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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 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:
⊕ 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 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]*. 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.
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. 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.
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 character. 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. 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 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 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 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
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 & 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 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.
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 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
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 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
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 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 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 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.
NetBSD 10.99 Arpil 18, 2023 NetBSD 10.99