Annotation of src/usr.bin/file/file.1, Revision 1.25
1.25 ! ian 1: .\" $OpenBSD: file.1,v 1.24 2007/02/19 13:02:08 tom Exp $
1.8 aaron 2: .\" $FreeBSD: src/usr.bin/file/file.1,v 1.16 2000/03/01 12:19:39 sheldonh Exp $
1.18 jmc 3: .\"
1.19 ian 4: .\" Copyright (c) Ian F. Darwin 1986-1995.
5: .\" Software written by Ian F. Darwin and others;
6: .\" maintained 1995-present by Christos Zoulas and others.
1.20 jmc 7: .\"
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9: .\" modification, are permitted provided that the following conditions
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14: .\" 2. Redistributions in binary form must reproduce the above copyright
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1.20 jmc 17: .\"
1.19 ian 18: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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1.18 jmc 29: .\"
1.23 jaredy 30: .Dd December 4, 2004
1.8 aaron 31: .Dt FILE 1
32: .Os
33: .Sh NAME
34: .Nm file
35: .Nd determine file type
36: .Sh SYNOPSIS
37: .Nm file
1.23 jaredy 38: .Op Fl bckLNnrsvz
39: .Op Fl F Ar separator
1.8 aaron 40: .Op Fl f Ar namefile
41: .Op Fl m Ar magicfiles
1.23 jaredy 42: .Bk -words
43: .Ar file ...
44: .Ek
45: .Nm file
46: .Op Fl m Ar magicfiles
47: .Fl C
1.8 aaron 48: .Sh DESCRIPTION
1.22 jaredy 49: The
1.8 aaron 50: .Nm
1.22 jaredy 51: utility
1.1 deraadt 52: tests each argument in an attempt to classify it.
53: There are three sets of tests, performed in this order:
54: filesystem tests, magic number tests, and language tests.
1.8 aaron 55: The first test that succeeds causes the file type to be printed.
56: .Pp
1.1 deraadt 57: The type printed will usually contain one of the words
1.8 aaron 58: .Dq text
1.4 millert 59: (the file contains only
1.8 aaron 60: .Tn ASCII
1.4 millert 61: characters and is probably safe to read on an
1.8 aaron 62: .Tn ASCII
1.4 millert 63: terminal),
1.8 aaron 64: .Dq executable
1.1 deraadt 65: (the file contains the result of compiling a program
1.8 aaron 66: in a form understandable to some
67: .Ux
68: kernel or another),
1.1 deraadt 69: or
1.8 aaron 70: .Dq data
71: meaning anything else (data is usually binary or non-printable).
72: .Pp
1.1 deraadt 73: Exceptions are well-known file formats (core files, tar archives)
74: that are known to contain binary data.
75: When modifying the file
1.8 aaron 76: .Pa /etc/magic
1.6 aaron 77: or the program itself,
1.8 aaron 78: .Em "preserve these keywords" .
79: .Pp
1.1 deraadt 80: People depend on knowing that all the readable files in a directory
1.8 aaron 81: have the word
82: .Dq text
83: printed.
84: Don't do as Berkeley did; change
85: .Dq shell commands text
86: to
87: .Dq shell script .
88: .Pp
1.1 deraadt 89: The filesystem tests are based on examining the return from a
1.8 aaron 90: .Xr stat 2
1.1 deraadt 91: system call.
92: The program checks to see if the file is empty,
93: or if it's some sort of special file.
94: Any known file types appropriate to the system you are running on
95: (sockets, symbolic links, or named pipes (FIFOs) on those systems that
96: implement them)
97: are intuited if they are defined in
98: the system header file
1.9 aaron 99: .Aq Pa sys/stat.h .
1.8 aaron 100: .Pp
1.1 deraadt 101: The magic number tests are used to check for files with data in
102: particular fixed formats.
103: The canonical example of this is a binary executable (compiled program)
1.8 aaron 104: .Pa a.out
1.6 aaron 105: file, whose format is defined in
1.8 aaron 106: .Aq Pa a.out.h
1.1 deraadt 107: and possibly
1.8 aaron 108: .Aq Pa exec.h
1.23 jaredy 109: in the standard include directory and is explained in
110: .Xr a.out 5 .
1.8 aaron 111: These files have a
112: .Dq magic number
113: stored in a particular place
114: near the beginning of the file that tells the
115: .Ux
116: operating system
1.1 deraadt 117: that the file is a binary executable, and which of several types thereof.
1.8 aaron 118: .Pp
119: The concept of magic number has been applied by extension to data files.
1.1 deraadt 120: Any file with some invariant identifier at a small fixed
121: offset into the file can usually be described in this way.
122: The information in these files is read from the magic file
1.8 aaron 123: .Pa /etc/magic .
124: .Pp
1.1 deraadt 125: If an argument appears to be an
1.8 aaron 126: .Tn ASCII
1.1 deraadt 127: file,
1.8 aaron 128: .Nm
1.1 deraadt 129: attempts to guess its language.
1.4 millert 130: The language tests look for particular strings (cf
1.8 aaron 131: .Pa names.h )
1.1 deraadt 132: that can appear anywhere in the first few blocks of a file.
133: For example, the keyword
1.8 aaron 134: .Em .br
1.4 millert 135: indicates that the file is most likely a
1.8 aaron 136: .Xr troff 1
1.6 aaron 137: input file, just as the keyword
1.8 aaron 138: .Li struct
1.1 deraadt 139: indicates a C program.
140: These tests are less reliable than the previous
141: two groups, so they are performed last.
142: The language test routines also test for some miscellany
1.6 aaron 143: (such as
1.8 aaron 144: .Xr tar 1
1.1 deraadt 145: archives) and determine whether an unknown file should be
1.8 aaron 146: labelled as
147: .Dq ASCII text
148: or
149: .Dq data .
150: .Pp
151: The options are as follows:
1.11 aaron 152: .Bl -tag -width Ds
1.17 millert 153: .It Fl b
154: Do not prepend filenames to output lines (brief mode).
1.23 jaredy 155: .It Fl C
156: For each magic number file, write a
157: .Pa magic.mgc
158: output file that contains a preparsed (compiled) version of it.
1.8 aaron 159: .It Fl c
1.1 deraadt 160: Cause a checking printout of the parsed form of the magic file.
1.6 aaron 161: This is usually used in conjunction with
1.8 aaron 162: .Fl m
1.1 deraadt 163: to debug a new magic file before installing it.
1.23 jaredy 164: .It Fl F Ar separator
165: Use the specified string as the separator between the filename and
166: the file result returned.
167: Defaults to
168: .Sq \&: .
1.8 aaron 169: .It Fl f Ar namefile
1.6 aaron 170: Read the names of the files to be examined from
1.8 aaron 171: .Ar namefile
1.6 aaron 172: (one per line)
1.1 deraadt 173: before the argument list.
1.6 aaron 174: Either
1.8 aaron 175: .Ar namefile
1.1 deraadt 176: or at least one filename argument must be present;
1.8 aaron 177: to test the standard input, use
1.23 jaredy 178: .Sq -
1.8 aaron 179: as a filename argument.
1.23 jaredy 180: .It Fl k
181: Don't stop at the first match, keep going.
1.8 aaron 182: .It Fl L
183: Cause symlinks to be followed, as the like-named option in
1.23 jaredy 184: .Xr ls 1
1.1 deraadt 185: (on systems that support symbolic links).
1.23 jaredy 186: .It Fl m Ar magiclist
187: Specify an alternate list,
188: .Ar magiclist ,
189: of files containing magic numbers.
190: This can be a single file or a colon-separated list of files.
191: If a compiled magic file is found alongside, it will be used instead.
192: .It Fl N
193: Don't pad filenames so that they align in the output.
194: .It Fl n
195: Force
196: .Em stdout
197: to be flushed after checking each file.
198: This is only useful if checking a list of files.
199: It is intended to be used by programs that want filetype output from a
200: pipe.
201: .It Fl r
202: Don't translate unprintable characters to
203: .Sq \e Ns Em ooo .
204: Normally
205: .Nm
206: translates unprintable characters to their octal representation
207: (raw mode).
208: .It Fl s
209: Normally,
210: .Nm
211: only attempts to read and determine the type of argument files which
212: .Xr stat 2
213: reports are ordinary files.
214: This prevents problems, because reading special files may have peculiar
215: consequences.
216: Specifying the
217: .Fl s
218: option causes
219: .Nm
220: to also read argument files which are block or character special files.
221: This is useful for determining the filesystem types of the data in raw
222: disk partitions, which are block special files.
223: This option also causes
224: .Nm
225: to disregard the file size as reported by
226: .Xr stat 2 ,
227: since on some systems it reports a zero size for raw disk partitions.
228: .It Fl v
229: Print the version of the program and exit.
230: .It Fl z
231: Try to look inside files that have been run through
232: .Xr compress 1 .
1.8 aaron 233: .El
234: .Sh ENVIRONMENT
235: .Bl -tag -width indent
1.13 smart 236: .It Ev MAGIC
1.23 jaredy 237: Default magic number files, separated by colon characters.
238: .Nm
239: adds
240: .Dq .mgc
241: to the value of this variable as appropriate.
1.8 aaron 242: .El
1.12 aaron 243: .Sh FILES
244: .Bl -tag -width /etc/magic -compact
245: .It Pa /etc/magic
246: default list of magic numbers
247: .El
1.8 aaron 248: .Sh SEE ALSO
1.23 jaredy 249: .Xr compress 1 ,
1.8 aaron 250: .Xr hexdump 1 ,
1.23 jaredy 251: .Xr ls 1 ,
1.8 aaron 252: .Xr od 1 ,
253: .Xr strings 1 ,
1.23 jaredy 254: .Xr a.out 5 ,
1.8 aaron 255: .Xr magic 5
256: .Sh STANDARDS CONFORMANCE
1.1 deraadt 257: This program is believed to exceed the System V Interface Definition
258: of FILE(CMD), as near as one can determine from the vague language
1.6 aaron 259: contained therein.
1.1 deraadt 260: Its behaviour is mostly compatible with the System V program of the same name.
261: This version knows more magic, however, so it will produce
1.6 aaron 262: different (albeit more accurate) output in many cases.
1.8 aaron 263: .Pp
1.6 aaron 264: The one significant difference
1.1 deraadt 265: between this version and System V
1.8 aaron 266: is that this version treats any white space
1.1 deraadt 267: as a delimiter, so that spaces in pattern strings must be escaped.
268: For example,
1.8 aaron 269: .Pp
270: >10 string language impress\ (imPRESS data)
271: .Pp
1.1 deraadt 272: in an existing magic file would have to be changed to
1.8 aaron 273: .Pp
274: >10 string language\e impress (imPRESS data)
275: .Pp
1.1 deraadt 276: In addition, in this version, if a pattern string contains a backslash,
1.9 aaron 277: it must be escaped.
278: For example
1.8 aaron 279: .Pp
280: 0 string \ebegindata Andrew Toolkit document
281: .Pp
1.1 deraadt 282: in an existing magic file would have to be changed to
1.8 aaron 283: .Pp
284: 0 string \e\ebegindata Andrew Toolkit document
285: .Pp
1.1 deraadt 286: SunOS releases 3.2 and later from Sun Microsystems include a
1.20 jmc 287: .Nm file
1.1 deraadt 288: command derived from the System V one, but with some extensions.
289: My version differs from Sun's only in minor ways.
1.8 aaron 290: It includes the extension of the
291: .Ql &
292: operator, used as,
1.1 deraadt 293: for example,
1.8 aaron 294: .Pp
295: >16 long&0x7fffffff >0 not stripped
296: .Sh MAGIC DIRECTORY
1.1 deraadt 297: The magic file entries have been collected from various sources,
298: mainly USENET, and contributed by various authors.
1.8 aaron 299: .An Christos Zoulas
300: (address below) will collect additional
1.1 deraadt 301: or corrected magic file entries.
1.6 aaron 302: A consolidation of magic file entries
1.1 deraadt 303: will be distributed periodically.
304: The order of entries in the magic file is significant.
305: Depending on what system you are using, the order that
306: they are put together may be incorrect.
307: If your old
1.8 aaron 308: .Nm
1.1 deraadt 309: command uses a magic file,
310: keep the old magic file around for comparison purposes
1.6 aaron 311: (rename it to
1.8 aaron 312: .Pa /etc/magic.orig ) .
313: .Sh HISTORY
1.6 aaron 314: There has been a
1.8 aaron 315: .Nm
316: command in every
317: .Ux
1.16 mickey 318: since at least Research Version 4
319: (man page dated November, 1973).
1.1 deraadt 320: The System V version introduced one significant major change:
321: the external list of magic number types.
322: This slowed the program down slightly but made it a lot more flexible.
1.8 aaron 323: .Pp
1.10 ian 324: This program, based on the System V version, was written by
1.25 ! ian 325: .An Ian F. Darwin
1.8 aaron 326: without looking at anybody else's source code.
327: .Pp
328: .An John Gilmore
329: revised the code extensively, making it better than
1.1 deraadt 330: the first version.
1.8 aaron 331: .An Geoff Collyer
332: found several inadequacies
1.1 deraadt 333: and provided some magic file entries.
1.23 jaredy 334: Contributions to the
335: .Ql &
336: operator by
1.25 ! ian 337: .An Rob McMahon ,
1.23 jaredy 338: 1989.
339: .Pp
1.25 ! ian 340: .An Guy Harris
1.23 jaredy 341: made many changes from 1993 to the present.
342: .Pp
343: Primary development and maintenence from 1990 to the present by
344: .An Christos Zoulas Aq christos@zoulas.com .
1.8 aaron 345: .Pp
346: Altered by
1.25 ! ian 347: .An Chris Lowth ,
1.24 tom 348: 2000, to optionally report MIME types.
349: This required an alternative magic file, and is not available in
350: .Ox .
1.8 aaron 351: .Pp
352: Altered by
1.25 ! ian 353: .An Eric Fischer ,
1.23 jaredy 354: July, 2000, to identify character codes and attempt to identify the
355: languages of non-ASCII files.
356: .Pp
357: The list of contributors to the
358: .Dq magdir
359: directory (source for the
360: .Pa /etc/magic
361: file) is too long to include here.
362: You know who you are; thank you.
1.8 aaron 363: .Sh LEGAL NOTICE
1.10 ian 364: Copyright (c) Ian F. Darwin, Toronto, Canada, 1986-1999.
365: Covered by the standard Berkeley Software Distribution copyright; see the file
366: LEGAL.NOTICE in the distribution.
1.8 aaron 367: .Pp
1.1 deraadt 368: The files
1.8 aaron 369: .Pa tar.h
1.1 deraadt 370: and
1.8 aaron 371: .Pa is_tar.c
372: were written by
373: .An John Gilmore
374: from his public-domain
375: .Nm tar
1.23 jaredy 376: program, and are not covered by the above license.
1.8 aaron 377: .Sh BUGS
1.1 deraadt 378: There must be a better way to automate the construction of the Magic
1.8 aaron 379: file from all the glop in Magdir.
380: What is it?
1.1 deraadt 381: Better yet, the magic file should be compiled into binary (say,
1.8 aaron 382: .Xr ndbm 3
1.4 millert 383: or, better yet, fixed-length
1.8 aaron 384: .Tn ASCII
1.4 millert 385: strings for use in heterogenous network environments) for faster startup.
1.1 deraadt 386: Then the program would run as fast as the Version 7 program of the same name,
387: with the flexibility of the System V version.
1.8 aaron 388: .Pp
389: .Nm
1.15 pjanzen 390: uses several algorithms that favor speed over accuracy;
1.4 millert 391: thus it can be misled about the contents of
1.8 aaron 392: .Tn ASCII
1.4 millert 393: files.
1.8 aaron 394: .Pp
1.4 millert 395: The support for
1.8 aaron 396: .Tn ASCII
1.4 millert 397: files (primarily for programming languages)
1.1 deraadt 398: is simplistic, inefficient and requires recompilation to update.
1.8 aaron 399: .Pp
400: There should be an
401: .Dq else
402: clause to follow a series of continuation lines.
403: .Pp
1.1 deraadt 404: The magic file and keywords should have regular expression support.
1.4 millert 405: Their use of
1.8 aaron 406: .Tn ASCII TAB
1.4 millert 407: as a field delimiter is ugly and makes
1.1 deraadt 408: it hard to edit the files, but is entrenched.
1.8 aaron 409: .Pp
1.1 deraadt 410: It might be advisable to allow upper-case letters in keywords
1.4 millert 411: for e.g.,
1.8 aaron 412: .Xr troff 1
1.4 millert 413: commands vs man page macros.
1.1 deraadt 414: Regular expression support would make this easy.
1.8 aaron 415: .Pp
1.1 deraadt 416: The program doesn't grok \s-2FORTRAN\s0.
1.6 aaron 417: It should be able to figure \s-2FORTRAN\s0 by seeing some keywords which
1.1 deraadt 418: appear indented at the start of line.
419: Regular expression support would make this easy.
1.8 aaron 420: .Pp
1.6 aaron 421: The list of keywords in
1.8 aaron 422: .Em ascmagic
1.1 deraadt 423: probably belongs in the Magic file.
1.8 aaron 424: This could be done by using some keyword like
425: .Ql *
426: for the offset value.
427: .Pp
428: Another optimization would be to sort
1.1 deraadt 429: the magic file so that we can just run down all the
430: tests for the first byte, first word, first long, etc, once we
1.9 aaron 431: have fetched it.
432: Complain about conflicts in the magic file entries.
1.1 deraadt 433: Make a rule that the magic entries sort based on file offset rather
434: than position within the magic file?
1.8 aaron 435: .Pp
1.6 aaron 436: The program should provide a way to give an estimate
1.8 aaron 437: of
438: .Dq how good
439: a guess is.
440: We end up removing guesses (e.g.,
1.20 jmc 441: .Dq From\ \&
1.8 aaron 442: as first 5 chars of file) because
443: they are not as good as other guesses (e.g.,
444: .Dq Newsgroups:
445: versus
446: .Qq Return-Path: ) .
447: Still, if the others don't pan out, it should be
1.6 aaron 448: possible to use the first guess.
1.8 aaron 449: .Pp
450: This program is slower than some vendors'
451: .Nm
452: commands.
453: .Pp
1.1 deraadt 454: This manual page, and particularly this section, is too long.
1.8 aaron 455: .Sh AVAILABILITY
1.1 deraadt 456: You can obtain the original author's latest version by anonymous FTP
1.8 aaron 457: on
1.15 pjanzen 458: .Em ftp.astron.com
1.8 aaron 459: in the directory
1.20 jmc 460: .Pa /pub/file/file-X.YY.tar.gz .
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