1.\" $File: file.man,v 1.129 2018/03/02 16:17:54 christos Exp $ 2.Dd March 2, 2018 3.Dt FILE __CSECTION__ 4.Os 5.Sh NAME 6.Nm file 7.Nd determine file type 8.Sh SYNOPSIS 9.Nm 10.Bk -words 11.Op Fl bcdEhiklLNnprsSvzZ0 12.Op Fl Fl apple 13.Op Fl Fl extension 14.Op Fl Fl mime-encoding 15.Op Fl Fl mime-type 16.Op Fl e Ar testname 17.Op Fl F Ar separator 18.Op Fl f Ar namefile 19.Op Fl m Ar magicfiles 20.Op Fl P Ar name=value 21.Ar 22.Ek 23.Nm 24.Fl C 25.Op Fl m Ar magicfiles 26.Nm 27.Op Fl Fl help 28.Sh DESCRIPTION 29This manual page documents version __VERSION__ of the 30.Nm 31command. 32.Pp 33.Nm 34tests each argument in an attempt to classify it. 35There are three sets of tests, performed in this order: 36filesystem tests, magic tests, and language tests. 37The 38.Em first 39test that succeeds causes the file type to be printed. 40.Pp 41The type printed will usually contain one of the words 42.Em text 43(the file contains only 44printing characters and a few common control 45characters and is probably safe to read on an 46.Dv ASCII 47terminal), 48.Em executable 49(the file contains the result of compiling a program 50in a form understandable to some 51.Tn UNIX 52kernel or another), 53or 54.Em data 55meaning anything else (data is usually 56.Dq binary 57or non-printable). 58Exceptions are well-known file formats (core files, tar archives) 59that are known to contain binary data. 60When modifying magic files or the program itself, make sure to 61.Em "preserve these keywords" . 62Users depend on knowing that all the readable files in a directory 63have the word 64.Dq text 65printed. 66Don't do as Berkeley did and change 67.Dq shell commands text 68to 69.Dq shell script . 70.Pp 71The filesystem tests are based on examining the return from a 72.Xr stat 2 73system call. 74The program checks to see if the file is empty, 75or if it's some sort of special file. 76Any known file types appropriate to the system you are running on 77(sockets, symbolic links, or named pipes (FIFOs) on those systems that 78implement them) 79are intuited if they are defined in the system header file 80.In sys/stat.h . 81.Pp 82The magic tests are used to check for files with data in 83particular fixed formats. 84The canonical example of this is a binary executable (compiled program) 85.Dv a.out 86file, whose format is defined in 87.In elf.h , 88.In a.out.h 89and possibly 90.In exec.h 91in the standard include directory. 92These files have a 93.Dq "magic number" 94stored in a particular place 95near the beginning of the file that tells the 96.Tn UNIX 97operating system 98that the file is a binary executable, and which of several types thereof. 99The concept of a 100.Dq "magic" 101has been applied by extension to data files. 102Any file with some invariant identifier at a small fixed 103offset into the file can usually be described in this way. 104The information identifying these files is read from the compiled 105magic file 106.Pa __MAGIC__.mgc , 107or the files in the directory 108.Pa __MAGIC__ 109if the compiled file does not exist. 110In addition, if 111.Pa $HOME/.magic.mgc 112or 113.Pa $HOME/.magic 114exists, it will be used in preference to the system magic files. 115.Pp 116If a file does not match any of the entries in the magic file, 117it is examined to see if it seems to be a text file. 118ASCII, ISO-8859-x, non-ISO 8-bit extended-ASCII character sets 119(such as those used on Macintosh and IBM PC systems), 120UTF-8-encoded Unicode, UTF-16-encoded Unicode, and EBCDIC 121character sets can be distinguished by the different 122ranges and sequences of bytes that constitute printable text 123in each set. 124If a file passes any of these tests, its character set is reported. 125ASCII, ISO-8859-x, UTF-8, and extended-ASCII files are identified 126as 127.Dq text 128because they will be mostly readable on nearly any terminal; 129UTF-16 and EBCDIC are only 130.Dq character data 131because, while 132they contain text, it is text that will require translation 133before it can be read. 134In addition, 135.Nm 136will attempt to determine other characteristics of text-type files. 137If the lines of a file are terminated by CR, CRLF, or NEL, instead 138of the Unix-standard LF, this will be reported. 139Files that contain embedded escape sequences or overstriking 140will also be identified. 141.Pp 142Once 143.Nm 144has determined the character set used in a text-type file, 145it will 146attempt to determine in what language the file is written. 147The language tests look for particular strings (cf. 148.In names.h ) 149that can appear anywhere in the first few blocks of a file. 150For example, the keyword 151.Em .br 152indicates that the file is most likely a 153.Xr troff 1 154input file, just as the keyword 155.Em struct 156indicates a C program. 157These tests are less reliable than the previous 158two groups, so they are performed last. 159The language test routines also test for some miscellany 160(such as 161.Xr tar 1 162archives). 163.Pp 164Any file that cannot be identified as having been written 165in any of the character sets listed above is simply said to be 166.Dq data . 167.Sh OPTIONS 168.Bl -tag -width indent 169.It Fl Fl apple 170Causes the file command to output the file type and creator code as 171used by older MacOS versions. 172The code consists of eight letters, 173the first describing the file type, the latter the creator. 174.It Fl b , Fl Fl brief 175Do not prepend filenames to output lines (brief mode). 176.It Fl C , Fl Fl compile 177Write a 178.Pa magic.mgc 179output file that contains a pre-parsed version of the magic file or directory. 180.It Fl c , Fl Fl checking-printout 181Cause a checking printout of the parsed form of the magic file. 182This is usually used in conjunction with the 183.Fl m 184flag to debug a new magic file before installing it. 185.It Fl d 186Prints internal debugging information to stderr. 187.It Fl E 188On filesystem errors (file not found etc), instead of handling the error 189as regular output as POSIX mandates and keep going, issue an error message 190and exit. 191.It Fl e , Fl Fl exclude Ar testname 192Exclude the test named in 193.Ar testname 194from the list of tests made to determine the file type. 195Valid test names are: 196.Bl -tag -width compress 197.It apptype 198.Dv EMX 199application type (only on EMX). 200.It ascii 201Various types of text files (this test will try to guess the text 202encoding, irrespective of the setting of the 203.Sq encoding 204option). 205.It encoding 206Different text encodings for soft magic tests. 207.It tokens 208Ignored for backwards compatibility. 209.It cdf 210Prints details of Compound Document Files. 211.It compress 212Checks for, and looks inside, compressed files. 213.It elf 214Prints ELF file details, provided soft magic tests are enabled and the 215elf magic is found. 216.It soft 217Consults magic files. 218.It tar 219Examines tar files by verifying the checksum of the 512 byte tar header. 220Excluding this test can provide more detailed content description by using 221the soft magic method. 222.It text 223A synonym for 224.Sq ascii . 225.El 226.It Fl Fl extension 227Print a slash-separated list of valid extensions for the file type found. 228.It Fl F , Fl Fl separator Ar separator 229Use the specified string as the separator between the filename and the 230file result returned. 231Defaults to 232.Sq \&: . 233.It Fl f , Fl Fl files-from Ar namefile 234Read the names of the files to be examined from 235.Ar namefile 236(one per line) 237before the argument list. 238Either 239.Ar namefile 240or at least one filename argument must be present; 241to test the standard input, use 242.Sq - 243as a filename argument. 244Please note that 245.Ar namefile 246is unwrapped and the enclosed filenames are processed when this option is 247encountered and before any further options processing is done. 248This allows one to process multiple lists of files with different command line 249arguments on the same 250.Nm 251invocation. 252Thus if you want to set the delimiter, you need to do it before you specify 253the list of files, like: 254.Dq Fl F Ar @ Fl f Ar namefile , 255instead of: 256.Dq Fl f Ar namefile Fl F Ar @ . 257.It Fl h , Fl Fl no-dereference 258option causes symlinks not to be followed 259(on systems that support symbolic links). 260This is the default if the environment variable 261.Dv POSIXLY_CORRECT 262is not defined. 263.It Fl i , Fl Fl mime 264Causes the file command to output mime type strings rather than the more 265traditional human readable ones. 266Thus it may say 267.Sq text/plain; charset=us-ascii 268rather than 269.Dq ASCII text . 270.It Fl Fl mime-type , Fl Fl mime-encoding 271Like 272.Fl i , 273but print only the specified element(s). 274.It Fl k , Fl Fl keep-going 275Don't stop at the first match, keep going. 276Subsequent matches will be 277have the string 278.Sq "\[rs]012\- " 279prepended. 280(If you want a newline, see the 281.Fl r 282option.) 283The magic pattern with the highest strength (see the 284.Fl l 285option) comes first. 286.It Fl l , Fl Fl list 287Shows a list of patterns and their strength sorted descending by 288.Xr magic 4 289strength 290which is used for the matching (see also the 291.Fl k 292option). 293.It Fl L , Fl Fl dereference 294option causes symlinks to be followed, as the like-named option in 295.Xr ls 1 296(on systems that support symbolic links). 297This is the default if the environment variable 298.Ev POSIXLY_CORRECT 299is defined. 300.It Fl m , Fl Fl magic-file Ar magicfiles 301Specify an alternate list of files and directories containing magic. 302This can be a single item, or a colon-separated list. 303If a compiled magic file is found alongside a file or directory, 304it will be used instead. 305.It Fl N , Fl Fl no-pad 306Don't pad filenames so that they align in the output. 307.It Fl n , Fl Fl no-buffer 308Force stdout to be flushed after checking each file. 309This is only useful if checking a list of files. 310It is intended to be used by programs that want filetype output from a pipe. 311.It Fl p , Fl Fl preserve-date 312On systems that support 313.Xr utime 3 314or 315.Xr utimes 2 , 316attempt to preserve the access time of files analyzed, to pretend that 317.Nm 318never read them. 319.It Fl P , Fl Fl parameter Ar name=value 320Set various parameter limits. 321.Bl -column "elf_phnum" "Default" "XXXXXXXXXXXXXXXXXXXXXXXXXXX" -offset indent 322.It Sy "Name" Ta Sy "Default" Ta Sy "Explanation" 323.It Li indir Ta 15 Ta recursion limit for indirect magic 324.It Li name Ta 30 Ta use count limit for name/use magic 325.It Li elf_notes Ta 256 Ta max ELF notes processed 326.It Li elf_phnum Ta 128 Ta max ELF program sections processed 327.It Li elf_shnum Ta 32768 Ta max ELF sections processed 328.It Li regex Ta 8192 Ta length limit for regex searches 329.It Li bytes Ta 1048576 Ta max number of bytes to read from file 330.El 331.It Fl r , Fl Fl raw 332Don't translate unprintable characters to \eooo. 333Normally 334.Nm 335translates unprintable characters to their octal representation. 336.It Fl s , Fl Fl special-files 337Normally, 338.Nm 339only attempts to read and determine the type of argument files which 340.Xr stat 2 341reports are ordinary files. 342This prevents problems, because reading special files may have peculiar 343consequences. 344Specifying the 345.Fl s 346option causes 347.Nm 348to also read argument files which are block or character special files. 349This is useful for determining the filesystem types of the data in raw 350disk partitions, which are block special files. 351This option also causes 352.Nm 353to disregard the file size as reported by 354.Xr stat 2 355since on some systems it reports a zero size for raw disk partitions. 356.If Fl S , Fl Fl no-sandbox 357On systems where libseccomp 358.Pa ( https://github.com/seccomp/libseccomp ) 359is available, the 360.Fl S 361flag disables sandboxing which is enabled by default. 362This option is needed for file to execute external descompressing programs, 363i.e. when the 364.Fl z 365flag is specified and the built-in decompressors are not available. 366.It Fl v , Fl Fl version 367Print the version of the program and exit. 368.It Fl z , Fl Fl uncompress 369Try to look inside compressed files. 370.It Fl Z , Fl Fl uncompress-noreport 371Try to look inside compressed files, but report information about the contents 372only not the compression. 373.It Fl 0 , Fl Fl print0 374Output a null character 375.Sq \e0 376after the end of the filename. 377Nice to 378.Xr cut 1 379the output. 380This does not affect the separator, which is still printed. 381.Pp 382If this option is repeated more than once, then 383.Nm 384prints just the filename followed by a NUL followed by the description 385(or ERROR: text) followed by a second NUL for each entry. 386.It Fl -help 387Print a help message and exit. 388.El 389.Sh ENVIRONMENT 390The environment variable 391.Ev MAGIC 392can be used to set the default magic file name. 393If that variable is set, then 394.Nm 395will not attempt to open 396.Pa $HOME/.magic . 397.Nm 398adds 399.Dq Pa .mgc 400to the value of this variable as appropriate. 401The environment variable 402.Ev POSIXLY_CORRECT 403controls (on systems that support symbolic links), whether 404.Nm 405will attempt to follow symlinks or not. 406If set, then 407.Nm 408follows symlink, otherwise it does not. 409This is also controlled by the 410.Fl L 411and 412.Fl h 413options. 414.Sh FILES 415.Bl -tag -width __MAGIC__.mgc -compact 416.It Pa __MAGIC__.mgc 417Default compiled list of magic. 418.It Pa __MAGIC__ 419Directory containing default magic files. 420.El 421.Sh EXIT STATUS 422.Nm 423will exit with 424.Dv 0 425if the operation was successful or 426.Dv >0 427if an error was encountered. 428The following errors cause diagnostic messages, but don't affect the program 429exit code (as POSIX requires), unless 430.Fl E 431is specified: 432.Bl -bullet -compact -offset indent 433.It 434A file cannot be found 435.It 436There is no permission to read a file 437.It 438The file type cannot be determined 439.El 440.Sh EXAMPLES 441.Bd -literal -offset indent 442$ file file.c file /dev/{wd0a,hda} 443file.c: C program text 444file: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), 445 dynamically linked (uses shared libs), stripped 446/dev/wd0a: block special (0/0) 447/dev/hda: block special (3/0) 448 449$ file -s /dev/wd0{b,d} 450/dev/wd0b: data 451/dev/wd0d: x86 boot sector 452 453$ file -s /dev/hda{,1,2,3,4,5,6,7,8,9,10} 454/dev/hda: x86 boot sector 455/dev/hda1: Linux/i386 ext2 filesystem 456/dev/hda2: x86 boot sector 457/dev/hda3: x86 boot sector, extended partition table 458/dev/hda4: Linux/i386 ext2 filesystem 459/dev/hda5: Linux/i386 swap file 460/dev/hda6: Linux/i386 swap file 461/dev/hda7: Linux/i386 swap file 462/dev/hda8: Linux/i386 swap file 463/dev/hda9: empty 464/dev/hda10: empty 465 466$ file -i file.c file /dev/{wd0a,hda} 467file.c: text/x-c 468file: application/x-executable 469/dev/hda: application/x-not-regular-file 470/dev/wd0a: application/x-not-regular-file 471 472.Ed 473.Sh SEE ALSO 474.Xr hexdump 1 , 475.Xr od 1 , 476.Xr strings 1 , 477.Xr magic __FSECTION__ , 478.Xr fstyp 8 479.Sh STANDARDS CONFORMANCE 480This program is believed to exceed the System V Interface Definition 481of FILE(CMD), as near as one can determine from the vague language 482contained therein. 483Its behavior is mostly compatible with the System V program of the same name. 484This version knows more magic, however, so it will produce 485different (albeit more accurate) output in many cases. 486.\" URL: http://www.opengroup.org/onlinepubs/009695399/utilities/file.html 487.Pp 488The one significant difference 489between this version and System V 490is that this version treats any white space 491as a delimiter, so that spaces in pattern strings must be escaped. 492For example, 493.Bd -literal -offset indent 494\*[Gt]10 string language impress\ (imPRESS data) 495.Ed 496.Pp 497in an existing magic file would have to be changed to 498.Bd -literal -offset indent 499\*[Gt]10 string language\e impress (imPRESS data) 500.Ed 501.Pp 502In addition, in this version, if a pattern string contains a backslash, 503it must be escaped. 504For example 505.Bd -literal -offset indent 5060 string \ebegindata Andrew Toolkit document 507.Ed 508.Pp 509in an existing magic file would have to be changed to 510.Bd -literal -offset indent 5110 string \e\ebegindata Andrew Toolkit document 512.Ed 513.Pp 514SunOS releases 3.2 and later from Sun Microsystems include a 515.Nm 516command derived from the System V one, but with some extensions. 517This version differs from Sun's only in minor ways. 518It includes the extension of the 519.Sq \*[Am] 520operator, used as, 521for example, 522.Bd -literal -offset indent 523\*[Gt]16 long\*[Am]0x7fffffff \*[Gt]0 not stripped 524.Ed 525.Sh SECURITY 526On systems where libseccomp 527.Pa ( https://github.com/seccomp/libseccomp ) 528is available, 529.Nm 530is enforces limiting system calls to only the ones necessary for the 531operation of the program. 532This enforcement does not provide any security benefit when 533.Nm 534is asked to decompress input files running external programs with 535the 536.Fl z 537option. 538To enable execution of external decompressors, one needs to disable 539sandboxing using the 540.Fl S 541flag. 542.Sh MAGIC DIRECTORY 543The magic file entries have been collected from various sources, 544mainly USENET, and contributed by various authors. 545Christos Zoulas (address below) will collect additional 546or corrected magic file entries. 547A consolidation of magic file entries 548will be distributed periodically. 549.Pp 550The order of entries in the magic file is significant. 551Depending on what system you are using, the order that 552they are put together may be incorrect. 553If your old 554.Nm 555command uses a magic file, 556keep the old magic file around for comparison purposes 557(rename it to 558.Pa __MAGIC__.orig ) . 559.Sh HISTORY 560There has been a 561.Nm 562command in every 563.Dv UNIX since at least Research Version 4 564(man page dated November, 1973). 565The System V version introduced one significant major change: 566the external list of magic types. 567This slowed the program down slightly but made it a lot more flexible. 568.Pp 569This program, based on the System V version, 570was written by Ian Darwin 571.Aq ian@darwinsys.com 572without looking at anybody else's source code. 573.Pp 574John Gilmore revised the code extensively, making it better than 575the first version. 576Geoff Collyer found several inadequacies 577and provided some magic file entries. 578Contributions of the 579.Sq \*[Am] 580operator by Rob McMahon, 581.Aq cudcv@warwick.ac.uk , 5821989. 583.Pp 584Guy Harris, 585.Aq guy@netapp.com , 586made many changes from 1993 to the present. 587.Pp 588Primary development and maintenance from 1990 to the present by 589Christos Zoulas 590.Aq christos@astron.com . 591.Pp 592Altered by Chris Lowth 593.Aq chris@lowth.com , 5942000: handle the 595.Fl i 596option to output mime type strings, using an alternative 597magic file and internal logic. 598.Pp 599Altered by Eric Fischer 600.Aq enf@pobox.com , 601July, 2000, 602to identify character codes and attempt to identify the languages 603of non-ASCII files. 604.Pp 605Altered by Reuben Thomas 606.Aq rrt@sc3d.org , 6072007-2011, to improve MIME support, merge MIME and non-MIME magic, 608support directories as well as files of magic, apply many bug fixes, 609update and fix a lot of magic, improve the build system, improve the 610documentation, and rewrite the Python bindings in pure Python. 611.Pp 612The list of contributors to the 613.Sq magic 614directory (magic files) 615is too long to include here. 616You know who you are; thank you. 617Many contributors are listed in the source files. 618.Sh LEGAL NOTICE 619Copyright (c) Ian F. Darwin, Toronto, Canada, 1986-1999. 620Covered by the standard Berkeley Software Distribution copyright; see the file 621COPYING in the source distribution. 622.Pp 623The files 624.Pa tar.h 625and 626.Pa is_tar.c 627were written by John Gilmore from his public-domain 628.Xr tar 1 629program, and are not covered by the above license. 630.Sh BUGS 631Please report bugs and send patches to the bug tracker at 632.Pa http://bugs.gw.com/ 633or the mailing list at 634.Aq file@mx.gw.com 635(visit 636.Pa http://mx.gw.com/mailman/listinfo/file 637first to subscribe). 638.Sh TODO 639Fix output so that tests for MIME and APPLE flags are not needed all 640over the place, and actual output is only done in one place. 641This needs a design. 642Suggestion: push possible outputs on to a list, then pick the 643last-pushed (most specific, one hopes) value at the end, or 644use a default if the list is empty. 645This should not slow down evaluation. 646.Pp 647The handling of 648.Dv MAGIC_CONTINUE 649and printing \e012- between entries is clumsy and complicated; refactor 650and centralize. 651.Pp 652Some of the encoding logic is hard-coded in encoding.c and can be moved 653to the magic files if we had a !:charset annotation 654.Pp 655Continue to squash all magic bugs. 656See Debian BTS for a good source. 657.Pp 658Store arbitrarily long strings, for example for %s patterns, so that 659they can be printed out. 660Fixes Debian bug #271672. 661This can be done by allocating strings in a string pool, storing the 662string pool at the end of the magic file and converting all the string 663pointers to relative offsets from the string pool. 664.Pp 665Add syntax for relative offsets after current level (Debian bug #466037). 666.Pp 667Make file -ki work, i.e. give multiple MIME types. 668.Pp 669Add a zip library so we can peek inside Office2007 documents to 670print more details about their contents. 671.Pp 672Add an option to print URLs for the sources of the file descriptions. 673.Pp 674Combine script searches and add a way to map executable names to MIME 675types (e.g. have a magic value for !:mime which causes the resulting 676string to be looked up in a table). 677This would avoid adding the same magic repeatedly for each new 678hash-bang interpreter. 679.Pp 680When a file descriptor is available, we can skip and adjust the buffer 681instead of the hacky buffer management we do now. 682.Pp 683Fix 684.Dq name 685and 686.Dq use 687to check for consistency at compile time (duplicate 688.Dq name , 689.Dq use 690pointing to undefined 691.Dq name 692). 693Make 694.Dq name 695/ 696.Dq use 697more efficient by keeping a sorted list of names. 698Special-case ^ to flip endianness in the parser so that it does not 699have to be escaped, and document it. 700.Pp 701If the offsets specified internally in the file exceed the buffer size 702( 703.Dv HOWMANY 704variable in file.h), then we don't seek to that offset, but we give up. 705It would be better if buffer managements was done when the file descriptor 706is available so move around the file. 707One must be careful though because this has performance (and thus security 708considerations). 709.Sh AVAILABILITY 710You can obtain the original author's latest version by anonymous FTP 711on 712.Pa ftp.astron.com 713in the directory 714.Pa /pub/file/file-X.YZ.tar.gz . 715