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  1. .\" $File:,v 1.82 2009/11/04 22:30:34 christos Exp $
  2. .Dd October 9, 2008
  3. .Dt FILE __CSECTION__
  4. .Os
  5. .Sh NAME
  6. .Nm file
  7. .Nd determine file type
  9. .Nm
  10. .Bk -words
  11. .Op Fl bchikLNnprsvz0
  12. .Op Fl -apple
  13. .Op Fl -mime-encoding
  14. .Op Fl -mime-type
  15. .Op Fl e Ar testname
  16. .Op Fl F Ar separator
  17. .Op Fl f Ar namefile
  18. .Op Fl m Ar magicfiles
  19. .Ar
  20. .Ek -words
  21. .Nm
  22. .Fl C
  23. .Op Fl m Ar magicfiles
  24. .Nm
  25. .Op Fl -help
  27. This manual page documents version __VERSION__ of the
  28. .Nm
  29. command.
  30. .Pp
  31. .Nm
  32. tests each argument in an attempt to classify it.
  33. There are three sets of tests, performed in this order:
  34. filesystem tests, magic tests, and language tests.
  35. The
  36. .Em first
  37. test that succeeds causes the file type to be printed.
  38. .Pp
  39. The type printed will usually contain one of the words
  40. .Em text
  41. (the file contains only
  42. printing characters and a few common control
  43. characters and is probably safe to read on an
  44. .Dv ASCII
  45. terminal),
  46. .Em executable
  47. (the file contains the result of compiling a program
  48. in a form understandable to some
  49. .Dv UNIX
  50. kernel or another),
  51. or
  52. .Em data
  53. meaning anything else (data is usually
  54. .Sq binary
  55. or non-printable).
  56. Exceptions are well-known file formats (core files, tar archives)
  57. that are known to contain binary data.
  58. When modifying magic files or the program itself, make sure to
  59. .Em "preserve these keywords" .
  60. Users depend on knowing that all the readable files in a directory
  61. have the word
  62. .Sq text
  63. printed.
  64. Don't do as Berkeley did and change
  65. .Sq shell commands text
  66. to
  67. .Sq shell script .
  68. .Pp
  69. The filesystem tests are based on examining the return from a
  70. .Xr stat 2
  71. system call.
  72. The program checks to see if the file is empty,
  73. or if it's some sort of special file.
  74. Any known file types appropriate to the system you are running on
  75. (sockets, symbolic links, or named pipes (FIFOs) on those systems that
  76. implement them)
  77. are intuited if they are defined in
  78. the system header file
  79. .In sys/stat.h .
  80. .Pp
  81. The magic tests are used to check for files with data in
  82. particular fixed formats.
  83. The canonical example of this is a binary executable (compiled program)
  84. .Dv a.out
  85. file, whose format is defined in
  86. .In elf.h ,
  87. .In a.out.h
  88. and possibly
  89. .In exec.h
  90. in the standard include directory.
  91. These files have a
  92. .Sq "magic number"
  93. stored in a particular place
  94. near the beginning of the file that tells the
  95. .Dv UNIX operating system
  96. that the file is a binary executable, and which of several types thereof.
  97. The concept of a
  98. .Sq "magic"
  99. has been applied by extension to data files.
  100. Any file with some invariant identifier at a small fixed
  101. offset into the file can usually be described in this way.
  102. The information identifying these files is read from the compiled
  103. magic file
  104. .Pa __MAGIC__.mgc ,
  105. or the files in the directory
  106. .Pa __MAGIC__
  107. if the compiled file does not exist. In addition, if
  108. .Pa $HOME/.magic.mgc
  109. or
  110. .Pa $HOME/.magic
  111. exists, it will be used in preference to the system magic files.
  112. .Pp
  113. If a file does not match any of the entries in the magic file,
  114. it is examined to see if it seems to be a text file.
  115. ASCII, ISO-8859-x, non-ISO 8-bit extended-ASCII character sets
  116. (such as those used on Macintosh and IBM PC systems),
  117. UTF-8-encoded Unicode, UTF-16-encoded Unicode, and EBCDIC
  118. character sets can be distinguished by the different
  119. ranges and sequences of bytes that constitute printable text
  120. in each set.
  121. If a file passes any of these tests, its character set is reported.
  122. ASCII, ISO-8859-x, UTF-8, and extended-ASCII files are identified
  123. as
  124. .Sq text
  125. because they will be mostly readable on nearly any terminal;
  126. UTF-16 and EBCDIC are only
  127. .Sq character data
  128. because, while
  129. they contain text, it is text that will require translation
  130. before it can be read.
  131. In addition,
  132. .Nm
  133. will attempt to determine other characteristics of text-type files.
  134. If the lines of a file are terminated by CR, CRLF, or NEL, instead
  135. of the Unix-standard LF, this will be reported.
  136. Files that contain embedded escape sequences or overstriking
  137. will also be identified.
  138. .Pp
  139. Once
  140. .Nm
  141. has determined the character set used in a text-type file,
  142. it will
  143. attempt to determine in what language the file is written.
  144. The language tests look for particular strings (cf.
  145. .In names.h
  146. ) that can appear anywhere in the first few blocks of a file.
  147. For example, the keyword
  148. .Em .br
  149. indicates that the file is most likely a
  150. .Xr troff 1
  151. input file, just as the keyword
  152. .Em struct
  153. indicates a C program.
  154. These tests are less reliable than the previous
  155. two groups, so they are performed last.
  156. The language test routines also test for some miscellany
  157. (such as
  158. .Xr tar 1
  159. archives).
  160. .Pp
  161. Any file that cannot be identified as having been written
  162. in any of the character sets listed above is simply said to be
  163. .Sq data .
  164. .Sh OPTIONS
  165. .Bl -tag -width indent
  166. .It Fl b , -brief
  167. Do not prepend filenames to output lines (brief mode).
  168. .It Fl C , -compile
  169. Write a
  170. .Pa magic.mgc
  171. output file that contains a pre-parsed version of the magic file or directory.
  172. .It Fl c , -checking-printout
  173. Cause a checking printout of the parsed form of the magic file.
  174. This is usually used in conjunction with the
  175. .Fl m
  176. flag to debug a new magic file before installing it.
  177. .It Fl e , -exclude Ar testname
  178. Exclude the test named in
  179. .Ar testname
  180. from the list of tests made to determine the file type. Valid test names
  181. are:
  182. .Bl -tag -width compress
  183. .It apptype
  184. .Dv EMX
  185. application type (only on EMX).
  186. .It text
  187. Various types of text files (this test will try to guess the text encoding, irrespective of the setting of the
  188. .Sq encoding
  189. option).
  190. .It encoding
  191. Different text encodings for soft magic tests.
  192. .It tokens
  193. Looks for known tokens inside text files.
  194. .It cdf
  195. Prints details of Compound Document Files.
  196. .It compress
  197. Checks for, and looks inside, compressed files.
  198. .It elf
  199. Prints ELF file details.
  200. .It soft
  201. Consults magic files.
  202. .It tar
  203. Examines tar files.
  204. .El
  205. .It Fl F , -separator Ar separator
  206. Use the specified string as the separator between the filename and the
  207. file result returned. Defaults to
  208. .Sq \&: .
  209. .It Fl f , -files-from Ar namefile
  210. Read the names of the files to be examined from
  211. .Ar namefile
  212. (one per line)
  213. before the argument list.
  214. Either
  215. .Ar namefile
  216. or at least one filename argument must be present;
  217. to test the standard input, use
  218. .Sq -
  219. as a filename argument.
  220. .It Fl h , -no-dereference
  221. option causes symlinks not to be followed
  222. (on systems that support symbolic links). This is the default if the
  223. environment variable
  225. is not defined.
  226. .It Fl i , -mime
  227. Causes the file command to output mime type strings rather than the more
  228. traditional human readable ones. Thus it may say
  229. .Sq text/plain; charset=us-ascii
  230. rather than
  231. .Sq ASCII text .
  232. In order for this option to work, file changes the way
  233. it handles files recognized by the command itself (such as many of the
  234. text file types, directories etc), and makes use of an alternative
  235. .Sq magic
  236. file.
  237. (See the FILES section, below).
  238. .It Fl -mime-type , -mime-encoding
  239. Like
  240. .Fl i ,
  241. but print only the specified element(s).
  242. .It Fl k , -keep-going
  243. Don't stop at the first match, keep going. Subsequent matches will be
  244. have the string
  245. .Sq "\[rs]012\- "
  246. prepended.
  247. (If you want a newline, see the
  248. .Sq "\-r"
  249. option.)
  250. .It Fl L , -dereference
  251. option causes symlinks to be followed, as the like-named option in
  252. .Xr ls 1
  253. (on systems that support symbolic links).
  254. This is the default if the environment variable
  256. is defined.
  257. .It Fl m , -magic-file Ar magicfiles
  258. Specify an alternate list of files and directories containing magic.
  259. This can be a single item, or a colon-separated list.
  260. If a compiled magic file is found alongside a file or directory, it will be used instead.
  261. .It Fl N , -no-pad
  262. Don't pad filenames so that they align in the output.
  263. .It Fl n , -no-buffer
  264. Force stdout to be flushed after checking each file.
  265. This is only useful if checking a list of files.
  266. It is intended to be used by programs that want filetype output from a pipe.
  267. .It Fl p , -preserve-date
  268. On systems that support
  269. .Xr utime 2
  270. or
  271. .Xr utimes 2 ,
  272. attempt to preserve the access time of files analyzed, to pretend that
  273. .Nm
  274. never read them.
  275. .It Fl r , -raw
  276. Don't translate unprintable characters to \eooo.
  277. Normally
  278. .Nm
  279. translates unprintable characters to their octal representation.
  280. .It Fl s , -special-files
  281. Normally,
  282. .Nm
  283. only attempts to read and determine the type of argument files which
  284. .Xr stat 2
  285. reports are ordinary files.
  286. This prevents problems, because reading special files may have peculiar
  287. consequences.
  288. Specifying the
  289. .Fl s
  290. option causes
  291. .Nm
  292. to also read argument files which are block or character special files.
  293. This is useful for determining the filesystem types of the data in raw
  294. disk partitions, which are block special files.
  295. This option also causes
  296. .Nm
  297. to disregard the file size as reported by
  298. .Xr stat 2
  299. since on some systems it reports a zero size for raw disk partitions.
  300. .It Fl v , -version
  301. Print the version of the program and exit.
  302. .It Fl z , -uncompress
  303. Try to look inside compressed files.
  304. .It Fl 0 , -print0
  305. Output a null character
  306. .Sq \e0
  307. after the end of the filename. Nice to
  308. .Xr cut 1
  309. the output. This does not affect the separator which is still printed.
  310. .It Fl -help
  311. Print a help message and exit.
  312. .El
  313. .Sh FILES
  314. .Bl -tag -width __MAGIC__.mgc -compact
  315. .It Pa __MAGIC__.mgc
  316. Default compiled list of magic.
  317. .It Pa __MAGIC__
  318. Directory containing default magic files.
  319. .El
  321. The environment variable
  322. .Dv MAGIC
  323. can be used to set the default magic file name.
  324. If that variable is set, then
  325. .Nm
  326. will not attempt to open
  327. .Pa $HOME/.magic .
  328. .Nm
  329. adds
  330. .Sq .mgc
  331. to the value of this variable as appropriate.
  332. The environment variable
  334. controls (on systems that support symbolic links), whether
  335. .Nm
  336. will attempt to follow symlinks or not. If set, then
  337. .Nm
  338. follows symlink, otherwise it does not. This is also controlled
  339. by the
  340. .Fl L
  341. and
  342. .Fl h
  343. options.
  344. .Sh SEE ALSO
  345. .Xr magic __FSECTION__ ,
  346. .Xr strings 1 ,
  347. .Xr od 1 ,
  348. .Xr hexdump 1,
  349. .Xr file 1posix
  351. This program is believed to exceed the System V Interface Definition
  352. of FILE(CMD), as near as one can determine from the vague language
  353. contained therein.
  354. Its behavior is mostly compatible with the System V program of the same name.
  355. This version knows more magic, however, so it will produce
  356. different (albeit more accurate) output in many cases.
  357. .\" URL:
  358. .Pp
  359. The one significant difference
  360. between this version and System V
  361. is that this version treats any white space
  362. as a delimiter, so that spaces in pattern strings must be escaped.
  363. For example,
  364. .Bd -literal -offset indent
  365. >10 string language impress\ (imPRESS data)
  366. .Ed
  367. .Pp
  368. in an existing magic file would have to be changed to
  369. .Bd -literal -offset indent
  370. >10 string language\e impress (imPRESS data)
  371. .Ed
  372. .Pp
  373. In addition, in this version, if a pattern string contains a backslash,
  374. it must be escaped.
  375. For example
  376. .Bd -literal -offset indent
  377. 0 string \ebegindata Andrew Toolkit document
  378. .Ed
  379. .Pp
  380. in an existing magic file would have to be changed to
  381. .Bd -literal -offset indent
  382. 0 string \e\ebegindata Andrew Toolkit document
  383. .Ed
  384. .Pp
  385. SunOS releases 3.2 and later from Sun Microsystems include a
  386. .Nm
  387. command derived from the System V one, but with some extensions.
  388. My version differs from Sun's only in minor ways.
  389. It includes the extension of the
  390. .Sq &
  391. operator, used as,
  392. for example,
  393. .Bd -literal -offset indent
  394. >16 long&0x7fffffff >0 not stripped
  395. .Ed
  397. The magic file entries have been collected from various sources,
  398. mainly USENET, and contributed by various authors.
  399. Christos Zoulas (address below) will collect additional
  400. or corrected magic file entries.
  401. A consolidation of magic file entries
  402. will be distributed periodically.
  403. .Pp
  404. The order of entries in the magic file is significant.
  405. Depending on what system you are using, the order that
  406. they are put together may be incorrect.
  407. If your old
  408. .Nm
  409. command uses a magic file,
  410. keep the old magic file around for comparison purposes
  411. (rename it to
  412. .Pa __MAGIC__.orig ).
  413. .Sh EXAMPLES
  414. .Bd -literal -offset indent
  415. $ file file.c file /dev/{wd0a,hda}
  416. file.c: C program text
  417. file: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV),
  418. dynamically linked (uses shared libs), stripped
  419. /dev/wd0a: block special (0/0)
  420. /dev/hda: block special (3/0)
  421. $ file -s /dev/wd0{b,d}
  422. /dev/wd0b: data
  423. /dev/wd0d: x86 boot sector
  424. $ file -s /dev/hda{,1,2,3,4,5,6,7,8,9,10}
  425. /dev/hda: x86 boot sector
  426. /dev/hda1: Linux/i386 ext2 filesystem
  427. /dev/hda2: x86 boot sector
  428. /dev/hda3: x86 boot sector, extended partition table
  429. /dev/hda4: Linux/i386 ext2 filesystem
  430. /dev/hda5: Linux/i386 swap file
  431. /dev/hda6: Linux/i386 swap file
  432. /dev/hda7: Linux/i386 swap file
  433. /dev/hda8: Linux/i386 swap file
  434. /dev/hda9: empty
  435. /dev/hda10: empty
  436. $ file -i file.c file /dev/{wd0a,hda}
  437. file.c: text/x-c
  438. file: application/x-executable
  439. /dev/hda: application/x-not-regular-file
  440. /dev/wd0a: application/x-not-regular-file
  441. .Ed
  442. .Sh HISTORY
  443. There has been a
  444. .Nm
  445. command in every
  446. .Dv UNIX since at least Research Version 4
  447. (man page dated November, 1973).
  448. The System V version introduced one significant major change:
  449. the external list of magic types.
  450. This slowed the program down slightly but made it a lot more flexible.
  451. .Pp
  452. This program, based on the System V version,
  453. was written by Ian Darwin <>
  454. without looking at anybody else's source code.
  455. .Pp
  456. John Gilmore revised the code extensively, making it better than
  457. the first version.
  458. Geoff Collyer found several inadequacies
  459. and provided some magic file entries.
  460. Contributions by the `&' operator by Rob McMahon,, 1989.
  461. .Pp
  462. Guy Harris,, made many changes from 1993 to the present.
  463. .Pp
  464. Primary development and maintenance from 1990 to the present by
  465. Christos Zoulas (
  466. .Pp
  467. Altered by Chris Lowth,, 2000:
  468. Handle the
  469. .Fl i
  470. option to output mime type strings, using an alternative
  471. magic file and internal logic.
  472. .Pp
  473. Altered by Eric Fischer (, July, 2000,
  474. to identify character codes and attempt to identify the languages
  475. of non-ASCII files.
  476. .Pp
  477. Altered by Reuben Thomas (, 2007 to 2008, to improve MIME
  478. support and merge MIME and non-MIME magic, support directories as well
  479. as files of magic, apply many bug fixes and improve the build system.
  480. .Pp
  481. The list of contributors to the
  482. .Sq magic
  483. directory (magic files)
  484. is too long to include here.
  485. You know who you are; thank you.
  486. Many contributors are listed in the source files.
  488. Copyright (c) Ian F. Darwin, Toronto, Canada, 1986-1999.
  489. Covered by the standard Berkeley Software Distribution copyright; see the file
  490. LEGAL.NOTICE in the source distribution.
  491. .Pp
  492. The files
  493. .Dv tar.h
  494. and
  495. .Dv is_tar.c
  496. were written by John Gilmore from his public-domain
  497. .Xr tar 1
  498. program, and are not covered by the above license.
  499. .Sh BUGS
  500. .Pp
  501. There must be a better way to automate the construction of the Magic
  502. file from all the glop in Magdir.
  503. What is it?
  504. .Pp
  505. .Nm
  506. uses several algorithms that favor speed over accuracy,
  507. thus it can be misled about the contents of
  508. text
  509. files.
  510. .Pp
  511. The support for text files (primarily for programming languages)
  512. is simplistic, inefficient and requires recompilation to update.
  513. .Pp
  514. The list of keywords in
  515. .Dv ascmagic
  516. probably belongs in the Magic file.
  517. This could be done by using some keyword like
  518. .Sq *
  519. for the offset value.
  520. .Pp
  521. Complain about conflicts in the magic file entries.
  522. Make a rule that the magic entries sort based on file offset rather
  523. than position within the magic file?
  524. .Pp
  525. The program should provide a way to give an estimate
  526. of
  527. .Sq how good
  528. a guess is.
  529. We end up removing guesses (e.g.
  530. .Sq From\
  531. as first 5 chars of file) because
  532. they are not as good as other guesses (e.g.
  533. .Sq Newsgroups:
  534. versus
  535. .Sq Return-Path:
  536. ).
  537. Still, if the others don't pan out, it should be possible to use the
  538. first guess.
  539. .Pp
  540. This manual page, and particularly this section, is too long.
  541. .Sh RETURN CODE
  542. .Nm
  543. returns 0 on success, and non-zero on error.
  545. You can obtain the original author's latest version by anonymous FTP
  546. on
  547. .Dv
  548. in the directory
  549. .Dv /pub/file/file-X.YZ.tar.gz