1MAGIC(5) BSD File Formats Manual MAGIC(5)
2
4 magic — file command's magic pattern file
5
7 This manual page documents the format of the magic file as used by the
8 file(1) command, version 5.04. The file(1) command identifies the type
9 of a file using, among other tests, a test for whether the file contains
10 certain “magic patterns”. The file /usr/share/misc/magic specifies what
11 patterns are to be tested for, what message or MIME type to print if a
12 particular pattern is found, and additional information to extract from
13 the file.
14 Each line of the file specifies a test to be performed. A test compares
16 the data starting at a particular offset in the file with a byte value, a
17 string or a numeric value. If the test succeeds, a message is printed.
18 The line consists of the following fields:
19 offset A number specifying the offset, in bytes, into the file of the
21 data which is to be tested.
22 type The type of the data to be tested. The possible values are:
24 byte A one-byte value.
26 short A two-byte value in this machine's native byte
28 order.
29 long A four-byte value in this machine's native byte
31 order.
32 quad An eight-byte value in this machine's native byte
34 order.
35 float A 32-bit single precision IEEE floating point number
37 in this machine's native byte order.
38 double A 64-bit double precision IEEE floating point number
40 in this machine's native byte order.
41 string A string of bytes. The string type specification
43 can be optionally followed by /[Bbc]*. The “B” flag
44 compacts whitespace in the target, which must con‐
45 tain at least one whitespace character. If the
46 magic has n consecutive blanks, the target needs at
47 least n consecutive blanks to match. The “b” flag
48 treats every blank in the target as an optional
49 blank. Finally the “c” flag, specifies case insen‐
50 sitive matching: lowercase characters in the magic
51 match both lower and upper case characters in the
52 target, whereas upper case characters in the magic
53 only match uppercase characters in the target.
54 pstring A Pascal-style string where the first byte is inter‐
56 preted as the unsigned length. The string is not
57 NUL terminated.
58 date A four-byte value interpreted as a UNIX date.
60 qdate A eight-byte value interpreted as a UNIX date.
62 ldate A four-byte value interpreted as a UNIX-style date,
64 but interpreted as local time rather than UTC.
65 qldate An eight-byte value interpreted as a UNIX-style
67 date, but interpreted as local time rather than UTC.
68 beid3 A 32-bit ID3 length in big-endian byte order.
70 beshort A two-byte value in big-endian byte order.
72 belong A four-byte value in big-endian byte order.
74 bequad An eight-byte value in big-endian byte order.
76 befloat A 32-bit single precision IEEE floating point number
78 in big-endian byte order.
79 bedouble A 64-bit double precision IEEE floating point number
81 in big-endian byte order.
82 bedate A four-byte value in big-endian byte order, inter‐
84 preted as a Unix date.
85 beqdate An eight-byte value in big-endian byte order, inter‐
87 preted as a Unix date.
88 beldate A four-byte value in big-endian byte order, inter‐
90 preted as a UNIX-style date, but interpreted as
91 local time rather than UTC.
92 beqldate An eight-byte value in big-endian byte order, inter‐
94 preted as a UNIX-style date, but interpreted as
95 local time rather than UTC.
96 bestring16 A two-byte unicode (UCS16) string in big-endian byte
98 order.
99 leid3 A 32-bit ID3 length in little-endian byte order.
101 leshort A two-byte value in little-endian byte order.
103 lelong A four-byte value in little-endian byte order.
105 lequad An eight-byte value in little-endian byte order.
107 lefloat A 32-bit single precision IEEE floating point number
109 in little-endian byte order.
110 ledouble A 64-bit double precision IEEE floating point number
112 in little-endian byte order.
113 ledate A four-byte value in little-endian byte order,
115 interpreted as a UNIX date.
116 leqdate An eight-byte value in little-endian byte order,
118 interpreted as a UNIX date.
119 leldate A four-byte value in little-endian byte order,
121 interpreted as a UNIX-style date, but interpreted as
122 local time rather than UTC.
123 leqldate An eight-byte value in little-endian byte order,
125 interpreted as a UNIX-style date, but interpreted as
126 local time rather than UTC.
127 lestring16 A two-byte unicode (UCS16) string in little-endian
129 byte order.
130 melong A four-byte value in middle-endian (PDP-11) byte
132 order.
133 medate A four-byte value in middle-endian (PDP-11) byte
135 order, interpreted as a UNIX date.
136 meldate A four-byte value in middle-endian (PDP-11) byte
138 order, interpreted as a UNIX-style date, but inter‐
139 preted as local time rather than UTC.
140 indirect Starting at the given offset, consult the magic
142 database again.
143 regex A regular expression match in extended POSIX regular
145 expression syntax (like egrep). Regular expressions
146 can take exponential time to process, and their per‐
147 formance is hard to predict, so their use is dis‐
148 couraged. When used in production environments,
149 their performance should be carefully checked. The
150 type specification can be optionally followed by
151 /[c][s]. The “c” flag makes the match case insensi‐
152 tive, while the “s” flag update the offset to the
153 start offset of the match, rather than the end. The
154 regular expression is tested against line N + 1
155 onwards, where N is the given offset. Line endings
156 are assumed to be in the machine's native format. ^
157 and $ match the beginning and end of individual
158 lines, respectively, not beginning and end of file.
159 search A literal string search starting at the given off‐
161 set. The same modifier flags can be used as for
162 string patterns. The modifier flags (if any) must be
163 followed by /number the range, that is, the number
164 of positions at which the match will be attempted,
165 starting from the start offset. This is suitable for
166 searching larger binary expressions with variable
167 offsets, using \ escapes for special characters. The
168 offset works as for regex.
169 default This is intended to be used with the test x (which
171 is always true) and a message that is to be used if
172 there are no other matches.
173 Each top-level magic pattern (see below for an explanation of
175 levels) is classified as text or binary according to the types
176 used. Types “regex” and “search” are classified as text tests,
177 unless non-printable characters are used in the pattern. All
178 other tests are classified as binary. A top-level pattern is
179 considered to be a test text when all its patterns are text pat‐
180 terns; otherwise, it is considered to be a binary pattern. When
181 matching a file, binary patterns are tried first; if no match is
182 found, and the file looks like text, then its encoding is deter‐
183 mined and the text patterns are tried.
184 The numeric types may optionally be followed by & and a numeric
186 value, to specify that the value is to be AND'ed with the
187 numeric value before any comparisons are done. Prepending a u
188 to the type indicates that ordered comparisons should be
189 unsigned.
190 test The value to be compared with the value from the file. If the
192 type is numeric, this value is specified in C form; if it is a
193 string, it is specified as a C string with the usual escapes
194 permitted (e.g. \n for new-line).
195 Numeric values may be preceded by a character indicating the
197 operation to be performed. It may be =, to specify that the
198 value from the file must equal the specified value, <, to spec‐
199 ify that the value from the file must be less than the specified
200 value, >, to specify that the value from the file must be
201 greater than the specified value, &, to specify that the value
202 from the file must have set all of the bits that are set in the
203 specified value, ^, to specify that the value from the file must
204 have clear any of the bits that are set in the specified value,
205 or ~, the value specified after is negated before tested. x, to
206 specify that any value will match. If the character is omitted,
207 it is assumed to be =. Operators &, ^, and ~ don't work with
208 floats and doubles. The operator ! specifies that the line
209 matches if the test does not succeed.
210 Numeric values are specified in C form; e.g. 13 is decimal, 013
212 is octal, and 0x13 is hexadecimal.
213 For string values, the string from the file must match the spec‐
215 ified string. The operators =, < and > (but not &) can be
216 applied to strings. The length used for matching is that of the
217 string argument in the magic file. This means that a line can
218 match any non-empty string (usually used to then print the
219 string), with >\0 (because all non-empty strings are greater
220 than the empty string).
221 The special test x always evaluates to true. message The mes‐
223 sage to be printed if the comparison succeeds. If the string
224 contains a printf(3) format specification, the value from the
225 file (with any specified masking performed) is printed using the
226 message as the format string. If the string begins with “\b”,
227 the message printed is the remainder of the string with no
228 whitespace added before it: multiple matches are normally sepa‐
229 rated by a single space.
230 An APPLE 4+4 character APPLE creator and type can be specified as:
232 !:apple CREATYPE
234 A MIME type is given on a separate line, which must be the next non-blank
236 or comment line after the magic line that identifies the file type, and
237 has the following format:
238 !:mime MIMETYPE
240 i.e. the literal string “!:mime” followed by the MIME type.
242 An optional strength can be supplied on a separate line which refers to
244 the current magic description using the following format:
245 !:strength OP VALUE
247 The operand OP can be: +, -, *, or / and VALUE is a constant between 0
249 and 255. This constant is applied using the specified operand to the
250 currently computed default magic strength.
251 Some file formats contain additional information which is to be printed
253 along with the file type or need additional tests to determine the true
254 file type. These additional tests are introduced by one or more > char‐
255 acters preceding the offset. The number of > on the line indicates the
256 level of the test; a line with no > at the beginning is considered to be
257 at level 0. Tests are arranged in a tree-like hierarchy: If a the test
258 on a line at level n succeeds, all following tests at level n+1 are per‐
259 formed, and the messages printed if the tests succeed, until a line with
260 level n (or less) appears. For more complex files, one can use empty
261 messages to get just the "if/then" effect, in the following way:
262 0 string MZ
264 >0x18 leshort <0x40 MS-DOS executable
265 >0x18 leshort >0x3f extended PC executable (e.g., MS Windows)
266 Offsets do not need to be constant, but can also be read from the file
268 being examined. If the first character following the last > is a ( then
269 the string after the parenthesis is interpreted as an indirect offset.
270 That means that the number after the parenthesis is used as an offset in
271 the file. The value at that offset is read, and is used again as an off‐
272 set in the file. Indirect offsets are of the form: (( x
273 [.[bislBISL]][+-][ y ]). The value of x is used as an offset in the
274 file. A byte, id3 length, short or long is read at that offset depending
275 on the [bislBISLm] type specifier. The capitalized types interpret the
276 number as a big endian value, whereas the small letter versions interpret
277 the number as a little endian value; the m type interprets the number as
278 a middle endian (PDP-11) value. To that number the value of y is added
279 and the result is used as an offset in the file. The default type if one
280 is not specified is long.
281 That way variable length structures can be examined:
283 # MS Windows executables are also valid MS-DOS executables
285 0 string MZ
286 >0x18 leshort <0x40 MZ executable (MS-DOS)
287 # skip the whole block below if it is not an extended executable
288 >0x18 leshort >0x3f
289 >>(0x3c.l) string PE\0\0 PE executable (MS-Windows)
290 >>(0x3c.l) string LX\0\0 LX executable (OS/2)
291 This strategy of examining has a drawback: You must make sure that you
293 eventually print something, or users may get empty output (like, when
294 there is neither PE\0\0 nor LE\0\0 in the above example)
295 If this indirect offset cannot be used directly, simple calculations are
297 possible: appending [+-*/%&|^]number inside parentheses allows one to
298 modify the value read from the file before it is used as an offset:
299 # MS Windows executables are also valid MS-DOS executables
301 0 string MZ
302 # sometimes, the value at 0x18 is less that 0x40 but there's still an
303 # extended executable, simply appended to the file
304 >0x18 leshort <0x40
305 >>(4.s*512) leshort 0x014c COFF executable (MS-DOS, DJGPP)
306 >>(4.s*512) leshort !0x014c MZ executable (MS-DOS)
307 Sometimes you do not know the exact offset as this depends on the length
309 or position (when indirection was used before) of preceding fields. You
310 can specify an offset relative to the end of the last up-level field
311 using ‘&’ as a prefix to the offset:
312 0 string MZ
314 >0x18 leshort >0x3f
315 >>(0x3c.l) string PE\0\0 PE executable (MS-Windows)
316 # immediately following the PE signature is the CPU type
317 >>>&0 leshort 0x14c for Intel 80386
318 >>>&0 leshort 0x184 for DEC Alpha
319 Indirect and relative offsets can be combined:
321 0 string MZ
323 >0x18 leshort <0x40
324 >>(4.s*512) leshort !0x014c MZ executable (MS-DOS)
325 # if it's not COFF, go back 512 bytes and add the offset taken
326 # from byte 2/3, which is yet another way of finding the start
327 # of the extended executable
328 >>>&(2.s-514) string LE LE executable (MS Windows VxD driver)
329 Or the other way around:
331 0 string MZ
333 >0x18 leshort >0x3f
334 >>(0x3c.l) string LE\0\0 LE executable (MS-Windows)
335 # at offset 0x80 (-4, since relative offsets start at the end
336 # of the up-level match) inside the LE header, we find the absolute
337 # offset to the code area, where we look for a specific signature
338 >>>(&0x7c.l+0x26) string UPX \b, UPX compressed
339 Or even both!
341 0 string MZ
343 >0x18 leshort >0x3f
344 >>(0x3c.l) string LE\0\0 LE executable (MS-Windows)
345 # at offset 0x58 inside the LE header, we find the relative offset
346 # to a data area where we look for a specific signature
347 >>>&(&0x54.l-3) string UNACE \b, ACE self-extracting archive
348 Finally, if you have to deal with offset/length pairs in your file, even
350 the second value in a parenthesized expression can be taken from the file
351 itself, using another set of parentheses. Note that this additional
352 indirect offset is always relative to the start of the main indirect off‐
353 set.
354 0 string MZ
356 >0x18 leshort >0x3f
357 >>(0x3c.l) string PE\0\0 PE executable (MS-Windows)
358 # search for the PE section called ".idata"...
359 >>>&0xf4 search/0x140 .idata
360 # ...and go to the end of it, calculated from start+length;
361 # these are located 14 and 10 bytes after the section name
362 >>>>(&0xe.l+(-4)) string PK\3\4 \b, ZIP self-extracting archive
363
365 file(1) - the command that reads this file.
366
368 The formats long, belong, lelong, melong, short, beshort, leshort, date,
369 bedate, medate, ledate, beldate, leldate, and meldate are system-depen‐
370 dent; perhaps they should be specified as a number of bytes (2B, 4B,
371 etc), since the files being recognized typically come from a system on
372 which the lengths are invariant.
373BSD August 30, 2008 BSD