1 .\" $File: magic.man,v 1.81 2014/03/08 17:28:08 christos Exp $
5 .\" install as magic.4 on USG, magic.5 on V7, Berkeley and Linux systems.
8 .Nd file command's magic pattern file
10 This manual page documents the format of the magic file as
13 command, version __VERSION__.
16 command identifies the type of a file using,
18 a test for whether the file contains certain
19 .Dq "magic patterns" .
22 specifies what patterns are to be tested for, what message or
23 MIME type to print if a particular pattern is found,
24 and additional information to extract from the file.
26 Each line of the file specifies a test to be performed.
27 A test compares the data starting at a particular offset
28 in the file with a byte value, a string or a numeric value.
29 If the test succeeds, a message is printed.
30 The line consists of the following fields:
31 .Bl -tag -width ".Dv message"
33 A number specifying the offset, in bytes, into the file of the data
34 which is to be tested.
36 The type of the data to be tested.
37 The possible values are:
38 .Bl -tag -width ".Dv lestring16"
42 A two-byte value in this machine's native byte order.
44 A four-byte value in this machine's native byte order.
46 An eight-byte value in this machine's native byte order.
48 A 32-bit single precision IEEE floating point number in this machine's native byte order.
50 A 64-bit double precision IEEE floating point number in this machine's native byte order.
53 The string type specification can be optionally followed
57 flag compacts whitespace in the target, which must
58 contain at least one whitespace character.
61 consecutive blanks, the target needs at least
63 consecutive blanks to match.
66 flag treats every blank in the magic as an optional blank.
69 flag specifies case insensitive matching: lower case
70 characters in the magic match both lower and upper case characters in the
71 target, whereas upper case characters in the magic only match upper case
72 characters in the target.
75 flag specifies case insensitive matching: upper case
76 characters in the magic match both lower and upper case characters in the
77 target, whereas lower case characters in the magic only match upper case
78 characters in the target.
79 To do a complete case insensitive match, specify both
85 flag forces the test to be done for text files, while the
87 flag forces the test to be done for binary files.
90 flag causes the string to be trimmed, i.e. leading and trailing whitespace
91 is deleted before the string is printed.
93 A Pascal-style string where the first byte/short/int is interpreted as the
95 The length defaults to byte and can be specified as a modifier.
96 The following modifiers are supported:
97 .Bl -tag -compact -width B
99 A byte length (default).
101 A 2 byte big endian length.
103 A 2 byte big little length.
105 A 4 byte big endian length.
107 A 4 byte big little length.
109 The length includes itself in its count.
111 The string is not NUL terminated.
113 is used rather than the more
116 because this type of length is a feature of the JPEG
119 A four-byte value interpreted as a UNIX date.
121 A eight-byte value interpreted as a UNIX date.
123 A four-byte value interpreted as a UNIX-style date, but interpreted as
124 local time rather than UTC.
126 An eight-byte value interpreted as a UNIX-style date, but interpreted as
127 local time rather than UTC.
129 An eight-byte value interpreted as a Windows-style date.
131 A 32-bit ID3 length in big-endian byte order.
133 A two-byte value in big-endian byte order.
135 A four-byte value in big-endian byte order.
137 An eight-byte value in big-endian byte order.
139 A 32-bit single precision IEEE floating point number in big-endian byte order.
141 A 64-bit double precision IEEE floating point number in big-endian byte order.
143 A four-byte value in big-endian byte order,
144 interpreted as a Unix date.
146 An eight-byte value in big-endian byte order,
147 interpreted as a Unix date.
149 A four-byte value in big-endian byte order,
150 interpreted as a UNIX-style date, but interpreted as local time rather
153 An eight-byte value in big-endian byte order,
154 interpreted as a UNIX-style date, but interpreted as local time rather
157 An eight-byte value in big-endian byte order,
158 interpreted as a Windows-style date.
160 A two-byte unicode (UCS16) string in big-endian byte order.
162 A 32-bit ID3 length in little-endian byte order.
164 A two-byte value in little-endian byte order.
166 A four-byte value in little-endian byte order.
168 An eight-byte value in little-endian byte order.
170 A 32-bit single precision IEEE floating point number in little-endian byte order.
172 A 64-bit double precision IEEE floating point number in little-endian byte order.
174 A four-byte value in little-endian byte order,
175 interpreted as a UNIX date.
177 An eight-byte value in little-endian byte order,
178 interpreted as a UNIX date.
180 A four-byte value in little-endian byte order,
181 interpreted as a UNIX-style date, but interpreted as local time rather
184 An eight-byte value in little-endian byte order,
185 interpreted as a UNIX-style date, but interpreted as local time rather
188 An eight-byte value in little-endian byte order,
189 interpreted as a Windows-style date.
191 A two-byte unicode (UCS16) string in little-endian byte order.
193 A four-byte value in middle-endian (PDP-11) byte order.
195 A four-byte value in middle-endian (PDP-11) byte order,
196 interpreted as a UNIX date.
198 A four-byte value in middle-endian (PDP-11) byte order,
199 interpreted as a UNIX-style date, but interpreted as local time rather
202 Starting at the given offset, consult the magic database again.
206 magic instance that can be called from another
208 magic entry, like a subroutine call.
209 Named instance direct magic offsets are relative to the offset of the
210 previous matched entry, but indirect offsets are relative to the beginning
211 of the file as usual.
212 Named magic entries always match.
214 Recursively call the named magic starting from the current offset.
215 If the name of the referenced begins with a
217 then the endianness of the magic is switched; if the magic mentioned
223 This is useful to avoid duplicating the rules for different endianness.
225 A regular expression match in extended POSIX regular expression syntax
227 Regular expressions can take exponential time to process, and their
228 performance is hard to predict, so their use is discouraged.
229 When used in production environments, their performance
230 should be carefully checked.
231 The type specification can be optionally followed by
235 flag makes the match case insensitive, while the
237 flag update the offset to the start offset of the match, rather than the end.
238 The regular expression is tested against line
243 Line endings are assumed to be in the machine's native format.
247 match the beginning and end of individual lines, respectively,
248 not beginning and end of file.
250 A literal string search starting at the given offset.
251 The same modifier flags can be used as for string patterns.
252 The search expression must contain the range in the form
254 that is the number of positions at which the match will be
255 attempted, starting from the start offset.
257 searching larger binary expressions with variable offsets, using
259 escapes for special characters.
260 The order of modifier and number is not relevant.
262 This is intended to be used with the test
264 (which is always true) and it has no type.
265 It matches when no other test at that continuation level has matched before.
266 Clearing that matched tests for a continuation level, can be done using the
270 This test is always true and clears the match flag for that continuation level.
271 It is intended to be used with the
276 For compatibility with the Single
278 Standard, the type specifiers
324 and the type specifier
328 In addition, the type specifier
332 and the type specifier
337 Each top-level magic pattern (see below for an explanation of levels)
338 is classified as text or binary according to the types used.
343 are classified as text tests, unless non-printable characters are used
345 All other tests are classified as binary.
347 pattern is considered to be a test text when all its patterns are text
348 patterns; otherwise, it is considered to be a binary pattern.
350 matching a file, binary patterns are tried first; if no match is
351 found, and the file looks like text, then its encoding is determined
352 and the text patterns are tried.
354 The numeric types may optionally be followed by
357 to specify that the value is to be AND'ed with the
358 numeric value before any comparisons are done.
361 to the type indicates that ordered comparisons should be unsigned.
363 The value to be compared with the value from the file.
366 is specified in C form; if it is a string, it is specified as a C string
367 with the usual escapes permitted (e.g. \en for new-line).
370 may be preceded by a character indicating the operation to be performed.
373 to specify that the value from the file must equal the specified value,
375 to specify that the value from the file must be less than the specified
378 to specify that the value from the file must be greater than the specified
381 to specify that the value from the file must have set all of the bits
382 that are set in the specified value,
384 to specify that the value from the file must have clear any of the bits
385 that are set in the specified value, or
387 the value specified after is negated before tested.
389 to specify that any value will match.
390 If the character is omitted, it is assumed to be
397 don't work with floats and doubles.
400 specifies that the line matches if the test does
404 Numeric values are specified in C form; e.g.
412 For string values, the string from the
413 file must match the specified string.
421 can be applied to strings.
422 The length used for matching is that of the string argument
424 This means that a line can match any non-empty string (usually used to
425 then print the string), with
427 (because all non-empty strings are greater than the empty string).
429 Dates are treated as numerical values in the respective internal
434 always evaluates to true.
436 The message to be printed if the comparison succeeds.
437 If the string contains a
439 format specification, the value from the file (with any specified masking
440 performed) is printed using the message as the format string.
441 If the string begins with
443 the message printed is the remainder of the string with no whitespace
444 added before it: multiple matches are normally separated by a single
448 An APPLE 4+4 character APPLE creator and type can be specified as:
449 .Bd -literal -offset indent
453 A MIME type is given on a separate line, which must be the next
454 non-blank or comment line after the magic line that identifies the
455 file type, and has the following format:
456 .Bd -literal -offset indent
460 i.e. the literal string
462 followed by the MIME type.
464 An optional strength can be supplied on a separate line which refers to
465 the current magic description using the following format:
466 .Bd -literal -offset indent
480 is a constant between 0 and 255.
481 This constant is applied using the specified operand
482 to the currently computed default magic strength.
484 Some file formats contain additional information which is to be printed
485 along with the file type or need additional tests to determine the true
487 These additional tests are introduced by one or more
489 characters preceding the offset.
492 on the line indicates the level of the test; a line with no
494 at the beginning is considered to be at level 0.
495 Tests are arranged in a tree-like hierarchy:
496 if the test on a line at level
498 succeeds, all following tests at level
500 are performed, and the messages printed if the tests succeed, until a line
504 For more complex files, one can use empty messages to get just the
505 "if/then" effect, in the following way:
506 .Bd -literal -offset indent
508 \*[Gt]0x18 leshort \*[Lt]0x40 MS-DOS executable
509 \*[Gt]0x18 leshort \*[Gt]0x3f extended PC executable (e.g., MS Windows)
512 Offsets do not need to be constant, but can also be read from the file
514 If the first character following the last
518 then the string after the parenthesis is interpreted as an indirect offset.
519 That means that the number after the parenthesis is used as an offset in
521 The value at that offset is read, and is used again as an offset
523 Indirect offsets are of the form:
524 .Em (( x [.[bislBISL]][+\-][ y ]) .
527 is used as an offset in the file.
528 A byte, id3 length, short or long is read at that offset depending on the
531 The capitalized types interpret the number as a big endian
532 value, whereas the small letter versions interpret the number as a little
536 type interprets the number as a middle endian (PDP-11) value.
537 To that number the value of
539 is added and the result is used as an offset in the file.
540 The default type if one is not specified is long.
542 That way variable length structures can be examined:
543 .Bd -literal -offset indent
544 # MS Windows executables are also valid MS-DOS executables
546 \*[Gt]0x18 leshort \*[Lt]0x40 MZ executable (MS-DOS)
547 # skip the whole block below if it is not an extended executable
548 \*[Gt]0x18 leshort \*[Gt]0x3f
549 \*[Gt]\*[Gt](0x3c.l) string PE\e0\e0 PE executable (MS-Windows)
550 \*[Gt]\*[Gt](0x3c.l) string LX\e0\e0 LX executable (OS/2)
553 This strategy of examining has a drawback: You must make sure that
554 you eventually print something, or users may get empty output (like, when
555 there is neither PE\e0\e0 nor LE\e0\e0 in the above example)
557 If this indirect offset cannot be used directly, simple calculations are
559 .Em [+-*/%\*[Am]|^]number
560 inside parentheses allows one to modify
561 the value read from the file before it is used as an offset:
562 .Bd -literal -offset indent
563 # MS Windows executables are also valid MS-DOS executables
565 # sometimes, the value at 0x18 is less that 0x40 but there's still an
566 # extended executable, simply appended to the file
567 \*[Gt]0x18 leshort \*[Lt]0x40
568 \*[Gt]\*[Gt](4.s*512) leshort 0x014c COFF executable (MS-DOS, DJGPP)
569 \*[Gt]\*[Gt](4.s*512) leshort !0x014c MZ executable (MS-DOS)
572 Sometimes you do not know the exact offset as this depends on the length or
573 position (when indirection was used before) of preceding fields.
574 You can specify an offset relative to the end of the last up-level
577 as a prefix to the offset:
578 .Bd -literal -offset indent
580 \*[Gt]0x18 leshort \*[Gt]0x3f
581 \*[Gt]\*[Gt](0x3c.l) string PE\e0\e0 PE executable (MS-Windows)
582 # immediately following the PE signature is the CPU type
583 \*[Gt]\*[Gt]\*[Gt]\*[Am]0 leshort 0x14c for Intel 80386
584 \*[Gt]\*[Gt]\*[Gt]\*[Am]0 leshort 0x184 for DEC Alpha
587 Indirect and relative offsets can be combined:
588 .Bd -literal -offset indent
590 \*[Gt]0x18 leshort \*[Lt]0x40
591 \*[Gt]\*[Gt](4.s*512) leshort !0x014c MZ executable (MS-DOS)
592 # if it's not COFF, go back 512 bytes and add the offset taken
593 # from byte 2/3, which is yet another way of finding the start
594 # of the extended executable
595 \*[Gt]\*[Gt]\*[Gt]\*[Am](2.s-514) string LE LE executable (MS Windows VxD driver)
598 Or the other way around:
599 .Bd -literal -offset indent
601 \*[Gt]0x18 leshort \*[Gt]0x3f
602 \*[Gt]\*[Gt](0x3c.l) string LE\e0\e0 LE executable (MS-Windows)
603 # at offset 0x80 (-4, since relative offsets start at the end
604 # of the up-level match) inside the LE header, we find the absolute
605 # offset to the code area, where we look for a specific signature
606 \*[Gt]\*[Gt]\*[Gt](\*[Am]0x7c.l+0x26) string UPX \eb, UPX compressed
610 .Bd -literal -offset indent
612 \*[Gt]0x18 leshort \*[Gt]0x3f
613 \*[Gt]\*[Gt](0x3c.l) string LE\e0\e0 LE executable (MS-Windows)
614 # at offset 0x58 inside the LE header, we find the relative offset
615 # to a data area where we look for a specific signature
616 \*[Gt]\*[Gt]\*[Gt]\*[Am](\*[Am]0x54.l-3) string UNACE \eb, ACE self-extracting archive
619 If you have to deal with offset/length pairs in your file, even the
620 second value in a parenthesized expression can be taken from the file itself,
621 using another set of parentheses.
622 Note that this additional indirect offset is always relative to the
623 start of the main indirect offset.
624 .Bd -literal -offset indent
626 \*[Gt]0x18 leshort \*[Gt]0x3f
627 \*[Gt]\*[Gt](0x3c.l) string PE\e0\e0 PE executable (MS-Windows)
628 # search for the PE section called ".idata"...
629 \*[Gt]\*[Gt]\*[Gt]\*[Am]0xf4 search/0x140 .idata
630 # ...and go to the end of it, calculated from start+length;
631 # these are located 14 and 10 bytes after the section name
632 \*[Gt]\*[Gt]\*[Gt]\*[Gt](\*[Am]0xe.l+(-4)) string PK\e3\e4 \eb, ZIP self-extracting archive
635 If you have a list of known avalues at a particular continuation level,
636 and you want to provide a switch-like default case:
637 .Bd -literal -offset indent
638 # clear that continuation level match
640 \*[Gt]18 lelong 1 one
641 \*[Gt]18 lelong 2 two
643 # print default match
644 \*[Gt]\*[Gt]18 lelong x unmatched 0x%x
647 .Xr file __CSECTION__
648 \- the command that reads this file.
659 do not depend on the length of the C data types
663 on the platform, even though the Single
665 Specification implies that they do. However, as OS X Mountain Lion has
668 Specification validation suite, and supplies a version of
669 .Xr file __CSECTION__
670 in which they do not depend on the sizes of the C data types and that is
671 built for a 64-bit environment in which
673 is 8 bytes rather than 4 bytes, presumably the validation suite does not
674 test whether, for example
676 refers to an item with the same size as the C data type
678 There should probably be
690 and specified-byte-order variants of them,
691 to make it clearer that those types have specified widths.
693 .\" From: guy@sun.uucp (Guy Harris)
694 .\" Newsgroups: net.bugs.usg
695 .\" Subject: /etc/magic's format isn't well documented
696 .\" Message-ID: <2752@sun.uucp>
697 .\" Date: 3 Sep 85 08:19:07 GMT
698 .\" Organization: Sun Microsystems, Inc.
701 .\" Here's a manual page for the format accepted by the "file" made by adding
702 .\" the changes I posted to the S5R2 version.
704 .\" Modified for Ian Darwin's version of the file command.