1 .\" $File: magic.man,v 1.84 2014/06/03 19:01:34 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 size of the string to search should also be limited by specifying
233 to avoid performance issues scanning long files.
234 The type specification can also be optionally followed by
238 flag makes the match case insensitive, while the
240 flag update the offset to the start offset of the match, rather than the end.
243 modifier, changes the limit of length to mean number of lines instead of a
245 Lines are delimited by the platforms native line delimiter.
246 When a line count is specified, an implicit byte count also computed assuming
247 each line is 80 characters long.
248 If neither a byte or line count is specified, the search is limited automatically
253 match the beginning and end of individual lines, respectively,
254 not beginning and end of file.
256 A literal string search starting at the given offset.
257 The same modifier flags can be used as for string patterns.
258 The search expression must contain the range in the form
260 that is the number of positions at which the match will be
261 attempted, starting from the start offset.
263 searching larger binary expressions with variable offsets, using
265 escapes for special characters.
266 The order of modifier and number is not relevant.
268 This is intended to be used with the test
270 (which is always true) and it has no type.
271 It matches when no other test at that continuation level has matched before.
272 Clearing that matched tests for a continuation level, can be done using the
276 This test is always true and clears the match flag for that continuation level.
277 It is intended to be used with the
282 For compatibility with the Single
284 Standard, the type specifiers
330 and the type specifier
334 In addition, the type specifier
338 and the type specifier
343 Each top-level magic pattern (see below for an explanation of levels)
344 is classified as text or binary according to the types used.
349 are classified as text tests, unless non-printable characters are used
351 All other tests are classified as binary.
353 pattern is considered to be a test text when all its patterns are text
354 patterns; otherwise, it is considered to be a binary pattern.
356 matching a file, binary patterns are tried first; if no match is
357 found, and the file looks like text, then its encoding is determined
358 and the text patterns are tried.
360 The numeric types may optionally be followed by
363 to specify that the value is to be AND'ed with the
364 numeric value before any comparisons are done.
367 to the type indicates that ordered comparisons should be unsigned.
369 The value to be compared with the value from the file.
372 is specified in C form; if it is a string, it is specified as a C string
373 with the usual escapes permitted (e.g. \en for new-line).
376 may be preceded by a character indicating the operation to be performed.
379 to specify that the value from the file must equal the specified value,
381 to specify that the value from the file must be less than the specified
384 to specify that the value from the file must be greater than the specified
387 to specify that the value from the file must have set all of the bits
388 that are set in the specified value,
390 to specify that the value from the file must have clear any of the bits
391 that are set in the specified value, or
393 the value specified after is negated before tested.
395 to specify that any value will match.
396 If the character is omitted, it is assumed to be
403 don't work with floats and doubles.
406 specifies that the line matches if the test does
410 Numeric values are specified in C form; e.g.
418 Numeric operations are not performed on date types, instead the numeric
419 value is interpreted as an offset.
421 For string values, the string from the
422 file must match the specified string.
430 can be applied to strings.
431 The length used for matching is that of the string argument
433 This means that a line can match any non-empty string (usually used to
434 then print the string), with
436 (because all non-empty strings are greater than the empty string).
438 Dates are treated as numerical values in the respective internal
443 always evaluates to true.
445 The message to be printed if the comparison succeeds.
446 If the string contains a
448 format specification, the value from the file (with any specified masking
449 performed) is printed using the message as the format string.
450 If the string begins with
452 the message printed is the remainder of the string with no whitespace
453 added before it: multiple matches are normally separated by a single
457 An APPLE 4+4 character APPLE creator and type can be specified as:
458 .Bd -literal -offset indent
462 A MIME type is given on a separate line, which must be the next
463 non-blank or comment line after the magic line that identifies the
464 file type, and has the following format:
465 .Bd -literal -offset indent
469 i.e. the literal string
471 followed by the MIME type.
473 An optional strength can be supplied on a separate line which refers to
474 the current magic description using the following format:
475 .Bd -literal -offset indent
489 is a constant between 0 and 255.
490 This constant is applied using the specified operand
491 to the currently computed default magic strength.
493 Some file formats contain additional information which is to be printed
494 along with the file type or need additional tests to determine the true
496 These additional tests are introduced by one or more
498 characters preceding the offset.
501 on the line indicates the level of the test; a line with no
503 at the beginning is considered to be at level 0.
504 Tests are arranged in a tree-like hierarchy:
505 if the test on a line at level
507 succeeds, all following tests at level
509 are performed, and the messages printed if the tests succeed, until a line
513 For more complex files, one can use empty messages to get just the
514 "if/then" effect, in the following way:
515 .Bd -literal -offset indent
517 \*[Gt]0x18 leshort \*[Lt]0x40 MS-DOS executable
518 \*[Gt]0x18 leshort \*[Gt]0x3f extended PC executable (e.g., MS Windows)
521 Offsets do not need to be constant, but can also be read from the file
523 If the first character following the last
527 then the string after the parenthesis is interpreted as an indirect offset.
528 That means that the number after the parenthesis is used as an offset in
530 The value at that offset is read, and is used again as an offset
532 Indirect offsets are of the form:
533 .Em (( x [.[bislBISL]][+\-][ y ]) .
536 is used as an offset in the file.
537 A byte, id3 length, short or long is read at that offset depending on the
540 The capitalized types interpret the number as a big endian
541 value, whereas the small letter versions interpret the number as a little
545 type interprets the number as a middle endian (PDP-11) value.
546 To that number the value of
548 is added and the result is used as an offset in the file.
549 The default type if one is not specified is long.
551 That way variable length structures can be examined:
552 .Bd -literal -offset indent
553 # MS Windows executables are also valid MS-DOS executables
555 \*[Gt]0x18 leshort \*[Lt]0x40 MZ executable (MS-DOS)
556 # skip the whole block below if it is not an extended executable
557 \*[Gt]0x18 leshort \*[Gt]0x3f
558 \*[Gt]\*[Gt](0x3c.l) string PE\e0\e0 PE executable (MS-Windows)
559 \*[Gt]\*[Gt](0x3c.l) string LX\e0\e0 LX executable (OS/2)
562 This strategy of examining has a drawback: You must make sure that
563 you eventually print something, or users may get empty output (like, when
564 there is neither PE\e0\e0 nor LE\e0\e0 in the above example)
566 If this indirect offset cannot be used directly, simple calculations are
568 .Em [+-*/%\*[Am]|^]number
569 inside parentheses allows one to modify
570 the value read from the file before it is used as an offset:
571 .Bd -literal -offset indent
572 # MS Windows executables are also valid MS-DOS executables
574 # sometimes, the value at 0x18 is less that 0x40 but there's still an
575 # extended executable, simply appended to the file
576 \*[Gt]0x18 leshort \*[Lt]0x40
577 \*[Gt]\*[Gt](4.s*512) leshort 0x014c COFF executable (MS-DOS, DJGPP)
578 \*[Gt]\*[Gt](4.s*512) leshort !0x014c MZ executable (MS-DOS)
581 Sometimes you do not know the exact offset as this depends on the length or
582 position (when indirection was used before) of preceding fields.
583 You can specify an offset relative to the end of the last up-level
586 as a prefix to the offset:
587 .Bd -literal -offset indent
589 \*[Gt]0x18 leshort \*[Gt]0x3f
590 \*[Gt]\*[Gt](0x3c.l) string PE\e0\e0 PE executable (MS-Windows)
591 # immediately following the PE signature is the CPU type
592 \*[Gt]\*[Gt]\*[Gt]\*[Am]0 leshort 0x14c for Intel 80386
593 \*[Gt]\*[Gt]\*[Gt]\*[Am]0 leshort 0x184 for DEC Alpha
596 Indirect and relative offsets can be combined:
597 .Bd -literal -offset indent
599 \*[Gt]0x18 leshort \*[Lt]0x40
600 \*[Gt]\*[Gt](4.s*512) leshort !0x014c MZ executable (MS-DOS)
601 # if it's not COFF, go back 512 bytes and add the offset taken
602 # from byte 2/3, which is yet another way of finding the start
603 # of the extended executable
604 \*[Gt]\*[Gt]\*[Gt]\*[Am](2.s-514) string LE LE executable (MS Windows VxD driver)
607 Or the other way around:
608 .Bd -literal -offset indent
610 \*[Gt]0x18 leshort \*[Gt]0x3f
611 \*[Gt]\*[Gt](0x3c.l) string LE\e0\e0 LE executable (MS-Windows)
612 # at offset 0x80 (-4, since relative offsets start at the end
613 # of the up-level match) inside the LE header, we find the absolute
614 # offset to the code area, where we look for a specific signature
615 \*[Gt]\*[Gt]\*[Gt](\*[Am]0x7c.l+0x26) string UPX \eb, UPX compressed
619 .Bd -literal -offset indent
621 \*[Gt]0x18 leshort \*[Gt]0x3f
622 \*[Gt]\*[Gt](0x3c.l) string LE\e0\e0 LE executable (MS-Windows)
623 # at offset 0x58 inside the LE header, we find the relative offset
624 # to a data area where we look for a specific signature
625 \*[Gt]\*[Gt]\*[Gt]\*[Am](\*[Am]0x54.l-3) string UNACE \eb, ACE self-extracting archive
628 If you have to deal with offset/length pairs in your file, even the
629 second value in a parenthesized expression can be taken from the file itself,
630 using another set of parentheses.
631 Note that this additional indirect offset is always relative to the
632 start of the main indirect offset.
633 .Bd -literal -offset indent
635 \*[Gt]0x18 leshort \*[Gt]0x3f
636 \*[Gt]\*[Gt](0x3c.l) string PE\e0\e0 PE executable (MS-Windows)
637 # search for the PE section called ".idata"...
638 \*[Gt]\*[Gt]\*[Gt]\*[Am]0xf4 search/0x140 .idata
639 # ...and go to the end of it, calculated from start+length;
640 # these are located 14 and 10 bytes after the section name
641 \*[Gt]\*[Gt]\*[Gt]\*[Gt](\*[Am]0xe.l+(-4)) string PK\e3\e4 \eb, ZIP self-extracting archive
644 If you have a list of known avalues at a particular continuation level,
645 and you want to provide a switch-like default case:
646 .Bd -literal -offset indent
647 # clear that continuation level match
649 \*[Gt]18 lelong 1 one
650 \*[Gt]18 lelong 2 two
652 # print default match
653 \*[Gt]\*[Gt]18 lelong x unmatched 0x%x
656 .Xr file __CSECTION__
657 \- the command that reads this file.
668 do not depend on the length of the C data types
672 on the platform, even though the Single
674 Specification implies that they do. However, as OS X Mountain Lion has
677 Specification validation suite, and supplies a version of
678 .Xr file __CSECTION__
679 in which they do not depend on the sizes of the C data types and that is
680 built for a 64-bit environment in which
682 is 8 bytes rather than 4 bytes, presumably the validation suite does not
683 test whether, for example
685 refers to an item with the same size as the C data type
687 There should probably be
699 and specified-byte-order variants of them,
700 to make it clearer that those types have specified widths.
702 .\" From: guy@sun.uucp (Guy Harris)
703 .\" Newsgroups: net.bugs.usg
704 .\" Subject: /etc/magic's format isn't well documented
705 .\" Message-ID: <2752@sun.uucp>
706 .\" Date: 3 Sep 85 08:19:07 GMT
707 .\" Organization: Sun Microsystems, Inc.
710 .\" Here's a manual page for the format accepted by the "file" made by adding
711 .\" the changes I posted to the S5R2 version.
713 .\" Modified for Ian Darwin's version of the file command.