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MAGIC(5) BSD 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
5.41. 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 start‐
ing 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:
•• 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.
•• 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 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 na‐
tive byte order.

double A 64-bit double precision IEEE floating point number in this machine's na‐
tive byte order.

string A string of bytes. The string type specification can be optionally fol‐
lowed by /[WwcCtbTf]*. The “W” flag compacts whitespace in the target,
which must contain at least one whitespace character. If the magic has n
consecutive blanks, the target needs at least n consecutive blanks to
match. The “w” flag treats every blank in the magic as an optional blank.
The “f” flags requires that the matched string is a full word, not a par‐
tial word match. The “c” flag specifies 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. The “C” flag specifies 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. To do a complete case in‐
sensitive match, specify both “c” and “C”. The “t” flag forces the test
to be done for text files, while the “b” flag forces the test to be done
for binary files. The “T” flag causes the string to be trimmed, i.e.
leading and trailing whitespace 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 valu‐
able “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 lo‐
cal 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 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.

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.

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 off‐
set 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
always 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 care‐
fully 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 as‐
suming 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 con‐
tain 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

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 equiv‐
alent 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 & 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.

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 per‐
formed. 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 in‐
terpreted as an offset.

For string values, the string from the file must match the specified string. The op‐
erators =, < and > (but not &) can be applied to strings. The length used for match‐
ing 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 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 de‐
scription 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 in‐
troduced by one or more > characters preceding the offset. The number of > on the line indi‐
cates 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, un‐
til 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 inter‐
preted 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 [[.,][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 specified. The capitalized types interpret the num‐
ber 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 num‐
ber 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
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 some‐
thing, 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 in‐
direction 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 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 second value in a parenthe‐
sized 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 off‐
set.

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 Specifi‐
cation implies that they do. However, as OS X Mountain Lion has passed the Single UNIX Speci‐
fication 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.

BSD May 9, 2021 BSD