MAGIC(5) BSD File Formats Manual MAGIC(5)
NAME
magic — file command's magic pattern file
DESCRIPTION
This manual page documents the format of the magic file as used by the file(1) command, version 5.11. 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 file /usr/share/misc/magic 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.
Each line of the file specifies a test to be performed. A test compares the data starting at a particular off‐
set 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.
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 /[WwcCtb]*.
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
“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 insensitive 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.
pstring A Pascal-style string where the first byte/short/int is interpreted as the an 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 big little length.
L A 4 byte big endian length.
l A 4 byte big little 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 A eight-byte value interpreted as a UNIX date.
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 inter‐
preted as local time rather than UTC.
beqldate An eight-byte value in big-endian byte order, interpreted as a UNIX-style date, but inter‐
preted as local time rather than UTC.
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 inter‐
preted 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.
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.
regex A regular expression match in extended POSIX regular expression syntax (like egrep). Regu‐
lar expressions can take exponential time to process, and their performance is hard to pre‐
sets, using \ escapes for special characters. The offset works as for regex.
default This is intended to be used with the test x (which is always true) and a message that is to
be used if there are no other matches.
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 con‐
sidered 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 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.
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).
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 speci‐
fication, 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.
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 [.[bislBISL]][+-][ 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 [bislBISLm] type specifier. 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 num‐
ber as a middle endian (PDP-11) value. To that number the value of y is added and the result is used as an off‐
set in the file. The default type if one is not specified is long.
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 (like, 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
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
Finally, 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 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
SEE ALSO
file(1) - the command that reads this file.
BUGS
The formats long, belong, lelong, melong, short, beshort, leshort, date, bedate, medate, ledate, beldate,
leldate, and meldate are system-dependent; perhaps they should be specified as a number of bytes (2B, 4B, etc),
since the files being recognized typically come from a system on which the lengths are invariant.
BSD April 20, 2011 BSD
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