SEARCH
NEW RPMS
DIRECTORIES
ABOUT
FAQ
VARIOUS
BLOG
DONATE


YUM REPOSITORY

 
 

MAN page from OpenSuSE file-magic-5.32-lp151.7.2.noarch.rpm

MAGIC

Section: File Formats (5)
Index
BSD mandoc
 

NAME

magic - file command's magic pattern file 

DESCRIPTION

This manual page documents the format of magic files asused by thefile(1)command, version 5.32.Thefile(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.mgcor 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 orMIME 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 databaseis as follows:Each line of a fragment file specifies a test to be performed.A test compares the data starting at a particular offsetin 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 datawhich 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 followedby /[WwcCtbT]*.The``W''flag compacts whitespace in the target, which mustcontain at least one whitespace character.If the magic hasnconsecutive blanks, the target needs at leastnconsecutive blanks to match.The``w''flag treats every blank in the magic as an optional blank.The``c''flag specifies case insensitive matching: lower casecharacters in the magic match both lower and upper case characters in thetarget, whereas upper case characters in the magic only match upper casecharacters in the target.The``C''flag specifies case insensitive matching: upper casecharacters in the magic match both lower and upper case characters in thetarget, whereas lower case characters in the magic only match upper casecharacters 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.The``T''flag causes the string to be trimmed, i.e. leading and trailing whitespaceis deleted before the string is printed.
pstring
A Pascal-style string where the first byte/short/int is interpreted as theunsigned 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 4 byte big endian length.
h
A 2 byte big endian length.
L
A 4 byte little endian length.
l
A 2 byte little endian length.
J
The length includes itself in its count.

The string is not NUL terminated.``J''is used rather than the morevaluable``I''because this type of length is a feature of the JPEGformat.

date
A four-byte value interpreted as a UNIX date.
qdate
A eight-byte value interpreted as a UNIX date.
ldate
A four-byte value interpreted as a UNIX-style date, but interpreted aslocal time rather than UTC.
qldate
An eight-byte value interpreted as a UNIX-style date, but interpreted aslocal 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 ratherthan UTC.
beqldate
An eight-byte value in big-endian byte order,interpreted as a UNIX-style date, but interpreted as local time ratherthan 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 ratherthan UTC.
leqldate
An eight-byte value in little-endian byte order,interpreted as a UNIX-style date, but interpreted as local time ratherthan 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 ratherthan UTC.
indirect
Starting at the given offset, consult the magic database again.The offset of theindirectmagic is by default absolute in the file, but one can specify/rto indicate that the offset is relative from the beginning of the entry.
name
Define a``named''magic instance that can be called from anotherusemagic entry, like a subroutine call.Named instance direct magic offsets are relative to the offset of theprevious matched entry, but indirect offsets are relative to the beginningof 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 mentionedleshortfor example,it is treated asbeshortand 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 theirperformance is hard to predict, so their use is discouraged.When used in production environments, their performanceshould 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 abyte count.Lines are delimited by the platforms native line delimiter.When a line count is specified, an implicit byte count also computed assumingeach line is 80 characters long.If neither a byte or line count is specified, the search is limited automaticallyto 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 beattempted, starting from the start offset.This is suitable forsearching 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 testx(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 thecleartest.
clear
This test is always true and clears the match flag for that continuation level.It is intended to be used with thedefaulttest.

For compatibility with the SingleUNIXStandard, the type specifiersdCandd1are equivalent tobyte the type specifiersuCandu1are equivalent toubyte the type specifiersdSandd2are equivalent toshort the type specifiersuSandu2are equivalent toushort the type specifiersdI dL andd4are equivalent tolong the type specifiersuI uL andu4are equivalent toulong the type specifierd8is equivalent toquad the type specifieru8is equivalent touquad and the type specifiersis equivalent tostring In addition, the type specifierdQis equivalent toquadand the type specifieruQis equivalent touquad

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 usedin the pattern.All other tests are classified as binary.A top-levelpattern is considered to be a test text when all its patterns are textpatterns; otherwise, it is considered to be a binary pattern.Whenmatching a file, binary patterns are tried first; if no match isfound, and the file looks like text, then its encoding is determinedand the text patterns are tried.

The numeric types may optionally be followed byAm]and a numeric value,to specify that the value is to be AND'ed with thenumeric value before any comparisons are done.Prepending auto the type indicates that ordered comparisons should be unsigned.

test
The value to be compared with the value from the file.If the type isnumeric, this valueis specified in C form; if it is a string, it is specified as a C stringwith the usual escapes permitted (e.g. \n for new-line).

Numeric valuesmay 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,Lt] to specify that the value from the file must be less than the specifiedvalue,Gt] to specify that the value from the file must be greater than the specifiedvalue,Am] to specify that the value from the file must have set all of the bitsthat are set in the specified value,^ to specify that the value from the file must have clear any of the bitsthat 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= OperatorsAm] ^ and~don't work with floats and doubles.The operator!specifies that the line matches if the test doesnotsucceed.

Numeric values are specified in C form; e.g.13is decimal,013is octal, and0x13is hexadecimal.

Numeric operations are not performed on date types, instead the numericvalue is interpreted as an offset.

For string values, the string from thefile must match the specified string.The operators= Lt]andGt](but notAm] can be applied to strings.The length used for matching is that of the string argumentin the magic file.This means that a line can match any non-empty string (usually used tothen print the string), withGt]\0(because all non-empty strings are greater than the empty string).

Dates are treated as numerical values in the respective internalrepresentation.

The special testxalways evaluates to true.

message
The message to be printed if the comparison succeeds.If the string contains aprintf(3)format specification, the value from the file (with any specified maskingperformed) 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 whitespaceadded before it: multiple matches are normally separated by a singlespace.

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 nextnon-blank or comment line after the magic line that identifies thefile 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 tothe current magic description using the following format:

!:strength OP VALUE

The operandOPcan be:+ - * or/andVALUEis a constant between 0 and 255.This constant is applied using the specified operandto the currently computed default magic strength.

Some file formats contain additional information which is to be printedalong with the file type or need additional tests to determine the truefile type.These additional tests are introduced by one or moreGt]characters preceding the offset.The number ofGt]on the line indicates the level of the test; a line with noGt]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 levelnsucceeds, all following tests at leveln+1are performed, and the messages printed if the tests succeed, until a linewith leveln(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   MZGt]0x18  leshort  Lt]0x40   MS-DOS executableGt]0x18  leshort  Gt]0x3f   extended PC executable (e.g., MS Windows)

Offsets do not need to be constant, but can also be read from the filebeing examined.If the first character following the lastGt]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 inthe file.The value at that offset is read, and is used again as an offsetin the file.Indirect offsets are of the form:(( x [[.,][bislBISL]][+-][ y ]) The value ofxis 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 value is treated as signed if``,''is specified or unsigned if``.''is specified.The capitalized types interpret the number as a big endianvalue, whereas the small letter versions interpret the number as a littleendian value;themtype interprets the number as a middle endian (PDP-11) value.To that number the value ofyis added and the result is used as an offset 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 executables0           string  MZGt]0x18       leshort Lt]0x40   MZ executable (MS-DOS)# skip the whole block below if it is not an extended executableGt]0x18       leshort Gt]0x3fGt]Gt](0x3c.l)  string  PE\0\0  PE executable (MS-Windows)Gt]Gt](0x3c.l)  string  LX\0\0  LX executable (OS/2)

This strategy of examining has a drawback: you must make sure that youeventually print something, or users may get empty output (such as whenthere is neither PE\0\0 nor LE\0\0 in the above example).

If this indirect offset cannot be used directly, simple calculations arepossible: appending[+-*/%Am]|^]numberinside parentheses allows one to modifythe value read from the file before it is used as an offset:

# MS Windows executables are also valid MS-DOS executables0           string  MZ# sometimes, the value at 0x18 is less that 0x40 but there's still an# extended executable, simply appended to the fileGt]0x18       leshort Lt]0x40Gt]Gt](4.s*512) leshort 0x014c  COFF executable (MS-DOS, DJGPP)Gt]Gt](4.s*512) leshort !0x014c MZ executable (MS-DOS)

Sometimes you do not know the exact offset as this depends on the length orposition (when indirection was used before) of preceding fields.You can specify an offset relative to the end of the last up-levelfield using`Am]'as a prefix to the offset:

0           string  MZGt]0x18       leshort Gt]0x3fGt]Gt](0x3c.l)  string  PE\0\0    PE executable (MS-Windows)# immediately following the PE signature is the CPU typeGt]Gt]Gt]Am]0       leshort 0x14c     for Intel 80386Gt]Gt]Gt]Am]0       leshort 0x184     for DEC Alpha

Indirect and relative offsets can be combined:

0             string  MZGt]0x18         leshort Lt]0x40Gt]Gt](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 executableGt]Gt]Gt]Am](2.s-514) string  LE      LE executable (MS Windows VxD driver)

Or the other way around:

0                 string  MZGt]0x18             leshort Gt]0x3fGt]Gt](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 signatureGt]Gt]Gt](Am]0x7c.l+0x26) string  UPX     \b, UPX compressed

Or even both!

0                string  MZGt]0x18            leshort Gt]0x3fGt]Gt](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 signatureGt]Gt]Gt]Am](Am]0x54.l-3)  string  UNACE  \b, ACE self-extracting archive

If you have to deal with offset/length pairs in your file, even thesecond 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 thestart of the main indirect offset.

0                 string       MZGt]0x18             leshort      Gt]0x3fGt]Gt](0x3c.l)        string       PE\0\0 PE executable (MS-Windows)# search for the PE section called ".idata"...Gt]Gt]Gt]Am]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 nameGt]Gt]Gt]Gt](Am]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 matchGt]18   clearGt]18   lelong  1       oneGt]18   lelong  2       twoGt]18   default x# print default matchGt]Gt]18        lelong  x       unmatched 0x%x
 

SEE ALSO

file(1)- the command that reads this file. 

BUGS

The formatslong belong lelong melong short beshort andleshortdo not depend on the length of the C data typesshortandlongon the platform, even though the SingleUNIXSpecification implies that they do. However, as OS X Mountain Lion haspassed the SingleUNIXSpecification validation suite, and supplies a version offile(1)in which they do not depend on the sizes of the C data types and that isbuilt for a 64-bit environment in whichlongis 8 bytes rather than 4 bytes, presumably the validation suite does nottest whether, for examplelongrefers to an item with the same size as the C data typelong There should probably betypenamesint8 uint8 int16 uint16 int32 uint32 int64 anduint64 and specified-byte-order variants of them,to make it clearer that those types have specified widths.


 

Index

NAME
DESCRIPTION
SEE ALSO
BUGS

This document was created byman2html,using the manual pages.