1FILE(1) BSD General Commands Manual FILE(1)
2
4 file — determine file type
5
7 file [-bchikLNnprsvz0] [--apple] [--mime-encoding] [--mime-type]
8 [-e testname] [-F separator] [-f namefile] [-m magicfiles] file ...
9 file -C [-m magicfiles]
10 file [--help]
11
13 This manual page documents version 5.04 of the file command.
14 file tests each argument in an attempt to classify it. There are three
16 sets of tests, performed in this order: filesystem tests, magic tests,
17 and language tests. The first test that succeeds causes the file type to
18 be printed.
19 The type printed will usually contain one of the words text (the file
21 contains only printing characters and a few common control characters and
22 is probably safe to read on an ASCII terminal), executable (the file con‐
23 tains the result of compiling a program in a form understandable to some
24 UNIX kernel or another), or data meaning anything else (data is usually
25 ‘binary’ or non-printable). Exceptions are well-known file formats (core
26 files, tar archives) that are known to contain binary data. When modify‐
27 ing magic files or the program itself, make sure to preserve these
28 keywords. Users depend on knowing that all the readable files in a
29 directory have the word ‘text’ printed. Don't do as Berkeley did and
30 change ‘shell commands text’ to ‘shell script’.
31 The filesystem tests are based on examining the return from a stat(2)
33 system call. The program checks to see if the file is empty, or if it's
34 some sort of special file. Any known file types appropriate to the sys‐
35 tem you are running on (sockets, symbolic links, or named pipes (FIFOs)
36 on those systems that implement them) are intuited if they are defined in
37 the system header file <sys/stat.h>.
38 The magic tests are used to check for files with data in particular fixed
40 formats. The canonical example of this is a binary executable (compiled
41 program) a.out file, whose format is defined in <elf.h>, <a.out.h> and
42 possibly <exec.h> in the standard include directory. These files have a
43 ‘magic number’ stored in a particular place near the beginning of the
44 file that tells the UNIX operating system that the file is a binary exe‐
45 cutable, and which of several types thereof. The concept of a ‘magic’
46 has been applied by extension to data files. Any file with some invari‐
47 ant identifier at a small fixed offset into the file can usually be
48 described in this way. The information identifying these files is read
49 from the compiled magic file /usr/share/misc/magic.mgc, or the files in
50 the directory /usr/share/misc/magic if the compiled file does not exist.
51 In addition, if $HOME/.magic.mgc or $HOME/.magic exists, it will be used
52 in preference to the system magic files.
53 If a file does not match any of the entries in the magic file, it is
55 examined to see if it seems to be a text file. ASCII, ISO-8859-x, non-
56 ISO 8-bit extended-ASCII character sets (such as those used on Macintosh
57 and IBM PC systems), UTF-8-encoded Unicode, UTF-16-encoded Unicode, and
58 EBCDIC character sets can be distinguished by the different ranges and
59 sequences of bytes that constitute printable text in each set. If a file
60 passes any of these tests, its character set is reported. ASCII,
61 ISO-8859-x, UTF-8, and extended-ASCII files are identified as ‘text’
62 because they will be mostly readable on nearly any terminal; UTF-16 and
63 EBCDIC are only ‘character data’ because, while they contain text, it is
64 text that will require translation before it can be read. In addition,
65 file will attempt to determine other characteristics of text-type files.
66 If the lines of a file are terminated by CR, CRLF, or NEL, instead of the
67 Unix-standard LF, this will be reported. Files that contain embedded
68 escape sequences or overstriking will also be identified.
69 Once file has determined the character set used in a text-type file, it
71 will attempt to determine in what language the file is written. The lan‐
72 guage tests look for particular strings (cf. <names.h> ) that can appear
73 anywhere in the first few blocks of a file. For example, the keyword .br
74 indicates that the file is most likely a troff(1) input file, just as the
75 keyword struct indicates a C program. These tests are less reliable than
76 the previous two groups, so they are performed last. The language test
77 routines also test for some miscellany (such as tar(1) archives).
78 Any file that cannot be identified as having been written in any of the
80 character sets listed above is simply said to be ‘data’.
81
83 -b, --brief
84 Do not prepend filenames to output lines (brief mode).
85 -C, --compile
87 Write a magic.mgc output file that contains a pre-parsed version
88 of the magic file or directory.
89 -c, --checking-printout
91 Cause a checking printout of the parsed form of the magic file.
92 This is usually used in conjunction with the -m flag to debug a
93 new magic file before installing it.
94 -e, --exclude testname
96 Exclude the test named in testname from the list of tests made to
97 determine the file type. Valid test names are:
98 apptype EMX application type (only on EMX).
100 text Various types of text files (this test will try to
102 guess the text encoding, irrespective of the setting of
103 the ‘encoding’ option).
104 encoding Different text encodings for soft magic tests.
106 tokens Looks for known tokens inside text files.
108 cdf Prints details of Compound Document Files.
110 compress Checks for, and looks inside, compressed files.
112 elf Prints ELF file details.
114 soft Consults magic files.
116 tar Examines tar files.
118 -F, --separator separator
120 Use the specified string as the separator between the filename
121 and the file result returned. Defaults to ‘:’.
122 -f, --files-from namefile
124 Read the names of the files to be examined from namefile (one per
125 line) before the argument list. Either namefile or at least one
126 filename argument must be present; to test the standard input,
127 use ‘-’ as a filename argument.
128 -h, --no-dereference
130 option causes symlinks not to be followed (on systems that sup‐
131 port symbolic links). This is the default if the environment
132 variable POSIXLY_CORRECT is not defined.
133 -i, --mime
135 Causes the file command to output mime type strings rather than
136 the more traditional human readable ones. Thus it may say
137 ‘text/plain; charset=us-ascii’ rather than ‘ASCII text’. In
138 order for this option to work, file changes the way it handles
139 files recognized by the command itself (such as many of the text
140 file types, directories etc), and makes use of an alternative
141 ‘magic’ file. (See the FILES section, below).
142 --mime-type, --mime-encoding
144 Like -i, but print only the specified element(s).
145 -k, --keep-going
147 Don't stop at the first match, keep going. Subsequent matches
148 will be have the string ‘\012- ’ prepended. (If you want a new‐
149 line, see the ‘-r’ option.)
150 -L, --dereference
152 option causes symlinks to be followed, as the like-named option
153 in ls(1) (on systems that support symbolic links). This is the
154 default if the environment variable POSIXLY_CORRECT is defined.
155 -m, --magic-file magicfiles
157 Specify an alternate list of files and directories containing
158 magic. This can be a single item, or a colon-separated list. If
159 a compiled magic file is found alongside a file or directory, it
160 will be used instead.
161 -N, --no-pad
163 Don't pad filenames so that they align in the output.
164 -n, --no-buffer
166 Force stdout to be flushed after checking each file. This is
167 only useful if checking a list of files. It is intended to be
168 used by programs that want filetype output from a pipe.
169 -p, --preserve-date
171 On systems that support utime(2) or utimes(2), attempt to pre‐
172 serve the access time of files analyzed, to pretend that file
173 never read them.
174 -r, --raw
176 Don't translate unprintable characters to \ooo. Normally file
177 translates unprintable characters to their octal representation.
178 -s, --special-files
180 Normally, file only attempts to read and determine the type of
181 argument files which stat(2) reports are ordinary files. This
182 prevents problems, because reading special files may have pecu‐
183 liar consequences. Specifying the -s option causes file to also
184 read argument files which are block or character special files.
185 This is useful for determining the filesystem types of the data
186 in raw disk partitions, which are block special files. This
187 option also causes file to disregard the file size as reported by
188 stat(2) since on some systems it reports a zero size for raw disk
189 partitions.
190 -v, --version
192 Print the version of the program and exit.
193 -z, --uncompress
195 Try to look inside compressed files.
196 -0, --print0
198 Output a null character ‘\0’ after the end of the filename. Nice
199 to cut(1) the output. This does not affect the separator which is
200 still printed.
201 --help Print a help message and exit.
203
205 /usr/share/misc/magic.mgc Default compiled list of magic.
206 /usr/share/misc/magic Directory containing default magic files.
207
209 The environment variable MAGIC can be used to set the default magic file
210 name. If that variable is set, then file will not attempt to open
211 $HOME/.magic. file adds ‘.mgc’ to the value of this variable as appro‐
212 priate. The environment variable POSIXLY_CORRECT controls (on systems
213 that support symbolic links), whether file will attempt to follow sym‐
214 links or not. If set, then file follows symlink, otherwise it does not.
215 This is also controlled by the -L and -h options.
216
218 magic(5), strings(1), od(1), hexdump(1,) file(1posix)
219
221 This program is believed to exceed the System V Interface Definition of
222 FILE(CMD), as near as one can determine from the vague language contained
223 therein. Its behavior is mostly compatible with the System V program of
224 the same name. This version knows more magic, however, so it will pro‐
225 duce different (albeit more accurate) output in many cases.
226 The one significant difference between this version and System V is that
228 this version treats any white space as a delimiter, so that spaces in
229 pattern strings must be escaped. For example,
230 >10 string language impress (imPRESS data)
232 in an existing magic file would have to be changed to
234 >10 string language\ impress (imPRESS data)
236 In addition, in this version, if a pattern string contains a backslash,
238 it must be escaped. For example
239 0 string \begindata Andrew Toolkit document
241 in an existing magic file would have to be changed to
243 0 string \\begindata Andrew Toolkit document
245 SunOS releases 3.2 and later from Sun Microsystems include a file command
247 derived from the System V one, but with some extensions. My version dif‐
248 fers from Sun's only in minor ways. It includes the extension of the ‘&’
249 operator, used as, for example,
250 >16 long&0x7fffffff >0 not stripped
252
254 The magic file entries have been collected from various sources, mainly
255 USENET, and contributed by various authors. Christos Zoulas (address
256 below) will collect additional or corrected magic file entries. A con‐
257 solidation of magic file entries will be distributed periodically.
258 The order of entries in the magic file is significant. Depending on what
260 system you are using, the order that they are put together may be incor‐
261 rect. If your old file command uses a magic file, keep the old magic
262 file around for comparison purposes (rename it to
263 /usr/share/misc/magic.orig ).
264
266 $ file file.c file /dev/{wd0a,hda}
267 file.c: C program text
268 file: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV),
269 dynamically linked (uses shared libs), stripped
270 /dev/wd0a: block special (0/0)
271 /dev/hda: block special (3/0)
272 $ file -s /dev/wd0{b,d}
274 /dev/wd0b: data
275 /dev/wd0d: x86 boot sector
276 $ file -s /dev/hda{,1,2,3,4,5,6,7,8,9,10}
278 /dev/hda: x86 boot sector
279 /dev/hda1: Linux/i386 ext2 filesystem
280 /dev/hda2: x86 boot sector
281 /dev/hda3: x86 boot sector, extended partition table
282 /dev/hda4: Linux/i386 ext2 filesystem
283 /dev/hda5: Linux/i386 swap file
284 /dev/hda6: Linux/i386 swap file
285 /dev/hda7: Linux/i386 swap file
286 /dev/hda8: Linux/i386 swap file
287 /dev/hda9: empty
288 /dev/hda10: empty
289 $ file -i file.c file /dev/{wd0a,hda}
291 file.c: text/x-c
292 file: application/x-executable
293 /dev/hda: application/x-not-regular-file
294 /dev/wd0a: application/x-not-regular-file
295
298 There has been a file command in every UNIX since at least Research
299 Version 4 (man page dated November, 1973). The System V version intro‐
300 duced one significant major change: the external list of magic types.
301 This slowed the program down slightly but made it a lot more flexible.
302 This program, based on the System V version, was written by Ian Darwin
304 <ian@darwinsys.com> without looking at anybody else's source code.
305 John Gilmore revised the code extensively, making it better than the
307 first version. Geoff Collyer found several inadequacies and provided
308 some magic file entries. Contributions by the `&' operator by Rob McMa‐
309 hon, cudcv@warwick.ac.uk, 1989.
310 Guy Harris, guy@netapp.com, made many changes from 1993 to the present.
312 Primary development and maintenance from 1990 to the present by Christos
314 Zoulas (christos@astron.com).
315 Altered by Chris Lowth, chris@lowth.com, 2000: Handle the -i option to
317 output mime type strings, using an alternative magic file and internal
318 logic.
319 Altered by Eric Fischer (enf@pobox.com), July, 2000, to identify charac‐
321 ter codes and attempt to identify the languages of non-ASCII files.
322 Altered by Reuben Thomas (rrt@sc3d.org), 2007 to 2008, to improve MIME
324 support and merge MIME and non-MIME magic, support directories as well as
325 files of magic, apply many bug fixes and improve the build system.
326 The list of contributors to the ‘magic’ directory (magic files) is too
328 long to include here. You know who you are; thank you. Many contribu‐
329 tors are listed in the source files.
330
332 Copyright (c) Ian F. Darwin, Toronto, Canada, 1986-1999. Covered by the
333 standard Berkeley Software Distribution copyright; see the file
334 LEGAL.NOTICE in the source distribution.
335 The files tar.h and is_tar.c were written by John Gilmore from his pub‐
337 lic-domain tar(1) program, and are not covered by the above license.
338
340 There must be a better way to automate the construction of the Magic file
341 from all the glop in Magdir. What is it?
342 file uses several algorithms that favor speed over accuracy, thus it can
344 be misled about the contents of text files.
345 The support for text files (primarily for programming languages) is sim‐
347 plistic, inefficient and requires recompilation to update.
348 The list of keywords in ascmagic probably belongs in the Magic file.
350 This could be done by using some keyword like ‘*’ for the offset value.
351 Complain about conflicts in the magic file entries. Make a rule that the
353 magic entries sort based on file offset rather than position within the
354 magic file?
355 The program should provide a way to give an estimate of ‘how good’ a
357 guess is. We end up removing guesses (e.g. ‘Fromas first 5 chars of
358 file) because’ they are not as good as other guesses (e.g. ‘Newsgroups:’
359 versus ‘Return-Path:’ ). Still, if the others don't pan out, it should
360 be possible to use the first guess.
361 This manual page, and particularly this section, is too long.
363
365 file returns 0 on success, and non-zero on error.
366
368 You can obtain the original author's latest version by anonymous FTP on
369 ftp.astron.com in the directory /pub/file/file-X.YZ.tar.gz
370BSD October 9, 2008 BSD