MAGIC(5) FreeBSD 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 "5.47". The file(1) command identifies the type
of a file using, among other tests, a test for whether the file contains
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 following
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:
o The first direct offset of the magic entry (at continuation
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.
o A continuation offset relative to the end of the last up-
level field (&).
If the offset starts with the symbol "+", then all offsets are
interpreted as from the beginning of the file (the default).
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
order.
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 number
in this machine's native byte order.
double A 64-bit double precision IEEE floating point number
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 [bCcftTtWw]*.
Slash characters can be used to separate options for
readability. The width limits the number of
characters 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 target,
whereas lower case characters in the magic
only match upper case characters in the
target. (not valid for regex)
c Use lower case insensitive matching: lower
case characters in the magic match both lower
and upper case characters in the target,
whereas upper case characters in the magic
only match upper case characters in the
target. (not valid for regex) To do a
complete case insensitive match, specify both
"c" and "C".
f Require that the matched string is a full
word, not a partial word match.
s Don't include the match length in the offset
computation. (only valid for search and
regex)
T Trim the string, i.e. leading and trailing
whitespace is deleted before the string is
printed.
t Force text file test.
W Compact whitespace in the target, which must
contain at least one whitespace character.
(not valid for regex) If the magic has n
consecutive blanks, the target needs at least
n consecutive blanks to match.
w Treat every blank in the magic as an optional
blank. (not valid for regex)
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.
msdosdate A two-byte value interpreted as FAT/DOS-style date.
msdostime A two-byte value interpreted as FAT/DOS-style time.
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 number
in big-endian byte order.
bedouble A 64-bit double precision IEEE floating point number
in big-endian byte order.
bedate A four-byte value in big-endian byte order,
interpreted as a Unix date.
beqdate An eight-byte value in big-endian byte order,
interpreted as a Unix date.
beldate A four-byte value in big-endian byte order,
interpreted as a UNIX-style date, but interpreted as
local time rather than UTC.
beqldate An eight-byte value in big-endian byte order,
interpreted as a UNIX-style date, but interpreted as
local time rather than UTC.
beqwdate An eight-byte value in big-endian byte order,
interpreted as a Windows-style date.
bemsdosdate
A two-byte value in big-endian byte order,
interpreted as FAT/DOS-style date.
bemsdostime
A two-byte value in big-endian byte order,
interpreted as FAT/DOS-style time.
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 number
in little-endian byte order.
ledouble A 64-bit double precision IEEE floating point number
in little-endian byte order.
ledate A four-byte value in little-endian byte order,
interpreted 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,
interpreted 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.
lemsdosdate
A two-byte value in little-endian byte order,
interpreted as FAT/DOS-style date.
lemsdostime
A two-byte value in little-endian byte order,
interpreted as FAT/DOS-style time.
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
interpreted 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
entry, but indirect offsets are relative to the
beginning of the file as usual. Named magic entries
return true if there was a match in the evaluation
of the entry, or if there was a previous existing
match.
use Recursively call the named magic starting from the
current offset. If the name of the referenced
begins with a ^ then the endianness of the magic is
switched; if the magic mentioned leshort for
example, 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 regular
expression syntax (like egrep). Regular expressions
can take exponential time to process, and their
performance is hard to predict, so their use is
discouraged. When used in production environments,
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 insensitive, 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 native line delimiter. When a line count
is specified, an implicit byte count also computed
assuming 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,
respectively, not beginning and end of file.
search A literal string search starting at the given
offset. The same modifier flags can be used as for
string patterns. The search expression must contain
the range in the form /number, that is the number of
positions at which the match will be attempted,
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 equivalent to ubyte, the type specifiers dS and d2
are equivalent to short, the type specifiers uS and u2 are
equivalent to ushort, the type specifiers 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 binary 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 an operand and a
numeric value, to specify that the value is to be modified
according to the operand and the numeric value before any
comparisons are done. The following operands are supported: &,
|, ^, +, -, *, /, %. Prepending a u to the type indicates that
ordered comparisons should be unsigned.
test 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 doubles. 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 octal, 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
representation.
The special test x always evaluates to true.
message 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: multiple 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
specified 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 >
characters 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
performed, 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 uleshort <0x40 MS-DOS executable
>0x18 uleshort >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
offset in the file. Indirect offsets are of the form: (x
[[.,][bBcCeEfFgGhHiIlmosSqQ]][+-][ 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 [bBcCeEfFgGhHiIlLmsSqQ] type specifier. The
value is treated as signed if "," is specified or unsigned if "." is
specified. 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
l Long Little 4
L Long 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 uleshort <0x40 MZ executable (MS-DOS)
# skip the whole block below if it is not an extended executable
>0x18 uleshort >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 uleshort <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
using `&' as a prefix to the offset:
0 string MZ
>0x18 uleshort >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 0x8664 for x86-64
>>>&0 leshort 0x184 for DEC Alpha
Indirect and relative offsets can be combined:
0 string MZ
>0x18 uleshort <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 uleshort >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 uleshort >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
second value in a parenthesized expression can be taken from the file
itself, using another set of parentheses. Note that this additional
indirect offset is always relative to the start of the main indirect
offset.
0 string MZ
>0x18 uleshort >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 x
>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 Specification
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.
FreeBSD 15.1-STABLE-HBSD November 24, 2025 MAGIC(5)