MAGIC(5) File Formats Manual MAGIC(5)
NAME
magic — file command's magic pattern file
DESCRIPTION
This manual page documents the format of magic files as used by the
file(1) command, version 5.45. The file(1) command identifies the type
of a file using, among other tests, a test for whether the file con-
tains certain “magic patterns”. The database of these “magic patterns”
is usually located in a binary file in /usr/share/misc/magic.mgc or a
directory of source text magic pattern fragment files in
/usr/share/misc/magic. The database specifies what patterns are to be
tested for, what message or MIME type to print if a particular pattern
is found, and additional information to extract from the file.
The format of the source fragment files that are used to build this
database is as follows: Each line of a fragment file specifies a test
to be performed. A test compares the data starting at a particular
offset in the file with a byte value, a string or a numeric value. If
the test succeeds, a message is printed. The line consists of the fol-
lowing fields:
offset A number specifying the offset (in bytes) into the file of the
data which is to be tested. This offset can be a negative
number if it is:
• The first direct offset of the magic entry (at continua-
tion level 0), in which case it is interpreted an offset
from end end of the file going backwards. This works only
when a file descriptor to the file is available and it is
a regular file.
• A continuation offset relative to the end of the last up-
level field (&).
type The type of the data to be tested. The possible values are:
byte A one-byte value.
short A two-byte value in this machine's native byte or-
der.
long A four-byte value in this machine's native byte
order.
quad An eight-byte value in this machine's native byte
order.
float A 32-bit single precision IEEE floating point num-
ber in this machine's native byte order.
double A 64-bit double precision IEEE floating point num-
ber in this machine's native byte order.
string A string of bytes. The string type specification
can be optionally followed by a /<width> option
and optionally followed by a set of flags /[bC-
cftTtWw]*. The width limits the number of charac-
ters to be copied. Zero means all characters.
The following flags are supported:
b Force binary file test.
C Use upper case insensitive matching: upper
case characters in the magic match both
lower and upper case characters in the tar-
get, whereas lower case characters in the
magic only match upper case characters in
the target.
c Use lower case insensitive matching: lower
case characters in the magic match both
lower and upper case characters in the tar-
get, whereas upper case characters in the
magic only match upper case characters in
the target. To do a complete case insensi-
tive match, specify both “c” and “C”.
f Require that the matched string is a full
word, not a partial word match.
T Trim the string, i.e. leading and trailing
whitespace
t Force text file test.
W Compact whitespace in the target, which
must contain at least one whitespace char-
acter. If the magic has n consecutive
blanks, the target needs at least n consec-
utive blanks to match.
w Treat every blank in the magic as an op-
tional blank. is deleted before the string
is printed.
pstring A Pascal-style string where the first
byte/short/int is interpreted as the unsigned
length. The length defaults to byte and can be
specified as a modifier. The following modifiers
are supported:
B A byte length (default).
H A 2 byte big endian length.
h A 2 byte little endian length.
L A 4 byte big endian length.
l A 4 byte little endian length.
J The length includes itself in its count.
The string is not NUL terminated. “J” is used
rather than the more valuable “I” because this
type of length is a feature of the JPEG format.
date A four-byte value interpreted as a UNIX date.
qdate An eight-byte value interpreted as a UNIX date.
ldate A four-byte value interpreted as a UNIX-style
date, but interpreted as local time rather than
UTC.
qldate An eight-byte value interpreted as a UNIX-style
date, but interpreted as local time rather than
UTC.
qwdate An eight-byte value interpreted as a Windows-style
date.
beid3 A 32-bit ID3 length in big-endian byte order.
beshort A two-byte value in big-endian byte order.
belong A four-byte value in big-endian byte order.
bequad An eight-byte value in big-endian byte order.
befloat A 32-bit single precision IEEE floating point num-
ber in big-endian byte order.
bedouble A 64-bit double precision IEEE floating point num-
ber in big-endian byte order.
bedate A four-byte value in big-endian byte order, inter-
preted as a Unix date.
beqdate An eight-byte value in big-endian byte order, in-
terpreted as a Unix date.
beldate A four-byte value in big-endian byte order, inter-
preted as a UNIX-style date, but interpreted as
local time rather than UTC.
beqldate An eight-byte value in big-endian byte order, in-
terpreted as a UNIX-style date, but interpreted as
local time rather than UTC.
beqwdate An eight-byte value in big-endian byte order, in-
terpreted as a Windows-style date.
bestring16 A two-byte unicode (UCS16) string in big-endian
byte order.
leid3 A 32-bit ID3 length in little-endian byte order.
leshort A two-byte value in little-endian byte order.
lelong A four-byte value in little-endian byte order.
lequad An eight-byte value in little-endian byte order.
lefloat A 32-bit single precision IEEE floating point num-
ber in little-endian byte order.
ledouble A 64-bit double precision IEEE floating point num-
ber in little-endian byte order.
ledate A four-byte value in little-endian byte order, in-
terpreted as a UNIX date.
leqdate An eight-byte value in little-endian byte order,
interpreted as a UNIX date.
leldate A four-byte value in little-endian byte order, in-
terpreted as a UNIX-style date, but interpreted as
local time rather than UTC.
leqldate An eight-byte value in little-endian byte order,
interpreted as a UNIX-style date, but interpreted
as local time rather than UTC.
leqwdate An eight-byte value in little-endian byte order,
interpreted as a Windows-style date.
lestring16 A two-byte unicode (UCS16) string in little-endian
byte order.
melong A four-byte value in middle-endian (PDP-11) byte
order.
medate A four-byte value in middle-endian (PDP-11) byte
order, interpreted as a UNIX date.
meldate A four-byte value in middle-endian (PDP-11) byte
order, interpreted as a UNIX-style date, but in-
terpreted as local time rather than UTC.
indirect Starting at the given offset, consult the magic
database again. The offset of the indirect magic
is by default absolute in the file, but one can
specify /r to indicate that the offset is relative
from the beginning of the entry.
name Define a “named” magic instance that can be called
from another use magic entry, like a subroutine
call. Named instance direct magic offsets are
relative to the offset of the previous matched en-
try, but indirect offsets are relative to the be-
ginning of the file as usual. Named magic entries
always match.
use Recursively call the named magic starting from the
current offset. If the name of the referenced be-
gins with a ^ then the endianness of the magic is
switched; if the magic mentioned leshort for exam-
ple, it is treated as beshort and vice versa.
This is useful to avoid duplicating the rules for
different endianness.
regex A regular expression match in extended POSIX regu-
lar expression syntax (like egrep). Regular ex-
pressions can take exponential time to process,
and their performance is hard to predict, so their
use is discouraged. When used in production envi-
ronments, their performance should be carefully
checked. The size of the string to search should
also be limited by specifying /<length>, to avoid
performance issues scanning long files. The type
specification can also be optionally followed by
/[c][s][l]. The “c” flag makes the match case in-
sensitive, while the “s” flag update the offset to
the start offset of the match, rather than the
end. The “l” modifier, changes the limit of
length to mean number of lines instead of a byte
count. Lines are delimited by the platforms na-
tive line delimiter. When a line count is speci-
fied, an implicit byte count also computed assum-
ing each line is 80 characters long. If neither a
byte or line count is specified, the search is
limited automatically to 8KiB. ^ and $ match the
beginning and end of individual lines, respec-
tively, not beginning and end of file.
search A literal string search starting at the given off-
set. The same modifier flags can be used as for
string patterns. The search expression must con-
tain the range in the form /number, that is the
number of positions at which the match will be at-
tempted, starting from the start offset. This is
suitable for searching larger binary expressions
with variable offsets, using \ escapes for special
characters. The order of modifier and number is
not relevant.
default This is intended to be used with the test x (which
is always true) and it has no type. It matches
when no other test at that continuation level has
matched before. Clearing that matched tests for a
continuation level, can be done using the clear
test.
clear This test is always true and clears the match flag
for that continuation level. It is intended to be
used with the default test.
der Parse the file as a DER Certificate file. The
test field is used as a der type that needs to be
matched. The DER types are: eoc, bool, int,
bit_str, octet_str, null, obj_id, obj_desc, ext,
real, enum, embed, utf8_str, rel_oid, time, res2,
seq, set, num_str, prt_str, t61_str, vid_str,
ia5_str, utc_time, gen_time, gr_str, vis_str,
gen_str, univ_str, char_str, bmp_str, date, tod,
datetime, duration, oid-iri, rel-oid-iri. These
types can be followed by an optional numeric size,
which indicates the field width in bytes.
guid A Globally Unique Identifier, parsed and printed
as XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX. It's
format is a string.
offset This is a quad value indicating the current offset
of the file. It can be used to determine the size
of the file or the magic buffer. For example the
magic entries:
-0 offset x this file is %lld bytes
-0 offset <=100 must be more than 100 \
bytes and is only %lld
octal A string representing an octal number.
For compatibility with the Single Unix Standard, the type specifiers dC
and d1 are equivalent to byte, the type specifiers uC and u1 are equiv-
alent to ubyte, the type specifiers dS and d2 are equivalent to short,
the type specifiers uS and u2 are equivalent to ushort, the type speci-
fiers dI, dL, and d4 are equivalent to long, the type specifiers uI,
uL, and u4 are equivalent to ulong, the type specifier d8 is equivalent
to quad, the type specifier u8 is equivalent to uquad, and the type
specifier s is equivalent to string. In addition, the type specifier
dQ is equivalent to quad and the type specifier uQ is equivalent to
uquad.
Each top-level magic pattern (see below for an explanation of levels)
is classified as text or binary according to the types used. Types
“regex” and “search” are classified as text tests, unless non-printable
characters are used in the pattern. All other tests are classified as
binary. A top-level pattern is considered to be a test text when all
its patterns are text patterns; otherwise, it is considered to be a bi-
nary pattern. When matching a file, binary patterns are tried first;
if no match is found, and the file looks like text, then its encoding
is determined and the text patterns are tried.
The numeric types may optionally be followed by & and a numeric value,
to specify that the value is to be AND'ed with the numeric value before
any comparisons are done. Prepending a u to the type indicates that
ordered comparisons should be unsigned.
The value to be compared with the value from the file. If the type is
numeric, this value is specified in C form; if it is a string, it is
specified as a C string with the usual escapes permitted (e.g. \n for
new-line).
Numeric values may be preceded by a character indicating the operation
to be performed. It may be =, to specify that the value from the file
must equal the specified value, <, to specify that the value from the
file must be less than the specified value, >, to specify that the
value from the file must be greater than the specified value, &, to
specify that the value from the file must have set all of the bits that
are set in the specified value, ^, to specify that the value from the
file must have clear any of the bits that are set in the specified
value, or ~, the value specified after is negated before tested. x, to
specify that any value will match. If the character is omitted, it is
assumed to be =. Operators &, ^, and ~ don't work with floats and dou-
bles. The operator ! specifies that the line matches if the test does
not succeed.
Numeric values are specified in C form; e.g. 13 is decimal, 013 is oc-
tal, and 0x13 is hexadecimal.
Numeric operations are not performed on date types, instead the numeric
value is interpreted as an offset.
For string values, the string from the file must match the specified
string. The operators =, < and > (but not &) can be applied to
strings. The length used for matching is that of the string argument
in the magic file. This means that a line can match any non-empty
string (usually used to then print the string), with >\0 (because all
non-empty strings are greater than the empty string).
Dates are treated as numerical values in the respective internal repre-
sentation.
The special test x always evaluates to true.
The message to be printed if the comparison succeeds. If the string
contains a printf(3) format specification, the value from the file
(with any specified masking performed) is printed using the message as
the format string. If the string begins with “\b”, the message printed
is the remainder of the string with no whitespace added before it: mul-
tiple matches are normally separated by a single space.
An APPLE 4+4 character APPLE creator and type can be specified as:
!:apple CREATYPE
A slash-separated list of commonly found filename extensions can be spec-
ified as:
!:ext ext[/ext...]
i.e. the literal string “!:ext” followed by a slash-separated list of
commonly found extensions; for example for JPEG images:
!:ext jpeg/jpg/jpe/jfif
A MIME type is given on a separate line, which must be the next non-blank
or comment line after the magic line that identifies the file type, and
has the following format:
!:mime MIMETYPE
i.e. the literal string “!:mime” followed by the MIME type.
An optional strength can be supplied on a separate line which refers to
the current magic description using the following format:
!:strength OP VALUE
The operand OP can be: +, -, *, or / and VALUE is a constant between 0
and 255. This constant is applied using the specified operand to the
currently computed default magic strength.
Some file formats contain additional information which is to be printed
along with the file type or need additional tests to determine the true
file type. These additional tests are introduced by one or more > char-
acters preceding the offset. The number of > on the line indicates the
level of the test; a line with no > at the beginning is considered to be
at level 0. Tests are arranged in a tree-like hierarchy: if the test on
a line at level n succeeds, all following tests at level n+1 are per-
formed, and the messages printed if the tests succeed, until a line with
level n (or less) appears. For more complex files, one can use empty
messages to get just the "if/then" effect, in the following way:
0 string MZ
>0x18 leshort <0x40 MS-DOS executable
>0x18 leshort >0x3f extended PC executable (e.g., MS Windows)
Offsets do not need to be constant, but can also be read from the file
being examined. If the first character following the last > is a ( then
the string after the parenthesis is interpreted as an indirect offset.
That means that the number after the parenthesis is used as an offset in
the file. The value at that offset is read, and is used again as an off-
set in the file. Indirect offsets are of the form: (( x
[[.,][bBcCeEfFgGhHiIlmsSqQ]][+-][ y ]). The value of x is used as an
offset in the file. A byte, id3 length, short or long is read at that
offset depending on the [bBcCeEfFgGhHiIlmsSqQ] type specifier. The value
is treated as signed if “”, is specified or unsigned if “”. is speci-
fied. The capitalized types interpret the number as a big endian value,
whereas the small letter versions interpret the number as a little endian
value; the m type interprets the number as a middle endian (PDP-11)
value. To that number the value of y is added and the result is used as
an offset in the file. The default type if one is not specified is long.
The following types are recognized:
Type Sy Mnemonic Sy Endian Sy Size
bcBc Byte/Char N/A 1
efg Double Little 8
EFG Double Big 8
hs Half/Short Little 2
HS Half/Short Big 2
i ID3 Little 4
I ID3 Big 4
m Middle Middle 4
o Octal Textual Variable
q Quad Little 8
Q Quad Big 8
That way variable length structures can be examined:
# MS Windows executables are also valid MS-DOS executables
0 string MZ
>0x18 leshort <0x40 MZ executable (MS-DOS)
# skip the whole block below if it is not an extended executable
>0x18 leshort >0x3f
>>(0x3c.l) string PE\0\0 PE executable (MS-Windows)
>>(0x3c.l) string LX\0\0 LX executable (OS/2)
This strategy of examining has a drawback: you must make sure that you
eventually print something, or users may get empty output (such as when
there is neither PE\0\0 nor LE\0\0 in the above example).
If this indirect offset cannot be used directly, simple calculations are
possible: appending [+-*/%&|^]number inside parentheses allows one to
modify the value read from the file before it is used as an offset:
# MS Windows executables are also valid MS-DOS executables
0 string MZ
# sometimes, the value at 0x18 is less that 0x40 but there's still an
# extended executable, simply appended to the file
>0x18 leshort <0x40
>>(4.s*512) leshort 0x014c COFF executable (MS-DOS, DJGPP)
>>(4.s*512) leshort !0x014c MZ executable (MS-DOS)
Sometimes you do not know the exact offset as this depends on the length
or position (when indirection was used before) of preceding fields. You
can specify an offset relative to the end of the last up-level field us-
ing ‘&’ as a prefix to the offset:
0 string MZ
>0x18 leshort >0x3f
>>(0x3c.l) string PE\0\0 PE executable (MS-Windows)
# immediately following the PE signature is the CPU type
>>>&0 leshort 0x14c for Intel 80386
>>>&0 leshort 0x184 for DEC Alpha
Indirect and relative offsets can be combined:
0 string MZ
>0x18 leshort <0x40
>>(4.s*512) leshort !0x014c MZ executable (MS-DOS)
# if it's not COFF, go back 512 bytes and add the offset taken
# from byte 2/3, which is yet another way of finding the start
# of the extended executable
>>>&(2.s-514) string LE LE executable (MS Windows VxD driver)
Or the other way around:
0 string MZ
>0x18 leshort >0x3f
>>(0x3c.l) string LE\0\0 LE executable (MS-Windows)
# at offset 0x80 (-4, since relative offsets start at the end
# of the up-level match) inside the LE header, we find the absolute
# offset to the code area, where we look for a specific signature
>>>(&0x7c.l+0x26) string UPX \b, UPX compressed
Or even both!
0 string MZ
>0x18 leshort >0x3f
>>(0x3c.l) string LE\0\0 LE executable (MS-Windows)
# at offset 0x58 inside the LE header, we find the relative offset
# to a data area where we look for a specific signature
>>>&(&0x54.l-3) string UNACE \b, ACE self-extracting archive
If you have to deal with offset/length pairs in your file, even the sec-
ond value in a parenthesized expression can be taken from the file it-
self, using another set of parentheses. Note that this additional indi-
rect offset is always relative to the start of the main indirect offset.
0 string MZ
>0x18 leshort >0x3f
>>(0x3c.l) string PE\0\0 PE executable (MS-Windows)
# search for the PE section called ".idata"...
>>>&0xf4 search/0x140 .idata
# ...and go to the end of it, calculated from start+length;
# these are located 14 and 10 bytes after the section name
>>>>(&0xe.l+(-4)) string PK\3\4 \b, ZIP self-extracting archive
If you have a list of known values at a particular continuation level,
and you want to provide a switch-like default case:
# clear that continuation level match
>18 clear
>18 lelong 1 one
>18 lelong 2 two
>18 default x
# print default match
>>18 lelong x unmatched 0x%x
SEE ALSO
file(1) - the command that reads this file.
BUGS
The formats long, belong, lelong, melong, short, beshort, and leshort
do not depend on the length of the C data types short and long on the
platform, even though the Single Unix Specification implies that they
do. However, as OS X Mountain Lion has passed the Single Unix Specifi-
cation validation suite, and supplies a version of file(1) in which
they do not depend on the sizes of the C data types and that is built
for a 64-bit environment in which long is 8 bytes rather than 4 bytes,
presumably the validation suite does not test whether, for example long
refers to an item with the same size as the C data type long. There
should probably be type names int8, uint8, int16, uint16, int32,
uint32, int64, and uint64, and specified-byte-order variants of them,
to make it clearer that those types have specified widths.
Debian Arpil 18, 2023 MAGIC(5)
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