Annotation of src/usr.bin/file/file.1, Revision 1.17
1.17 ! millert 1: .\" $OpenBSD: file.1,v 1.16 2002/01/24 19:34:48 mickey Exp $
1.8 aaron 2: .\" $FreeBSD: src/usr.bin/file/file.1,v 1.16 2000/03/01 12:19:39 sheldonh Exp $
3: .Dd July 30, 1997
4: .Dt FILE 1
5: .Os
6: .Sh NAME
7: .Nm file
8: .Nd determine file type
9: .Sh SYNOPSIS
10: .Nm file
1.17 ! millert 11: .Op Fl vbczL
1.8 aaron 12: .Op Fl f Ar namefile
13: .Op Fl m Ar magicfiles
14: .Ar file Op Ar ...
15: .Sh DESCRIPTION
1.4 millert 16: This manual page documents version 3.22 of the
1.8 aaron 17: .Nm
1.4 millert 18: command.
1.8 aaron 19: .Nm
1.1 deraadt 20: tests each argument in an attempt to classify it.
21: There are three sets of tests, performed in this order:
22: filesystem tests, magic number tests, and language tests.
1.8 aaron 23: The first test that succeeds causes the file type to be printed.
24: .Pp
1.1 deraadt 25: The type printed will usually contain one of the words
1.8 aaron 26: .Dq text
1.4 millert 27: (the file contains only
1.8 aaron 28: .Tn ASCII
1.4 millert 29: characters and is probably safe to read on an
1.8 aaron 30: .Tn ASCII
1.4 millert 31: terminal),
1.8 aaron 32: .Dq executable
1.1 deraadt 33: (the file contains the result of compiling a program
1.8 aaron 34: in a form understandable to some
35: .Ux
36: kernel or another),
1.1 deraadt 37: or
1.8 aaron 38: .Dq data
39: meaning anything else (data is usually binary or non-printable).
40: .Pp
1.1 deraadt 41: Exceptions are well-known file formats (core files, tar archives)
42: that are known to contain binary data.
43: When modifying the file
1.8 aaron 44: .Pa /etc/magic
1.6 aaron 45: or the program itself,
1.8 aaron 46: .Em "preserve these keywords" .
47: .Pp
1.1 deraadt 48: People depend on knowing that all the readable files in a directory
1.8 aaron 49: have the word
50: .Dq text
51: printed.
52: Don't do as Berkeley did; change
53: .Dq shell commands text
54: to
55: .Dq shell script .
56: .Pp
1.1 deraadt 57: The filesystem tests are based on examining the return from a
1.8 aaron 58: .Xr stat 2
1.1 deraadt 59: system call.
60: The program checks to see if the file is empty,
61: or if it's some sort of special file.
62: Any known file types appropriate to the system you are running on
63: (sockets, symbolic links, or named pipes (FIFOs) on those systems that
64: implement them)
65: are intuited if they are defined in
66: the system header file
1.9 aaron 67: .Aq Pa sys/stat.h .
1.8 aaron 68: .Pp
1.1 deraadt 69: The magic number tests are used to check for files with data in
70: particular fixed formats.
71: The canonical example of this is a binary executable (compiled program)
1.8 aaron 72: .Pa a.out
1.6 aaron 73: file, whose format is defined in
1.8 aaron 74: .Aq Pa a.out.h
1.1 deraadt 75: and possibly
1.8 aaron 76: .Aq Pa exec.h
1.1 deraadt 77: in the standard include directory.
1.8 aaron 78: These files have a
79: .Dq magic number
80: stored in a particular place
81: near the beginning of the file that tells the
82: .Ux
83: operating system
1.1 deraadt 84: that the file is a binary executable, and which of several types thereof.
1.8 aaron 85: .Pp
86: The concept of magic number has been applied by extension to data files.
1.1 deraadt 87: Any file with some invariant identifier at a small fixed
88: offset into the file can usually be described in this way.
89: The information in these files is read from the magic file
1.8 aaron 90: .Pa /etc/magic .
91: .Pp
1.1 deraadt 92: If an argument appears to be an
1.8 aaron 93: .Tn ASCII
1.1 deraadt 94: file,
1.8 aaron 95: .Nm
1.1 deraadt 96: attempts to guess its language.
1.4 millert 97: The language tests look for particular strings (cf
1.8 aaron 98: .Pa names.h )
1.1 deraadt 99: that can appear anywhere in the first few blocks of a file.
100: For example, the keyword
1.8 aaron 101: .Em .br
1.4 millert 102: indicates that the file is most likely a
1.8 aaron 103: .Xr troff 1
1.6 aaron 104: input file, just as the keyword
1.8 aaron 105: .Li struct
1.1 deraadt 106: indicates a C program.
107: These tests are less reliable than the previous
108: two groups, so they are performed last.
109: The language test routines also test for some miscellany
1.6 aaron 110: (such as
1.8 aaron 111: .Xr tar 1
1.1 deraadt 112: archives) and determine whether an unknown file should be
1.8 aaron 113: labelled as
114: .Dq ASCII text
115: or
116: .Dq data .
117: .Pp
118: The options are as follows:
1.11 aaron 119: .Bl -tag -width Ds
1.8 aaron 120: .It Fl v
1.1 deraadt 121: Print the version of the program and exit.
1.8 aaron 122: .It Fl m Ar list
123: Specify an alternate
124: .Ar list
125: of files containing magic numbers.
1.2 deraadt 126: This can be a single file, or a colon-separated list of files.
1.8 aaron 127: .It Fl z
1.1 deraadt 128: Try to look inside compressed files.
1.17 ! millert 129: .It Fl b
! 130: Do not prepend filenames to output lines (brief mode).
1.8 aaron 131: .It Fl c
1.1 deraadt 132: Cause a checking printout of the parsed form of the magic file.
1.6 aaron 133: This is usually used in conjunction with
1.8 aaron 134: .Fl m
1.1 deraadt 135: to debug a new magic file before installing it.
1.8 aaron 136: .It Fl f Ar namefile
1.6 aaron 137: Read the names of the files to be examined from
1.8 aaron 138: .Ar namefile
1.6 aaron 139: (one per line)
1.1 deraadt 140: before the argument list.
1.6 aaron 141: Either
1.8 aaron 142: .Ar namefile
1.1 deraadt 143: or at least one filename argument must be present;
1.8 aaron 144: to test the standard input, use
145: .Dq -
146: as a filename argument.
147: .It Fl L
148: Cause symlinks to be followed, as the like-named option in
149: .Xr ls 1 .
1.1 deraadt 150: (on systems that support symbolic links).
1.8 aaron 151: .El
152: .Sh ENVIRONMENT
153: .Bl -tag -width indent
1.13 smart 154: .It Ev MAGIC
1.8 aaron 155: Default magic number files.
156: .El
1.12 aaron 157: .Sh FILES
158: .Bl -tag -width /etc/magic -compact
159: .It Pa /etc/magic
160: default list of magic numbers
161: .El
1.8 aaron 162: .Sh SEE ALSO
163: .Xr hexdump 1 ,
164: .Xr od 1 ,
165: .Xr strings 1 ,
166: .Xr magic 5
167: .Sh STANDARDS CONFORMANCE
1.1 deraadt 168: This program is believed to exceed the System V Interface Definition
169: of FILE(CMD), as near as one can determine from the vague language
1.6 aaron 170: contained therein.
1.1 deraadt 171: Its behaviour is mostly compatible with the System V program of the same name.
172: This version knows more magic, however, so it will produce
1.6 aaron 173: different (albeit more accurate) output in many cases.
1.8 aaron 174: .Pp
1.6 aaron 175: The one significant difference
1.1 deraadt 176: between this version and System V
1.8 aaron 177: is that this version treats any white space
1.1 deraadt 178: as a delimiter, so that spaces in pattern strings must be escaped.
179: For example,
1.8 aaron 180: .Pp
181: >10 string language impress\ (imPRESS data)
182: .Pp
1.1 deraadt 183: in an existing magic file would have to be changed to
1.8 aaron 184: .Pp
185: >10 string language\e impress (imPRESS data)
186: .Pp
1.1 deraadt 187: In addition, in this version, if a pattern string contains a backslash,
1.9 aaron 188: it must be escaped.
189: For example
1.8 aaron 190: .Pp
191: 0 string \ebegindata Andrew Toolkit document
192: .Pp
1.1 deraadt 193: in an existing magic file would have to be changed to
1.8 aaron 194: .Pp
195: 0 string \e\ebegindata Andrew Toolkit document
196: .Pp
1.1 deraadt 197: SunOS releases 3.2 and later from Sun Microsystems include a
1.8 aaron 198: .Xr file 1
1.1 deraadt 199: command derived from the System V one, but with some extensions.
200: My version differs from Sun's only in minor ways.
1.8 aaron 201: It includes the extension of the
202: .Ql &
203: operator, used as,
1.1 deraadt 204: for example,
1.8 aaron 205: .Pp
206: >16 long&0x7fffffff >0 not stripped
207: .Sh MAGIC DIRECTORY
1.1 deraadt 208: The magic file entries have been collected from various sources,
209: mainly USENET, and contributed by various authors.
1.8 aaron 210: .An Christos Zoulas
211: (address below) will collect additional
1.1 deraadt 212: or corrected magic file entries.
1.6 aaron 213: A consolidation of magic file entries
1.1 deraadt 214: will be distributed periodically.
215: The order of entries in the magic file is significant.
216: Depending on what system you are using, the order that
217: they are put together may be incorrect.
218: If your old
1.8 aaron 219: .Nm
1.1 deraadt 220: command uses a magic file,
221: keep the old magic file around for comparison purposes
1.6 aaron 222: (rename it to
1.8 aaron 223: .Pa /etc/magic.orig ) .
224: .Sh HISTORY
1.6 aaron 225: There has been a
1.8 aaron 226: .Nm
227: command in every
228: .Ux
1.16 mickey 229: since at least Research Version 4
230: (man page dated November, 1973).
1.1 deraadt 231: The System V version introduced one significant major change:
232: the external list of magic number types.
233: This slowed the program down slightly but made it a lot more flexible.
1.8 aaron 234: .Pp
1.10 ian 235: This program, based on the System V version, was written by
236: .An Ian F. Darwin Aq ian@darwinisys.com
1.8 aaron 237: without looking at anybody else's source code.
238: .Pp
239: .An John Gilmore
240: revised the code extensively, making it better than
1.1 deraadt 241: the first version.
1.8 aaron 242: .An Geoff Collyer
243: found several inadequacies
1.1 deraadt 244: and provided some magic file entries.
1.8 aaron 245: .Pp
246: Altered by
247: .An Rob McMahon Aq cudcv@warwick.ac.uk ,
248: 1989, to extend the
249: .Ql &
250: operator from simple
251: .Dq x&y != 0
252: to
253: .Dq x&y op z .
254: .Pp
255: Altered by
256: .An Guy Harris Aq guy@auspex.com ,
257: 1993, to:
258: .Bl -item -offset indent
259: .It
260: put the
261: .Dq old-style
262: .Ql &
263: operator back the way it was, because
264: .Bl -enum -offset indent
265: .It
266: Rob McMahon's change broke the
267: previous style of usage,
268: .It
269: The SunOS
270: .Dq new-style
271: .Ql &
272: operator, which this version of
273: .Nm
274: supports, also handles
275: .Dq x&y op z ,
276: .It
277: Rob's change wasn't documented in any case;
278: .El
279: .It
280: put in multiple levels of
281: .Ql > ;
282: .It
283: put in
284: .Dq beshort ,
285: .Dq leshort ,
286: etc. keywords to look at numbers in the
1.1 deraadt 287: file in a specific byte order, rather than in the native byte order of
288: the process running
1.8 aaron 289: .Nm file .
290: .El
291: .Pp
1.10 ian 292: Currently maintained by
293: .An Christos Zoulas Aq christos@zoulas.com .
1.8 aaron 294: .Sh LEGAL NOTICE
1.10 ian 295: Copyright (c) Ian F. Darwin, Toronto, Canada, 1986-1999.
296: Covered by the standard Berkeley Software Distribution copyright; see the file
297: LEGAL.NOTICE in the distribution.
1.8 aaron 298: .Pp
1.1 deraadt 299: The files
1.8 aaron 300: .Pa tar.h
1.1 deraadt 301: and
1.8 aaron 302: .Pa is_tar.c
303: were written by
304: .An John Gilmore
305: from his public-domain
306: .Nm tar
1.10 ian 307: program.
1.8 aaron 308: .Sh BUGS
1.1 deraadt 309: There must be a better way to automate the construction of the Magic
1.8 aaron 310: file from all the glop in Magdir.
311: What is it?
1.1 deraadt 312: Better yet, the magic file should be compiled into binary (say,
1.8 aaron 313: .Xr ndbm 3
1.4 millert 314: or, better yet, fixed-length
1.8 aaron 315: .Tn ASCII
1.4 millert 316: strings for use in heterogenous network environments) for faster startup.
1.1 deraadt 317: Then the program would run as fast as the Version 7 program of the same name,
318: with the flexibility of the System V version.
1.8 aaron 319: .Pp
320: .Nm
1.15 pjanzen 321: uses several algorithms that favor speed over accuracy;
1.4 millert 322: thus it can be misled about the contents of
1.8 aaron 323: .Tn ASCII
1.4 millert 324: files.
1.8 aaron 325: .Pp
1.4 millert 326: The support for
1.8 aaron 327: .Tn ASCII
1.4 millert 328: files (primarily for programming languages)
1.1 deraadt 329: is simplistic, inefficient and requires recompilation to update.
1.8 aaron 330: .Pp
331: There should be an
332: .Dq else
333: clause to follow a series of continuation lines.
334: .Pp
1.1 deraadt 335: The magic file and keywords should have regular expression support.
1.4 millert 336: Their use of
1.8 aaron 337: .Tn ASCII TAB
1.4 millert 338: as a field delimiter is ugly and makes
1.1 deraadt 339: it hard to edit the files, but is entrenched.
1.8 aaron 340: .Pp
1.1 deraadt 341: It might be advisable to allow upper-case letters in keywords
1.4 millert 342: for e.g.,
1.8 aaron 343: .Xr troff 1
1.4 millert 344: commands vs man page macros.
1.1 deraadt 345: Regular expression support would make this easy.
1.8 aaron 346: .Pp
1.1 deraadt 347: The program doesn't grok \s-2FORTRAN\s0.
1.6 aaron 348: It should be able to figure \s-2FORTRAN\s0 by seeing some keywords which
1.1 deraadt 349: appear indented at the start of line.
350: Regular expression support would make this easy.
1.8 aaron 351: .Pp
1.6 aaron 352: The list of keywords in
1.8 aaron 353: .Em ascmagic
1.1 deraadt 354: probably belongs in the Magic file.
1.8 aaron 355: This could be done by using some keyword like
356: .Ql *
357: for the offset value.
358: .Pp
359: Another optimization would be to sort
1.1 deraadt 360: the magic file so that we can just run down all the
361: tests for the first byte, first word, first long, etc, once we
1.9 aaron 362: have fetched it.
363: Complain about conflicts in the magic file entries.
1.1 deraadt 364: Make a rule that the magic entries sort based on file offset rather
365: than position within the magic file?
1.8 aaron 366: .Pp
1.6 aaron 367: The program should provide a way to give an estimate
1.8 aaron 368: of
369: .Dq how good
370: a guess is.
371: We end up removing guesses (e.g.,
372: .Dq From\
373: as first 5 chars of file) because
374: they are not as good as other guesses (e.g.,
375: .Dq Newsgroups:
376: versus
377: .Qq Return-Path: ) .
378: Still, if the others don't pan out, it should be
1.6 aaron 379: possible to use the first guess.
1.8 aaron 380: .Pp
381: This program is slower than some vendors'
382: .Nm
383: commands.
384: .Pp
1.1 deraadt 385: This manual page, and particularly this section, is too long.
1.8 aaron 386: .Sh AVAILABILITY
1.1 deraadt 387: You can obtain the original author's latest version by anonymous FTP
1.8 aaron 388: on
1.15 pjanzen 389: .Em ftp.astron.com
1.8 aaron 390: in the directory
391: .Pa /pub/file/file-X.YY.tar.gz
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