1.\" $File: file.man,v 1.135 2019/03/03 02:32:40 christos Exp $ 2.Dd February 18, 2019 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, JSON files). 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. 174This option works properly only for file formats that have the 175apple-style output defined. 176.It Fl b , Fl Fl brief 177Do not prepend filenames to output lines (brief mode). 178.It Fl C , Fl Fl compile 179Write a 180.Pa magic.mgc 181output file that contains a pre-parsed version of the magic file or directory. 182.It Fl c , Fl Fl checking-printout 183Cause a checking printout of the parsed form of the magic file. 184This is usually used in conjunction with the 185.Fl m 186flag to debug a new magic file before installing it. 187.It Fl d 188Prints internal debugging information to stderr. 189.It Fl E 190On filesystem errors (file not found etc), instead of handling the error 191as regular output as POSIX mandates and keep going, issue an error message 192and exit. 193.It Fl e , Fl Fl exclude Ar testname 194Exclude the test named in 195.Ar testname 196from the list of tests made to determine the file type. 197Valid test names are: 198.Bl -tag -width compress 199.It apptype 200.Dv EMX 201application type (only on EMX). 202.It ascii 203Various types of text files (this test will try to guess the text 204encoding, irrespective of the setting of the 205.Sq encoding 206option). 207.It encoding 208Different text encodings for soft magic tests. 209.It tokens 210Ignored for backwards compatibility. 211.It cdf 212Prints details of Compound Document Files. 213.It compress 214Checks for, and looks inside, compressed files. 215.It elf 216Prints ELF file details, provided soft magic tests are enabled and the 217elf magic is found. 218.It json 219Examines JSON (RFC-7159) files by parsing them for compliance. 220.It soft 221Consults magic files. 222.It tar 223Examines tar files by verifying the checksum of the 512 byte tar header. 224Excluding this test can provide more detailed content description by using 225the soft magic method. 226.It text 227A synonym for 228.Sq ascii . 229.El 230.It Fl Fl extension 231Print a slash-separated list of valid extensions for the file type found. 232.It Fl F , Fl Fl separator Ar separator 233Use the specified string as the separator between the filename and the 234file result returned. 235Defaults to 236.Sq \&: . 237.It Fl f , Fl Fl files-from Ar namefile 238Read the names of the files to be examined from 239.Ar namefile 240(one per line) 241before the argument list. 242Either 243.Ar namefile 244or at least one filename argument must be present; 245to test the standard input, use 246.Sq - 247as a filename argument. 248Please note that 249.Ar namefile 250is unwrapped and the enclosed filenames are processed when this option is 251encountered and before any further options processing is done. 252This allows one to process multiple lists of files with different command line 253arguments on the same 254.Nm 255invocation. 256Thus if you want to set the delimiter, you need to do it before you specify 257the list of files, like: 258.Dq Fl F Ar @ Fl f Ar namefile , 259instead of: 260.Dq Fl f Ar namefile Fl F Ar @ . 261.It Fl h , Fl Fl no-dereference 262option causes symlinks not to be followed 263(on systems that support symbolic links). 264This is the default if the environment variable 265.Dv POSIXLY_CORRECT 266is not defined. 267.It Fl i , Fl Fl mime 268Causes the file command to output mime type strings rather than the more 269traditional human readable ones. 270Thus it may say 271.Sq text/plain; charset=us-ascii 272rather than 273.Dq ASCII text . 274.It Fl Fl mime-type , Fl Fl mime-encoding 275Like 276.Fl i , 277but print only the specified element(s). 278.It Fl k , Fl Fl keep-going 279Don't stop at the first match, keep going. 280Subsequent matches will be 281have the string 282.Sq "\[rs]012\- " 283prepended. 284(If you want a newline, see the 285.Fl r 286option.) 287The magic pattern with the highest strength (see the 288.Fl l 289option) comes first. 290.It Fl l , Fl Fl list 291Shows a list of patterns and their strength sorted descending by 292.Xr magic 4 293strength 294which is used for the matching (see also the 295.Fl k 296option). 297.It Fl L , Fl Fl dereference 298option causes symlinks to be followed, as the like-named option in 299.Xr ls 1 300(on systems that support symbolic links). 301This is the default if the environment variable 302.Ev POSIXLY_CORRECT 303is defined. 304.It Fl m , Fl Fl magic-file Ar magicfiles 305Specify an alternate list of files and directories containing magic. 306This can be a single item, or a colon-separated list. 307If a compiled magic file is found alongside a file or directory, 308it will be used instead. 309.It Fl N , Fl Fl no-pad 310Don't pad filenames so that they align in the output. 311.It Fl n , Fl Fl no-buffer 312Force stdout to be flushed after checking each file. 313This is only useful if checking a list of files. 314It is intended to be used by programs that want filetype output from a pipe. 315.It Fl p , Fl Fl preserve-date 316On systems that support 317.Xr utime 3 318or 319.Xr utimes 2 , 320attempt to preserve the access time of files analyzed, to pretend that 321.Nm 322never read them. 323.It Fl P , Fl Fl parameter Ar name=value 324Set various parameter limits. 325.Bl -column "elf_phnum" "Default" "XXXXXXXXXXXXXXXXXXXXXXXXXXX" -offset indent 326.It Sy "Name" Ta Sy "Default" Ta Sy "Explanation" 327.It Li indir Ta 15 Ta recursion limit for indirect magic 328.It Li name Ta 30 Ta use count limit for name/use magic 329.It Li elf_notes Ta 256 Ta max ELF notes processed 330.It Li elf_phnum Ta 128 Ta max ELF program sections processed 331.It Li elf_shnum Ta 32768 Ta max ELF sections processed 332.It Li regex Ta 8192 Ta length limit for regex searches 333.It Li bytes Ta 1048576 Ta max number of bytes to read from file 334.El 335.It Fl r , Fl Fl raw 336Don't translate unprintable characters to \eooo. 337Normally 338.Nm 339translates unprintable characters to their octal representation. 340.It Fl s , Fl Fl special-files 341Normally, 342.Nm 343only attempts to read and determine the type of argument files which 344.Xr stat 2 345reports are ordinary files. 346This prevents problems, because reading special files may have peculiar 347consequences. 348Specifying the 349.Fl s 350option causes 351.Nm 352to also read argument files which are block or character special files. 353This is useful for determining the filesystem types of the data in raw 354disk partitions, which are block special files. 355This option also causes 356.Nm 357to disregard the file size as reported by 358.Xr stat 2 359since on some systems it reports a zero size for raw disk partitions. 360.It Fl S , Fl Fl no-sandbox 361On systems where libseccomp 362.Pa ( https://github.com/seccomp/libseccomp ) 363is available, the 364.Fl S 365flag disables sandboxing which is enabled by default. 366This option is needed for file to execute external descompressing programs, 367i.e. when the 368.Fl z 369flag is specified and the built-in decompressors are not available. 370.It Fl v , Fl Fl version 371Print the version of the program and exit. 372.It Fl z , Fl Fl uncompress 373Try to look inside compressed files. 374.It Fl Z , Fl Fl uncompress-noreport 375Try to look inside compressed files, but report information about the contents 376only not the compression. 377.It Fl 0 , Fl Fl print0 378Output a null character 379.Sq \e0 380after the end of the filename. 381Nice to 382.Xr cut 1 383the output. 384This does not affect the separator, which is still printed. 385.Pp 386If this option is repeated more than once, then 387.Nm 388prints just the filename followed by a NUL followed by the description 389(or ERROR: text) followed by a second NUL for each entry. 390.It Fl -help 391Print a help message and exit. 392.El 393.Sh ENVIRONMENT 394The environment variable 395.Ev MAGIC 396can be used to set the default magic file name. 397If that variable is set, then 398.Nm 399will not attempt to open 400.Pa $HOME/.magic . 401.Nm 402adds 403.Dq Pa .mgc 404to the value of this variable as appropriate. 405The environment variable 406.Ev POSIXLY_CORRECT 407controls (on systems that support symbolic links), whether 408.Nm 409will attempt to follow symlinks or not. 410If set, then 411.Nm 412follows symlink, otherwise it does not. 413This is also controlled by the 414.Fl L 415and 416.Fl h 417options. 418.Sh FILES 419.Bl -tag -width __MAGIC__.mgc -compact 420.It Pa __MAGIC__.mgc 421Default compiled list of magic. 422.It Pa __MAGIC__ 423Directory containing default magic files. 424.El 425.Sh EXIT STATUS 426.Nm 427will exit with 428.Dv 0 429if the operation was successful or 430.Dv >0 431if an error was encountered. 432The following errors cause diagnostic messages, but don't affect the program 433exit code (as POSIX requires), unless 434.Fl E 435is specified: 436.Bl -bullet -compact -offset indent 437.It 438A file cannot be found 439.It 440There is no permission to read a file 441.It 442The file type cannot be determined 443.El 444.Sh EXAMPLES 445.Bd -literal -offset indent 446$ file file.c file /dev/{wd0a,hda} 447file.c: C program text 448file: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), 449 dynamically linked (uses shared libs), stripped 450/dev/wd0a: block special (0/0) 451/dev/hda: block special (3/0) 452 453$ file -s /dev/wd0{b,d} 454/dev/wd0b: data 455/dev/wd0d: x86 boot sector 456 457$ file -s /dev/hda{,1,2,3,4,5,6,7,8,9,10} 458/dev/hda: x86 boot sector 459/dev/hda1: Linux/i386 ext2 filesystem 460/dev/hda2: x86 boot sector 461/dev/hda3: x86 boot sector, extended partition table 462/dev/hda4: Linux/i386 ext2 filesystem 463/dev/hda5: Linux/i386 swap file 464/dev/hda6: Linux/i386 swap file 465/dev/hda7: Linux/i386 swap file 466/dev/hda8: Linux/i386 swap file 467/dev/hda9: empty 468/dev/hda10: empty 469 470$ file -i file.c file /dev/{wd0a,hda} 471file.c: text/x-c 472file: application/x-executable 473/dev/hda: application/x-not-regular-file 474/dev/wd0a: application/x-not-regular-file 475 476.Ed 477.Sh SEE ALSO 478.Xr hexdump 1 , 479.Xr od 1 , 480.Xr strings 1 , 481.Xr magic __FSECTION__ , 482.Xr fstyp 8 483.Sh STANDARDS CONFORMANCE 484This program is believed to exceed the System V Interface Definition 485of FILE(CMD), as near as one can determine from the vague language 486contained therein. 487Its behavior is mostly compatible with the System V program of the same name. 488This version knows more magic, however, so it will produce 489different (albeit more accurate) output in many cases. 490.\" URL: http://www.opengroup.org/onlinepubs/009695399/utilities/file.html 491.Pp 492The one significant difference 493between this version and System V 494is that this version treats any white space 495as a delimiter, so that spaces in pattern strings must be escaped. 496For example, 497.Bd -literal -offset indent 498\*[Gt]10 string language impress\ (imPRESS data) 499.Ed 500.Pp 501in an existing magic file would have to be changed to 502.Bd -literal -offset indent 503\*[Gt]10 string language\e impress (imPRESS data) 504.Ed 505.Pp 506In addition, in this version, if a pattern string contains a backslash, 507it must be escaped. 508For example 509.Bd -literal -offset indent 5100 string \ebegindata Andrew Toolkit document 511.Ed 512.Pp 513in an existing magic file would have to be changed to 514.Bd -literal -offset indent 5150 string \e\ebegindata Andrew Toolkit document 516.Ed 517.Pp 518SunOS releases 3.2 and later from Sun Microsystems include a 519.Nm 520command derived from the System V one, but with some extensions. 521This version differs from Sun's only in minor ways. 522It includes the extension of the 523.Sq \*[Am] 524operator, used as, 525for example, 526.Bd -literal -offset indent 527\*[Gt]16 long\*[Am]0x7fffffff \*[Gt]0 not stripped 528.Ed 529.Sh SECURITY 530On systems where libseccomp 531.Pa ( https://github.com/seccomp/libseccomp ) 532is available, 533.Nm 534is enforces limiting system calls to only the ones necessary for the 535operation of the program. 536This enforcement does not provide any security benefit when 537.Nm 538is asked to decompress input files running external programs with 539the 540.Fl z 541option. 542To enable execution of external decompressors, one needs to disable 543sandboxing using the 544.Fl S 545flag. 546.Sh MAGIC DIRECTORY 547The magic file entries have been collected from various sources, 548mainly USENET, and contributed by various authors. 549Christos Zoulas (address below) will collect additional 550or corrected magic file entries. 551A consolidation of magic file entries 552will be distributed periodically. 553.Pp 554The order of entries in the magic file is significant. 555Depending on what system you are using, the order that 556they are put together may be incorrect. 557If your old 558.Nm 559command uses a magic file, 560keep the old magic file around for comparison purposes 561(rename it to 562.Pa __MAGIC__.orig ) . 563.Sh HISTORY 564There has been a 565.Nm 566command in every 567.Dv UNIX since at least Research Version 4 568(man page dated November, 1973). 569The System V version introduced one significant major change: 570the external list of magic types. 571This slowed the program down slightly but made it a lot more flexible. 572.Pp 573This program, based on the System V version, 574was written by Ian Darwin 575.Aq ian@darwinsys.com 576without looking at anybody else's source code. 577.Pp 578John Gilmore revised the code extensively, making it better than 579the first version. 580Geoff Collyer found several inadequacies 581and provided some magic file entries. 582Contributions of the 583.Sq \*[Am] 584operator by Rob McMahon, 585.Aq cudcv@warwick.ac.uk , 5861989. 587.Pp 588Guy Harris, 589.Aq guy@netapp.com , 590made many changes from 1993 to the present. 591.Pp 592Primary development and maintenance from 1990 to the present by 593Christos Zoulas 594.Aq christos@astron.com . 595.Pp 596Altered by Chris Lowth 597.Aq chris@lowth.com , 5982000: handle the 599.Fl i 600option to output mime type strings, using an alternative 601magic file and internal logic. 602.Pp 603Altered by Eric Fischer 604.Aq enf@pobox.com , 605July, 2000, 606to identify character codes and attempt to identify the languages 607of non-ASCII files. 608.Pp 609Altered by Reuben Thomas 610.Aq rrt@sc3d.org , 6112007-2011, to improve MIME support, merge MIME and non-MIME magic, 612support directories as well as files of magic, apply many bug fixes, 613update and fix a lot of magic, improve the build system, improve the 614documentation, and rewrite the Python bindings in pure Python. 615.Pp 616The list of contributors to the 617.Sq magic 618directory (magic files) 619is too long to include here. 620You know who you are; thank you. 621Many contributors are listed in the source files. 622.Sh LEGAL NOTICE 623Copyright (c) Ian F. Darwin, Toronto, Canada, 1986-1999. 624Covered by the standard Berkeley Software Distribution copyright; see the file 625COPYING in the source distribution. 626.Pp 627The files 628.Pa tar.h 629and 630.Pa is_tar.c 631were written by John Gilmore from his public-domain 632.Xr tar 1 633program, and are not covered by the above license. 634.Sh BUGS 635Please report bugs and send patches to the bug tracker at 636.Pa https://bugs.astron.com/ 637or the mailing list at 638.Aq file@astron.com 639(visit 640.Pa https://mailman.astron.com/mailman/listinfo/file 641first to subscribe). 642.Sh TODO 643Fix output so that tests for MIME and APPLE flags are not needed all 644over the place, and actual output is only done in one place. 645This needs a design. 646Suggestion: push possible outputs on to a list, then pick the 647last-pushed (most specific, one hopes) value at the end, or 648use a default if the list is empty. 649This should not slow down evaluation. 650.Pp 651The handling of 652.Dv MAGIC_CONTINUE 653and printing \e012- between entries is clumsy and complicated; refactor 654and centralize. 655.Pp 656Some of the encoding logic is hard-coded in encoding.c and can be moved 657to the magic files if we had a !:charset annotation 658.Pp 659Continue to squash all magic bugs. 660See Debian BTS for a good source. 661.Pp 662Store arbitrarily long strings, for example for %s patterns, so that 663they can be printed out. 664Fixes Debian bug #271672. 665This can be done by allocating strings in a string pool, storing the 666string pool at the end of the magic file and converting all the string 667pointers to relative offsets from the string pool. 668.Pp 669Add syntax for relative offsets after current level (Debian bug #466037). 670.Pp 671Make file -ki work, i.e. give multiple MIME types. 672.Pp 673Add a zip library so we can peek inside Office2007 documents to 674print more details about their contents. 675.Pp 676Add an option to print URLs for the sources of the file descriptions. 677.Pp 678Combine script searches and add a way to map executable names to MIME 679types (e.g. have a magic value for !:mime which causes the resulting 680string to be looked up in a table). 681This would avoid adding the same magic repeatedly for each new 682hash-bang interpreter. 683.Pp 684When a file descriptor is available, we can skip and adjust the buffer 685instead of the hacky buffer management we do now. 686.Pp 687Fix 688.Dq name 689and 690.Dq use 691to check for consistency at compile time (duplicate 692.Dq name , 693.Dq use 694pointing to undefined 695.Dq name 696). 697Make 698.Dq name 699/ 700.Dq use 701more efficient by keeping a sorted list of names. 702Special-case ^ to flip endianness in the parser so that it does not 703have to be escaped, and document it. 704.Pp 705If the offsets specified internally in the file exceed the buffer size 706( 707.Dv HOWMANY 708variable in file.h), then we don't seek to that offset, but we give up. 709It would be better if buffer managements was done when the file descriptor 710is available so move around the file. 711One must be careful though because this has performance (and thus security 712considerations). 713.Sh AVAILABILITY 714You can obtain the original author's latest version by anonymous FTP 715on 716.Pa ftp.astron.com 717in the directory 718.Pa /pub/file/file-X.YZ.tar.gz . 719