 = "date" | "bedate" | "ledate" | "medate"	;; UTC dates
ldate32 = "ldate" | "beldate" | "leldate" | "meldate"	;; local dates
udate64 = "qdate" | "leqdate" | "beqdate"		;; UTC dates
ldate64 = "qldate" | "leqldate" | "beqldate"		;; local dates

nummask = op NUMBER

strtype = regex | search | string8 | string16

regex = "regex" [ "/" 1*regflag ]

regflag = "c" | "s" | linecnt

linecnt = NUMBER	;; The number of lines to search.  If this
			;; is missing or zero, the rest of the
			;; file is searched.

search = "string" [ "/" 1*srchflag ]

srchflag = strflag | srchcnt

srchcnt = NUMBER	;; The number of search tries.  If this
			;; is missing or zero, the rest of the
			;; file is searched.

string8 = ( "string" | "pstring" ) [ "/" 1*strflag ]

strflag = "b" | "B" | "c" | "C"

string16 = "bestring16" | "lestring16"

default = "default"	;; This is intended to be used with the
			;; <truetest> ("x" below).  It is matched if
			;; there has been no previous match at its
			;; level or none since the last default at
			;; that level.  It is useful for implementing
			;; switch-like and if/else constructions.

------------------------------------------------------------------------
test = numtest | strtest | truetest
				;; Test to preform on <type> read from file.

numtest = [ compare ] NUMBER	;; If compare is missing, "=" is assumed.

strtest = [ compare ] STRING	;; If compare is missing, "=" is assumed.
				;; Note: If the STRING begins with a <compare>
				;; character, the <compare> field cannot be
				;; omitted.

compare = "=" | "!" | "<" | ">" | "&" | "^"

truetest = "x"		;; This always returns true.
			;; To test for the string "x" use "=x".

------------------------------------------------------------------------
message = [ nospflag ] ( STRING | FMT_STRING )
			;; Message to print if test result is true.

nospflag = %x08 | "\\b"	;; Do not insert a space before the message.
			;; By default, messages are separated by a " ".

------------------------------------------------------------------------
HWS = <horizontal white space>
EOL = <end of line marker>
NUMBER = <C-style unsigned number>
STRING = <C-style string without delimiting quotes>
FMTSTR = <printf format string with exactly one % construct>

------------------------------------------------------------------------