1.\" $NetBSD: file.1,v 1.24 2019/12/17 02:31:05 christos Exp $ 2.\" 3.\" $File: file.man,v 1.138 2019/10/15 18:00:40 christos Exp $ 4.Dd July 13, 2019 5.Dt FILE 1 6.Os 7.Sh NAME 8.Nm file 9.Nd determine file type 10.Sh SYNOPSIS 11.Nm 12.Bk -words 13.Op Fl bcdEhiklLNnprsSvzZ0 14.Op Fl Fl apple 15.Op Fl Fl extension 16.Op Fl Fl mime-encoding 17.Op Fl Fl mime-type 18.Op Fl e Ar testname 19.Op Fl F Ar separator 20.Op Fl f Ar namefile 21.Op Fl m Ar magicfiles 22.Op Fl P Ar name=value 23.Ar 24.Ek 25.Nm 26.Fl C 27.Op Fl m Ar magicfiles 28.Nm 29.Op Fl Fl help 30.Sh DESCRIPTION 31This manual page documents version 5.38 of the 32.Nm 33command. 34.Pp 35.Nm 36tests each argument in an attempt to classify it. 37There are three sets of tests, performed in this order: 38filesystem tests, magic tests, and language tests. 39The 40.Em first 41test that succeeds causes the file type to be printed. 42.Pp 43The type printed will usually contain one of the words 44.Em text 45(the file contains only 46printing characters and a few common control 47characters and is probably safe to read on an 48.Dv ASCII 49terminal), 50.Em executable 51(the file contains the result of compiling a program 52in a form understandable to some 53.Tn UNIX 54kernel or another), 55or 56.Em data 57meaning anything else (data is usually 58.Dq binary 59or non-printable). 60Exceptions are well-known file formats (core files, tar archives) 61that are known to contain binary data. 62When modifying magic files or the program itself, make sure to 63.Em "preserve these keywords" . 64Users depend on knowing that all the readable files in a directory 65have the word 66.Dq text 67printed. 68Don't do as Berkeley did and change 69.Dq shell commands text 70to 71.Dq shell script . 72.Pp 73The filesystem tests are based on examining the return from a 74.Xr stat 2 75system call. 76The program checks to see if the file is empty, 77or if it's some sort of special file. 78Any known file types appropriate to the system you are running on 79(sockets, symbolic links, or named pipes (FIFOs) on those systems that 80implement them) 81are intuited if they are defined in the system header file 82.In sys/stat.h . 83.Pp 84The magic tests are used to check for files with data in 85particular fixed formats. 86The canonical example of this is a binary executable (compiled program) 87.Dv a.out 88file, whose format is defined in 89.In elf.h , 90.In a.out.h 91and possibly 92.In exec.h 93in the standard include directory. 94These files have a 95.Dq "magic number" 96stored in a particular place 97near the beginning of the file that tells the 98.Tn UNIX 99operating system 100that the file is a binary executable, and which of several types thereof. 101The concept of a 102.Dq "magic" 103has been applied by extension to data files. 104Any file with some invariant identifier at a small fixed 105offset into the file can usually be described in this way. 106The information identifying these files is read from the compiled 107magic file 108.Pa /usr/share/misc/magic.mgc , 109or the files in the directory 110.Pa /usr/share/misc/magic 111if the compiled file does not exist. 112In addition, if 113.Pa $HOME/.magic.mgc 114or 115.Pa $HOME/.magic 116exists, it will be used in preference to the system magic files. 117.Pp 118If a file does not match any of the entries in the magic file, 119it is examined to see if it seems to be a text file. 120ASCII, ISO-8859-x, non-ISO 8-bit extended-ASCII character sets 121(such as those used on Macintosh and IBM PC systems), 122UTF-8-encoded Unicode, UTF-16-encoded Unicode, and EBCDIC 123character sets can be distinguished by the different 124ranges and sequences of bytes that constitute printable text 125in each set. 126If a file passes any of these tests, its character set is reported. 127ASCII, ISO-8859-x, UTF-8, and extended-ASCII files are identified 128as 129.Dq text 130because they will be mostly readable on nearly any terminal; 131UTF-16 and EBCDIC are only 132.Dq character data 133because, while 134they contain text, it is text that will require translation 135before it can be read. 136In addition, 137.Nm 138will attempt to determine other characteristics of text-type files. 139If the lines of a file are terminated by CR, CRLF, or NEL, instead 140of the Unix-standard LF, this will be reported. 141Files that contain embedded escape sequences or overstriking 142will also be identified. 143.Pp 144Once 145.Nm 146has determined the character set used in a text-type file, 147it will 148attempt to determine in what language the file is written. 149The language tests look for particular strings (cf. 150.In names.h ) 151that can appear anywhere in the first few blocks of a file. 152For example, the keyword 153.Em .br 154indicates that the file is most likely a 155.Xr troff 1 156input file, just as the keyword 157.Em struct 158indicates a C program. 159These tests are less reliable than the previous 160two groups, so they are performed last. 161The language test routines also test for some miscellany 162(such as 163.Xr tar 1 164archives, JSON files). 165.Pp 166Any file that cannot be identified as having been written 167in any of the character sets listed above is simply said to be 168.Dq data . 169.Sh OPTIONS 170.Bl -tag -width indent 171.It Fl Fl apple 172Causes the file command to output the file type and creator code as 173used by older MacOS versions. 174The code consists of eight letters, 175the first describing the file type, the latter the creator. 176This option works properly only for file formats that have the 177apple-style output defined. 178.It Fl b , Fl Fl brief 179Do not prepend filenames to output lines (brief mode). 180.It Fl C , Fl Fl compile 181Write a 182.Pa magic.mgc 183output file that contains a pre-parsed version of the magic file or directory. 184.It Fl c , Fl Fl checking-printout 185Cause a checking printout of the parsed form of the magic file. 186This is usually used in conjunction with the 187.Fl m 188flag to debug a new magic file before installing it. 189.It Fl d 190Prints internal debugging information to stderr. 191.It Fl E 192On filesystem errors (file not found etc), instead of handling the error 193as regular output as POSIX mandates and keep going, issue an error message 194and exit. 195.It Fl e , Fl Fl exclude Ar testname 196Exclude the test named in 197.Ar testname 198from the list of tests made to determine the file type. 199Valid test names are: 200.Bl -tag -width compress 201.It apptype 202.Dv EMX 203application type (only on EMX). 204.It ascii 205Various types of text files (this test will try to guess the text 206encoding, irrespective of the setting of the 207.Sq encoding 208option). 209.It encoding 210Different text encodings for soft magic tests. 211.It tokens 212Ignored for backwards compatibility. 213.It cdf 214Prints details of Compound Document Files. 215.It compress 216Checks for, and looks inside, compressed files. 217.It csv 218Checks Comma Separated Value files. 219.It elf 220Prints ELF file details, provided soft magic tests are enabled and the 221elf magic is found. 222.It json 223Examines JSON (RFC-7159) files by parsing them for compliance. 224.It soft 225Consults magic files. 226.It tar 227Examines tar files by verifying the checksum of the 512 byte tar header. 228Excluding this test can provide more detailed content description by using 229the soft magic method. 230.It text 231A synonym for 232.Sq ascii . 233.El 234.It Fl Fl extension 235Print a slash-separated list of valid extensions for the file type found. 236.It Fl F , Fl Fl separator Ar separator 237Use the specified string as the separator between the filename and the 238file result returned. 239Defaults to 240.Sq \&: . 241.It Fl f , Fl Fl files-from Ar namefile 242Read the names of the files to be examined from 243.Ar namefile 244(one per line) 245before the argument list. 246Either 247.Ar namefile 248or at least one filename argument must be present; 249to test the standard input, use 250.Sq - 251as a filename argument. 252Please note that 253.Ar namefile 254is unwrapped and the enclosed filenames are processed when this option is 255encountered and before any further options processing is done. 256This allows one to process multiple lists of files with different command line 257arguments on the same 258.Nm 259invocation. 260Thus if you want to set the delimiter, you need to do it before you specify 261the list of files, like: 262.Dq Fl F Ar @ Fl f Ar namefile , 263instead of: 264.Dq Fl f Ar namefile Fl F Ar @ . 265.It Fl h , Fl Fl no-dereference 266option causes symlinks not to be followed 267(on systems that support symbolic links). 268This is the default if the environment variable 269.Dv POSIXLY_CORRECT 270is not defined. 271.It Fl i , Fl Fl mime 272Causes the file command to output mime type strings rather than the more 273traditional human readable ones. 274Thus it may say 275.Sq text/plain; charset=us-ascii 276rather than 277.Dq ASCII text . 278.It Fl Fl mime-type , Fl Fl mime-encoding 279Like 280.Fl i , 281but print only the specified element(s). 282.It Fl k , Fl Fl keep-going 283Don't stop at the first match, keep going. 284Subsequent matches will be 285have the string 286.Sq "\[rs]012\- " 287prepended. 288(If you want a newline, see the 289.Fl r 290option.) 291The magic pattern with the highest strength (see the 292.Fl l 293option) comes first. 294.It Fl l , Fl Fl list 295Shows a list of patterns and their strength sorted descending by 296.Xr magic 5 297strength 298which is used for the matching (see also the 299.Fl k 300option). 301.It Fl L , Fl Fl dereference 302option causes symlinks to be followed, as the like-named option in 303.Xr ls 1 304(on systems that support symbolic links). 305This is the default if the environment variable 306.Ev POSIXLY_CORRECT 307is defined. 308.It Fl m , Fl Fl magic-file Ar magicfiles 309Specify an alternate list of files and directories containing magic. 310This can be a single item, or a colon-separated list. 311If a compiled magic file is found alongside a file or directory, 312it will be used instead. 313.It Fl N , Fl Fl no-pad 314Don't pad filenames so that they align in the output. 315.It Fl n , Fl Fl no-buffer 316Force stdout to be flushed after checking each file. 317This is only useful if checking a list of files. 318It is intended to be used by programs that want filetype output from a pipe. 319.It Fl p , Fl Fl preserve-date 320On systems that support 321.Xr utime 3 322or 323.Xr utimes 2 , 324attempt to preserve the access time of files analyzed, to pretend that 325.Nm 326never read them. 327.It Fl P , Fl Fl parameter Ar name=value 328Set various parameter limits. 329.Bl -column "elf_phnum" "Default" "XXXXXXXXXXXXXXXXXXXXXXXXXXX" -offset indent 330.It Sy "Name" Ta Sy "Default" Ta Sy "Explanation" 331.It Li indir Ta 15 Ta recursion limit for indirect magic 332.It Li name Ta 30 Ta use count limit for name/use magic 333.It Li elf_notes Ta 256 Ta max ELF notes processed 334.It Li elf_phnum Ta 128 Ta max ELF program sections processed 335.It Li elf_shnum Ta 32768 Ta max ELF sections processed 336.It Li regex Ta 8192 Ta length limit for regex searches 337.It Li bytes Ta 1048576 Ta max number of bytes to read from file 338.El 339.It Fl r , Fl Fl raw 340Don't translate unprintable characters to \eooo. 341Normally 342.Nm 343translates unprintable characters to their octal representation. 344.It Fl s , Fl Fl special-files 345Normally, 346.Nm 347only attempts to read and determine the type of argument files which 348.Xr stat 2 349reports are ordinary files. 350This prevents problems, because reading special files may have peculiar 351consequences. 352Specifying the 353.Fl s 354option causes 355.Nm 356to also read argument files which are block or character special files. 357This is useful for determining the filesystem types of the data in raw 358disk partitions, which are block special files. 359This option also causes 360.Nm 361to disregard the file size as reported by 362.Xr stat 2 363since on some systems it reports a zero size for raw disk partitions. 364.It Fl S , Fl Fl no-sandbox 365On systems where libseccomp 366.Pa ( https://github.com/seccomp/libseccomp ) 367is available, the 368.Fl S 369flag disables sandboxing which is enabled by default. 370This option is needed for file to execute external decompressing programs, 371i.e. when the 372.Fl z 373flag is specified and the built-in decompressors are not available. 374On systems where sandboxing is not available, this option has no effect. 375.It Fl v , Fl Fl version 376Print the version of the program and exit. 377.It Fl z , Fl Fl uncompress 378Try to look inside compressed files. 379.It Fl Z , Fl Fl uncompress-noreport 380Try to look inside compressed files, but report information about the contents 381only not the compression. 382.It Fl 0 , Fl Fl print0 383Output a null character 384.Sq \e0 385after the end of the filename. 386Nice to 387.Xr cut 1 388the output. 389This does not affect the separator, which is still printed. 390.Pp 391If this option is repeated more than once, then 392.Nm 393prints just the filename followed by a NUL followed by the description 394(or ERROR: text) followed by a second NUL for each entry. 395.It Fl -help 396Print a help message and exit. 397.El 398.Sh ENVIRONMENT 399The environment variable 400.Ev MAGIC 401can be used to set the default magic file name. 402If that variable is set, then 403.Nm 404will not attempt to open 405.Pa $HOME/.magic . 406.Nm 407adds 408.Dq Pa .mgc 409to the value of this variable as appropriate. 410The environment variable 411.Ev POSIXLY_CORRECT 412controls (on systems that support symbolic links), whether 413.Nm 414will attempt to follow symlinks or not. 415If set, then 416.Nm 417follows symlink, otherwise it does not. 418This is also controlled by the 419.Fl L 420and 421.Fl h 422options. 423.Sh FILES 424.Bl -tag -width /usr/share/misc/magic.mgc -compact 425.It Pa /usr/share/misc/magic.mgc 426Default compiled list of magic. 427.It Pa /usr/share/misc/magic 428Directory containing default magic files. 429.El 430.Sh EXIT STATUS 431.Nm 432will exit with 433.Dv 0 434if the operation was successful or 435.Dv >0 436if an error was encountered. 437The following errors cause diagnostic messages, but don't affect the program 438exit code (as POSIX requires), unless 439.Fl E 440is specified: 441.Bl -bullet -compact -offset indent 442.It 443A file cannot be found 444.It 445There is no permission to read a file 446.It 447The file type cannot be determined 448.El 449.Sh EXAMPLES 450.Bd -literal -offset indent 451$ file file.c file /dev/{wd0a,hda} 452file.c: C program text 453file: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), 454 dynamically linked (uses shared libs), stripped 455/dev/wd0a: block special (0/0) 456/dev/hda: block special (3/0) 457 458$ file -s /dev/wd0{b,d} 459/dev/wd0b: data 460/dev/wd0d: x86 boot sector 461 462$ file -s /dev/hda{,1,2,3,4,5,6,7,8,9,10} 463/dev/hda: x86 boot sector 464/dev/hda1: Linux/i386 ext2 filesystem 465/dev/hda2: x86 boot sector 466/dev/hda3: x86 boot sector, extended partition table 467/dev/hda4: Linux/i386 ext2 filesystem 468/dev/hda5: Linux/i386 swap file 469/dev/hda6: Linux/i386 swap file 470/dev/hda7: Linux/i386 swap file 471/dev/hda8: Linux/i386 swap file 472/dev/hda9: empty 473/dev/hda10: empty 474 475$ file -i file.c file /dev/{wd0a,hda} 476file.c: text/x-c 477file: application/x-executable 478/dev/hda: application/x-not-regular-file 479/dev/wd0a: application/x-not-regular-file 480 481.Ed 482.Sh SEE ALSO 483.Xr hexdump 1 , 484.Xr od 1 , 485.Xr strings 1 , 486.Xr magic 5 487.Sh STANDARDS CONFORMANCE 488This program is believed to exceed the System V Interface Definition 489of FILE(CMD), as near as one can determine from the vague language 490contained therein. 491Its behavior is mostly compatible with the System V program of the same name. 492This version knows more magic, however, so it will produce 493different (albeit more accurate) output in many cases. 494.\" URL: http://www.opengroup.org/onlinepubs/009695399/utilities/file.html 495.Pp 496The one significant difference 497between this version and System V 498is that this version treats any white space 499as a delimiter, so that spaces in pattern strings must be escaped. 500For example, 501.Bd -literal -offset indent 502\*[Gt]10 string language impress\ (imPRESS data) 503.Ed 504.Pp 505in an existing magic file would have to be changed to 506.Bd -literal -offset indent 507\*[Gt]10 string language\e impress (imPRESS data) 508.Ed 509.Pp 510In addition, in this version, if a pattern string contains a backslash, 511it must be escaped. 512For example 513.Bd -literal -offset indent 5140 string \ebegindata Andrew Toolkit document 515.Ed 516.Pp 517in an existing magic file would have to be changed to 518.Bd -literal -offset indent 5190 string \e\ebegindata Andrew Toolkit document 520.Ed 521.Pp 522SunOS releases 3.2 and later from Sun Microsystems include a 523.Nm 524command derived from the System V one, but with some extensions. 525This version differs from Sun's only in minor ways. 526It includes the extension of the 527.Sq \*[Am] 528operator, used as, 529for example, 530.Bd -literal -offset indent 531\*[Gt]16 long\*[Am]0x7fffffff \*[Gt]0 not stripped 532.Ed 533.Sh SECURITY 534On systems where libseccomp 535.Pa ( https://github.com/seccomp/libseccomp ) 536is available, 537.Nm 538is enforces limiting system calls to only the ones necessary for the 539operation of the program. 540This enforcement does not provide any security benefit when 541.Nm 542is asked to decompress input files running external programs with 543the 544.Fl z 545option. 546To enable execution of external decompressors, one needs to disable 547sandboxing using the 548.Fl S 549flag. 550.Sh MAGIC DIRECTORY 551The magic file entries have been collected from various sources, 552mainly USENET, and contributed by various authors. 553Christos Zoulas (address below) will collect additional 554or corrected magic file entries. 555A consolidation of magic file entries 556will be distributed periodically. 557.Pp 558The order of entries in the magic file is significant. 559Depending on what system you are using, the order that 560they are put together may be incorrect. 561If your old 562.Nm 563command uses a magic file, 564keep the old magic file around for comparison purposes 565(rename it to 566.Pa /usr/share/misc/magic.orig ) . 567.Sh HISTORY 568There has been a 569.Nm 570command in every 571.Dv UNIX since at least Research Version 4 572(man page dated November, 1973). 573The System V version introduced one significant major change: 574the external list of magic types. 575This slowed the program down slightly but made it a lot more flexible. 576.Pp 577This program, based on the System V version, 578was written by Ian Darwin 579.Aq ian@darwinsys.com 580without looking at anybody else's source code. 581.Pp 582John Gilmore revised the code extensively, making it better than 583the first version. 584Geoff Collyer found several inadequacies 585and provided some magic file entries. 586Contributions of the 587.Sq \*[Am] 588operator by Rob McMahon, 589.Aq cudcv@warwick.ac.uk , 5901989. 591.Pp 592Guy Harris, 593.Aq guy@netapp.com , 594made many changes from 1993 to the present. 595.Pp 596Primary development and maintenance from 1990 to the present by 597Christos Zoulas 598.Aq christos@astron.com . 599.Pp 600Altered by Chris Lowth 601.Aq chris@lowth.com , 6022000: handle the 603.Fl i 604option to output mime type strings, using an alternative 605magic file and internal logic. 606.Pp 607Altered by Eric Fischer 608.Aq enf@pobox.com , 609July, 2000, 610to identify character codes and attempt to identify the languages 611of non-ASCII files. 612.Pp 613Altered by Reuben Thomas 614.Aq rrt@sc3d.org , 6152007-2011, to improve MIME support, merge MIME and non-MIME magic, 616support directories as well as files of magic, apply many bug fixes, 617update and fix a lot of magic, improve the build system, improve the 618documentation, and rewrite the Python bindings in pure Python. 619.Pp 620The list of contributors to the 621.Sq magic 622directory (magic files) 623is too long to include here. 624You know who you are; thank you. 625Many contributors are listed in the source files. 626.Sh LEGAL NOTICE 627Copyright (c) Ian F. Darwin, Toronto, Canada, 1986-1999. 628Covered by the standard Berkeley Software Distribution copyright; see the file 629COPYING in the source distribution. 630.Pp 631The files 632.Pa tar.h 633and 634.Pa is_tar.c 635were written by John Gilmore from his public-domain 636.Xr tar 1 637program, and are not covered by the above license. 638.Sh BUGS 639Please report bugs and send patches to the bug tracker at 640.Pa https://bugs.astron.com/ 641or the mailing list at 642.Aq file@astron.com 643(visit 644.Pa https://mailman.astron.com/mailman/listinfo/file 645first to subscribe). 646.Sh TODO 647Fix output so that tests for MIME and APPLE flags are not needed all 648over the place, and actual output is only done in one place. 649This needs a design. 650Suggestion: push possible outputs on to a list, then pick the 651last-pushed (most specific, one hopes) value at the end, or 652use a default if the list is empty. 653This should not slow down evaluation. 654.Pp 655The handling of 656.Dv MAGIC_CONTINUE 657and printing \e012- between entries is clumsy and complicated; refactor 658and centralize. 659.Pp 660Some of the encoding logic is hard-coded in encoding.c and can be moved 661to the magic files if we had a !:charset annotation 662.Pp 663Continue to squash all magic bugs. 664See Debian BTS for a good source. 665.Pp 666Store arbitrarily long strings, for example for %s patterns, so that 667they can be printed out. 668Fixes Debian bug #271672. 669This can be done by allocating strings in a string pool, storing the 670string pool at the end of the magic file and converting all the string 671pointers to relative offsets from the string pool. 672.Pp 673Add syntax for relative offsets after current level (Debian bug #466037). 674.Pp 675Make file -ki work, i.e. give multiple MIME types. 676.Pp 677Add a zip library so we can peek inside Office2007 documents to 678print more details about their contents. 679.Pp 680Add an option to print URLs for the sources of the file descriptions. 681.Pp 682Combine script searches and add a way to map executable names to MIME 683types (e.g. have a magic value for !:mime which causes the resulting 684string to be looked up in a table). 685This would avoid adding the same magic repeatedly for each new 686hash-bang interpreter. 687.Pp 688When a file descriptor is available, we can skip and adjust the buffer 689instead of the hacky buffer management we do now. 690.Pp 691Fix 692.Dq name 693and 694.Dq use 695to check for consistency at compile time (duplicate 696.Dq name , 697.Dq use 698pointing to undefined 699.Dq name 700). 701Make 702.Dq name 703/ 704.Dq use 705more efficient by keeping a sorted list of names. 706Special-case ^ to flip endianness in the parser so that it does not 707have to be escaped, and document it. 708.Pp 709If the offsets specified internally in the file exceed the buffer size 710( 711.Dv HOWMANY 712variable in file.h), then we don't seek to that offset, but we give up. 713It would be better if buffer managements was done when the file descriptor 714is available so move around the file. 715One must be careful though because this has performance (and thus security 716considerations). 717.Sh AVAILABILITY 718You can obtain the original author's latest version by anonymous FTP 719on 720.Pa ftp.astron.com 721in the directory 722.Pa /pub/file/file-X.YZ.tar.gz . 723