1 .\" @(#)magic.5 1.1 98/05/20 joerg
2 .TH MAGIC 5 "Public Domain"
3 .\" install as magic.4 on USG, magic.5 on V7 or Berkeley systems.
5 magic \- file command's magic number file
7 This manual page documents the format of the magic file as
10 command, version 3.22. The
12 command identifies the type of a file using,
14 a test for whether the file begins with a certain
17 .I /usr/local/etc/magic
18 specifies what magic numbers are to be tested for,
19 what message to print if a particular magic number is found,
20 and additional information to extract from the file.
22 Each line of the file specifies a test to be performed.
23 A test compares the data starting at a particular offset
24 in the file with a 1-byte, 2-byte, or 4-byte numeric value or
25 a string. If the test succeeds, a message is printed.
26 The line consists of the following fields:
27 .IP offset \w'message'u+2n
28 A number specifying the offset, in bytes, into the file of the data
29 which is to be tested.
31 The type of the data to be tested. The possible values are:
33 .IP byte \w'message'u+2n
36 A two-byte value (on most systems) in this machine's native byte order.
38 A four-byte value (on most systems) in this machine's native byte order.
42 A four-byte value interpreted as a unix date.
44 A two-byte value (on most systems) in big-endian byte order.
46 A four-byte value (on most systems) in big-endian byte order.
48 A four-byte value (on most systems) in big-endian byte order,
49 interpreted as a unix date.
51 A two-byte value (on most systems) in little-endian byte order.
53 A four-byte value (on most systems) in little-endian byte order.
55 A four-byte value (on most systems) in little-endian byte order,
56 interpreted as a unix date.
59 The numeric types may optionally be followed by
62 to specify that the value is to be AND'ed with the
63 numeric value before any comparisons are done. Prepending a
65 to the type indicates that ordered comparisons should be unsigned.
67 The value to be compared with the value from the file. If the type is
69 is specified in C form; if it is a string, it is specified as a C string
70 with the usual escapes permitted (e.g. \en for new-line).
73 may be preceded by a character indicating the operation to be performed.
76 to specify that the value from the file must equal the specified value,
78 to specify that the value from the file must be less than the specified
81 to specify that the value from the file must be greater than the specified
84 to specify that the value from the file must have set all of the bits
85 that are set in the specified value,
87 to specify that the value from the file must have clear any of the bits
88 that are set in the specified value, or
90 to specify that any value will match. If the character is omitted,
94 Numeric values are specified in C form; e.g.
102 For string values, the byte string from the
103 file must match the specified byte string.
111 can be applied to strings.
112 The length used for matching is that of the string argument
113 in the magic file. This means that a line can match any string, and
114 then presumably print that string, by doing
116 (because all strings are greater than the null string).
118 The message to be printed if the comparison succeeds. If the string
121 format specification, the value from the file (with any specified masking
122 performed) is printed using the message as the format string.
124 Some file formats contain additional information which is to be printed
125 along with the file type. A line which begins with the character
127 indicates additional tests and messages to be printed. The number of
129 on the line indicates the level of the test; a line with no
131 at the beginning is considered to be at level 0.
134 is under the control of the line at level
136 most closely preceding it in the magic file.
137 If the test on a line at level
139 succeeds, the tests specified in all the subsequent lines at level
141 are performed, and the messages printed if the tests succeed. The next
145 If the first character following the last
149 then the string after the parenthesis is interpreted as an indirect offset.
150 That means that the number after the parenthesis is used as an offset in
151 the file. The value at that offset is read, and is used again as an offset
152 in the file. Indirect offsets are of the form:
153 .BI (( x [.[bsl]][+-][ y ]).
156 is used as an offset in the file. A byte, short or long is read at that offset
159 type specifier. To that number the value of
161 is added and the result is used as an offset in the file. The default type
162 if one is not specified is long.
164 Sometimes you do not know the exact offset as this depends on the length of
165 preceding fields. You can specify an offset relative to the end of the
166 last uplevel field (of course this may only be done for sublevel tests, i.e.
169 ). Such a relative offset is specified using
171 as a prefix to the offset.
184 are system-dependent; perhaps they should be specified as a number
185 of bytes (2B, 4B, etc),
186 since the files being recognized typically come from
187 a system on which the lengths are invariant.
189 There is (currently) no support for specified-endian data to be used in
193 \- the command that reads this file.
195 .\" From: guy@sun.uucp (Guy Harris)
196 .\" Newsgroups: net.bugs.usg
197 .\" Subject: /etc/magic's format isn't well documented
198 .\" Message-ID: <2752@sun.uucp>
199 .\" Date: 3 Sep 85 08:19:07 GMT
200 .\" Organization: Sun Microsystems, Inc.
203 .\" Here's a manual page for the format accepted by the "file" made by adding
204 .\" the changes I posted to the S5R2 version.
206 .\" Modified for Ian Darwin's version of the file command.
207 .\" @(#)$Id: magic.5,v 1.2 2001/11/25 17:18:22 ysato Exp $