1.\" $File: magic.man,v 1.71 2011/12/07 11:58:24 rrt Exp $ 2.Dd April 20, 2011 3.Dt MAGIC __FSECTION__ 4.Os 5.\" install as magic.4 on USG, magic.5 on V7, Berkeley and Linux systems. 6.Sh NAME 7.Nm magic 8.Nd file command's magic pattern file 9.Sh DESCRIPTION 10This manual page documents the format of the magic file as 11used by the 12.Xr file __CSECTION__ 13command, version __VERSION__. 14The 15.Xr file __CSECTION__ 16command identifies the type of a file using, 17among other tests, 18a test for whether the file contains certain 19.Dq "magic patterns" . 20The file 21.Pa __MAGIC__ 22specifies what patterns are to be tested for, what message or 23MIME type to print if a particular pattern is found, 24and additional information to extract from the file. 25.Pp 26Each line of the file specifies a test to be performed. 27A test compares the data starting at a particular offset 28in the file with a byte value, a string or a numeric value. 29If the test succeeds, a message is printed. 30The line consists of the following fields: 31.Bl -tag -width ".Dv message" 32.It Dv offset 33A number specifying the offset, in bytes, into the file of the data 34which is to be tested. 35.It Dv type 36The type of the data to be tested. 37The possible values are: 38.Bl -tag -width ".Dv lestring16" 39.It Dv byte 40A one-byte value. 41.It Dv short 42A two-byte value in this machine's native byte order. 43.It Dv long 44A four-byte value in this machine's native byte order. 45.It Dv quad 46An eight-byte value in this machine's native byte order. 47.It Dv float 48A 32-bit single precision IEEE floating point number in this machine's native byte order. 49.It Dv double 50A 64-bit double precision IEEE floating point number in this machine's native byte order. 51.It Dv string 52A string of bytes. 53The string type specification can be optionally followed 54by /[WwcCtb]*. 55The 56.Dq W 57flag compacts whitespace in the target, which must 58contain at least one whitespace character. 59If the magic has 60.Dv n 61consecutive blanks, the target needs at least 62.Dv n 63consecutive blanks to match. 64The 65.Dq w 66flag treats every blank in the magic as an optional blank. 67The 68.Dq c 69flag specifies case insensitive matching: lower case 70characters in the magic match both lower and upper case characters in the 71target, whereas upper case characters in the magic only match upper case 72characters in the target. 73The 74.Dq C 75flag specifies case insensitive matching: upper case 76characters in the magic match both lower and upper case characters in the 77target, whereas lower case characters in the magic only match upper case 78characters in the target. 79To do a complete case insensitive match, specify both 80.Dq c 81and 82.Dq C . 83The 84.Dq t 85flag forces the test to be done for text files, while the 86.Dq b 87flag forces the test to be done for binary files. 88.It Dv pstring 89A Pascal-style string where the first byte/short/int is interpreted as the an 90unsigned length. 91The length defaults to byte and can be specified as a modifier. 92The following modifiers are supported: 93.Bl -tag -compact -width B 94.It B 95A byte length (default). 96.It H 97A 2 byte big endian length. 98.It h 99A 2 byte big little length. 100.It L 101A 4 byte big endian length. 102.It l 103A 4 byte big little length. 104.It J 105The length includes itself in its count. 106.El 107The string is not NUL terminated. 108.Dq J 109is used rather than the more 110valuable 111.Dq I 112because this type of length is a feature of the JPEG 113format. 114.It Dv date 115A four-byte value interpreted as a UNIX date. 116.It Dv qdate 117A eight-byte value interpreted as a UNIX date. 118.It Dv ldate 119A four-byte value interpreted as a UNIX-style date, but interpreted as 120local time rather than UTC. 121.It Dv qldate 122An eight-byte value interpreted as a UNIX-style date, but interpreted as 123local time rather than UTC. 124.It Dv beid3 125A 32-bit ID3 length in big-endian byte order. 126.It Dv beshort 127A two-byte value in big-endian byte order. 128.It Dv belong 129A four-byte value in big-endian byte order. 130.It Dv bequad 131An eight-byte value in big-endian byte order. 132.It Dv befloat 133A 32-bit single precision IEEE floating point number in big-endian byte order. 134.It Dv bedouble 135A 64-bit double precision IEEE floating point number in big-endian byte order. 136.It Dv bedate 137A four-byte value in big-endian byte order, 138interpreted as a Unix date. 139.It Dv beqdate 140An eight-byte value in big-endian byte order, 141interpreted as a Unix date. 142.It Dv beldate 143A four-byte value in big-endian byte order, 144interpreted as a UNIX-style date, but interpreted as local time rather 145than UTC. 146.It Dv beqldate 147An eight-byte value in big-endian byte order, 148interpreted as a UNIX-style date, but interpreted as local time rather 149than UTC. 150.It Dv bestring16 151A two-byte unicode (UCS16) string in big-endian byte order. 152.It Dv leid3 153A 32-bit ID3 length in little-endian byte order. 154.It Dv leshort 155A two-byte value in little-endian byte order. 156.It Dv lelong 157A four-byte value in little-endian byte order. 158.It Dv lequad 159An eight-byte value in little-endian byte order. 160.It Dv lefloat 161A 32-bit single precision IEEE floating point number in little-endian byte order. 162.It Dv ledouble 163A 64-bit double precision IEEE floating point number in little-endian byte order. 164.It Dv ledate 165A four-byte value in little-endian byte order, 166interpreted as a UNIX date. 167.It Dv leqdate 168An eight-byte value in little-endian byte order, 169interpreted as a UNIX date. 170.It Dv leldate 171A four-byte value in little-endian byte order, 172interpreted as a UNIX-style date, but interpreted as local time rather 173than UTC. 174.It Dv leqldate 175An eight-byte value in little-endian byte order, 176interpreted as a UNIX-style date, but interpreted as local time rather 177than UTC. 178.It Dv lestring16 179A two-byte unicode (UCS16) string in little-endian byte order. 180.It Dv melong 181A four-byte value in middle-endian (PDP-11) byte order. 182.It Dv medate 183A four-byte value in middle-endian (PDP-11) byte order, 184interpreted as a UNIX date. 185.It Dv meldate 186A four-byte value in middle-endian (PDP-11) byte order, 187interpreted as a UNIX-style date, but interpreted as local time rather 188than UTC. 189.It Dv indirect 190Starting at the given offset, consult the magic database again. 191.It Dv regex 192A regular expression match in extended POSIX regular expression syntax 193(like egrep). 194Regular expressions can take exponential time to process, and their 195performance is hard to predict, so their use is discouraged. 196When used in production environments, their performance 197should be carefully checked. 198The type specification can be optionally followed by 199.Dv /[c][s] . 200The 201.Dq c 202flag makes the match case insensitive, while the 203.Dq s 204flag update the offset to the start offset of the match, rather than the end. 205The regular expression is tested against line 206.Dv N + 1 207onwards, where 208.Dv N 209is the given offset. 210Line endings are assumed to be in the machine's native format. 211.Dv ^ 212and 213.Dv $ 214match the beginning and end of individual lines, respectively, 215not beginning and end of file. 216.It Dv search 217A literal string search starting at the given offset. 218The same modifier flags can be used as for string patterns. 219The modifier flags (if any) must be followed by 220.Dv /number 221the range, that is, the number of positions at which the match will be 222attempted, starting from the start offset. 223This is suitable for 224searching larger binary expressions with variable offsets, using 225.Dv \e 226escapes for special characters. 227The offset works as for regex. 228.It Dv default 229This is intended to be used with the test 230.Em x 231(which is always true) and a message that is to be used if there are 232no other matches. 233.El 234.Pp 235Each top-level magic pattern (see below for an explanation of levels) 236is classified as text or binary according to the types used. 237Types 238.Dq regex 239and 240.Dq search 241are classified as text tests, unless non-printable characters are used 242in the pattern. 243All other tests are classified as binary. 244A top-level 245pattern is considered to be a test text when all its patterns are text 246patterns; otherwise, it is considered to be a binary pattern. 247When 248matching a file, binary patterns are tried first; if no match is 249found, and the file looks like text, then its encoding is determined 250and the text patterns are tried. 251.Pp 252The numeric types may optionally be followed by 253.Dv \*[Am] 254and a numeric value, 255to specify that the value is to be AND'ed with the 256numeric value before any comparisons are done. 257Prepending a 258.Dv u 259to the type indicates that ordered comparisons should be unsigned. 260.It Dv test 261The value to be compared with the value from the file. 262If the type is 263numeric, this value 264is specified in C form; if it is a string, it is specified as a C string 265with the usual escapes permitted (e.g. \en for new-line). 266.Pp 267Numeric values 268may be preceded by a character indicating the operation to be performed. 269It may be 270.Dv = , 271to specify that the value from the file must equal the specified value, 272.Dv \*[Lt] , 273to specify that the value from the file must be less than the specified 274value, 275.Dv \*[Gt] , 276to specify that the value from the file must be greater than the specified 277value, 278.Dv \*[Am] , 279to specify that the value from the file must have set all of the bits 280that are set in the specified value, 281.Dv ^ , 282to specify that the value from the file must have clear any of the bits 283that are set in the specified value, or 284.Dv ~ , 285the value specified after is negated before tested. 286.Dv x , 287to specify that any value will match. 288If the character is omitted, it is assumed to be 289.Dv = . 290Operators 291.Dv \*[Am] , 292.Dv ^ , 293and 294.Dv ~ 295don't work with floats and doubles. 296The operator 297.Dv !\& 298specifies that the line matches if the test does 299.Em not 300succeed. 301.Pp 302Numeric values are specified in C form; e.g. 303.Dv 13 304is decimal, 305.Dv 013 306is octal, and 307.Dv 0x13 308is hexadecimal. 309.Pp 310For string values, the string from the 311file must match the specified string. 312The operators 313.Dv = , 314.Dv \*[Lt] 315and 316.Dv \*[Gt] 317(but not 318.Dv \*[Am] ) 319can be applied to strings. 320The length used for matching is that of the string argument 321in the magic file. 322This means that a line can match any non-empty string (usually used to 323then print the string), with 324.Em \*[Gt]\e0 325(because all non-empty strings are greater than the empty string). 326.Pp 327The special test 328.Em x 329always evaluates to true. 330.It Dv message 331The message to be printed if the comparison succeeds. 332If the string contains a 333.Xr printf 3 334format specification, the value from the file (with any specified masking 335performed) is printed using the message as the format string. 336If the string begins with 337.Dq \eb , 338the message printed is the remainder of the string with no whitespace 339added before it: multiple matches are normally separated by a single 340space. 341.El 342.Pp 343An APPLE 4+4 character APPLE creator and type can be specified as: 344.Bd -literal -offset indent 345!:apple CREATYPE 346.Ed 347.Pp 348A MIME type is given on a separate line, which must be the next 349non-blank or comment line after the magic line that identifies the 350file type, and has the following format: 351.Bd -literal -offset indent 352!:mime MIMETYPE 353.Ed 354.Pp 355i.e. the literal string 356.Dq !:mime 357followed by the MIME type. 358.Pp 359An optional strength can be supplied on a separate line which refers to 360the current magic description using the following format: 361.Bd -literal -offset indent 362!:strength OP VALUE 363.Ed 364.Pp 365The operand 366.Dv OP 367can be: 368.Dv + , 369.Dv - , 370.Dv * , 371or 372.Dv / 373and 374.Dv VALUE 375is a constant between 0 and 255. 376This constant is applied using the specified operand 377to the currently computed default magic strength. 378.Pp 379Some file formats contain additional information which is to be printed 380along with the file type or need additional tests to determine the true 381file type. 382These additional tests are introduced by one or more 383.Em \*[Gt] 384characters preceding the offset. 385The number of 386.Em \*[Gt] 387on the line indicates the level of the test; a line with no 388.Em \*[Gt] 389at the beginning is considered to be at level 0. 390Tests are arranged in a tree-like hierarchy: 391if the test on a line at level 392.Em n 393succeeds, all following tests at level 394.Em n+1 395are performed, and the messages printed if the tests succeed, until a line 396with level 397.Em n 398(or less) appears. 399For more complex files, one can use empty messages to get just the 400"if/then" effect, in the following way: 401.Bd -literal -offset indent 4020 string MZ 403\*[Gt]0x18 leshort \*[Lt]0x40 MS-DOS executable 404\*[Gt]0x18 leshort \*[Gt]0x3f extended PC executable (e.g., MS Windows) 405.Ed 406.Pp 407Offsets do not need to be constant, but can also be read from the file 408being examined. 409If the first character following the last 410.Em \*[Gt] 411is a 412.Em \&( 413then the string after the parenthesis is interpreted as an indirect offset. 414That means that the number after the parenthesis is used as an offset in 415the file. 416The value at that offset is read, and is used again as an offset 417in the file. 418Indirect offsets are of the form: 419.Em (( x [.[bislBISL]][+\-][ y ]) . 420The value of 421.Em x 422is used as an offset in the file. 423A byte, id3 length, short or long is read at that offset depending on the 424.Em [bislBISLm] 425type specifier. 426The capitalized types interpret the number as a big endian 427value, whereas the small letter versions interpret the number as a little 428endian value; 429the 430.Em m 431type interprets the number as a middle endian (PDP-11) value. 432To that number the value of 433.Em y 434is added and the result is used as an offset in the file. 435The default type if one is not specified is long. 436.Pp 437That way variable length structures can be examined: 438.Bd -literal -offset indent 439# MS Windows executables are also valid MS-DOS executables 4400 string MZ 441\*[Gt]0x18 leshort \*[Lt]0x40 MZ executable (MS-DOS) 442# skip the whole block below if it is not an extended executable 443\*[Gt]0x18 leshort \*[Gt]0x3f 444\*[Gt]\*[Gt](0x3c.l) string PE\e0\e0 PE executable (MS-Windows) 445\*[Gt]\*[Gt](0x3c.l) string LX\e0\e0 LX executable (OS/2) 446.Ed 447.Pp 448This strategy of examining has a drawback: You must make sure that 449you eventually print something, or users may get empty output (like, when 450there is neither PE\e0\e0 nor LE\e0\e0 in the above example) 451.Pp 452If this indirect offset cannot be used directly, simple calculations are 453possible: appending 454.Em [+-*/%\*[Am]|^]number 455inside parentheses allows one to modify 456the value read from the file before it is used as an offset: 457.Bd -literal -offset indent 458# MS Windows executables are also valid MS-DOS executables 4590 string MZ 460# sometimes, the value at 0x18 is less that 0x40 but there's still an 461# extended executable, simply appended to the file 462\*[Gt]0x18 leshort \*[Lt]0x40 463\*[Gt]\*[Gt](4.s*512) leshort 0x014c COFF executable (MS-DOS, DJGPP) 464\*[Gt]\*[Gt](4.s*512) leshort !0x014c MZ executable (MS-DOS) 465.Ed 466.Pp 467Sometimes you do not know the exact offset as this depends on the length or 468position (when indirection was used before) of preceding fields. 469You can specify an offset relative to the end of the last up-level 470field using 471.Sq \*[Am] 472as a prefix to the offset: 473.Bd -literal -offset indent 4740 string MZ 475\*[Gt]0x18 leshort \*[Gt]0x3f 476\*[Gt]\*[Gt](0x3c.l) string PE\e0\e0 PE executable (MS-Windows) 477# immediately following the PE signature is the CPU type 478\*[Gt]\*[Gt]\*[Gt]\*[Am]0 leshort 0x14c for Intel 80386 479\*[Gt]\*[Gt]\*[Gt]\*[Am]0 leshort 0x184 for DEC Alpha 480.Ed 481.Pp 482Indirect and relative offsets can be combined: 483.Bd -literal -offset indent 4840 string MZ 485\*[Gt]0x18 leshort \*[Lt]0x40 486\*[Gt]\*[Gt](4.s*512) leshort !0x014c MZ executable (MS-DOS) 487# if it's not COFF, go back 512 bytes and add the offset taken 488# from byte 2/3, which is yet another way of finding the start 489# of the extended executable 490\*[Gt]\*[Gt]\*[Gt]\*[Am](2.s-514) string LE LE executable (MS Windows VxD driver) 491.Ed 492.Pp 493Or the other way around: 494.Bd -literal -offset indent 4950 string MZ 496\*[Gt]0x18 leshort \*[Gt]0x3f 497\*[Gt]\*[Gt](0x3c.l) string LE\e0\e0 LE executable (MS-Windows) 498# at offset 0x80 (-4, since relative offsets start at the end 499# of the up-level match) inside the LE header, we find the absolute 500# offset to the code area, where we look for a specific signature 501\*[Gt]\*[Gt]\*[Gt](\*[Am]0x7c.l+0x26) string UPX \eb, UPX compressed 502.Ed 503.Pp 504Or even both! 505.Bd -literal -offset indent 5060 string MZ 507\*[Gt]0x18 leshort \*[Gt]0x3f 508\*[Gt]\*[Gt](0x3c.l) string LE\e0\e0 LE executable (MS-Windows) 509# at offset 0x58 inside the LE header, we find the relative offset 510# to a data area where we look for a specific signature 511\*[Gt]\*[Gt]\*[Gt]\*[Am](\*[Am]0x54.l-3) string UNACE \eb, ACE self-extracting archive 512.Ed 513.Pp 514Finally, if you have to deal with offset/length pairs in your file, even the 515second value in a parenthesized expression can be taken from the file itself, 516using another set of parentheses. 517Note that this additional indirect offset is always relative to the 518start of the main indirect offset. 519.Bd -literal -offset indent 5200 string MZ 521\*[Gt]0x18 leshort \*[Gt]0x3f 522\*[Gt]\*[Gt](0x3c.l) string PE\e0\e0 PE executable (MS-Windows) 523# search for the PE section called ".idata"... 524\*[Gt]\*[Gt]\*[Gt]\*[Am]0xf4 search/0x140 .idata 525# ...and go to the end of it, calculated from start+length; 526# these are located 14 and 10 bytes after the section name 527\*[Gt]\*[Gt]\*[Gt]\*[Gt](\*[Am]0xe.l+(-4)) string PK\e3\e4 \eb, ZIP self-extracting archive 528.Ed 529.Sh SEE ALSO 530.Xr file __CSECTION__ 531\- the command that reads this file. 532.Sh BUGS 533The formats 534.Dv long , 535.Dv belong , 536.Dv lelong , 537.Dv melong , 538.Dv short , 539.Dv beshort , 540.Dv leshort , 541.Dv date , 542.Dv bedate , 543.Dv medate , 544.Dv ledate , 545.Dv beldate , 546.Dv leldate , 547and 548.Dv meldate 549are system-dependent; perhaps they should be specified as a number 550of bytes (2B, 4B, etc), 551since the files being recognized typically come from 552a system on which the lengths are invariant. 553.\" 554.\" From: guy@sun.uucp (Guy Harris) 555.\" Newsgroups: net.bugs.usg 556.\" Subject: /etc/magic's format isn't well documented 557.\" Message-ID: <2752@sun.uucp> 558.\" Date: 3 Sep 85 08:19:07 GMT 559.\" Organization: Sun Microsystems, Inc. 560.\" Lines: 136 561.\" 562.\" Here's a manual page for the format accepted by the "file" made by adding 563.\" the changes I posted to the S5R2 version. 564.\" 565.\" Modified for Ian Darwin's version of the file command. 566