magic.man 24 KB

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  1. .\" $File: magic.man,v 1.98 2020/05/09 18:55:23 christos Exp $
  2. .Dd May 9, 2020
  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 magic files 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 database of these
  21. .Dq "magic patterns"
  22. is usually located in a binary file in
  23. .Pa __MAGIC__.mgc
  24. or a directory of source text magic pattern fragment files in
  25. .Pa __MAGIC__ .
  26. The database specifies what patterns are to be tested for, what message or
  27. MIME type to print if a particular pattern is found,
  28. and additional information to extract from the file.
  29. .Pp
  30. The format of the source fragment files that are used to build this database
  31. is as follows:
  32. Each line of a fragment file specifies a test to be performed.
  33. A test compares the data starting at a particular offset
  34. in the file with a byte value, a string or a numeric value.
  35. If the test succeeds, a message is printed.
  36. The line consists of the following fields:
  37. .Bl -tag -width ".Dv message"
  38. .It Dv offset
  39. A number specifying the offset (in bytes) into the file of the data
  40. which is to be tested.
  41. This offset can be a negative number if it is:
  42. .Bl -bullet -compact
  43. .It
  44. The first direct offset of the magic entry (at continuation level 0),
  45. in which case it is interpreted an offset from end end of the file
  46. going backwards.
  47. This works only when a file descriptor to the file is available and it
  48. is a regular file.
  49. .It
  50. A continuation offset relative to the end of the last up-level field
  51. .Dv ( \*[Am] ) .
  52. .El
  53. .It Dv type
  54. The type of the data to be tested.
  55. The possible values are:
  56. .Bl -tag -width ".Dv lestring16"
  57. .It Dv byte
  58. A one-byte value.
  59. .It Dv short
  60. A two-byte value in this machine's native byte order.
  61. .It Dv long
  62. A four-byte value in this machine's native byte order.
  63. .It Dv quad
  64. An eight-byte value in this machine's native byte order.
  65. .It Dv float
  66. A 32-bit single precision IEEE floating point number in this machine's native byte order.
  67. .It Dv double
  68. A 64-bit double precision IEEE floating point number in this machine's native byte order.
  69. .It Dv string
  70. A string of bytes.
  71. The string type specification can be optionally followed
  72. by /[WwcCtbT]*.
  73. The
  74. .Dq W
  75. flag compacts whitespace in the target, which must
  76. contain at least one whitespace character.
  77. If the magic has
  78. .Dv n
  79. consecutive blanks, the target needs at least
  80. .Dv n
  81. consecutive blanks to match.
  82. The
  83. .Dq w
  84. flag treats every blank in the magic as an optional blank.
  85. The
  86. .Dq c
  87. flag specifies case insensitive matching: lower case
  88. characters in the magic match both lower and upper case characters in the
  89. target, whereas upper case characters in the magic only match upper case
  90. characters in the target.
  91. The
  92. .Dq C
  93. flag specifies case insensitive matching: upper case
  94. characters in the magic match both lower and upper case characters in the
  95. target, whereas lower case characters in the magic only match upper case
  96. characters in the target.
  97. To do a complete case insensitive match, specify both
  98. .Dq c
  99. and
  100. .Dq C .
  101. The
  102. .Dq t
  103. flag forces the test to be done for text files, while the
  104. .Dq b
  105. flag forces the test to be done for binary files.
  106. The
  107. .Dq T
  108. flag causes the string to be trimmed, i.e. leading and trailing whitespace
  109. is deleted before the string is printed.
  110. .It Dv pstring
  111. A Pascal-style string where the first byte/short/int is interpreted as the
  112. unsigned length.
  113. The length defaults to byte and can be specified as a modifier.
  114. The following modifiers are supported:
  115. .Bl -tag -compact -width B
  116. .It B
  117. A byte length (default).
  118. .It H
  119. A 2 byte big endian length.
  120. .It h
  121. A 2 byte little endian length.
  122. .It L
  123. A 4 byte big endian length.
  124. .It l
  125. A 4 byte little endian length.
  126. .It J
  127. The length includes itself in its count.
  128. .El
  129. The string is not NUL terminated.
  130. .Dq J
  131. is used rather than the more
  132. valuable
  133. .Dq I
  134. because this type of length is a feature of the JPEG
  135. format.
  136. .It Dv date
  137. A four-byte value interpreted as a UNIX date.
  138. .It Dv qdate
  139. An eight-byte value interpreted as a UNIX date.
  140. .It Dv ldate
  141. A four-byte value interpreted as a UNIX-style date, but interpreted as
  142. local time rather than UTC.
  143. .It Dv qldate
  144. An eight-byte value interpreted as a UNIX-style date, but interpreted as
  145. local time rather than UTC.
  146. .It Dv qwdate
  147. An eight-byte value interpreted as a Windows-style date.
  148. .It Dv beid3
  149. A 32-bit ID3 length in big-endian byte order.
  150. .It Dv beshort
  151. A two-byte value in big-endian byte order.
  152. .It Dv belong
  153. A four-byte value in big-endian byte order.
  154. .It Dv bequad
  155. An eight-byte value in big-endian byte order.
  156. .It Dv befloat
  157. A 32-bit single precision IEEE floating point number in big-endian byte order.
  158. .It Dv bedouble
  159. A 64-bit double precision IEEE floating point number in big-endian byte order.
  160. .It Dv bedate
  161. A four-byte value in big-endian byte order,
  162. interpreted as a Unix date.
  163. .It Dv beqdate
  164. An eight-byte value in big-endian byte order,
  165. interpreted as a Unix date.
  166. .It Dv beldate
  167. A four-byte value in big-endian byte order,
  168. interpreted as a UNIX-style date, but interpreted as local time rather
  169. than UTC.
  170. .It Dv beqldate
  171. An eight-byte value in big-endian byte order,
  172. interpreted as a UNIX-style date, but interpreted as local time rather
  173. than UTC.
  174. .It Dv beqwdate
  175. An eight-byte value in big-endian byte order,
  176. interpreted as a Windows-style date.
  177. .It Dv bestring16
  178. A two-byte unicode (UCS16) string in big-endian byte order.
  179. .It Dv leid3
  180. A 32-bit ID3 length in little-endian byte order.
  181. .It Dv leshort
  182. A two-byte value in little-endian byte order.
  183. .It Dv lelong
  184. A four-byte value in little-endian byte order.
  185. .It Dv lequad
  186. An eight-byte value in little-endian byte order.
  187. .It Dv lefloat
  188. A 32-bit single precision IEEE floating point number in little-endian byte order.
  189. .It Dv ledouble
  190. A 64-bit double precision IEEE floating point number in little-endian byte order.
  191. .It Dv ledate
  192. A four-byte value in little-endian byte order,
  193. interpreted as a UNIX date.
  194. .It Dv leqdate
  195. An eight-byte value in little-endian byte order,
  196. interpreted as a UNIX date.
  197. .It Dv leldate
  198. A four-byte value in little-endian byte order,
  199. interpreted as a UNIX-style date, but interpreted as local time rather
  200. than UTC.
  201. .It Dv leqldate
  202. An eight-byte value in little-endian byte order,
  203. interpreted as a UNIX-style date, but interpreted as local time rather
  204. than UTC.
  205. .It Dv leqwdate
  206. An eight-byte value in little-endian byte order,
  207. interpreted as a Windows-style date.
  208. .It Dv lestring16
  209. A two-byte unicode (UCS16) string in little-endian byte order.
  210. .It Dv melong
  211. A four-byte value in middle-endian (PDP-11) byte order.
  212. .It Dv medate
  213. A four-byte value in middle-endian (PDP-11) byte order,
  214. interpreted as a UNIX date.
  215. .It Dv meldate
  216. A four-byte value in middle-endian (PDP-11) byte order,
  217. interpreted as a UNIX-style date, but interpreted as local time rather
  218. than UTC.
  219. .It Dv indirect
  220. Starting at the given offset, consult the magic database again.
  221. The offset of the
  222. .Dv indirect
  223. magic is by default absolute in the file, but one can specify
  224. .Dv /r
  225. to indicate that the offset is relative from the beginning of the entry.
  226. .It Dv name
  227. Define a
  228. .Dq named
  229. magic instance that can be called from another
  230. .Dv use
  231. magic entry, like a subroutine call.
  232. Named instance direct magic offsets are relative to the offset of the
  233. previous matched entry, but indirect offsets are relative to the beginning
  234. of the file as usual.
  235. Named magic entries always match.
  236. .It Dv use
  237. Recursively call the named magic starting from the current offset.
  238. If the name of the referenced begins with a
  239. .Dv ^
  240. then the endianness of the magic is switched; if the magic mentioned
  241. .Dv leshort
  242. for example,
  243. it is treated as
  244. .Dv beshort
  245. and vice versa.
  246. This is useful to avoid duplicating the rules for different endianness.
  247. .It Dv regex
  248. A regular expression match in extended POSIX regular expression syntax
  249. (like egrep).
  250. Regular expressions can take exponential time to process, and their
  251. performance is hard to predict, so their use is discouraged.
  252. When used in production environments, their performance
  253. should be carefully checked.
  254. The size of the string to search should also be limited by specifying
  255. .Dv /<length> ,
  256. to avoid performance issues scanning long files.
  257. The type specification can also be optionally followed by
  258. .Dv /[c][s][l] .
  259. The
  260. .Dq c
  261. flag makes the match case insensitive, while the
  262. .Dq s
  263. flag update the offset to the start offset of the match, rather than the end.
  264. The
  265. .Dq l
  266. modifier, changes the limit of length to mean number of lines instead of a
  267. byte count.
  268. Lines are delimited by the platforms native line delimiter.
  269. When a line count is specified, an implicit byte count also computed assuming
  270. each line is 80 characters long.
  271. If neither a byte or line count is specified, the search is limited automatically
  272. to 8KiB.
  273. .Dv ^
  274. and
  275. .Dv $
  276. match the beginning and end of individual lines, respectively,
  277. not beginning and end of file.
  278. .It Dv search
  279. A literal string search starting at the given offset.
  280. The same modifier flags can be used as for string patterns.
  281. The search expression must contain the range in the form
  282. .Dv /number,
  283. that is the number of positions at which the match will be
  284. attempted, starting from the start offset.
  285. This is suitable for
  286. searching larger binary expressions with variable offsets, using
  287. .Dv \e
  288. escapes for special characters.
  289. The order of modifier and number is not relevant.
  290. .It Dv default
  291. This is intended to be used with the test
  292. .Em x
  293. (which is always true) and it has no type.
  294. It matches when no other test at that continuation level has matched before.
  295. Clearing that matched tests for a continuation level, can be done using the
  296. .Dv clear
  297. test.
  298. .It Dv clear
  299. This test is always true and clears the match flag for that continuation level.
  300. It is intended to be used with the
  301. .Dv default
  302. test.
  303. .It Dv der
  304. Parse the file as a DER Certificate file.
  305. The test field is used as a der type that needs to be matched.
  306. The DER types are:
  307. .Dv eoc ,
  308. .Dv bool ,
  309. .Dv int ,
  310. .Dv bit_str ,
  311. .Dv octet_str ,
  312. .Dv null ,
  313. .Dv obj_id ,
  314. .Dv obj_desc ,
  315. .Dv ext ,
  316. .Dv real ,
  317. .Dv enum ,
  318. .Dv embed ,
  319. .Dv utf8_str ,
  320. .Dv rel_oid ,
  321. .Dv time ,
  322. .Dv res2 ,
  323. .Dv seq ,
  324. .Dv set ,
  325. .Dv num_str ,
  326. .Dv prt_str ,
  327. .Dv t61_str ,
  328. .Dv vid_str ,
  329. .Dv ia5_str ,
  330. .Dv utc_time ,
  331. .Dv gen_time ,
  332. .Dv gr_str ,
  333. .Dv vis_str ,
  334. .Dv gen_str ,
  335. .Dv univ_str ,
  336. .Dv char_str ,
  337. .Dv bmp_str ,
  338. .Dv date ,
  339. .Dv tod ,
  340. .Dv datetime ,
  341. .Dv duration ,
  342. .Dv oid-iri ,
  343. .Dv rel-oid-iri .
  344. These types can be followed by an optional numeric size, which indicates
  345. the field width in bytes.
  346. .It Dv guid
  347. A Globally Unique Identifier, parsed and printed as
  348. XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX.
  349. It's format is a string.
  350. .It Dv offset
  351. This is a quad value indicating the current offset of the file.
  352. It can be used to determine the size of the file or the magic buffer.
  353. For example the magic entries:
  354. .Bd -literal -offset indent
  355. -0 offset x this file is %lld bytes
  356. -0 offset <=100 must be more than 100 \e
  357. bytes and is only %lld
  358. .Ed
  359. .El
  360. .Pp
  361. For compatibility with the Single
  362. .Ux
  363. Standard, the type specifiers
  364. .Dv dC
  365. and
  366. .Dv d1
  367. are equivalent to
  368. .Dv byte ,
  369. the type specifiers
  370. .Dv uC
  371. and
  372. .Dv u1
  373. are equivalent to
  374. .Dv ubyte ,
  375. the type specifiers
  376. .Dv dS
  377. and
  378. .Dv d2
  379. are equivalent to
  380. .Dv short ,
  381. the type specifiers
  382. .Dv uS
  383. and
  384. .Dv u2
  385. are equivalent to
  386. .Dv ushort ,
  387. the type specifiers
  388. .Dv dI ,
  389. .Dv dL ,
  390. and
  391. .Dv d4
  392. are equivalent to
  393. .Dv long ,
  394. the type specifiers
  395. .Dv uI ,
  396. .Dv uL ,
  397. and
  398. .Dv u4
  399. are equivalent to
  400. .Dv ulong ,
  401. the type specifier
  402. .Dv d8
  403. is equivalent to
  404. .Dv quad ,
  405. the type specifier
  406. .Dv u8
  407. is equivalent to
  408. .Dv uquad ,
  409. and the type specifier
  410. .Dv s
  411. is equivalent to
  412. .Dv string .
  413. In addition, the type specifier
  414. .Dv dQ
  415. is equivalent to
  416. .Dv quad
  417. and the type specifier
  418. .Dv uQ
  419. is equivalent to
  420. .Dv uquad .
  421. .Pp
  422. Each top-level magic pattern (see below for an explanation of levels)
  423. is classified as text or binary according to the types used.
  424. Types
  425. .Dq regex
  426. and
  427. .Dq search
  428. are classified as text tests, unless non-printable characters are used
  429. in the pattern.
  430. All other tests are classified as binary.
  431. A top-level
  432. pattern is considered to be a test text when all its patterns are text
  433. patterns; otherwise, it is considered to be a binary pattern.
  434. When
  435. matching a file, binary patterns are tried first; if no match is
  436. found, and the file looks like text, then its encoding is determined
  437. and the text patterns are tried.
  438. .Pp
  439. The numeric types may optionally be followed by
  440. .Dv \*[Am]
  441. and a numeric value,
  442. to specify that the value is to be AND'ed with the
  443. numeric value before any comparisons are done.
  444. Prepending a
  445. .Dv u
  446. to the type indicates that ordered comparisons should be unsigned.
  447. .It Dv test
  448. The value to be compared with the value from the file.
  449. If the type is
  450. numeric, this value
  451. is specified in C form; if it is a string, it is specified as a C string
  452. with the usual escapes permitted (e.g. \en for new-line).
  453. .Pp
  454. Numeric values
  455. may be preceded by a character indicating the operation to be performed.
  456. It may be
  457. .Dv = ,
  458. to specify that the value from the file must equal the specified value,
  459. .Dv \*[Lt] ,
  460. to specify that the value from the file must be less than the specified
  461. value,
  462. .Dv \*[Gt] ,
  463. to specify that the value from the file must be greater than the specified
  464. value,
  465. .Dv \*[Am] ,
  466. to specify that the value from the file must have set all of the bits
  467. that are set in the specified value,
  468. .Dv ^ ,
  469. to specify that the value from the file must have clear any of the bits
  470. that are set in the specified value, or
  471. .Dv ~ ,
  472. the value specified after is negated before tested.
  473. .Dv x ,
  474. to specify that any value will match.
  475. If the character is omitted, it is assumed to be
  476. .Dv = .
  477. Operators
  478. .Dv \*[Am] ,
  479. .Dv ^ ,
  480. and
  481. .Dv ~
  482. don't work with floats and doubles.
  483. The operator
  484. .Dv !\&
  485. specifies that the line matches if the test does
  486. .Em not
  487. succeed.
  488. .Pp
  489. Numeric values are specified in C form; e.g.
  490. .Dv 13
  491. is decimal,
  492. .Dv 013
  493. is octal, and
  494. .Dv 0x13
  495. is hexadecimal.
  496. .Pp
  497. Numeric operations are not performed on date types, instead the numeric
  498. value is interpreted as an offset.
  499. .Pp
  500. For string values, the string from the
  501. file must match the specified string.
  502. The operators
  503. .Dv = ,
  504. .Dv \*[Lt]
  505. and
  506. .Dv \*[Gt]
  507. (but not
  508. .Dv \*[Am] )
  509. can be applied to strings.
  510. The length used for matching is that of the string argument
  511. in the magic file.
  512. This means that a line can match any non-empty string (usually used to
  513. then print the string), with
  514. .Em \*[Gt]\e0
  515. (because all non-empty strings are greater than the empty string).
  516. .Pp
  517. Dates are treated as numerical values in the respective internal
  518. representation.
  519. .Pp
  520. The special test
  521. .Em x
  522. always evaluates to true.
  523. .It Dv message
  524. The message to be printed if the comparison succeeds.
  525. If the string contains a
  526. .Xr printf 3
  527. format specification, the value from the file (with any specified masking
  528. performed) is printed using the message as the format string.
  529. If the string begins with
  530. .Dq \eb ,
  531. the message printed is the remainder of the string with no whitespace
  532. added before it: multiple matches are normally separated by a single
  533. space.
  534. .El
  535. .Pp
  536. An APPLE 4+4 character APPLE creator and type can be specified as:
  537. .Bd -literal -offset indent
  538. !:apple CREATYPE
  539. .Ed
  540. .Pp
  541. A MIME type is given on a separate line, which must be the next
  542. non-blank or comment line after the magic line that identifies the
  543. file type, and has the following format:
  544. .Bd -literal -offset indent
  545. !:mime MIMETYPE
  546. .Ed
  547. .Pp
  548. i.e. the literal string
  549. .Dq !:mime
  550. followed by the MIME type.
  551. .Pp
  552. An optional strength can be supplied on a separate line which refers to
  553. the current magic description using the following format:
  554. .Bd -literal -offset indent
  555. !:strength OP VALUE
  556. .Ed
  557. .Pp
  558. The operand
  559. .Dv OP
  560. can be:
  561. .Dv + ,
  562. .Dv - ,
  563. .Dv * ,
  564. or
  565. .Dv /
  566. and
  567. .Dv VALUE
  568. is a constant between 0 and 255.
  569. This constant is applied using the specified operand
  570. to the currently computed default magic strength.
  571. .Pp
  572. Some file formats contain additional information which is to be printed
  573. along with the file type or need additional tests to determine the true
  574. file type.
  575. These additional tests are introduced by one or more
  576. .Em \*[Gt]
  577. characters preceding the offset.
  578. The number of
  579. .Em \*[Gt]
  580. on the line indicates the level of the test; a line with no
  581. .Em \*[Gt]
  582. at the beginning is considered to be at level 0.
  583. Tests are arranged in a tree-like hierarchy:
  584. if the test on a line at level
  585. .Em n
  586. succeeds, all following tests at level
  587. .Em n+1
  588. are performed, and the messages printed if the tests succeed, until a line
  589. with level
  590. .Em n
  591. (or less) appears.
  592. For more complex files, one can use empty messages to get just the
  593. "if/then" effect, in the following way:
  594. .Bd -literal -offset indent
  595. 0 string MZ
  596. \*[Gt]0x18 leshort \*[Lt]0x40 MS-DOS executable
  597. \*[Gt]0x18 leshort \*[Gt]0x3f extended PC executable (e.g., MS Windows)
  598. .Ed
  599. .Pp
  600. Offsets do not need to be constant, but can also be read from the file
  601. being examined.
  602. If the first character following the last
  603. .Em \*[Gt]
  604. is a
  605. .Em \&(
  606. then the string after the parenthesis is interpreted as an indirect offset.
  607. That means that the number after the parenthesis is used as an offset in
  608. the file.
  609. The value at that offset is read, and is used again as an offset
  610. in the file.
  611. Indirect offsets are of the form:
  612. .Em (( x [[.,][bBcCeEfFgGhHiIlmsSqQ]][+\-][ y ]) .
  613. The value of
  614. .Em x
  615. is used as an offset in the file.
  616. A byte, id3 length, short or long is read at that offset depending on the
  617. .Em [bBcCeEfFgGhHiIlmsSqQ]
  618. type specifier.
  619. The value is treated as signed if
  620. .Dq ,
  621. is specified or unsigned if
  622. .Dq .
  623. is specified.
  624. The capitalized types interpret the number as a big endian
  625. value, whereas the small letter versions interpret the number as a little
  626. endian value;
  627. the
  628. .Em m
  629. type interprets the number as a middle endian (PDP-11) value.
  630. To that number the value of
  631. .Em y
  632. is added and the result is used as an offset in the file.
  633. The default type if one is not specified is long.
  634. The following types are recognized:
  635. .Bl -column -offset indent "Type" "Half/Short" "Little" "Size"
  636. .It Sy Type Sy Mnemonic Sy Endian Sy Size
  637. .It bcBc Byte/Char N/A 1
  638. .It efg Double Little 8
  639. .It EFG Double Big 8
  640. .It hs Half/Short Little 2
  641. .It HS Half/Short Big 2
  642. .It i ID3 Little 4
  643. .It I ID3 Big 4
  644. .It m Middle Middle 4
  645. .It q Quad Little 8
  646. .It Q Quad Big 8
  647. .El
  648. .Pp
  649. That way variable length structures can be examined:
  650. .Bd -literal -offset indent
  651. # MS Windows executables are also valid MS-DOS executables
  652. 0 string MZ
  653. \*[Gt]0x18 leshort \*[Lt]0x40 MZ executable (MS-DOS)
  654. # skip the whole block below if it is not an extended executable
  655. \*[Gt]0x18 leshort \*[Gt]0x3f
  656. \*[Gt]\*[Gt](0x3c.l) string PE\e0\e0 PE executable (MS-Windows)
  657. \*[Gt]\*[Gt](0x3c.l) string LX\e0\e0 LX executable (OS/2)
  658. .Ed
  659. .Pp
  660. This strategy of examining has a drawback: you must make sure that you
  661. eventually print something, or users may get empty output (such as when
  662. there is neither PE\e0\e0 nor LE\e0\e0 in the above example).
  663. .Pp
  664. If this indirect offset cannot be used directly, simple calculations are
  665. possible: appending
  666. .Em [+-*/%\*[Am]|^]number
  667. inside parentheses allows one to modify
  668. the value read from the file before it is used as an offset:
  669. .Bd -literal -offset indent
  670. # MS Windows executables are also valid MS-DOS executables
  671. 0 string MZ
  672. # sometimes, the value at 0x18 is less that 0x40 but there's still an
  673. # extended executable, simply appended to the file
  674. \*[Gt]0x18 leshort \*[Lt]0x40
  675. \*[Gt]\*[Gt](4.s*512) leshort 0x014c COFF executable (MS-DOS, DJGPP)
  676. \*[Gt]\*[Gt](4.s*512) leshort !0x014c MZ executable (MS-DOS)
  677. .Ed
  678. .Pp
  679. Sometimes you do not know the exact offset as this depends on the length or
  680. position (when indirection was used before) of preceding fields.
  681. You can specify an offset relative to the end of the last up-level
  682. field using
  683. .Sq \*[Am]
  684. as a prefix to the offset:
  685. .Bd -literal -offset indent
  686. 0 string MZ
  687. \*[Gt]0x18 leshort \*[Gt]0x3f
  688. \*[Gt]\*[Gt](0x3c.l) string PE\e0\e0 PE executable (MS-Windows)
  689. # immediately following the PE signature is the CPU type
  690. \*[Gt]\*[Gt]\*[Gt]\*[Am]0 leshort 0x14c for Intel 80386
  691. \*[Gt]\*[Gt]\*[Gt]\*[Am]0 leshort 0x184 for DEC Alpha
  692. .Ed
  693. .Pp
  694. Indirect and relative offsets can be combined:
  695. .Bd -literal -offset indent
  696. 0 string MZ
  697. \*[Gt]0x18 leshort \*[Lt]0x40
  698. \*[Gt]\*[Gt](4.s*512) leshort !0x014c MZ executable (MS-DOS)
  699. # if it's not COFF, go back 512 bytes and add the offset taken
  700. # from byte 2/3, which is yet another way of finding the start
  701. # of the extended executable
  702. \*[Gt]\*[Gt]\*[Gt]\*[Am](2.s-514) string LE LE executable (MS Windows VxD driver)
  703. .Ed
  704. .Pp
  705. Or the other way around:
  706. .Bd -literal -offset indent
  707. 0 string MZ
  708. \*[Gt]0x18 leshort \*[Gt]0x3f
  709. \*[Gt]\*[Gt](0x3c.l) string LE\e0\e0 LE executable (MS-Windows)
  710. # at offset 0x80 (-4, since relative offsets start at the end
  711. # of the up-level match) inside the LE header, we find the absolute
  712. # offset to the code area, where we look for a specific signature
  713. \*[Gt]\*[Gt]\*[Gt](\*[Am]0x7c.l+0x26) string UPX \eb, UPX compressed
  714. .Ed
  715. .Pp
  716. Or even both!
  717. .Bd -literal -offset indent
  718. 0 string MZ
  719. \*[Gt]0x18 leshort \*[Gt]0x3f
  720. \*[Gt]\*[Gt](0x3c.l) string LE\e0\e0 LE executable (MS-Windows)
  721. # at offset 0x58 inside the LE header, we find the relative offset
  722. # to a data area where we look for a specific signature
  723. \*[Gt]\*[Gt]\*[Gt]\*[Am](\*[Am]0x54.l-3) string UNACE \eb, ACE self-extracting archive
  724. .Ed
  725. .Pp
  726. If you have to deal with offset/length pairs in your file, even the
  727. second value in a parenthesized expression can be taken from the file itself,
  728. using another set of parentheses.
  729. Note that this additional indirect offset is always relative to the
  730. start of the main indirect offset.
  731. .Bd -literal -offset indent
  732. 0 string MZ
  733. \*[Gt]0x18 leshort \*[Gt]0x3f
  734. \*[Gt]\*[Gt](0x3c.l) string PE\e0\e0 PE executable (MS-Windows)
  735. # search for the PE section called ".idata"...
  736. \*[Gt]\*[Gt]\*[Gt]\*[Am]0xf4 search/0x140 .idata
  737. # ...and go to the end of it, calculated from start+length;
  738. # these are located 14 and 10 bytes after the section name
  739. \*[Gt]\*[Gt]\*[Gt]\*[Gt](\*[Am]0xe.l+(-4)) string PK\e3\e4 \eb, ZIP self-extracting archive
  740. .Ed
  741. .Pp
  742. If you have a list of known values at a particular continuation level,
  743. and you want to provide a switch-like default case:
  744. .Bd -literal -offset indent
  745. # clear that continuation level match
  746. \*[Gt]18 clear
  747. \*[Gt]18 lelong 1 one
  748. \*[Gt]18 lelong 2 two
  749. \*[Gt]18 default x
  750. # print default match
  751. \*[Gt]\*[Gt]18 lelong x unmatched 0x%x
  752. .Ed
  753. .Sh SEE ALSO
  754. .Xr file __CSECTION__
  755. \- the command that reads this file.
  756. .Sh BUGS
  757. The formats
  758. .Dv long ,
  759. .Dv belong ,
  760. .Dv lelong ,
  761. .Dv melong ,
  762. .Dv short ,
  763. .Dv beshort ,
  764. and
  765. .Dv leshort
  766. do not depend on the length of the C data types
  767. .Dv short
  768. and
  769. .Dv long
  770. on the platform, even though the Single
  771. .Ux
  772. Specification implies that they do. However, as OS X Mountain Lion has
  773. passed the Single
  774. .Ux
  775. Specification validation suite, and supplies a version of
  776. .Xr file __CSECTION__
  777. in which they do not depend on the sizes of the C data types and that is
  778. built for a 64-bit environment in which
  779. .Dv long
  780. is 8 bytes rather than 4 bytes, presumably the validation suite does not
  781. test whether, for example
  782. .Dv long
  783. refers to an item with the same size as the C data type
  784. .Dv long .
  785. There should probably be
  786. .Dv type
  787. names
  788. .Dv int8 ,
  789. .Dv uint8 ,
  790. .Dv int16 ,
  791. .Dv uint16 ,
  792. .Dv int32 ,
  793. .Dv uint32 ,
  794. .Dv int64 ,
  795. and
  796. .Dv uint64 ,
  797. and specified-byte-order variants of them,
  798. to make it clearer that those types have specified widths.
  799. .\"
  800. .\" From: guy@sun.uucp (Guy Harris)
  801. .\" Newsgroups: net.bugs.usg
  802. .\" Subject: /etc/magic's format isn't well documented
  803. .\" Message-ID: <2752@sun.uucp>
  804. .\" Date: 3 Sep 85 08:19:07 GMT
  805. .\" Organization: Sun Microsystems, Inc.
  806. .\" Lines: 136
  807. .\"
  808. .\" Here's a manual page for the format accepted by the "file" made by adding
  809. .\" the changes I posted to the S5R2 version.
  810. .\"
  811. .\" Modified for Ian Darwin's version of the file command.