magic.man 21 KB

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312313314315316317318319320321322323324325326327328329330331332333334335336337338339340341342343344345346347348349350351352353354355356357358359360361362363364365366367368369370371372373374375376377378379380381382383384385386387388389390391392393394395396397398399400401402403404405406407408409410411412413414415416417418419420421422423424425426427428429430431432433434435436437438439440441442443444445446447448449450451452453454455456457458459460461462463464465466467468469470471472473474475476477478479480481482483484485486487488489490491492493494495496497498499500501502503504505506507508509510511512513514515516517518519520521522523524525526527528529530531532533534535536537538539540541542543544545546547548549550551552553554555556557558559560561562563564565566567568569570571572573574575576577578579580581582583584585586587588589590591592593594595596597598599600601602603604605606607608609610611612613614615616617618619620621622623624625626627628629630631632633634635636637638639640641642643644645646647648649650651652653654655656657658659660661662663664665666667668669670671672673674675676677678679680681682683684685686687688689690691692693694695696697698699700701702703704705706707708709710711712713714715716717718
  1. .\" $File: magic.man,v 1.86 2015/09/08 13:48:44 christos Exp $
  2. .Dd January 1, 2015
  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
  10. This manual page documents the format of the magic file as
  11. used by the
  12. .Xr file __CSECTION__
  13. command, version __VERSION__.
  14. The
  15. .Xr file __CSECTION__
  16. command identifies the type of a file using,
  17. among other tests,
  18. a test for whether the file contains certain
  19. .Dq "magic patterns" .
  20. The file
  21. .Pa __MAGIC__
  22. specifies what patterns are to be tested for, what message or
  23. MIME type to print if a particular pattern is found,
  24. and additional information to extract from the file.
  25. .Pp
  26. Each line of the file specifies a test to be performed.
  27. A test compares the data starting at a particular offset
  28. in the file with a byte value, a string or a numeric value.
  29. If the test succeeds, a message is printed.
  30. The line consists of the following fields:
  31. .Bl -tag -width ".Dv message"
  32. .It Dv offset
  33. A number specifying the offset, in bytes, into the file of the data
  34. which is to be tested.
  35. .It Dv type
  36. The type of the data to be tested.
  37. The possible values are:
  38. .Bl -tag -width ".Dv lestring16"
  39. .It Dv byte
  40. A one-byte value.
  41. .It Dv short
  42. A two-byte value in this machine's native byte order.
  43. .It Dv long
  44. A four-byte value in this machine's native byte order.
  45. .It Dv quad
  46. An eight-byte value in this machine's native byte order.
  47. .It Dv float
  48. A 32-bit single precision IEEE floating point number in this machine's native byte order.
  49. .It Dv double
  50. A 64-bit double precision IEEE floating point number in this machine's native byte order.
  51. .It Dv string
  52. A string of bytes.
  53. The string type specification can be optionally followed
  54. by /[WwcCtbT]*.
  55. The
  56. .Dq W
  57. flag compacts whitespace in the target, which must
  58. contain at least one whitespace character.
  59. If the magic has
  60. .Dv n
  61. consecutive blanks, the target needs at least
  62. .Dv n
  63. consecutive blanks to match.
  64. The
  65. .Dq w
  66. flag treats every blank in the magic as an optional blank.
  67. The
  68. .Dq c
  69. flag specifies case insensitive matching: lower case
  70. characters in the magic match both lower and upper case characters in the
  71. target, whereas upper case characters in the magic only match upper case
  72. characters in the target.
  73. The
  74. .Dq C
  75. flag specifies case insensitive matching: upper case
  76. characters in the magic match both lower and upper case characters in the
  77. target, whereas lower case characters in the magic only match upper case
  78. characters in the target.
  79. To do a complete case insensitive match, specify both
  80. .Dq c
  81. and
  82. .Dq C .
  83. The
  84. .Dq t
  85. flag forces the test to be done for text files, while the
  86. .Dq b
  87. flag forces the test to be done for binary files.
  88. The
  89. .Dq T
  90. flag causes the string to be trimmed, i.e. leading and trailing whitespace
  91. is deleted before the string is printed.
  92. .It Dv pstring
  93. A Pascal-style string where the first byte/short/int is interpreted as the
  94. unsigned length.
  95. The length defaults to byte and can be specified as a modifier.
  96. The following modifiers are supported:
  97. .Bl -tag -compact -width B
  98. .It B
  99. A byte length (default).
  100. .It H
  101. A 2 byte big endian length.
  102. .It h
  103. A 2 byte big little length.
  104. .It L
  105. A 4 byte big endian length.
  106. .It l
  107. A 4 byte big little length.
  108. .It J
  109. The length includes itself in its count.
  110. .El
  111. The string is not NUL terminated.
  112. .Dq J
  113. is used rather than the more
  114. valuable
  115. .Dq I
  116. because this type of length is a feature of the JPEG
  117. format.
  118. .It Dv date
  119. A four-byte value interpreted as a UNIX date.
  120. .It Dv qdate
  121. A eight-byte value interpreted as a UNIX date.
  122. .It Dv ldate
  123. A four-byte value interpreted as a UNIX-style date, but interpreted as
  124. local time rather than UTC.
  125. .It Dv qldate
  126. An eight-byte value interpreted as a UNIX-style date, but interpreted as
  127. local time rather than UTC.
  128. .It Dv qwdate
  129. An eight-byte value interpreted as a Windows-style date.
  130. .It Dv beid3
  131. A 32-bit ID3 length in big-endian byte order.
  132. .It Dv beshort
  133. A two-byte value in big-endian byte order.
  134. .It Dv belong
  135. A four-byte value in big-endian byte order.
  136. .It Dv bequad
  137. An eight-byte value in big-endian byte order.
  138. .It Dv befloat
  139. A 32-bit single precision IEEE floating point number in big-endian byte order.
  140. .It Dv bedouble
  141. A 64-bit double precision IEEE floating point number in big-endian byte order.
  142. .It Dv bedate
  143. A four-byte value in big-endian byte order,
  144. interpreted as a Unix date.
  145. .It Dv beqdate
  146. An eight-byte value in big-endian byte order,
  147. interpreted as a Unix date.
  148. .It Dv beldate
  149. A four-byte value in big-endian byte order,
  150. interpreted as a UNIX-style date, but interpreted as local time rather
  151. than UTC.
  152. .It Dv beqldate
  153. An eight-byte value in big-endian byte order,
  154. interpreted as a UNIX-style date, but interpreted as local time rather
  155. than UTC.
  156. .It Dv beqwdate
  157. An eight-byte value in big-endian byte order,
  158. interpreted as a Windows-style date.
  159. .It Dv bestring16
  160. A two-byte unicode (UCS16) string in big-endian byte order.
  161. .It Dv leid3
  162. A 32-bit ID3 length in little-endian byte order.
  163. .It Dv leshort
  164. A two-byte value in little-endian byte order.
  165. .It Dv lelong
  166. A four-byte value in little-endian byte order.
  167. .It Dv lequad
  168. An eight-byte value in little-endian byte order.
  169. .It Dv lefloat
  170. A 32-bit single precision IEEE floating point number in little-endian byte order.
  171. .It Dv ledouble
  172. A 64-bit double precision IEEE floating point number in little-endian byte order.
  173. .It Dv ledate
  174. A four-byte value in little-endian byte order,
  175. interpreted as a UNIX date.
  176. .It Dv leqdate
  177. An eight-byte value in little-endian byte order,
  178. interpreted as a UNIX date.
  179. .It Dv leldate
  180. A four-byte value in little-endian byte order,
  181. interpreted as a UNIX-style date, but interpreted as local time rather
  182. than UTC.
  183. .It Dv leqldate
  184. An eight-byte value in little-endian byte order,
  185. interpreted as a UNIX-style date, but interpreted as local time rather
  186. than UTC.
  187. .It Dv leqwdate
  188. An eight-byte value in little-endian byte order,
  189. interpreted as a Windows-style date.
  190. .It Dv lestring16
  191. A two-byte unicode (UCS16) string in little-endian byte order.
  192. .It Dv melong
  193. A four-byte value in middle-endian (PDP-11) byte order.
  194. .It Dv medate
  195. A four-byte value in middle-endian (PDP-11) byte order,
  196. interpreted as a UNIX date.
  197. .It Dv meldate
  198. A four-byte value in middle-endian (PDP-11) byte order,
  199. interpreted as a UNIX-style date, but interpreted as local time rather
  200. than UTC.
  201. .It Dv indirect
  202. Starting at the given offset, consult the magic database again.
  203. The offset of the
  204. .Dv indirect
  205. magic is by default absolute in the file, but one can specify
  206. .Dv /r
  207. to indicate that the offset is relative from the beginning of the entry.
  208. .It Dv name
  209. Define a
  210. .Dq named
  211. magic instance that can be called from another
  212. .Dv use
  213. magic entry, like a subroutine call.
  214. Named instance direct magic offsets are relative to the offset of the
  215. previous matched entry, but indirect offsets are relative to the beginning
  216. of the file as usual.
  217. Named magic entries always match.
  218. .It Dv use
  219. Recursively call the named magic starting from the current offset.
  220. If the name of the referenced begins with a
  221. .Dv ^
  222. then the endianness of the magic is switched; if the magic mentioned
  223. .Dv leshort
  224. for example,
  225. it is treated as
  226. .Dv beshort
  227. and vice versa.
  228. This is useful to avoid duplicating the rules for different endianness.
  229. .It Dv regex
  230. A regular expression match in extended POSIX regular expression syntax
  231. (like egrep).
  232. Regular expressions can take exponential time to process, and their
  233. performance is hard to predict, so their use is discouraged.
  234. When used in production environments, their performance
  235. should be carefully checked.
  236. The size of the string to search should also be limited by specifying
  237. .Dv /<length> ,
  238. to avoid performance issues scanning long files.
  239. The type specification can also be optionally followed by
  240. .Dv /[c][s][l] .
  241. The
  242. .Dq c
  243. flag makes the match case insensitive, while the
  244. .Dq s
  245. flag update the offset to the start offset of the match, rather than the end.
  246. The
  247. .Dq l
  248. modifier, changes the limit of length to mean number of lines instead of a
  249. byte count.
  250. Lines are delimited by the platforms native line delimiter.
  251. When a line count is specified, an implicit byte count also computed assuming
  252. each line is 80 characters long.
  253. If neither a byte or line count is specified, the search is limited automatically
  254. to 8KiB.
  255. .Dv ^
  256. and
  257. .Dv $
  258. match the beginning and end of individual lines, respectively,
  259. not beginning and end of file.
  260. .It Dv search
  261. A literal string search starting at the given offset.
  262. The same modifier flags can be used as for string patterns.
  263. The search expression must contain the range in the form
  264. .Dv /number,
  265. that is the number of positions at which the match will be
  266. attempted, starting from the start offset.
  267. This is suitable for
  268. searching larger binary expressions with variable offsets, using
  269. .Dv \e
  270. escapes for special characters.
  271. The order of modifier and number is not relevant.
  272. .It Dv default
  273. This is intended to be used with the test
  274. .Em x
  275. (which is always true) and it has no type.
  276. It matches when no other test at that continuation level has matched before.
  277. Clearing that matched tests for a continuation level, can be done using the
  278. .Dv clear
  279. test.
  280. .It Dv clear
  281. This test is always true and clears the match flag for that continuation level.
  282. It is intended to be used with the
  283. .Dv default
  284. test.
  285. .El
  286. .Pp
  287. For compatibility with the Single
  288. .Ux
  289. Standard, the type specifiers
  290. .Dv dC
  291. and
  292. .Dv d1
  293. are equivalent to
  294. .Dv byte ,
  295. the type specifiers
  296. .Dv uC
  297. and
  298. .Dv u1
  299. are equivalent to
  300. .Dv ubyte ,
  301. the type specifiers
  302. .Dv dS
  303. and
  304. .Dv d2
  305. are equivalent to
  306. .Dv short ,
  307. the type specifiers
  308. .Dv uS
  309. and
  310. .Dv u2
  311. are equivalent to
  312. .Dv ushort ,
  313. the type specifiers
  314. .Dv dI ,
  315. .Dv dL ,
  316. and
  317. .Dv d4
  318. are equivalent to
  319. .Dv long ,
  320. the type specifiers
  321. .Dv uI ,
  322. .Dv uL ,
  323. and
  324. .Dv u4
  325. are equivalent to
  326. .Dv ulong ,
  327. the type specifier
  328. .Dv d8
  329. is equivalent to
  330. .Dv quad ,
  331. the type specifier
  332. .Dv u8
  333. is equivalent to
  334. .Dv uquad ,
  335. and the type specifier
  336. .Dv s
  337. is equivalent to
  338. .Dv string .
  339. In addition, the type specifier
  340. .Dv dQ
  341. is equivalent to
  342. .Dv quad
  343. and the type specifier
  344. .Dv uQ
  345. is equivalent to
  346. .Dv uquad .
  347. .Pp
  348. Each top-level magic pattern (see below for an explanation of levels)
  349. is classified as text or binary according to the types used.
  350. Types
  351. .Dq regex
  352. and
  353. .Dq search
  354. are classified as text tests, unless non-printable characters are used
  355. in the pattern.
  356. All other tests are classified as binary.
  357. A top-level
  358. pattern is considered to be a test text when all its patterns are text
  359. patterns; otherwise, it is considered to be a binary pattern.
  360. When
  361. matching a file, binary patterns are tried first; if no match is
  362. found, and the file looks like text, then its encoding is determined
  363. and the text patterns are tried.
  364. .Pp
  365. The numeric types may optionally be followed by
  366. .Dv \*[Am]
  367. and a numeric value,
  368. to specify that the value is to be AND'ed with the
  369. numeric value before any comparisons are done.
  370. Prepending a
  371. .Dv u
  372. to the type indicates that ordered comparisons should be unsigned.
  373. .It Dv test
  374. The value to be compared with the value from the file.
  375. If the type is
  376. numeric, this value
  377. is specified in C form; if it is a string, it is specified as a C string
  378. with the usual escapes permitted (e.g. \en for new-line).
  379. .Pp
  380. Numeric values
  381. may be preceded by a character indicating the operation to be performed.
  382. It may be
  383. .Dv = ,
  384. to specify that the value from the file must equal the specified value,
  385. .Dv \*[Lt] ,
  386. to specify that the value from the file must be less than the specified
  387. value,
  388. .Dv \*[Gt] ,
  389. to specify that the value from the file must be greater than the specified
  390. value,
  391. .Dv \*[Am] ,
  392. to specify that the value from the file must have set all of the bits
  393. that are set in the specified value,
  394. .Dv ^ ,
  395. to specify that the value from the file must have clear any of the bits
  396. that are set in the specified value, or
  397. .Dv ~ ,
  398. the value specified after is negated before tested.
  399. .Dv x ,
  400. to specify that any value will match.
  401. If the character is omitted, it is assumed to be
  402. .Dv = .
  403. Operators
  404. .Dv \*[Am] ,
  405. .Dv ^ ,
  406. and
  407. .Dv ~
  408. don't work with floats and doubles.
  409. The operator
  410. .Dv !\&
  411. specifies that the line matches if the test does
  412. .Em not
  413. succeed.
  414. .Pp
  415. Numeric values are specified in C form; e.g.
  416. .Dv 13
  417. is decimal,
  418. .Dv 013
  419. is octal, and
  420. .Dv 0x13
  421. is hexadecimal.
  422. .Pp
  423. Numeric operations are not performed on date types, instead the numeric
  424. value is interpreted as an offset.
  425. .Pp
  426. For string values, the string from the
  427. file must match the specified string.
  428. The operators
  429. .Dv = ,
  430. .Dv \*[Lt]
  431. and
  432. .Dv \*[Gt]
  433. (but not
  434. .Dv \*[Am] )
  435. can be applied to strings.
  436. The length used for matching is that of the string argument
  437. in the magic file.
  438. This means that a line can match any non-empty string (usually used to
  439. then print the string), with
  440. .Em \*[Gt]\e0
  441. (because all non-empty strings are greater than the empty string).
  442. .Pp
  443. Dates are treated as numerical values in the respective internal
  444. representation.
  445. .Pp
  446. The special test
  447. .Em x
  448. always evaluates to true.
  449. .It Dv message
  450. The message to be printed if the comparison succeeds.
  451. If the string contains a
  452. .Xr printf 3
  453. format specification, the value from the file (with any specified masking
  454. performed) is printed using the message as the format string.
  455. If the string begins with
  456. .Dq \eb ,
  457. the message printed is the remainder of the string with no whitespace
  458. added before it: multiple matches are normally separated by a single
  459. space.
  460. .El
  461. .Pp
  462. An APPLE 4+4 character APPLE creator and type can be specified as:
  463. .Bd -literal -offset indent
  464. !:apple CREATYPE
  465. .Ed
  466. .Pp
  467. A MIME type is given on a separate line, which must be the next
  468. non-blank or comment line after the magic line that identifies the
  469. file type, and has the following format:
  470. .Bd -literal -offset indent
  471. !:mime MIMETYPE
  472. .Ed
  473. .Pp
  474. i.e. the literal string
  475. .Dq !:mime
  476. followed by the MIME type.
  477. .Pp
  478. An optional strength can be supplied on a separate line which refers to
  479. the current magic description using the following format:
  480. .Bd -literal -offset indent
  481. !:strength OP VALUE
  482. .Ed
  483. .Pp
  484. The operand
  485. .Dv OP
  486. can be:
  487. .Dv + ,
  488. .Dv - ,
  489. .Dv * ,
  490. or
  491. .Dv /
  492. and
  493. .Dv VALUE
  494. is a constant between 0 and 255.
  495. This constant is applied using the specified operand
  496. to the currently computed default magic strength.
  497. .Pp
  498. Some file formats contain additional information which is to be printed
  499. along with the file type or need additional tests to determine the true
  500. file type.
  501. These additional tests are introduced by one or more
  502. .Em \*[Gt]
  503. characters preceding the offset.
  504. The number of
  505. .Em \*[Gt]
  506. on the line indicates the level of the test; a line with no
  507. .Em \*[Gt]
  508. at the beginning is considered to be at level 0.
  509. Tests are arranged in a tree-like hierarchy:
  510. if the test on a line at level
  511. .Em n
  512. succeeds, all following tests at level
  513. .Em n+1
  514. are performed, and the messages printed if the tests succeed, until a line
  515. with level
  516. .Em n
  517. (or less) appears.
  518. For more complex files, one can use empty messages to get just the
  519. "if/then" effect, in the following way:
  520. .Bd -literal -offset indent
  521. 0 string MZ
  522. \*[Gt]0x18 leshort \*[Lt]0x40 MS-DOS executable
  523. \*[Gt]0x18 leshort \*[Gt]0x3f extended PC executable (e.g., MS Windows)
  524. .Ed
  525. .Pp
  526. Offsets do not need to be constant, but can also be read from the file
  527. being examined.
  528. If the first character following the last
  529. .Em \*[Gt]
  530. is a
  531. .Em \&(
  532. then the string after the parenthesis is interpreted as an indirect offset.
  533. That means that the number after the parenthesis is used as an offset in
  534. the file.
  535. The value at that offset is read, and is used again as an offset
  536. in the file.
  537. Indirect offsets are of the form:
  538. .Em (( x [.[bislBISL]][+\-][ y ]) .
  539. The value of
  540. .Em x
  541. is used as an offset in the file.
  542. A byte, id3 length, short or long is read at that offset depending on the
  543. .Em [bislBISLm]
  544. type specifier.
  545. The capitalized types interpret the number as a big endian
  546. value, whereas the small letter versions interpret the number as a little
  547. endian value;
  548. the
  549. .Em m
  550. type interprets the number as a middle endian (PDP-11) value.
  551. To that number the value of
  552. .Em y
  553. is added and the result is used as an offset in the file.
  554. The default type if one is not specified is long.
  555. .Pp
  556. That way variable length structures can be examined:
  557. .Bd -literal -offset indent
  558. # MS Windows executables are also valid MS-DOS executables
  559. 0 string MZ
  560. \*[Gt]0x18 leshort \*[Lt]0x40 MZ executable (MS-DOS)
  561. # skip the whole block below if it is not an extended executable
  562. \*[Gt]0x18 leshort \*[Gt]0x3f
  563. \*[Gt]\*[Gt](0x3c.l) string PE\e0\e0 PE executable (MS-Windows)
  564. \*[Gt]\*[Gt](0x3c.l) string LX\e0\e0 LX executable (OS/2)
  565. .Ed
  566. .Pp
  567. This strategy of examining has a drawback: You must make sure that
  568. you eventually print something, or users may get empty output (like, when
  569. there is neither PE\e0\e0 nor LE\e0\e0 in the above example)
  570. .Pp
  571. If this indirect offset cannot be used directly, simple calculations are
  572. possible: appending
  573. .Em [+-*/%\*[Am]|^]number
  574. inside parentheses allows one to modify
  575. the value read from the file before it is used as an offset:
  576. .Bd -literal -offset indent
  577. # MS Windows executables are also valid MS-DOS executables
  578. 0 string MZ
  579. # sometimes, the value at 0x18 is less that 0x40 but there's still an
  580. # extended executable, simply appended to the file
  581. \*[Gt]0x18 leshort \*[Lt]0x40
  582. \*[Gt]\*[Gt](4.s*512) leshort 0x014c COFF executable (MS-DOS, DJGPP)
  583. \*[Gt]\*[Gt](4.s*512) leshort !0x014c MZ executable (MS-DOS)
  584. .Ed
  585. .Pp
  586. Sometimes you do not know the exact offset as this depends on the length or
  587. position (when indirection was used before) of preceding fields.
  588. You can specify an offset relative to the end of the last up-level
  589. field using
  590. .Sq \*[Am]
  591. as a prefix to the offset:
  592. .Bd -literal -offset indent
  593. 0 string MZ
  594. \*[Gt]0x18 leshort \*[Gt]0x3f
  595. \*[Gt]\*[Gt](0x3c.l) string PE\e0\e0 PE executable (MS-Windows)
  596. # immediately following the PE signature is the CPU type
  597. \*[Gt]\*[Gt]\*[Gt]\*[Am]0 leshort 0x14c for Intel 80386
  598. \*[Gt]\*[Gt]\*[Gt]\*[Am]0 leshort 0x184 for DEC Alpha
  599. .Ed
  600. .Pp
  601. Indirect and relative offsets can be combined:
  602. .Bd -literal -offset indent
  603. 0 string MZ
  604. \*[Gt]0x18 leshort \*[Lt]0x40
  605. \*[Gt]\*[Gt](4.s*512) leshort !0x014c MZ executable (MS-DOS)
  606. # if it's not COFF, go back 512 bytes and add the offset taken
  607. # from byte 2/3, which is yet another way of finding the start
  608. # of the extended executable
  609. \*[Gt]\*[Gt]\*[Gt]\*[Am](2.s-514) string LE LE executable (MS Windows VxD driver)
  610. .Ed
  611. .Pp
  612. Or the other way around:
  613. .Bd -literal -offset indent
  614. 0 string MZ
  615. \*[Gt]0x18 leshort \*[Gt]0x3f
  616. \*[Gt]\*[Gt](0x3c.l) string LE\e0\e0 LE executable (MS-Windows)
  617. # at offset 0x80 (-4, since relative offsets start at the end
  618. # of the up-level match) inside the LE header, we find the absolute
  619. # offset to the code area, where we look for a specific signature
  620. \*[Gt]\*[Gt]\*[Gt](\*[Am]0x7c.l+0x26) string UPX \eb, UPX compressed
  621. .Ed
  622. .Pp
  623. Or even both!
  624. .Bd -literal -offset indent
  625. 0 string MZ
  626. \*[Gt]0x18 leshort \*[Gt]0x3f
  627. \*[Gt]\*[Gt](0x3c.l) string LE\e0\e0 LE executable (MS-Windows)
  628. # at offset 0x58 inside the LE header, we find the relative offset
  629. # to a data area where we look for a specific signature
  630. \*[Gt]\*[Gt]\*[Gt]\*[Am](\*[Am]0x54.l-3) string UNACE \eb, ACE self-extracting archive
  631. .Ed
  632. .Pp
  633. If you have to deal with offset/length pairs in your file, even the
  634. second value in a parenthesized expression can be taken from the file itself,
  635. using another set of parentheses.
  636. Note that this additional indirect offset is always relative to the
  637. start of the main indirect offset.
  638. .Bd -literal -offset indent
  639. 0 string MZ
  640. \*[Gt]0x18 leshort \*[Gt]0x3f
  641. \*[Gt]\*[Gt](0x3c.l) string PE\e0\e0 PE executable (MS-Windows)
  642. # search for the PE section called ".idata"...
  643. \*[Gt]\*[Gt]\*[Gt]\*[Am]0xf4 search/0x140 .idata
  644. # ...and go to the end of it, calculated from start+length;
  645. # these are located 14 and 10 bytes after the section name
  646. \*[Gt]\*[Gt]\*[Gt]\*[Gt](\*[Am]0xe.l+(-4)) string PK\e3\e4 \eb, ZIP self-extracting archive
  647. .Ed
  648. .Pp
  649. If you have a list of known avalues at a particular continuation level,
  650. and you want to provide a switch-like default case:
  651. .Bd -literal -offset indent
  652. # clear that continuation level match
  653. \*[Gt]18 clear
  654. \*[Gt]18 lelong 1 one
  655. \*[Gt]18 lelong 2 two
  656. \*[Gt]18 default x
  657. # print default match
  658. \*[Gt]\*[Gt]18 lelong x unmatched 0x%x
  659. .Ed
  660. .Sh SEE ALSO
  661. .Xr file __CSECTION__
  662. \- the command that reads this file.
  663. .Sh BUGS
  664. The formats
  665. .Dv long ,
  666. .Dv belong ,
  667. .Dv lelong ,
  668. .Dv melong ,
  669. .Dv short ,
  670. .Dv beshort ,
  671. and
  672. .Dv leshort
  673. do not depend on the length of the C data types
  674. .Dv short
  675. and
  676. .Dv long
  677. on the platform, even though the Single
  678. .Ux
  679. Specification implies that they do. However, as OS X Mountain Lion has
  680. passed the Single
  681. .Ux
  682. Specification validation suite, and supplies a version of
  683. .Xr file __CSECTION__
  684. in which they do not depend on the sizes of the C data types and that is
  685. built for a 64-bit environment in which
  686. .Dv long
  687. is 8 bytes rather than 4 bytes, presumably the validation suite does not
  688. test whether, for example
  689. .Dv long
  690. refers to an item with the same size as the C data type
  691. .Dv long .
  692. There should probably be
  693. .Dv type
  694. names
  695. .Dv int8 ,
  696. .Dv uint8 ,
  697. .Dv int16 ,
  698. .Dv uint16 ,
  699. .Dv int32 ,
  700. .Dv uint32 ,
  701. .Dv int64 ,
  702. and
  703. .Dv uint64 ,
  704. and specified-byte-order variants of them,
  705. to make it clearer that those types have specified widths.
  706. .\"
  707. .\" From: guy@sun.uucp (Guy Harris)
  708. .\" Newsgroups: net.bugs.usg
  709. .\" Subject: /etc/magic's format isn't well documented
  710. .\" Message-ID: <2752@sun.uucp>
  711. .\" Date: 3 Sep 85 08:19:07 GMT
  712. .\" Organization: Sun Microsystems, Inc.
  713. .\" Lines: 136
  714. .\"
  715. .\" Here's a manual page for the format accepted by the "file" made by adding
  716. .\" the changes I posted to the S5R2 version.
  717. .\"
  718. .\" Modified for Ian Darwin's version of the file command.