FreeBSD Manual Pages
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 "5.46". 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 lo- cated 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 data- base 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 (&). If the offset starts with the symbol "+", then all offsets are in- terpreted 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 or- der. 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 op- tionally 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 de- faults 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, inter- preted as a Unix date. beqdate An eight-byte value in big-endian byte order, inter- preted 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, inter- preted as a UNIX-style date, but interpreted as local time rather than UTC. beqwdate An eight-byte value in big-endian byte order, inter- preted 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, inter- preted as a UNIX date. leqdate An eight-byte value in little-endian byte order, in- terpreted as a UNIX date. leldate A four-byte value in little-endian byte order, inter- preted as a UNIX-style date, but interpreted as local time rather than UTC. leqldate An eight-byte value in little-endian byte order, in- terpreted as a UNIX-style date, but interpreted as lo- cal time rather than UTC. leqwdate An eight-byte value in little-endian byte order, in- terpreted as a Windows-style date. lemsdosdate A two-byte value in big-endian byte order, interpreted as FAT/DOS-style date. lemsdostime A two-byte value in big-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 or- der. medate A four-byte value in middle-endian (PDP-11) byte or- der, interpreted as a UNIX date. meldate A four-byte value in middle-endian (PDP-11) byte or- der, interpreted as a UNIX-style date, but interpreted as local time rather than UTC. indirect Starting at the given offset, consult the magic data- base 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 be- ginning 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 per- formance is hard to predict, so their use is discour- aged. When used in production environments, their performance should be carefully checked. The size of the string to search should also be limited by speci- fying /<length>, to avoid performance issues scanning long files. The type specification can also be op- tionally 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 automati- cally 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 pat- terns. 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 modi- fier 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 be- fore. 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 en- tries: -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 speci- fiers 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 lev- els) 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, bi- nary patterns are tried first; if no match is found, and the file looks like text, then its encoding is determined and the text pat- terns 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 per- mitted (e.g. \n for new-line). Numeric values may be preceded by a character indicating the oper- ation 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 speci- fied 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 op- erator ! specifies that the line matches if the test does not suc- ceed. 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 speci- fied 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 white- space 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 speci- fied as: !:ext ext[/ext...] i.e. the literal string "!:ext" followed by a slash-separated list of com- monly 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 > charac- ters 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 be- ing 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 off- set 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 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 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 mod- ify 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, us- ing 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 plat- form, even though the Single Unix Specification implies that they do. How- ever, as OS X Mountain Lion has passed the Single Unix Specification vali- dation 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 speci- fied-byte-order variants of them, to make it clearer that those types have specified widths. FreeBSD ports 15.1 November 27, 2024 MAGIC(5)
NAME | DESCRIPTION | SEE ALSO | BUGS
Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=magic&manpath=FreeBSD+15.1-RELEASE+and+Ports>